The preceding 4 posts have explored background air pollution. It is one thing to measure the quality of air in and around our major metropolitan areas and major pollution sources. That kind of air quality has clearly improved markedly over the decades. It is another thing to ask what the background level of pollution is. That you must measure in isolated areas, far away from large cities and pollution sources.

In Background Sulfur Dioxide and Nitric Acid Pollution Improves I reported that the background level of those two pollutants has markedly improved in the eastern part of the United States.
In The Worst Is Better, but the Best Is Worse I reported that at a monitoring site in Adair County, Oklahoma, the ozone level has increased slightly on the best air quality days, and it has decreased slightly on the worst air quality days.

In The Best is Better, but the Worst is Worse, I reported that the level of particulate matter at Bryce Canyon National Park has decreased slightly on the best air days, but it has increased significantly on the worst air days.

In Ozone on the Rise in the Mid-Troposphere, I reported that the background level of ozone at 10-16,000 ft. above sea level was rising in Hawaii and in the western United States, as a result from ozone precursors emitted in Asia.

Combined, these posts suggest that there is no single, simple answer about the background quality of air. In some ways it seems to have improved nationally, in others it seems to have deteriorated. In Missouri, the overall level of sulfur dioxide and nitric acid seems to have decreased. However, some of the measurements that show increased background pollution have not been made in Missouri, and we don’t know what they would show here. The data also does not address trends in peak and low values. The paper by Jack Fishman that I mentioned in a previous post may shed some light. I’ll report on it when it gets published.