From the ABC 7 Weather team

Washington D.C. Forecast: Air Quality Index Explained

July 16, 2013 - 10:00 AM
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It's that time of year again when you will hear about the Air Quality Index (AQI).

The AQI is a daily report that gives the quality of the air across the region. This index becomes increasing more important in the summer months when our air quality is more at risk for being unhealthy.

A color coded chart was designed to more easily inform the public about the anticipated air quality level, what impacts it may have on health and what actions you can do to help reduce the pollution levels!

AQI Action Guide

For example, today is forecast to be a Code Orange Day, which means the air is unhealthy for sensitive groups of people. According to the professionals at Clean Air Partners, “children and adults with respiratory and heart ailments, may experience health effects and should limit time spent outside. The general public is not likely to be affected.”

But throughout the course of the summer we will likely have some Code Red days as well and those days impact all of us. But what exactly causes the pollution? My Storm Watch 7 colleague and friend Ryan Miller who also happens to teaches Environmental Science at Washington and Lee High School does a great job explaining the ins and outs of air quality!

Poor air quality days occur because of the emission of certain chemical compounds into the atmosphere that often times react with light from the sun to produce pollutants.

The emission of these chemical compounds, primarily through the burning of fossil fuels for electricity production (coal) and for transportation (gasoline and diesel) couple with other pollutants to give us bad air to breathe.

The two most prevalent pollutants that give us poor air quality in the D.C region are ground-level ozone and incredibly tiny particles of materials like dust and carbon (among other things).

The reason for more poor air quality days in the summer has to do with several factors:

1. Ground-level ozone, the bad ozone, forms when our power plants and cars emit a chemical compounds called nitrogen oxides and volatile organic compounds that react with sunlight to produce this form of unhealthy ozone. We use more electricity right now to power more air conditioning systems, that allow for more emissions of these aforementioned chemicals into the atmosphere, that increases ground-level ozone concentrations and degrades the air.

2. Our summer months have days that are filled with much more light from the sun and it is this sunlight that works in tandem with the chemical compounds we emit from fossil fuel use (again electricity production and transportation) to create more atmospheric pollutants than at any other time of the year.

3. From a weather standpoint in the summer much of the North American continent is heated up in an almost semi-uniform manner and thus we often do not get very strong frontal systems (like cold fronts) to pass by and deliver big changes in air. These frontal systems are often accompanied by strong winds, think of the winds our region gets in the fall, winter, and spring, and because of the lack of strong winds over a large geographic area during the summer months the air in our atmosphere can stick around for days and become stagnant. We keep emitting pollutants into our atmosphere in the summertime and without strong winds to move these pollutants away from our region they accumulate more and more into the air we breathe and degrade the air quality.

A cautionary note about exercising outside during poor air quality days.

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Out of our two primary pollutants that cause bad air quality, ground-level ozone and particle matter, its ground-level ozone that accumulates and can be very detrimental to our health. Remember, it takes sunlight to make ground-level ozone, and we are getting sunlight all day long that works to form this harmful air pollutant, so it is the afternoon and evening that has the largest amount of ground-level ozone present in the atmosphere (with the highest concentrations).

Exercising in the evening will expose you to more harmful pollution that at most other times of the day. Don't do it. Exercise in the morning or inside at a gym on these poor air quality days.

Monitor our air quality be visiting this web site from the Metropolitan Washington Council of Governments and their charter partner organization Clean Air Partners!

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