Understanding Air Quality Information

Confused about what the colors green, yellow, and red really mean with respect to our air quality? Wondering what a 24-hour average is and how it differs from current air quality data?

Air quality data is constantly being updated online from a few stations around the state, and with a little orientation we each can get the information we want and make sense of it.

What Air Quality Information is Available in Utah?

There are two websites that provide current information on air quality in our area, one
sponsored by the Utah Department of Air Quality (DAQ) and the other by the EPA. 

The DAQ website provides both straightforward interpretations of air conditions and the most technical information if you would like to become handy at predicting air quality and health hazards for yourself. 

The EPA also uses data collected by the DAQ and displays a simplified readout as well as some specific pollutant levels, but processes the data by a different formula.

The DAQ Website, www.airquality.utah.gov

The welcome page at the DAQ shows an overall prediction for how severe the air pollution is for the next three days, ranked as Green, Yellow, or Red. This is the simplest digest of the pollution hazard level for our area, but it’s only as accurate as the weather information it’s based on. (When the weather report says it’s raining today, it’s probably right! Tomorrow, well, you know how it goes.) Once at the site, you may choose your favorite Wasatch Front region. Utah has its own color coding for air quality conditions: 0 – 24 micrograms/cubic meter concentration of PM2.5 is considered Green, 25 – 34 ug/m3 is Yellow, and 35+ ug/m3 is Red. As you may guess, the cutoffs are somewhat arbitrary and subject to change the more studies reveal about the hazards of breathing air pollution, the lower those cutoffs will get shifted.

The “Current Conditions” button brings you to a thermometer-type readout of the current levels of whichever air pollutant is prevalent (usually PM2.5 in the winter and ozone in the summer.) This is a 1-hr average readout, and is updated hourly. The live photo is cool. If you want to know what you’re breathing when you open the door right now, this is your number. Check your nearest skyline to see what this pollution level looks like!

The “Trends” button is for you data heads. Graphs showing the levels of 3 criteria pollutants, PM2.5, ozone, and nitrogen oxides (NOx) over the last 5 days let you see the daily rise and fall over time of day and weather patterns. For two of the pollutants there is a second data line, of 8-hr and 24-hr averages (for ozone and PM2.5, respectively) that is simply the average of the 1-hr numbers from the previous 8 or 24 hours. The 8-hr and 24-hr averages are important for two reasons: one, the longer averages say
more about our overall exposure to the pollutant, and two, averages are what get evaluated by the EPA, with vast financial and legal ramifications for the State if we are in “non-attainment” too often.

The EPA Website, www.airnow.gov

Lastly, the EPA uses a numerical Air Quality Index, or AQI, that is derived from the longer average level of each pollutant. For example, you can see EPA’s assessment of Salt Lake City. The number, which is NOT the actual concentration of any one pollutant, corresponds to a Life Saver color describing grades of health hazard.  The EPA explains the AQI thoroughly.

The AQI is meant to give you a standardized estimate of the day’s health risk regardless of the actual pollutant, so the scale is the same in winter (PM season) and summer (ozone season). Since the EPA gets its data from our own DAQ, the only difference is interpretation.

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