Canada - United States Air Quality Agreement Progress Report 2014: chapter 2
Section 2: Scientific and Technical Cooperation and Research
- Emission Inventories and Trends
- Air Quality Reporting and Mapping
- Air Quality Standards
- Ecological Effects
- Critical Loads and Exceedances
- Canada-United States Scientific Cooperation
Emission Inventories and Trends
The United States and Canada have updated and improved their emission inventories and projections on pollutants, including PM10, PM2.5, VOCs, NOx and SO2, to reflect the latest information available. In Canada, the most recent complete emission inventory data are for the year 2012. In the United States, the most recent complete emission inventory data are for the year 2011 (2011 NEI). The 2012 emission data in this section are based on the estimation methods used to develop the national emissions trends (http://www.epa.gov/ ttn/chief/trends/index.html).
Emissions for 2012 are held constant from the 2011 NEI for all pollutants and emission categories, with the following exceptions: the 2012 NOx and SO2 emissions for EGUs are from the EPA’s database of CEM data for regulated EGU sources; and the on-road and non-road mobile source emissions are interpolated between the 2011 NEI and projected 2020 inventory. The 2020 projected inventory was used to support EPA rulemaking on the ambient air health standard for PM, and is a product of the 2008-based modelling platform described at http://www.epa.gov/ttn/chief/emch/ index.html#2008. For Canada, the 2012 emission inventory was developed using the latest emission estimation methods and statistics, and includes the pollutant emission information reported by approximately 6500 facilities to the NPRI for 2012. The Canadian inventories are available at www.ec.gc.ca/ inrp-npri/default.asp?lang=en&n=0EC58C98-1.
Figure 25 shows the distribution of emissions by source category grouping for SO2, NOx and VOCs. The following observations can be made from this figure:
- Canadian SO2emissions originate mostly from the nonferrous smelting and refining industry, upstream petroleum industry, and coal-fired electric power generation. The relative contribution from electric power generation utilities is lower in Canada due to the large hydroelectric and nuclear capacity in place, and differences in population and demand.
- SO2 emissions in the United States originate primarily from coal-fired combustion in the electric power sector and from industrial boilers.
- In Canada, non-road and on-road vehicles account for the greatest portion of NOx emissions.
- Similarly, in the U.S., non-road and on-road vehicles account for the greatest portion of NOx emissions, followed by industrial sources, of which half of the portion indicated is contributed by industrial boilers.
VOC emissions are the most diverse of the emission profiles in each country. The most significant difference is that most VOCs (37 percent) in Canada originate from the industrial sector because of the proportionately higher contribution of oil and gas production in Canada. In the United States, solvent utilization and other anthropogenic sources (e.g. gas stations and bulk gas terminals, petroleum storage and transport, and prescribed fires) contribute the highest percentage of VOCs, representing 19 percent and 27 percent, respectively. In the U.S., the on-road and non-road mobile sources together contribute 30 percent of VOCemissions.
- Emissions exclude natural sources (biogenics and forest fires).
- Percentages may not add up to 100 due to rounding.
Source: U.S. EPA and Environment Canada, 2014
Figure 25. U.S. and Canadian National Emissions by Sector for Selected Pollutants, 2012
Figure 25 depicts U.S. and Canada national emissions by sector for selected pollutants in 2012. It includes six pie charts. This figure shows that SO2 emissions in the United States stem primarily from coal-fired combustion in the electric power sector and industrial boilers. Canadian SO2 emissions come mostly from the non-ferrous smelting and refining industry, upstream petroleum industry, and coal-fired electric power generation. The relative contribution from electric power generation utilities is lower in Canada due to the large hydroelectric and nuclear capacity in place, and differences in population and demand. The distribution of NOX emissions in the two countries is similar, with non-road and on-road vehicles accounting for the greatest portion of NOX emissions. VOC emissions are the most diverse of the emission profiles in each country. The most significant difference is that most VOCs in Canada originate from the industrial sector because of the proportionately higher contribution of oil and gas production in Canada. In the United States, solvent utilization and other anthropogenic sources (e.g., gas stations and bulk gas terminals, petroleum storage and transport and prescribed fires) contrinute the highest percentage of VOCs.
In the United States, there is an overall trend of emission reduction for all three pollutants, with the largest percentage decrease occurring in SO2 emissions (78 percent), followed by NOx (46 percent) and VOCs (37 percent). The major reductions in SO2emissions came from electric power generation sources as well as industrial boilers. For NOx, the largest reductions since 1990 came from on-road and non-road mobile sources, and electric power generation sources. As noted earlier, the increase in NOx emissions in 2002 is due to a different estimation method beginning in 2002.
For VOC emissions, the largest reductions were mainly from on-road and non-road mobile sources, and for solvent utilization processes. Similar to NOx, the increase in VOC emissions in 2002 reflects the EPA’s more recent mobile estimation model, but is also due to improved characterization methods for residential fuel combustion, and more complete characterization and exclusion of wildfires to account for anthropogenic sources only. Around 2005, there was an increase in emissions reporting and improved characterization of emissions from oil and gas production activities as well as prescribed fires. VOC emissions were also slightly higher in 2007 than 2008, which is attributed to more on-road mobile source emissions during 2007 than 2006 or 2008, and the effect of excluding wildfire emissions (which were much higher in 2008 than the previous estimate in 2005).
In Canada, the reductions in SO2 emissions came from the non-ferrous smelting and refining industry and the electric power generation utilities. For NOx, the reductions were from on-road mobile sources, electric power generation utilities, and the mining and rock quarrying industry. The VOC reductions came from on-road mobile sources and the downstream petroleum industry, with additional reductions from various industrial sectors such as chemical, pulp and paper, wood products, and iron and steel industries.
Source: U.S. EPA and Environment Canada, 2014
Figure 26. National SO2 Emissions in the United States and Canada from All Sources, 1990-2012
Figure 26 depicts SO2 emission trends in the U.S. and Canada in million short tons and million metric tons, respectively, from 1990 to 2012. In the U.S., the major reductions in SO2 emissions came from electric power generation sources as well as industrial boilers. In Canada, the reductions in SO2 emissions came from the non-ferrous smelting and refining industry and the electric power generation utilities
Source: U.S. EPA and Environment Canada, 2014
Figure 27. National NOx Emissions in the United States and Canada from All Sources, 1990-2012
Figure 27 depicts NOx emission trends in the U.S. and Canada in million short tons and million metric tons, respectively, from 1990 to 2012. In the U.S., the major reductions in NOx emissions came from on-road and non-road mobile sources and electric power generation sources. In Canada, NOx, reductions were from on-road mobile sources, electric power generation utilities, and the mining and rock quarrying industry
Source: U.S. EPA and Environment Canada, 2014
Figure 28. National VOC Emissions in the United States and Canada from All Sources, 1990-2012
Figure 28 depicts VOC emission trends in the U.S. and Canada in million tons and million tonnes, respectively, from 1990 to 2012. In the U.S., the reductions in VOC emissions came from on-road and non-road mobile sources and solvent utilization processes. In Canada, VOC reductions came from on-road mobile sources and the downstream petroleum industry, with additional reductions from various industrial sectors such as chemical, pulp and paper, wood products, and iron and steel industries.
Air Quality Reporting and Mapping
The National Air Pollution Surveillance (NAPS) program and the Canadian Air and Precipitation Monitoring Network (CAPMoN) are the two major ambient air monitoring networks in Canada. The NAPS program, a joint initiative of the federal, provincial and territorial governments, coordinates the collection of air quality data from existing provincial, territorial and regional air quality monitoring networks, and provides accurate and long-term air quality data of a uniform standard in a unified Canada-wide air quality database. For more information on NAPS and CAPMoN, visit www.ec.gc.ca/rnspa-naps/Default.asp?lang=En&n=5C0D33CF-1 and www.ec.gc.ca/rs-mn/default.asp?lang=En&n=752CE271-1.
The associated federal and provincial/territorial/regional monitoring networks reporting data to the Canada-wide database comprise 290 air monitoring stations located in 150 communities. In total, over 800 instruments, including continuous analyzers for SO2, CO, NO2, O3 and fine PM, are used to provide continuous air quality measurements. Time-integrated samples are also analyzed for polycyclic aromatic hydrocarbons (PAHs), VOCs and the chemical components of PM10and PM2.5, for 24-hour events at scheduled intervals of one every three days or one every six days.
CAPMoN consists of 30 stations located in rural or remote areas, including one station in the United States. The objectives of CAPMoN differ from those of NAPS in that CAPMoN measurements provide data for research into: (1) regional-scale spatial and temporal variations of air pollutants and deposition, (2) long-range transport of air pollutants (including transboundary transport), (3) atmospheric processes, and (4) chemical transport model evaluation.
Figure 29 shows the location of PM2.5and O3 sites reporting to the Canada-wide air quality database in 2012. These sites are located in over 100 communities, including all communities with a population greater than 100 000. In total, these communities account for approximately 75 percent of the Canadian population. Updates to these air monitoring networks include the following:
|Measurement Parameter||Number of Sites (2012)||Frequency||Initiated|
|Source: Environment Canada, 2012|
|Nitrogen oxides (NOx)||161||Hourly||1980|
|Sulphur dioxide (SOx)||128||Hourly||1970|
|Carbon monoxide (CO)||63||Hourly||1970|
|PM10 (manual)||23||24 hours; 1 in 3 or 6 days||1984|
|PM2.5 (manual reference method)||37||24 hours; 1 in 3 or 6 days||1984|
|PM2.5 speciation||12||24 hours; 1 in 3 or 6 days||2003|
|Volatile organic Compounds (VOCs)||49||Urban: 24 hours; 1 in 6 days
Rural: 4 hours; 1 in 3 days
|Polycyclic aromatic hydrocarbons (PAHs)||5||24 hours; 1 in 6 days||1990|
- As of the beginning of 2013, all continuous PM2.5monitors reporting to the NAPS program are U.S. Class III Federal Equivalent Method instruments.
- The launch of a new NAPS Data Products public website, which now includes integrated sampling data for the chemical components of PM10 and PM2.5, VOCs and PAHs.
- Resumption of the carbonyl measurement program at several VOC sites.
- Development of an analytical method for routine chromium (VI) measurements.
- Expansion of the laboratories and analytical equipment used to carry out detailed chemical analysis such as VOC and PM2.5 speciation.
- CAPMoN has begun to deploy continuous PM2.5instruments at its ozone monitoring stations.
- CAPMoN is also expanding its air filter pack, continuous PM2.5 yand O3 monitoring, and precipitation chemistry measurements in western Canada with the installation of new sites.
Environment Canada provides daily air quality forecasts for Canadian cities using the Canadian Air Quality Health Index (AQHI) (www.airhealth.ca). This index presents the combined short-term health risk associated with the smog mixture (as indicated by concentrations of PM2.5, O3 and NO2) on a 1-10 open-ended scale. The index includes health protection advice for the at-risk population and the general public across all ranges.
Source: Environment Canada, 2014
Figure 29. O3 and Continuous PM2.5 Monitors Reporting to the NAPS Canada-wide Air Quality Database, 2012
Figure 29 depicts the number of PM2.5 and ozone (O3) sites reporting to the Canada-wide air quality database in 2012. These sites are located in over 100 communities. In total, these communities account for approximately 75 percent of the Canadian population.
The majority of air quality monitoring in the United States is carried out by state, local and tribal agencies in four major networks of monitoring stations: State and Local Monitoring Stations (SLAMS), Photochemical Assessment Monitoring Stations (PAMS), the PM2.5 Chemical Speciation Network (CSN), and air toxics monitoring stations including the National Air Toxics Trends Stations (NATTS). In addition, ambient air monitoring is performed by the federal government (EPA, NPS, NOAA, U.S. Geological Survey and U.S. Department of Agriculture), tribes and industry. Air quality monitoring in the United States supports several air quality management objectives:
- NAAQS attainment/non-attainment determination
- Human exposure assessment for health research studies
- Public air quality reporting and forecasting (AQI/AirNow)
- Accountability of control studies (ARP, NOx SIP Call, NBP and CAIR)
- Model evaluation
- Determination of source receptor relationships
- Characterization of regional air masses and transport
- Ecological exposure assessments (acidity; nutrients; ozone; mercury; and other persistent, bioaccumulative, and toxic chemicals)
- Assessments for toxic air pollutants; trends, hotspots, human health exposure, research
A summary of monitoring networks is provided in Table 3.
The EPA introduced a new multi-pollutant monitoring network, referred to as NCore, that became operational in 2011. Monitors at NCore sites measure particles (e.g. PM2.5, speciated PM2.5, PM10-2.5), O3, SO2, CO, nitrogen monoxide (NO), total reactive nitrogen (NOy), lead (Pb), and basic meteorological parameters. Sites are placed in broadly representative urban locations (about 60 sites) and rural locations (about 20 sites) throughout the United States. During 2014, additional NCore sites are being added in St. Marks, Florida (rural) and San Juan, Puerto Rico (urban). The EPA collaborates on site selection with individual state and local agencies and multi-state organizations. Where possible, states have located urban NCore sites next to existing monitoring operations, including PAMS or NATTS, in order to leverage existing resources. Similarly, the EPA coordinates with states and other monitoring network programs (i.e. IMPROVE and CASTNET) to establish rural based NCore sites. The objective of the NCore network is to gather additional information needed to support emissions and air quality model development, air quality program accountability, and future health studies. General information on the NCore network is available at www.epa.gov/ttn/ amtic/ncore/index.html. More specific information on each candidate NCore site can be viewed at or downloaded from http://ncore.sonomatechdata.com/.
The EPA has completed transitioning of the carbon measurement at CSN-speciated PM2.5 stations to the IMPROVE protocol, in order to support better comparability between the CSN and IMPROVE networks. This effort was initiated in 2007. The EPA finalized revisions to monitoring requirements for Pb in 2008 in order to support the tightening of the Pb NAAQS from 1.5 micrograms per cubic metre (µg/m³) (quarterly average) to 0.15 µg/m³ (rolling three-month average). New monitoring requirements included the establishment of source-oriented Pb monitoring sites around Pb sources emitting 1.0 or greater tons of Pb per year by January 1, 2010. Additional Pb monitoring requirements were finalized at the end of 2010, including: 1) the establishment of source-oriented Pb monitoring sites around Pb sources emitting between 0.5 and 1.0 tons (0.5 and 1.0 metric tons) of Pb per year; 2) the addition of trends monitoring at urban NCore sites; and 3) the establishment of a short-term monitoring study at 15 general aviation airports across the United States. Information on changes to the Pb NAAQS and associated monitoring requirements can be found at http://www.epa.gov/air/lead/actions.html.
New ambient monitoring requirements have been established for the recently (2013) revised PM2.5 NAAQS (http://www.epa.gov/airquality/particlepollution/2012/ decfsimp.pdf). These requirements include the addition of PM2.5 to the near-road monitoring requirements that have been established previously for NO2and CO. The NO2 portion of the near-road network is being implemented in phases, with sites being established in the biggest metropolitan areas by January 1, 2015. The CO and PM2.5 monitors will be phased into this network by January 1, 2017. Information on the near-roadway effort is available at http://www.epa.gov/ttnamti1/nearroad.html. The NADP, with support from the EPA and other partners, operates an international network that measures atmospheric mercury concentrations to estimate dry and total deposition of mercury. The Atmospheric Mercury Network (AMNet) measures concentrations of the three forms of atmospheric mercury: gaseous oxidized (GOM), elemental (GEM), and particle-bound (PBM). Established in 2009, the network now consists of 20 sites throughout the United States, Canada and Taiwan. Mercury fractions are measured continuously using an automated system. GEM is measured at a 5-minute interval, whereas GOM and PBM are measured at a 60- or 120-minute interval. The data from this network will indicate the status and trends of atmospheric mercury concentrations at select locations, and information for model development and validation as well as source apportionment.
Table 3. U.S. Air Quality Monitoring Networks
Major Routine Operating Air Monitoring Networks: State / Local / Tribal / Federal Networks
|NetworkFootnotea||Sites||Initiated||Measurement Parameters||Source of Information and/or Data|
|National Core Monitoring Network (NCore)||~80||2011||O3, NO/NOy, SO2, CO, PM2.5/PM10-2.5, PM2.5 speciation, surface meteorology||www.epa.gov/ttn/amtic/ncore/index.html|
|SLAMS||~4500||1978||O3, NOx/NO2, SO2, PM2.5/PM10, CO, Pb||www.epa.gov/airdata|
|CSN||189 currently active||1999||PM2.5 mass, PM2.5 speciation, major ions, metals||www.epa.gov/airdata|
|PAMS||75||1994||O3, NOx/NOy, CO, speciated VOCs, carbonyls, surface meteorology, upper air||www.epa.gov/ttn/amtic/ pamsmain.html|
|Near-Road Network||74||2014||NO2, CO, PM2.5||
Optional measurements include British Columbia, ultrafine particles, air toxics, meteorology, traffic counts
|NetworkFootnotea||Sites||Initiated||Measurement Parameters||Source of Information and/or Data|
|IMPROVE||110 plus 67 protocol sites||1988||PM2.5/PM10, major ions, metals, light extinction, scattering coefficient||http://vista.cira.colostate. edu/IMPROVE/|
|CASTNET||80+||1987||O3, weekly concentrations of SO2, HNO3, SO42-, NO3-, Cl-, NH4+, Ca2+, Mg2+, Na+, K+ for Dry and Total Deposition||www.epa.gov/castnet|
|Gaseous Pollutant Monitoring Program (GPMP)||33||1987||O3, NOx/NO/NO2, SO2, CO, surface meteorology, enhanced monitoring of CO, NO, NOx, NOy and SO2, canister samples for VOC at three sites||www.nature.nps.gov/air/Monitoring/network.cfm|
|NADP/NTN||250+||1978||Precipitation chemistry and wet deposition for major ions (SO42-, NO3-, NH4+, Ca2+, Mg2+, Na+, K+, H+ as pH)||http://nadp.sws.uiuc.edu/|
|NADP/AMNet||20||2009||Atmospheric mercury concentrations of gaseous oxidized, particulate-bound, and elemental mercury forms||http://nadp.sws.uiuc.edu/|
|NADP/MDN||100+||1996||Mercury measured in precipitation and Wet Deposition||http://nadp.sws.uiuc.edu/ mdn/|
|NADP/AMoN||66||2007||Bi-weekly concentrations of gaseous NH3||http://nadp.isws.illinois.edu/ amon|
|IADN||20||1990||PAHs, PCBs, and organochlorine compounds are measured in air and precipitation||http://www.epa.gov/greatlakes/ monitoring/air2/iadn/|
|NetworkFootnotea||Sites||Initiated||Measurement Parameters||Source of Information and/or Data|
|National Air Toxics Trends Stations (NATTS)||27||2005||VOCs, Carbonyls, PM10 metalsFootnoteb, Hg||http://www.epa.gov/ttn/ amtic/natts.html|
|State/Local Air Toxics Monitoring||250+||1987||VOCs, Carbonyls, PM10 metalsFootnoteb, Hg|
|NDAMN||34||1998-2005||CDDs, CDFs, dioxin-like PCBs||http://cfpub.epa.gov/ncea/cfm/recordisplay. cfm?deid=54812|
Source: U.S. EPA, 2014
The EPA is also providing support to the NADP’s Ammonia Monitoring Network (AMoN), which uses passive devices to measure gaseous NH3 concentrations. Currently there are 66 sites collecting bi-weekly samples of ambient NH3 concentrations, providing measurements that are needed to enhance atmospheric and deposition models, validate emission inventories, and understand the chemistry driving PM2.5 formation. Both efforts aim to utilize the NADP committee structure as a platform for initiation and continued growth. For data, maps and other program information, consult the NADP website at http://nadp.isws. illinois.edu.
In 2011, all CASTNET ozone monitors and quality assurance methods were upgraded to meet the regulatory requirements applicable to SLAMS. CASTNET O3 data are submitted to the EPA’s Air Quality System (AQS), and were included in the 2011-2013 O3 design value calculations. The EPA is continuing to support and evaluate methods for measuring highly time-resolved concentrations of both gaseous (SO2, HNO3, NH3) and aerosol (sulphate [SO42-], ammonium [NH4+], NO3-, chlorine [Cl-] and other base cations) pollutants. Five small-footprint, filter-pack-only CASTNET sites have been installed since 2012 to assess sulphur and nitrogen impacts on sensitive ecosystems and tribal lands. Additionally, the EPA and NPS have installed AMoN samplers at 41 CASTNET sites, and the EPA recently added 5 NOy trace gas analyzers at CASTNET sites to provide a more complete nitrogen budget. The website for CASTNET includes program information, data and maps, annual network reports, and quality assurance information (www.epa.gov/castnet).
Note: This map is an illustration of the highest O3 concentrations reached throughout the region on a given day. It does not represent a snapshot at a particular time of the day, but is more like the daily high temperature portion of a weather forecast. The AQI shown in the legend is based on 8-hour average O3.
Source: U.S. EPA, 2014
Figure 30. AIRNow Map Illustrating the Air Quality Index (AQI) for 8-hour Ozone
Figure 30 depicts an AIRNow map illustrating pollutant concentration data expressed in terms of colour-coded air quality index (AQI).
The AirNow program (www.airnow.gov) was initiated by the EPA more than a decade ago, to provide current and forecasted air quality information for monitoring sites throughout the United States and Canada; it presents PM and O3 pollutant concentrations in terms of the U.S. Air Quality Index (AQI). Each country is responsible for ensuring instrument calibration and comparability of ambient measurements of O3 and PM2.5. In 2004, the AirNow program was expanded to provide information on PM2.5 and O3 measurements on a continental scale year-round. Figure 30 is an example of the type of maps available on the AirNow website; they display pollutant concentration data expressed in terms of the color-coded U.S. AQI. AirNow also distributes air quality data via web services and text files through the AirNow Application Programming Interface (API), at http://www.airnowapi.org.
Note: The AQI for O3 reflects 8-hour average O3 concentrations. Areas shaded in orange indicate values that are “unhealthy for sensitive groups.” More information on the AQI is available at www.airnow.gov.
Air Quality Standards
Canadian Ambient Air Quality Standards
New ambient air quality standards for PM2.5 and ground level O3 were implemented under CEPA 1999, as approved by federal, provincial and territorial Ministers of the Environment. The new standards are more stringent and replace the existing CWS for these two pollutants. In addition, the federal, provincial and territorial governments have initiated development of the CAAQS for other air pollutants of concern (SO2 and NO2), and are expecting to complete the work in 2015.
Air Zone Management/ Regional Airsheds
Canada’s AQMS includes a framework for managing air quality through local air zones (geographic areas within each province or territory) with unique air quality issues and challenges. The framework contains four air quality management levels with threshold values based on CAAQS that encourage progressively more rigorous actions by jurisdictions as air quality approaches or exceeds the CAAQS. Provinces and territories will lead air quality management in their jurisdiction guided by this framework and select air quality management actions tailored to each air zone. The AQMS also promotes proactive measures to protect air quality ensuring that the CAAQS are not exceeded and do not become “pollute up to” levels.
In addition to the air zones, six regional airsheds have been established to coordinate air quality management actions across the country and to better understand the transboundary flow of pollutants. The airsheds are larger areas, cutting across jurisdictional boundaries where air quality characteristics and air movement patterns are similar. They provide a framework for interjurisdictional collaboration and coordination of overall system reporting.
Review of U.S. O3, PM, SO2 and NO2 Air Quality Standards
Under the Clean Air Act (CAA), the EPA is required to set NAAQS for widespread pollutants from numerous and diverse sources considered harmful to public health and the environment. The CAA established two types of NAAQS:
- Primary standards set limits with an adequate margin of safety to protect public health, including the health of at risk populations such as children, older adults, and persons with pre-existing cardiovascular or respiratory disease such as asthma.
- Secondary standards set limits to protect public welfare from any known or anticipated adverse effects, including protection against decreased visibility and damage to animals, crops, vegetation and buildings.
The EPA has established NAAQS for six common pollutants, which are often referred to as “criteria” pollutants: PM, O3, SO2, NO2, CO and Pb. The CAA requires the EPA to review each standard every five years and determine whether there is sufficient new scientific information to warrant a revision of the standard. Reviewing a NAAQS is a lengthy undertaking that follows a well-established process: each involves a comprehensive review, synthesis and evaluation of the scientific information, or “criteria,” available to inform a decision (Integrated Science Assessment [ISA]); the design and conduct of complex air quality and risk and exposure analyses (Risk and Exposure Assessment [REA]); the development of a comprehensive Policy Assessment providing a transparent staff analysis of the scientific basis for the broadest range of alternative policy options supported by the scientific and technical information; and the issuance of a proposed rule in the Federal Register, opportunity for public comment, and publication of the final rule in the Federal Register. These assessments, which provide the foundation for the EPA Administrator’s decision, undergo extensive internal and external scientific peer review.
Exposure to O3 is associated with a wide variety of adverse health effects, ranging from decreased lung function and increased respiratory symptoms to serious indicators of respiratory morbidity, including emergency department visits and hospital admissions for respiratory causes, new-onset asthma and premature mortality. Children and individuals with lung disease are considered at-risk populations. Ozone exposure also leads to detrimental environmental effects: repeated exposure to O3 during the growing season damages sensitive vegetation; and cumulative O3 exposure can lead to reduced tree growth, visibly injured leaves, and increased susceptibility to disease, damage from insects, and harsh weather.
On March 12, 2008, the EPA strengthened the primary and secondary 8-hour standards for O3 by lowering the levels of the standards from 0.08 to 0.075 ppm, in order to improve protection of public health and of sensitive trees and plants. Final area designations for these standards were completed in May 2012, with 46 areas being designated as non-attainment.
The EPA is in the midst of its next review of the ozone standards to ensure that the NAAQS provide appropriate public health and environmental protection. As part of this ongoing review, EPA has issued a number of documents for external scientific and public review. Under the terms of a consent decree, EPA is expected to issue a proposed notice by December 1, 2014, and a final action by October 1, 2015. Additional information on the current and previous O3 NAAQS reviews can be found at www.epa.gov/ttn/naaqs/ standards/ozone/s_o3_index.html.
Particulate Matter NAAQS
An extensive body of scientific evidence demonstrates that exposure to PM can lead to premature death, and is linked to a variety of significant health problems, such as increased hospital admissions and emergency department visits for cardiovascular and respiratory effects, including non-fatal heart attacks. Exposure to PM is also linked to the development of chronic respiratory disease. Several groups within the general population are at greater risk for experiencing PM-related effects, including individuals with pre-existing heart and lung disease, older adults, children, and people of lower socio-economic standing. Research indicates that pregnant women, newborns and people with certain health conditions, such as obesity or diabetes, may also be at increased risk of PM-related health effects.
It has been further recognized for many years that PM in the atmosphere (particularly fine PM) causes visibility impairment. Hazy conditions due to air pollution can be experienced in all types of areas, from urban areas to national parks. Visibility is affected by particles that scatter and absorb light, and the composition and size of these particles, as well as relative humidity, are important factors in understanding the impacts of particle pollution on visibility impairment. Particles are also associated with a wide range of non-visibility welfare effects, including ecological effects, effects on materials, and climate impacts.
In December 2012, the EPA finalized revisions to the PM NAAQS, which strengthened the primary annual average PM2.5 standard to a level of 12 μg/m³. This revised standard provides increased protection against health effects associated with long- and short-term PM2.5 exposures. The primary 24-hour PM2.5standard of 35 μg/m³, originally established in 2006, was retained. The existing secondary standards for PM2.5 (an annual standard of 15.0 μg/m³ and a 24-hour standard of 35 μg/m³) were also retained to address PM-related welfare effects such as visibility impairment, ecological effects, damage to materials and climate impacts.
The EPA is working with state governments to designate non-attainment areas for the 2012 standards. Additional information on the revised PM NAAQS, including supporting documents, can be found at http://www.epa.gov/air/ particlepollution/.
SO2 NAAQS (Primary Standard)
Asthmatics are especially susceptible to the effects of SO2. Short-term exposure of asthmatic individuals to elevated levels of SO2 while exercising at a moderate level may result in breathing difficulties, accompanied by symptoms such as wheezing, chest tightness or shortness of breath. Studies also provide consistent evidence of an association between shortterm exposure to SO2 and increased respiratory symptoms in children, especially those with asthma or chronic respiratory symptoms. In addition, short-term exposure to SO2 has been associated with respiratory-related emergency department visits and hospital admissions, particularly for children and older adults.
On June 2, 2010, based on the results of SO2 health effects evidence assessed in the ISA, and on estimates of SO2 associated exposure and health risks presented in the REA, the EPA strengthened the primary NAAQS for SO2, revising the primary SO2 standard by establishing a new 1-hour standard at a level of 75 ppb. The revised standard will improve public health protection, especially for children, older adults, and people with asthma. The EPA’s evaluation of the scientific information and the risks posed by inhaling SO2 indicate that this new 1-hour standard will protect public health by reducing people’s exposure to high, short-term concentrations (5 minutes to 24 hours) of SO2. The EPA revoked the two existing primary standards of 140 ppb evaluated over 24 hours and 30 ppb evaluated over a year, because they will not add additional public health protection given a 1-hour standard at 75 ppb.
The EPA recently started its next periodic review of the primary SO2 standards; the draft integrated review plan was published in March 2014 and a final version is scheduled for release later in 2014. Additional information on the SO2 NAAQS, including supporting documents, can be found at www.epa.gov/air/sulfurdioxide.
NO2 NAAQS (Primary Standard)
Exposure to NO2 has been associated with a variety of health effects, including respiratory symptoms, especially among asthmatic children; and to respiratory-related emergency department visits and hospital admissions, particularly for children and older adults. On January 22, 2010, based on the results of NO2 health effects evidence as assessed in the ISA and estimates of NO2 associated exposures and health risks presented in the REA, the EPA revised the primary NO2 NAAQS, and established new requirements for the NO2 monitoring network.
Specifically, the EPA promulgated a new 1-hour primary NO2 standard with a level of 100 ppb, retained the existing annual standard with a level of 53 ppb, and established a requirement for more than 50 NO2 monitors to be sited within 50 metres of major roads and in other locations where maximum NO2 concentrations are expected to occur. The states are deploying new monitors in three phases: by the beginning of 2014, 2015 and 2017.
The EPA recently started its next periodic review of the primary NO2 standards; the final integrated review plan was issued in June 2014. Additional information on the NO2 NAAQS can be found at http://www.epa.gov/air/ nitrogenoxides.
Oxides of Sulphur and Nitrogen NAAQS (Secondary Standards)
NOx and SOx in the air can damage the leaves of plants, decrease their ability to produce food (photosynthesis), and decrease their growth. In addition to directly affecting plants, NOx and SOx can, when deposited on land and in estuaries, lakes and streams, acidify and over-fertilize sensitive ecosystems, resulting in a range of harmful deposition-related effects on plants, soils, water quality, and fish and wildlife (e.g. changes in biodiversity and loss of habitat, reduced tree growth, loss of fish species, and harmful algal blooms).
On March 20, 2012, the U.S. EPA completed its review of the secondary NOx and SOx standards, representing the first time that the Agency reviewed the environmental impacts separately from the health impacts of these pollutants. It is also the first time that the EPA examined the effects of multiple pollutants in one NAAQS review. Based on its review of the currently available scientific information, the EPA retained the current annual NO2 secondary standard set at a level of 0.53 ppm and 2-hour SO2 secondary standard set at a level of 0.5 ppm, in order to address the direct effects on vegetation (e.g. decreased growth and foliar injury). With regard to the deposition-related effects, the final rule recognized that the existing secondary standards do not provide adequate public welfare protection. Although there is strong scientific support for developing a multi-pollutant standard to address these deposition-related effects, the EPA concluded that it does not yet have sufficient information to set such a standard that would adequately protect the diverse ecosystems across the country.
The EPA recently started its next periodic review of the NOx and SOx secondary standards; the draft integrated review plan is scheduled for release in Fall 2014. Additional information on the past and current reviews of these secondary standards, and supporting documentation, can be found at http://www.epa. gov/ttn/naaqs/standards/no2so2sec/index.html.
Research and Monitoring of Acid Deposition Effects on Aquatic Ecosystems
Recovery of Acidified Lakes and Streams in the United States
Acid rain, resulting from SO2 and NOx emissions, is one of many large-scale anthropogenic effects that negatively affect the health of water bodies (lakes and streams) in the United States and Canada. Surface water chemistry provides direct indicators of the potential effects of acidic deposition on the overall health of aquatic ecosystems, and, in this regard and in collaboration with federal and state agencies as well as universities, the EPA administers two monitoring programs that provide information on the impacts of acidic deposition on otherwise protected aquatic systems: Temporally Integrated Monitoring of Ecosystems (TIME) and Long-term Monitoring (LTM) programs. These programs are designed to track changes in surface water chemistry in the four acid-sensitive regions shown in Figure 31: New England, the Adirondack Mountains, the Northern Appalachian Plateau, and the central Appalachians (the Valley and Ridge geologic province and Blue Ridge geologic province).
Five chemical indicators of aquatic ecosystem response to emission changes are presented: trends in sulphate and nitrate anions, sum of base cations, acid neutralizing capacity (ANC), and dissolved organic carbon (DOC). These indicators provide information regarding the surface water sensitivity to acidification and the degree of impact on the aquatic ecosystem. Trends in these measured chemical indicators in drainage waters allow for the determination of whether the water bodies are improving and heading towards recovery or still acidifying. The following is a description of each indicator:
Sulphate is the primary anion in most acid-sensitive waters and has the potential to acidify drainage waters and leach base cations and toxic forms of aluminum from the soils.
Nitrate has the same potential as sulphate to acidify drainage waters. However, nitrogen is an important nutrient for plant and algae growth, and a large portion of nitrogen inputs from deposition are quickly taken up by plants, leaving less leaching of nitrate into surface waters.
Base cations are the positively charged ions in soils and surface waters that buffer both sulphate and nitrate anions, thereby preventing surface water acidification. Base cation availability is largely a function of underlying geology and soil age, such that young soils of cation-rich bedrock will tend to have a greater buffering capacity.
Source: EPA, 2013
Figure 31. Long-Term Monitoring Program Sites
Figure 31 depicts the Long-Term Monitoring Program sites that are designed to track changes in surface water chemistry in the four acid sensitive regions: New England, the Adirondack Mountains, the North Appalachian Plateau, and the central Appalachians.
Acid Neutralizing Capacity (ANC) is a measure of overall buffering capacity against acidification, and indicates the ability to neutralize strong acids that enter aquatic systems. When ANC is low, and especially when it is negative, stream water pH is also low (less than pH 6, commonly less than pH 5), and may be harmful to fish and other aquatic organisms essential for a healthy aquatic ecosystem. Figure 32 shows how waterbody acidification is categorized by ANC concentration. Recovery of an aquatic ecosystem is indicated by increasing trends in ANC and base cations, and decreasing trends in sulphate and nitrate concentrations.
Dissolved organic carbon (DOC) is essentially dissolved organic material that is an important part of the acid-base chemistry of most freshwater systems (particular low ANC waterbodies) because it can assist in neutralizing strong acids. A host of factors control DOC concentrations in surface waters, and increases can indicate reduced acidification and/or increased decomposition of organic matter in the watershed.
Table 4 shows regional trends in indicators of acidified surface waters from 1990 (before implementation of the ARP) to 2012 in lakes and streams, through the LTM program. Over this time frame, significant improving trends in sulphate concentrations are found at nearly all LTM monitoring sites in New England, the Adirondacks and the Catskill Mountains/Northern Appalachian Plateau. However, in the Central Appalachians, only 15 percent of monitored streams have a decreasing sulphate trend, while 20 percent of monitored streams had increasing sulphate concentrations. This is due to the highly weathered soils of the Central Appalachians, which are able to store deposited sulphate such that the decrease in acidic deposition has not yet resulted in lower sulphate concentrations in most streams. However, as long-term sulphate deposition exhausts the soil’s ability to store more sulphate, a decreasing proportion of the deposited sulphate is retained in the soil and an increasing proportion is exported to surface waters. Thus, sulphate concentrations in some streams in this region are not changing or are still increasing despite reduced sulphate deposition.
|Region||Water Bodies Covered||Percentage of Sites with Improving Sulphate Trend||Percentage of Sites with Improving Nitrate Trend||Percentage of Sites with Improving ANC Trend||Percentage of Sites with Improving Base Cations Trend||Percentage of Sites with Improving DOC Trend|
Source: U.S. EPA, 2013
|Adirondack Mountains||50 lakes in New York||100%||54%||76%||88%||62% (29 sites)|
|New England||26 lakes in Maine and Vermont||100%||18%||43%||74%||39% (13 sites)|
|Catskills / N. Appalachian Plateau Footnotec||9 streams in NY and PA||80%||40%||58%||90%||0% (9 sites)|
|Central Appalachians||66 streams in Virginia||15%||58%||15%||14%||N/A|
Nitrate concentration trends are variable across the LTM site network, with improving trends measured at approximately half of all monitored sites. This improvement in nitrate trend may only be partially explained by decreasing deposition. Ecosystem factors, such as vegetation disturbances, increased uptake by vegetation, and soil retention, are also known to affect surface water nitrate concentrations.
Improving ANC trends are likely the result of reductions in sulphate deposition. Recovery in ANC, however, often lags behind declining surface water sulphate and nitrate concentrations. Dynamics in surface water chemistry are complicated and highly dependent on local factors, such as watershed size, geology and hydrology, which can influence the availability of base cations and DOC and thereby inhibit ANC recovery. From 1990 to 2012, ANC concentration increased markedly at LTM monitoring sites in the Adirondacks (76 percent), in the Catskills / northern Appalachian Plateau (58 percent), and New England (43 percent). In contrast, only 15 percent of LTM streams in the Central Appalachians had improving ANC trends, likely due to decreasing base cation levels and the still-increasing sulphate concentrations at some sites.
Figure 33 presents a comparison of the average ANC value of the 580 lakes in the northeast monitored and modelled under the TIME program for the 1991-1994 and 2010-2012 time periods. Seven percent of lakes in the 1991-1994 time period had mean ANC levels below 0 µeq/L, and were categorized as acute concern, but less than 4 percent of lakes were categorized as acute concern in the 2010-2012 time frame, and the percentage of lakes in the elevated concern category dropped from 14 to 10 percent over the same time frame. Meanwhile, the net percentage of lakes in the moderate concern category increased from 7 to 12 percent. These results point to a decrease in acidity, particularly for the subset of TIME lakes in the acute and elevated concern categories.
Source: EPA, 2013
Figure 32. Acid Neutralizing Capacity and Aquatic Ecosystem Concern Levels
Figure 32 shows how waterbody acidification is categorized by acid neutralizing capacity (ANC) concentration. Recovery of an aquatic ecosystem is indicated by increasing trends in ANC and base cations, and decreasing trends in sulphate and nitrate concentrations.
Source: EPA, 2013
Figure 33. TIME Lakes by ANC Category, 1991-1994 vs. 2010-2012
Figure 33 presents a comparison of the average ANC value of the 580 lakes in the northeast monitored and modelled under the Temporally Integrated Monitoring of Ecosystems (TIME) program for the 1991-1994 and 2010-2012 time periods. Seven percent of lakes in the 1991-1994 time period had mean ANC levels below 0 µeq/L, and were categorized as acute concern, but less than 4 percent of lakes were categorized as acute concern in the 2010-2012 time frame, and the percentage of lakes in the elevated concern category dropped from 14 to 10 percent over the same time frame. Meanwhile, the net percentage of lakes in the moderate concern category increased from 7 to 12 percent. These results point to a decrease in acidity, particularly for the subset of TIME lakes in the acute and elevated concern categories.
Critical Loads and Exceedances
Updating Canadian Critical Loads of Acidity for Lakes and Upland Forest Soils
Canada has created a new national critical load map for acidity that combines current information for lakes and soils.
Critical load values were estimated using the steady-state water chemistry (SSWC) model (Henriksen and Posch 2001) for lakes, and the steady-state simple mass balance (SMB) model (Sverdrup and De Vries 1994 ) for forest soils. Both models depend on a chemical threshold that defines the onset of harmful ecosystem effects. For lakes, the threshold is an acid neutralizing capacity (ANClimit), and, for soil water, the threshold is the ratio of base cations (Bc) to aluminum (Al) (ratio denoted by Bc:Al). For this report, ANClimit was set at a value related to the DOC concentration in the lake water (Lyderson et al. 2004), or, in the absence of a DOC value, set at the typical value of 40 micromoles of charge per litre (µmolc L-1); the Bc:Al threshold was set at 10. The SSWC calculates an aquatic critical load for each sampled lake, and the SMB calculates critical loads for every upland forest soil type (or “polygon”) across the modelled areas of Canada. In total, critical loads were estimated for 4702 lakes and 7867 soil polygons across Canada. These critical loads were superimposed on the 45x45 km grid generated by the atmospheric deposition model AURAMS (A Unified Regional Air-Quality Modelling System). When a grid square contained multiple lake and/or soil critical load values, the 5th percentile for each type was calculated (area-weighted in the case of soil polygons). The lower 5th percentile critical load value was then selected to represent the critical load for that square. If a square did not have any sampled lakes, the critical load value for the square was the 5th percentile value for forest soils. In this manner, a single critical load value was assigned to each of 2874 grid squares across Canada (Figure 34 ). Using the 5th percentile critical load value is a way of ensuring that some of the most sensitive elements of an ecosystem are protected. If actual acid deposition does not exceed the 5th percentile critical load value, at least 95% of all lakes and soil ecosystems within the grid are protected from the adverse effects of acid deposition.
Some squares in Figure 34 were not assigned a critical load because they contained neither sampled lakes nor forest soils that could be modelled. In other cases, the square consisted entirely or mostly of cultivated soils, and critical load values are not established for cultivated soils because the physical, chemical and biological composition of these soils is altered and managed by human activities.
Note: Lake or upland forest soil critical loads for acidity (wet + dry deposition in eq/ha/yr) is calculated using either the SSWC or SMB models. The index map (lower left) indicates the model selected for each grid square: yellow = SSWC, green = SMB. The CL value for a given square is either the 5th percentile lake value or the 5th percentile soil polygon value. Areas that cannot be classified by either the lake or forest soil models are white.
Source: Environment Canada, 2014
Figure 34. Critical Loads of Acidity for Lakes or Upland Forest Soils across Canada
Figure 34 depicts a critical load map of acidity for Canada that combines current information for lakes and soils. Critical loads are shown in ranges consisting of seven classes. Overall, approximately 0.4 million km2 or 6.6 percent of the Canadian terrain covered by the analysis shown in Figure 34 is extremely sensitive to acidic deposition, i.e., falling within the two lowest critical load classes. An additional 2.1 million km2 or 35 percent of the total falls within the next two critical load classes.
In Figure 34, critical loads are shown in ranges consisting of seven classes. The four lowest classes range from background (Bkd) deposition to 400 equivalents per hectare per year (eq/ha/yr), and grid squares within these classes are the most sensitive to the adverse effects of acid deposition and of greatest concern. Critical load values for upland forest soils cover the greater portion of the map. Of the 2874 grid squares (representing an area of approximately 5.8 million km2), 89 percent have a critical load defined by forest soils. This is due to the nature of the data available for modelling. Spatial coverage by the geology, soil and land cover characteristic databases used to obtain input data for the SMB model is much greater than the coverage provided by the lake chemistry database (sampled lakes occurred in 633 grid squares, or 18 percent of the total).
All grid squares with critical loads in the classes from Bkd to 100 eq/ha/yr and from >100 to 200 eq/ha/yr were defined by the aquatic critical load. Within the remaining five classes, lakes defined the critical load from 18% of the squares for the >200-300 eq/ha/yr class to <1 percent of the squares for the >300-400 eq/ha/yr class. This was expected in eastern Canada, because many lakes sampled for the purpose of acid rain assessment occur in areas that are acid sensitive or have known aquatic effects. Nevertheless, lakes recently sampled on acid-sensitive terrain in western Canada (but without any pre-knowledge of acidification or effects) show the same pattern.
There are obvious “hot spots” of sensitive ecosystems, represented by very low critical loads (red and orange squares in Figure 34). These are located in southern Quebec, northwestern Saskatchewan and extreme northeastern Alberta, and the coastal mountain range of southwestern British Columbia (including some parts of Vancouver Island). There are also isolated occurrences of very low critical loads in southern Nova Scotia, Newfoundland, northern Ontario, northwestern Manitoba, and east central Alberta. The commonality among all these areas with low critical load values is the occurrence of lakes with very low base cation and ANCconcentrations.
Overall, approximately 0.4 million km2 or 6.6 percent of the Canadian terrain covered by the analysis shown in Figure 34 is extremely sensitive to acidic deposition, i.e., falling within the two lowest critical load classes. An additional 2.1 million km2 or 35 percent of the total falls within the next two critical load classes.
Use of Critical Loads in the United States
In the United States, the critical loads approach is not an officially accepted approach to ecosystem protection. Language specifically requiring a critical loads approach does not exist in the CAA. Nevertheless, the critical loads approach provides a useful lens through which to help understand the potential aquatic ecological benefits that have resulted from emission reduction programs such as the ARP and CAIR.
|Region||Number of Waterbodies Modelled||Waterbodies in Exceedance of Critical Load
Number of Sites
|Waterbodies in Exceedance of Critical Load
Percentage of Sites
|Waterbodies in Exceedance of Critical Load
Number of Sites
|Waterbodies in Exceedance of Critical Load
Percentage of Sites
|Source: U.S. EPA, 2013|
|New England (ME, NH, VT, RI, CT)||1298||273||21%||147||11%||46%|
|Adirondack Mountains (NY)||341||160||47%||70||21%||56%|
|Northern mid-Atlantic (PA, NY, NJ)||784||263||34%||155||20%||41%|
|Southern mid-Atlantic (VA, WV, MD)||1690||1070||63%||745||44%||30%|
|Southern Appalachian Mountains (NC, TN, SC, GA, AL)||773||308||40%||192||25%||38%|
Estimations of critical load exceedances serve as a measurement for determining if present acid deposition levels will provide sufficient reductions to allow the systems to recover over time, or if they will never recover under present loading scenarios. If acidic deposition is less than the calculated critical load, harmful ecological effects (e.g. reduced reproductive success, stunted growth, loss of biological diversity) are not anticipated, and ecosystems damaged by past exposure are expected to eventually recover.Footnote5 Lake and stream waters having an ANC value greater than 50 μeq/L are classified as having a moderately healthy aquatic community; therefore, this ANC value is often used as a goal for ecological protection of drainage waters affected by acid deposition.
Figure 35 shows a comparison of the estimated critical load exceedances for waterbodies for the periods 2000-2002 and 2010-2012. For this analysis, the critical load represents the annual deposition load of sulphur and nitrogen to which a lake or stream could be subjected and still support a moderately healthy ecosystem (i.e. having an ANC greater than 50 μeq/L). Surface water samples from 4886 lakes and streams along acid-sensitive regions of the Appalachian Mountains and some adjoining northern coastal plain regions were collected through a number of water quality monitoring programs. Critical load exceedances for those waterbodies were calculated using the SSWC model.Footnote6,Footnote7
For the period 2010-2012, 27 percent of all the represented waterbodies were shown to still receive levels of combined total sulphur and nitrogen deposition in excess of their critical load, a 37-percent improvement over the 2000-2002 period when 42 percent were in exceedance. Regional differences in critical load exceedances were examined for New England, the Adirondack Mountains, the northern mid-Atlantic, the southern mid-Atlantic, and the southern Appalachian Mountains, as summarized in Table 5.
This analysis suggests that emission reductions achieved since 2000 are anticipated to contribute to broad surface water improvements and increased aquatic ecosystem protection across the five regions along the Appalachian Mountains. This result is consistent with the water quality monitoring findings (see Table 4), except that the anticipated improvements (e.g. reduction of exceedances) based on the critical load analysis are much larger. This is expected, as water quality improvements often lag behind the reduction in acidic deposition while critical loads represent the equilibrium conditions between deposition and water quality. Based on this critical load analysis, current acidic deposition loadings still fall short for recovery of many modelled waterbodies, which indicates additional emission reductions would be necessary for acid-sensitive aquatic ecosystems along the Appalachian Mountains to recover and be protected from acid deposition.
- Surface water samples from the represented waterbodies were collected through the National Surface Water Survey (NSWS), Environmental Monitoring and Assessment Program, Wadeable Stream Assessment (WSA), National Lake Assessment (NLA), TIME, LTM, and other water quality programs.
- Steady-state exceedances were calculated in units of microequivalents per square metre per year (meq/m²/yr).
Source: EPA, 2013
Figure 35. Lake and Stream Exceedances of Estimated Critical Loads for Total Nitrogen and Sulfur Deposition for the Periods 2000-2002 and 2010-2012.
Figure 35 depicts a map of northeastern U.S. It presents a comparison of the estimated critical load exceedances for waterbodies for the periods 2000-2002 and 2010-2012. The analysis suggests that emission reductions achieved since 2000 are anticipated to contribute to broad surface water improvements and increased aquatic ecosystem protection across the five regions along the Appalachian Mountains
Canada-United States Scientific Cooperation
Transboundary PM Science Assessment
Scientists from Canada and the United States have prepared a Transboundary PM Science Assessment that updates findings from the 2004 Canada-United States Transboundary Particulate Matter Science Assessment. This updated assessment was developed to provide the scientific and technical basis for discussions regarding the possibility of adding a PM annex to the Canada-United States AQA, to assess the potential impacts of a PM annex, and to help determine whether such an annex is currently warranted.
This assessment focuses on the fine particle fraction of PM, i.e., PM2.5, because a fraction of this size can remain suspended in the air for several days to weeks and can be transported by winds over large distances, and therefore is subject to atmospheric transboundary transport in North America.
This document is organized around five key science questions:
- What are the impacts of PM2.5 on human/ecosystem health and public welfare, and what are the current air quality standards to protect human and ecosystem health in the United States and Canada?
- What are the recent levels of PM2.5 in the United States and Canada?
- What are the emissions and emission trends of the pollutants that contribute to ambient PM2.5 concentrations in the United States and Canada?
- What is the evidence that transboundary flow of PM2.5 occurs across the U.S.-Canada border, and what changes are projected, given future emission rates in both countries?
- Are there emerging science issues that could affect the understanding of PM2.5 formation and levels, and its impacts on human and ecosystem health?
The key findings from the updated assessment are bulleted below.
- PM2.5 and its precursors have significant effects on the health of humans and ecosystems.
The extensive body of studies providing evidence on the effects of fine particles on health has grown further and significantly since the 2004 assessment. These studies provide evidence of consistent increases in premature mortality and morbidity related to ambient PM2.5 concentrations, with the strongest evidence being reported for cardiovascularrelated effects. Furthermore, the ubiquity of PM2.5 implies that exposure to ambient PM2.5 concentrations can have a substantial public health impact, even with recent reductions.
In addition, although deposition (wet and dry) of acidifying sulphur and nitrogen compounds related to PM2.5 in Canada and the United States has been reduced since 2004, recent deposition in both countries continues to exceed thresholds (critical loads) in some geographic areas, thus posing a risk of harmful effects to terrestrial and aquatic ecosystems. In addition, although significantly reduced in most border areas, PM2.5 continues contributing to visibility impairment in the United States and Canada, particularly in highly populated regions of southern Ontario and Quebec in Canada and the midwest and Montana in the United States. In response, both countries recently lowered ambient air quality standards to protect human and ecosystem health from the harmful impacts of PM2.5.
- Recent levels of ambient PM2.5 have been declining in the United States and Canada.
In both countries, ambient concentrations of PM2.5 have diminished significantly from the levels reported in the 2004 assessment. More specifically, between 2000 and 2012 the national U.S. average annual and 24-hour concentrations of PM2.5 decreased by 33% and 37%, respectively. Data from Canadian PM2.5 speciation sites indicate that, between 2003 and 2010, average annual concentrations of PM2.5 declined by approximately 4 μg/m³ in eastern Canada, while average levels across western Canada remained fairly constant. In 2012, ambient concentrations reported at most monitoring sites in the United States along the Canadian border met the annual and 24-hour NAAQS for PM2.5 set in 2012. In eastern and western Canada, data from the filter-based monitoring network indicate that average annual concentrations (2008- 2010) met the CAAQS set for 2015.
- The decline of most PM2.5 precursors is expected to continue, while direct emissions of PM2.5 and ammonia (NH3) have remained and are expected to remain relatively stable.
National emission inventories in the United States and Canada show that emissions of the PM2.5 precursors SO2, NOx and VOCs declined between 2002 and 2010. However, total direct emissions of anthropogenic PM2.5 have remained fairly stable in both countries during this period, as have emissions of NH3.
Projections based upon known policies established in Canada and the United States for governing future emissions indicate that emissions of PM2.5 and its precursors will follow recent trends. In Canada, primary emissions of PM2.5 are expected to remain stable through 2020, while emissions of SOx and NOx are projected to decline by 33% and 13%, respectively, between 2006 and 2020. By contrast, Canadian VOC and NH3 emissions are not projected to change significantly during this period. In the United States, emissions of SO2, NOx and VOCs are forecast to decrease by 65%, 42% and 21%, respectively, from 2008 to 2020, while emissions of PM2.5 are projected to decrease modestly (8%). NH3 emissions in the United States are expected to be 2% higher in 2020 than 2008.
- It is projected that the influence of transboundary transport between Canada and the United States will be reduced, and that current and planned PM2.5 ambient air standards will likely not be exceeded.
Modelling analyses of the impact of future emission projections show notable anticipated reductions in ambient PM2.5 concentrations between 2006 and 2020 in the United States and Canada. Significant declines in ambient PM2.5 concentrations are expected to occur in most border region cities, with percentage reductions ranging up to 35% in major U.S. cities near the border and up to 25% in their Canadian counterparts.
There is ongoing evidence that PM2.5 is transported across the U.S.-Canada border. However, for most cities in both countries, the dominant sources of PM2.5 in 2020 will continue to be domestic emissions; overall, transboundary influence is projected to be less in 2020 than 2006. The influence of U.S. emissions on PM2.5 concentrations in Canadian cities near the border is projected to decrease by approximately 2-10%, with the largest reductions occurring in eastern Ontario and southwestern Quebec. The exception is Abbotsford, B.C., where there is a small projected increase in U.S. influence. The influence of Canadian emissions on select U.S. cities near the border is also projected to decrease--but by less, in the range of 1-3%, with the exceptions of Seattle, WA, Buffalo, NY, and Rochester, NY, where the Canadian influence is projected to increase slightly.
In the United States, no areas in the border region are predicted to exceed the current annual or 24-hour PM2.5 NAAQS (12 μg/m³) in 2020, including areas with projected increases in Canadian influence. In Canada, the predicted 2006-2020 decreases in PM2.5 are expected to result in rural/regional background PM2.5 concentrations in the region near the southern Ontario and southern Quebec borders, expected to be below the 2015 and 2020 annual and 24-hour CAAQS. However, these levels are close enough to the CAAQS that some populated areas with relatively large local emissions may experience PM2.5 above the CAAQS. In the border regions of western and Atlantic Canada, 2015 and 2020 CAAQS levels are not projected to be exceeded.
- Emerging air quality issues could influence future concentrations of PM2.5 in both countries, and therefore there is a continued need to improve the scientific understanding of health and ecological effects, the impacts of air quality management activities, and the magnitude of transboundary transport.
The following emerging science issues are expected to affect future ambient PM2.5 concentrations and/or how air quality management activities are developed to address PM2.5:
- The need for improved understanding of the health effects of PM2.5 and its components in the context of exposure to other pollutants, and how these combined effects could affect air quality standards and management strategies
- The need for increased understanding of the impacts of climate change on PM2.5 concentrations and of the effects of PM2.5 and its components on climate change
- The effects of changes in the mix of energy generation and end-use technologies on the concentrations of PM2.5 and the impacts of growing domestic fossil fuel extraction activities, such as the oil sands, and unconventional oil and gas development, such as the use of hydraulic fracturing (fracking)
- Changes in the relative importance of natural sources and intercontinental transport that could affect the management of ambient PM2.5 concentrations in Canada and the United States
As the science continues to evolve on these issues, air quality management activities in the United States and Canada may require adjustment in order to continue effectively protecting public health and the environment.
Global Assessment of Precipitation Chemistry and Deposition
Canadian and U.S. scientists co-led and co-authored a global assessment of precipitation chemistry and deposition of sulphur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus, which was published in a special issue of the journal Atmospheric Environment.Footnote8 The global assessment was written by 21 authors from 14 countries under the auspices of the World Meteorological Organization’s Global Atmosphere Watch Scientific Advisory Group for Precipitation Chemistry. The objective was to understand spatial patterns and temporal changes of precipitation chemistry and wet, dry and total deposition, as well as to identify the major uncertainties and gaps in measurement programs and current scientific understanding.
This global assessment was based on worldwide measurement data and chemical transport modelling results provided by Phase 1 of the Coordinated Model Studies Activities of the United Nations Economic Commission for Europe’s Task Force on Hemispheric Transport of Air Pollution (UNECE TF HTAP). The measurement data included wet and dry deposition results from the U.S. National Atmospheric Deposition Program, the U.S. Clean Air Status and Trends Network, the Canadian Air and Precipitation Monitoring Network, and a number of provincial networks in Canada. The broad geographical and chemical coverage of the assessment greatly expanded scientific understanding of U.S. and Canadian deposition relative to the rest of the world. Focusing on sulphur and nitrogen results, the assessment indicated that deposition in eastern North America has declined significantly due to SO2 and NOX emission regulations in Canada and the U.S. However, eastern North America continues to receive very high deposition of sulphur and nitrogen relative to the rest of the world, while western North America receives relatively low deposition. Gaps in deposition monitoring identified for North America include insufficient measurements in western and northern Canada, and incomplete nitrogen deposition measurements in both countries. Figure 36 shows a map from the assessment that illustrates the global pattern of non-sea salt sulphate as sulphur wet deposition, based on combined measurement and modelling results.
Air Quality Model Evaluation International Initiative
The Air Quality Model Evaluation International Initiative (AQMEII) seeks to advance regional air quality modelling science through the development of a common model evaluation framework and joint evaluation and analysis of European and North American regional air quality models. AQMEII is coordinated by two chairs, one for North America and the other for Europe. It is supported by the European Commission’s Joint Research Centre/Institute for Environment and Sustainability, Environment Canada and Environmental Protection Agency.
Note: Measurement values represent 3-year averages (2000-2002) of nssS; model results represent 2001 nssS values.
Source: (Vet et al. 2014).
Figure 36. Measurement-model Wet Deposition of Non-sea salt sulphate as sulphur (nssS) in kg S ha-1 a-1
Figure 36 shows a map from a Canadian and U.S. co-led and co-authored global assessment of precipitation chemistry and deposition of various pollutants. The map illustrates the global pattern of non-sea salt sulphate as sulphur wet deposition, based on combined measurement and modelling results
Phase 1 of AQMEII, which concluded in 2011, included annual regional air quality simulations over North America and Europe for 2006 that allowed regional air quality models from those two areas to be compared for common long-term case studies. The key findings from AQMEII Phase 1 are summarized in a series of manuscripts published in Atmospheric Environment 53, 2012, and EM, the Air and Waste Management Association’s magazine for environmental managers, July 2012.
Phase 2 of AQMEII began in 2012 to compare the “next generation” of air-quality models (which include feedback effects between weather and air pollution) to one other and to observations. Seventeen modelling groups from various governments and universities contributed to the effort. Emissions data for the North America simulations were contributed by the EPA and Environment Canada; the EPA is co-chair for AQMEIIPhase 2 and is leading the development of a special issue of Atmospheric Environment to be published in 2015; Environment Canada is leading a paper comparing the performance of the models for both “feedback” and “non-feedback” simulations. This initiative is contributing to our understanding of the significance of air quality’s effect on weather and to identifying strengths and weaknesses in the various air quality models developed by various agencies.
Tropospheric Ozone Monitoring of Pollution
Tropospheric Emissions: Monitoring of Pollution (TEMPO) is a satellite instrument funded by the U.S. National Aeronautics and Space Administration (NASA), scheduled for launch in 2019. TEMPO will provide observations several times per day of air pollutants over North America, from the Atlantic to the Pacific and from Mexico City to the Alberta oil sands region. TEMPO, the first air quality instrument to be placed in a geostationary orbit over North America, will provide unprecedented coverage and precision in observing important pollutants such as O3, aerosols, NO2, SO2, formaldehyde and others. As such, TEMPO will be ideal for capturing rapidly varying emissions and chemistry, and will significantly enhance air quality monitoring and prediction capabilities.
Canada and the United States are members of the TEMPO science team. In the fall of 2013, the Government of Canada formed a Canadian TEMPO science team comprising leading Canadian scientists from government and academia, to contribute to and complement the objectives of the U.S. TEMPO science team, which comprises scientists from the EPA collaborating with NASA scientists as part of the DISCOVER-AQ research program to evaluate and enhance the capabilities of remote-sensing instruments that will be deployed in TEMPO.
Report a problem or mistake on this page
- Date modified: