A recent AP News article, published on June 18 just before the announcement of the final Affordable Clean Energy rule, begins with the ominous headline, “US air quality is slipping after years of improvement.” The timing and tone of the article seem conspicuously fine-tuned to make a case that because the Trump Administration is not continuing the Obama-era EPA’s tightening of air quality regulations, our air quality will get worse. It begs the question whether an article like this would have been written after the pauses in air quality improvements that occurred during the Obama Administration. Richard Truzpek of the Heartland Institute wrote a longer rebuttal of the article, and here is a shorter summary of the main errors.
1. The authors do not acknowledge the fact that the Trump Administration has not relaxed any of the National Ambient Air Quality Standards (NAAQS) for the six criteria pollutants.
2. They focus on the Air Quality Index (AQI) and ignore the continued declines in average ambient levels of pollution.
3. The recent uptick in the percentage of unhealthy AQI days, which the article is based on, is from 1.39% in 2016 to 1.70% in 2018. Larger blips occurred during the Obama administration (see plot below), such as a rise from 1.83% in 2009 to 3.29% in 2012.
4. Lower emissions have made the number of unhealthy AQI days so low that changes are increasingly susceptible to factors other than emissions, such as wildfires, weather patterns, and pollution from Asia. 1843 of the 5762 unhealthy days in 2018 (32%) occurred in California, which suffered from all these influences.
Check out this dramatic decline in days with a low AQI rating (which means more recorded days with better air quality):
Let’s cover some of these errors in greater detail. First is the recent uptick in the percentage of unhealthy AQI days, from 1.39% in 2016 to 1.70% in 2018, a statistically insignificant amount compared to the improvements in air quality over the past 40 years. Larger blips occurred during the Obama administration – such as a rise from 1.83% in 2009 to 3.29% in 2012 – but only an occasional whisper was heard about air quality slipping. The level of pollutants is already so low, and the number of unhealthy AQI days so close to zero, that it is very hard to get much lower.
However, the article’s primary error is its use of the AQI in the first place and the way it confuses overall air quality with the number of days that U.S. cities have “unhealthy” AQI ratings. The AQI measures how the pollution in a given area compares to the NAAQS for each pollutant. Any time a pollutant that exceeds the NAAQS value will trigger an unhealthy AQI rating for that day.
The AQI has never been, nor was it intended to be, a clear measure of average ambient levels of air pollution. It was meant to warn people in a given area that pollution levels were higher than normal so that they could adjust their behavior that day if necessary. A better measure of air quality is the average ambient level of pollution across a wide geographic area, especially when compared over many years. By this measure, we have reduced average pollutant levels by more than 70% since 1990.
AQI is also heavily affected by changes in weather, wildfires, and other variables and is not always directly tied to our emissions of pollutants. As Richard Truzpek points out, the 2014 National Emissions Inventory (the most recent inventory) found that only about 12% of the emissions of fine particulate matter (PM2.5) come from US industrial sources. Wildfires in the Western U.S., dust from Africa, and migration of pollution from Asia likely all contributed to increase in PM2.5 in 2018. 1843 of the 5762 unhealthy days in 2018 (32%) occurred in California, which suffered from all these factors.
Finally, the data on which EPA calculates the index comes from monitors that do not report every day. The AP journalists further compound the problem by looking only at the data from cities, not the more geographically comprehensive county-level data.
What this article should focus on are the “years of improvement” it mentions, really decades of improvement, in US air quality and the fact that we have every reason to expect that it will continue to get better.