EPA’s Air Quality Index (AQI)

Posted: December 5th, 2008 under Green Places.

Overview:

After four posts about scales measuring the environmental performance of automobiles, auto companies, city transportation policies, and even our personal driving skills, we might think that if we do well on each of these measures, our environment should be doing okay.  But how would we know?  We also need measures of environmental quality — the current state of our environment — to assess whether our actions are making a difference; indeed, these are the “Scales of Green” that ultimately matter the most.

One measure that may be a good start is the Air Quality Index (AQI), which the federal government requires all metropolitan areas with populations greater than 350,000 to calculate and distribute to local media outlets.  The scale is from 0 to 500, with five levels and colors of increasing health concern, and highlights pollutant levels that may be particularly hazardous for at-risk groups (e.g. people with heart conditions, asthma, etc.).

Transparency: Air*

EPA’s AirNow.gov website provides in-depth descriptions of the AQI and how it is calculated.  A particularly detailed document oriented towards state and local air quality monitoring agencies provides the methods, equations, and tables that should be used to generate the AQI.  The site discusses both what is measured and is not measured, and the limitations of the metric.

Governance: Republic

The AQI is calculated by government agencies based on data from approved air monitoring stations across the country. The EPA provides overall guidance and regulation of the process, while state and local agencies implement it.

Coverage: Hedgehog

While Air Quality Indexes can be calculated for as many as five air pollutants, it does not cover any of the 188 air toxics covered by the Clean Air Act nor any water and ground pollutants.  And often only ozone and particulate matter AQIs are calculated and distributed (if the others are generally shown to be below 50).  Therefore it is a relatively narrow measure of environmental performance, but it is also one of the most precise environmental quality measures available.

This Scale’s “Greenness:”

According to the EPA’s AirNow site, the AQI “tells you how clean or polluted your air is, and what associated health effects might be a concern for you.”  But let’s remember a few important points about this scale:

1. The AQI measures concentrations of five primary pollutants, not toxic pollutants that are more likely to result in longer-term, chronic health outcomes like cancer. An EPA study showed that in some areas these chronic risks may indeed be significant (click here for more info).

2. The AQI focuses on hourly and daily pollutant levels, not long-term trends. The EPA’s National Ambient Air Quality Standards (NAAQS) are more relevant to evaluating our national air quality progress, and EPA’s most recent Trends Report shows that while air quality for the five primary pollutants discussed above has improved over the last 30 years, there are still 158.5 million Americans (more than half) who live in counties with air quality concentrations above the NAAQS.

3. The AQI is focused on human health effects of the air pollutants it measures, not their effects on visibility, either locally or in National Parks, or their effects on vegegation, crops, buildings, and wildlife. Such effects can be significant — see this site on crop damage from ozone as an example.  So while a low AQI may be good for your personal health, it may not necessarily mean the environment is not still being affected.

* For an explanation of the Transparency, Governance, and Coverage “ratings” above, please click here.

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