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On Some Days, Air Quality is Good


The Air Quality System Data Mart maintained by the EPA contains data on the air quality of a number of Missouri counties going back to the early 1980s. I downloaded data going back 10 years (2012-1993), and for a longer term perspective, for 1993 and 1983.

Good Mississippi ChartNineteen counties have been monitored for more than 6 of those 12 years. I put them in three groups: a group along the Mississippi River north and south of St. Louis, a group in the Kansas City-St. Joseph region, and a widely dispersed “other” group.

For a fuller discussion of the data maintained by the EPA, see my previous post Is Air Quality Better or Worse?

The graphs at right show the percent of monitored days on which the Air Quality Index was in the Good Range. The top graph is for the Mississippi counties, the middle one is for the Kansas City-St. Joseph counties, and the bottom one is for the Other counties.

There is a higher percentage of good air days in the Other counties. This is, perhaps, not surprising, as these counties tend to be more rural in character, and they lack the very large metropolitan areas in the other two groups.

Good KC ChartThe counties along the Mississippi seem to fall into a group of four counties that has more good air quality days, and a group of three that has fewer. The latter group includes St. Louis City and St. Louis County, plus Jefferson County. Air quality in these three was good in less than 60% of the monitored days. It is difficult to infer trends over time, but the general trend seems to be towards more good air quality days. In particular, St. Louis City, St. Louis County, and St Charles County all experienced significant increases in the number of good air quality days between 1983 and 1993. Jefferson County, on the other hand, experienced a large decrease in the number of good air quality days.

In the Kansas City-St. Joseph area, the counties generally started off in 1983 with a higher percentage of good air quality days. However, the trend seems to be towards fewer good air quality days. Jackson, Cass, and Buchanan Counties now have less than 70% good air quality days. The drop in air quality experienced by Buchanan County in 2008 stands out, and I do not know its cause.

Good Outstate ChartThe Other counties are distributed widely around the state. All had more than 50% good air quality days throughout the entire period, and a significant fraction above 70%. The trend here appears to be variable, with some counties experiencing more good air quality days, some fewer.

It is important to know whether air quality is good, but it is also important to know if it is bad enough to be unhealthy. I will report on that in my next post.


Air Data, EPA, http://www.epa.gov/airquality/airdata/

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