June 2013: How Does Indiana’s Air Quality Compare to Other States?

This is the eighth article in a series about air quality in general and how it applies to Indiana. I am planning to publish an article every two weeks to cover air pollution topics. This article will discuss how air quality between states might be compared.

How does Indiana’s air quality compare to other states? We continue to hear that Indiana “has some of the worst air in the nation.” Careful analysis of national air quality would not support this conclusion. Data to make these comparisons can be obtained from the U.S. EPA website. One of the footnotes that accompanies the data states:

“Readers are cautioned not to rank order geographic areas based on AirData reports. Air pollution levels measured at a particular monitoring site are not necessarily representative of the air quality for an entire county or urban area.”

One of the major problems in comparing air quality from one state to another is that not all states have similar monitoring networks. U.S. EPA establishes minimum monitoring requirements that are normally related to population. However, some states go above and beyond these minimum requirements which may cause a state to show lower air quality levels due to running additional monitors. For example, Florida had a population of 19 million in 2011 and ran 27 PM-2.5 monitors. Indiana has a population of 6.5 million in 2011 and ran 35 PM-2.5 monitors. On a monitors per million people basis, Indiana has nearly 4 times as many PM-2.5 monitors as Florida. Indiana has higher PM-2.5 levels than Florida. How much of this is due to the fact that we run more PM-2.5 monitors?

Some states do not monitor for all pollutants. Two states did not monitor for PM-10 in 2011. Four states did not monitor for NO2 in 2011. Fifteen states did not monitor lead in 2011. How do you compare air quality between states when states are not even monitoring all pollutants?

Another problem is that there is no established grading system. Currently there are seven criteria pollutants (PM-10, PM-2.5, SO2, NO2, ozone, CO and lead) with a total of nine averaging periods. Thus a state that measures all criteria pollutants would have nine different values to use for grading purposes. Do you compare maximum values or average values for each state? Should you consider how many people are exposed to the varying levels of air quality when doing the grading? Without any established standards, people can make it up as they go along. This is how Indiana got such a poor rating from one group. They chose to look at only annual PM-2.5 values and ignored all other pollutants and averaging periods.

A fair assessment should look at all pollutants. However, when some states do not measure certain pollutants and there is such a difference in how many monitors states run, there is not a fair way to compare one state versus another.

One way of looking at this is to use only PM-2.5 and ozone data and review how states compare with the national ambient air quality standards. Only PM-2.5 and ozone are selected because all states measure these pollutants and the monitoring networks are more extensive/comprehensive than those for other pollutants. Using data for the most recent three years (2009 – 2011) which is readily available, design values were determined. For each state, using the highest measured value which was then compared to the national ambient air quality standard. This results in the following:

National Ambient Air Quality Standards (NAAQS)
Pollutant Average Period Number of States
Meet NAAQS Do Not Meet NAAQS
Ozone 8-hour 28 22
PM-2.5 24-hour 42 8
PM-2.5 Annual 49 1
Overall: 22 28

Only 22 of the 50 states meet the NAAQS for PM-2.5 and ozone. Indiana meets all three. Thus we would argue that the air quality in Indiana is in the better half of the nation, not some of the worst in the nation. However, this is only one way of looking at air quality data.

Until there is a widely accepted way of grading air quality and a way to evaluate the differences between monitoring networks, there will be no universally accepted answer to this question.

Keith Baugues