Behind the Forecast: How cold weather affects air quality

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Science Behind the Forecast: How cold weather affects air quality

LOUISVILLE, Ky. (WAVE) - Air quality is critical to the quality of our everyday life. Air quality is impacted by the number of pollutants, like smoke, dust, and smog in the air. When pollution levels are too high, it poses a risk to humans, animals, plants, and natural resources.

Man-made or natural sources of pollutants can degrade air quality. Natural sources include dust and volcanoes. Cars, power plants, burning wood, and landfills are types of human-produced air pollution.

Rain, hot temperatures, wind speed, sunshine, and air turbulence can affect the concentration of pollutants in our atmosphere.

When temperatures drop, car and home exhaust become more visible. Pollutants collect near the ground during colder, calmer months due to temperature inversions. During a temperature inversion, smoke is unable to rise and disperse in the atmosphere and carbon monoxide may increase to unsafe levels.

There are two ways that cold air can settle over an area. First, when Canadian or Arctic air drives into the United States accompanied by strong winds and frigid wind chills. Another way is when a shallow layer of dry, cold, calm air settles over a snow-covered region. The second type of cold wave may last longer than the first, but it covers a smaller area. "The first is strengthened by large-scale atmospheric circulation patterns favoring cold air advection, while the second is reinforced by clear-sky radiative cooling," according to researchers. That means air quality in the winter is dependent on the type of cold wave. Temperature inversions are more likely with the second type of cold wave as well. A temperature inversion is defined as " a layer in the atmosphere in which air temperature increases with height." Cool air can't rise since the warm air acts like a bottle cap, trapping the pollutants near the ground and keeping them from dispersing.

Ground-level ozone forms when nitrogen oxides from car exhaust and industrial pollution react with organic compounds with the help of heat and sunshine, according to the National Weather Service (NWS). Sunshine can instigate some chemical reactions creating smog. Hot temperatures speed up those chemical reactions. Ozone can cause numerous health problems ranging from coughing to lung damage, according to the Environmental Protection Agency (EPA).

Storms help to clear pollutants because they wash problematic particles out of the atmosphere and circulate the air. Winds and air turbulence affect how pollutants spread out across an area.

The Air Quality Index (AQI) reports how unhealthy or clean the air is and potential health impacts. The EPA calculates the AQI for several major pollutants that are regulated by the Clean Air Act: carbon monoxide, nitrogen dioxide, ozone, and particle pollution. The higher the AQI, the worse the air pollution. Values above 100 are considered unhealthy. The primary focus in Kentucky and Indiana is ground-level ozone (O3) and particle pollution (PM2.5).

EPA has assigned a specific color to each AQI category to make it easier for people to understand quickly whether air pollution is reaching unhealthy levels in their communities.
EPA has assigned a specific color to each AQI category to make it easier for people to understand quickly whether air pollution is reaching unhealthy levels in their communities. (Source: Environmental Protection Agency)

During the winter, indoor air quality can quickly deteriorate because of poor ventilation. If circulation is improper, carbon dioxide can collect in a home, causing headaches and lethargy.

For the latest air quality forecasts from the EPA and NWS, head over to https://www.airnow.gov/ or https://airquality.weather.gov/.

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