Air quality and weather

Air Quality Models

Air quality models are complex systems that help us predict air quality conditions. They pull together multiple sources of data and simulate how pollutants, including wildfire smoke, spread and transform in the air.

The model helps us calculate the Air Quality Health Index.

Regional Air Quality Deterministic Prediction System

We use the Regional Air Quality Deterministic Prediction System (RAQDPS) to forecast air quality conditions in the atmosphere for entire regions.

The animated maps provide hourly forecasts across North America for the next 72 hours. The RAQDPS is a model that pulls together different sources of air quality information:

• meteorological data, and models with inputs such as temperature, wind, precipitation and cloud cover
• emissions inventories for accounting sources like industrial activities, transportation and residential wood combustion
• chemical transport models that simulate the complex physical and chemical processes that affect air pollutants, such as gas phases, aerosol dynamics, and precipitation.

The maps provide forecasts of:

• nitrogen dioxide (NO2)
• ozone (O3)
• total fine particulate matter (PM2.5) for all sources
• wildfire smoke fine particulate matter (PM2.5)
• average fine particulate matter (PM2.5)
• maximum fine particulate matter (PM2.5)

View more Air Quality Model Forecast Maps.

Get the data products on the MSC Datamart and GeoMet open data platform.

Wildfire smoke and the RAQDPS

During wildfire events, we use the RAQDPS to simulate the spread of smoke plumes and how they will affect air quality. The model pulls together information on:

• fire location
• size
• behaviour
• fuel types
• weather (meteorological) conditions

How the prediction system helps with safety during wildfires

When we receive information on how wildfire smoke will spread and the effect on air quality, our meteorologists are able to create forecasts. Our forecasts help authorities:

• expect where the smoke will travel
• issue warnings to people that could be affected, and
• determine the resources they need to manage wildfires and protect public health

Ventilation Index

We offer a national ventilation forecast data product across Canada. Get the ventilation forecasts on MSC Open Data and MSC AniMet.

In Canada, forestry and farming often need open burning. Some people burn yard waste or wood for heat during the winter. However, these activities can lead to poor air quality depending on the weather.

A ventilation forecast can help industries, governments, and individuals plan their burning activities. It shows the best time to burn, based on the weather and air quality.

The ventilation index measures how the atmosphere can mix or spread pollutants. It uses data from many weather simulations to create a grid that predicts ventilation.

Ventilation Index ranges

Level: 0

• the worst level of ventilation
  • air is stagnant and stays in an area
  • low capacity to disperse pollutants results in poor air quality

Level: 100

• the best level of ventilation
  • air is well mixed in the atmosphere and transported by the wind
  • wind minimizes local air quality impacts

How weather conditions affect air quality

Different types of weather conditions can affect air quality and how much pollution is in the air. These conditions include:

• wind
• temperature inversion
• topography (shape of the landscape)
• clear, cloudless sky
• precipitation (fog, rain, snow, etc.)

Wind

When wind blows, it can carry pollution over long distances towards us or away from us. Sometimes it can create a channel in the air that starts at a pollution source and carries pollutants out to hundreds and even thousands of kilometres away (long-range transport). Particulate matter less than 2.5 microns and ground-level ozone are examples of pollutants that can be transported over long-ranges.

When wind is still or very light, local pollutants can also build up. During summer or winter, this happens when light wind or no wind combines with a temperature inversion.

Temperature Inversion

A temperature inversion happens when cool air is on the ground and warmer air is above. In normal conditions, warm air is at the ground level and cool air is over the top.

During an inversion, the temperatures are upside down. The warm air acts like a ‘lid’ and traps pollutants with the cool air at ground level where we live and breathe. Inversions can last for hours or days.

Topography

Topography, or the shape of the landscape, can cause conditions that trap pollutants. For example, low-lying basins and valleys can trap the cool air that settles there at night. Because of the dip in the landscape, the cool air is unable to rise. Unable to rise, the cool air settles and traps air pollutants that accumulate in these valleys.

Clear, cloudless skies

A clear, cloudless sky can cause higher air pollution since it lets more sunlight and UV (ultraviolet rays) get to the Earth’s surface. The increased sunlight on a cloudless day, especially strong summer sunlight, causes chemical reactions in existing air pollutants. For example, the increased sunlight causes more reactions in nitrogen oxides, which creates ground-level ozone. Ground level ozone is a major part of smog.

Precipitation

Precipitation (rain, snow, fog, etc.) acts like a ‘cleaner’ for the atmosphere when pollution particles attach to water droplets in the air. The water droplets can stay hanging in the air as part of clouds or fog. Droplets can also carry the pollution to the ground (wet deposition) and into our rivers and streams through rain or snow.

How weather affects wildfires

Weather plays an important part in wildfires. Dry conditions, heat, heat waves, and wind all influence wildfires because they affect:

• the likelihood of a fire starting
• the fire behaviour when it is burning
• the spread of the smoke

Dry weather and wildfires

Dry weather conditions can make it easier for wildfires to happen, such as:

• a long dry spell when fuel sources (trees and especially resinous trees, leaves and branches on the ground, other fuel) dry out and ignite easily
• low snowpack in winter and a lack of rainfall in spring and summer
• high temperatures increase evaporation and moisture loss

Heat, heatwaves and wildfire smoke

Heat and heat waves (extreme heat events) affect how often and how likely fires will be. For example, lightning strikes (one of the key causes of wildfires) are more likely during heat waves.

Heat waves often form with dry conditions. It is easier for air temperatures to rise because dry air has less water droplets to evaporate. Climate change causes warmer temperatures and changes precipitation patterns. As a result, we get drier and hotter summers. These increased temperatures don’t get balanced with precipitation, which causes favourable conditions for wildfires.

Wind, lack of wind and wildfires

Wind and lack of wind can affect the spread of wildfires and smoke pollution:

• strong winds feed a wildfire with oxygen, and cause it to grow and spread
• strong winds can spread the smoke out over large areas
• wind can make the fire travel in different directions
• light wind keeps the smoke plume in one area
  • light wind makes smoke rise very high in the atmosphere
  • it can travel hundreds and even thousands of kilometres away from the fire
• light winds often happen with temperature inversions
  • inversions trap smoke near the ground and cause severe air pollution in the local area

Related links

• Weather information and alerts
• Local Air Quality Health Index
• Wildfire smoke, air quality and your health
• Weather and smog
• Extreme heat events and heat warnings
• Weather impact guides
• Navigate the weather information map