Residential wood combustion, particulate matter 2.5 sampling project, Whitehorse: chapter 2

• 2.1 Sampling Sites
• 2.2 Sampling and Analysis
  • 2.2.1 PM_2.5 Filter-based Sampling
  • 2.2.2 Continuous Measurements
  • 2.2.3 Quality Control

2. Methodology

2.1 Sampling Sites

Sampling for this study was conducted at two sites in the city of Whitehorse: one in the downtown core and one in the neighbourhood of Riverdale. The city is located along the Yukon River, approximately 150 km northeast of the waters of the Gulf of Alaska. The Yukon River runs from south-southeast to north-northeast to the east of the downtown core as seen in Figure 2, and is approximately 620 m above sea level. To the west of the downtown area, an escarpment rises to a height of approximately 700 m above sea level, upon which Whitehorse Airport is located. The subdivision of Riverdale is on the eastern bank of the Yukon River southeast of the downtown area. Riverdale is situated in a bowl with an escarpment partially encircling the subdivision to the south and east.

The locations of the sampling sites are shown in Figure 2. The sampling site in downtown Whitehorse was located at the Wood Street Annex School, at Wood Street and 4th Avenue (60° 43’ 12.1”, -135° 03’ 31.4”). Sampling took place on the rooftop, approximately 8 m above ground level. The area surrounding the sampling site in downtown Whitehorse is a mix of residential and commercial development. The Riverdale site was located on the rooftop of Vanier Senior Secondary School at 16 Duke Street (60° 42’ 9.0”, -135° 01’ 46.0”), approximately 2.5 km southeast of the downtown sampling site, with sampling taking place approximately 4 m above ground level. The surrounding area is residential, consisting primarily of detached homes and some apartment buildings. Both buildings upon which the samplers were located are heated by diesel boiler, with exhaust chimneys on the roof. Impact on the samplers was expected to be minimal, however, as the chimneys were approximately 50 m away, above the level of the sampling inlets and not located in the predominant upwind direction.

 

2.2 Sampling and Analysis

2.2.1 PM_2.5 Filter-based Sampling

Integrated 24-hour ambient PM_2.5 samples were collected using Partisol 2000H samplers (Thermo Scientific, Waltham, MA), following a 1-day-in-3 schedule (midnight to midnight) for 2 months from January 24 to March 22, 2009, for a total of 20 sampling events. One Partisol sampler (Sampler A) was located at the Downtown site, sampling a single Teflon filter for each sampling event, which was subsequently analyzed for PM_2.5 mass and levoglucosan. Two Partisol samplers were located at the Riverdale site. One sampler (Sampler B) was modified to house a dual stage filter pack. A Teflon front filter was analyzed for PM_2.5 mass and levoglucosan, while the back-up quartz filter was analyzed for organic and elemental carbon (OC/EC). A second Partisol sampler (Sampler C) at the Riverdale site employed a single quartz filter, which was subsequently analyzed for OC/EC and ¹⁴C. OC results from this sampler were corrected for positive artifacts by subtracting the value from the back-up quartz filter on Sampler B.

All filters were prepared at Chester Labnet (Tigard, Oregon) and sent to Whitehorse in coolers on ice. Filters were stored in a freezer at the Environment Canada office until the day prior to sampling. After sampling, all filters were wrapped in aluminum foil and stored in a freezer, prior to shipping to the laboratory on ice.

All Teflon filters were analysed for PM_2.5 mass by gravimetry at Chester Labnet and subsequently sent to the University of British Columbia School of Environment Health Laboratory (Vancouver, B.C.) for analysis of levoglucosan by gas chromatography mass spectrometry following a modified version of a method developed by Simpson et al. (2004).

A 1.5 cm² punch from each quartz filter was analyzed for OC/EC at Chester Labnet by thermal optical transmittance using the NIOSH Method 5040 temperature program. The remainder of the quartz filters from Sampler C were sent to the University of Arizona Accelerator Mass Spectrometry Laboratory Facility for analysis of ¹⁴C by a method described by Ward et al. (2006).

2.2.2 Continuous Measurements

In addition to filter-based sampling at the Riverdale site, a Magee Scientific AE-21 Dual Wavelength aethalometer (Magee Scientific Company, Berkeley, CA) with a PM_2.5 sharp cut cyclone was installed to continuously measure black carbon at 880 nm and 370 nm (UV channel). The aethalometer was set up in a ground floor room with the inlet line running outside to a height of ~4 m through a ventilation duct. Sampling took place from January 27 to March 31, 2009.

Meteorological sensors were installed adjacent to the Partisol samplers at both sites to measure hourly temperature and wind speed/direction from January 26 to March 31, 2009. Sensors were mounted on 2 m poles; therefore, winds were measured at approximately 10 m and 6 m above ground level at the Downtown and Riverdale sites, respectively. In addition, temperature, 10 m winds and twice-daily sounding data from the Environment Canada climate station at Whitehorse Airport were used in this study.

2.2.3 Quality Control

Two field blank samples were taken for each sampler. PM_2.5 mass, levoglucosan and OC/EC results were corrected for these blank values, while ¹⁴C results were corrected based on laboratory blank filters. One duplicate sample was taken to assess any differences in comparing results from a standard Partisol 2000 set-up to that with the filter pack set-up. Results for the duplicate sample were 7.1/8.1 µg/m³ and 552/590 ng/m³ for PM_2.5 and levoglucosan, respectively. Average laboratory surrogate recoveries for levoglucosan were 105%; results were not recovery corrected.