What’s with all these AQI’s?

There are several Indices of Air Quality (AQI) provided to you on this website: hourly traditional AQI; most current hour AQI; and the twice-daily news release AQI. All provide accurate information about the air you breathe, and the one you choose to use depends upon your individual needs.

So which AQI is for me?

The US EPA requires communities with a population of 350,000 or greater to report Air Quality Index numbers on a daily basis to the local media. EPA specifies how the AQI should be calculated and reported. (See the link at the end of this page for more information.)

Up to the hour traditional AQI – The “traditional” Current and Historic Air Quality Index (AQI) reports that are located in the data area of AirInfoNow, calculate index values by finding the highest appropriate average according to the EPA health standards (8-hour averages for ozone and carbon monoxide and 24-hour averages for PM10 and PM2.5) for the various pollutants going back for 24 hours. For ozone and carbon monoxide, the highest of these averages over the last 24 hours is used to calculate the index values.

In AirInfoNow these reports are calculated on an hourly basis for every hour of the current day. Then, after the last hour of the current day, the system archives that report and moves on to the next day’s reports and repeats the process. Hourly and archived data are referenced in this section of AirInfoNow. Use these reports in AirInfoNow to see how today’s air quality compares with previous days and/or what air quality was like for a particular day in the past.

Most current averages AQI – This is the AQI report you see on the home page of AirInfoNow. We call it most current averages because we only look at the most current 8-hour average for ozone and carbon monoxide, and the most current 24-hour average for PM10 and PM2.5. The index value is based on these current averages, instead of going back for 24 hours. This gives a better idea of what the air quality conditions are right now. You can use this table to decide what impact the current air quality will have on your health.

This still isn’t an ideal indicator of what is happening right now because of the nature of averaging over the 8-hour or 24-hour interval. In general, this ending hour AQI tends to under report index values when ozone pollution levels are rising (early afternoon), and over report values when ozone pollution levels are decreasing (late afternoon). However, it is based on the most current levels for pollutants and therefore, gives you a better indication of what pollution levels are now.

Twice daily news release AQI – Pima County DEQ is required to report AQI values on a daily basis to the local news media. The Air Quality Index report link in the data section of AirInfoNow will take you to a copy of the current version of this report. PDEQ prepares this report twice daily, at 9:00AM and 3:00PM, and sends it to various news organizations around the County. The reports are calculated using the “most current averages AQI” method.  Index values are based on the most current 8-hour average for ozone and carbon monoxide, and the most current 24-hour average for PM10 and PM2.5.  Use this report in AirInfoNow to see the daily reports that are being sent to the news departments of the local television stations and to the daily newspapers.

Click on this link for an explanation of the EPA Air Quality Index; Air Quality Index – A Guide to Air Quality and Your Health (PDF-816KB): This booklet explains EPA’s Air Quality Index (AQI) and the health effects of major air pollutants.

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