NRPLUS MEMBER ARTICLE J ust about every day, someone claims that the air is cleaner. That, we are told, is a small benefit of the coronavirus-induced economic lockdowns. By reducing traffic on our roads, we are polluting the air less, providing a visible example of the supposed benefits of imposing more environmental regulation.
In my hometown of Seattle, one environmental activist told the local paper that people can “physically see that difference in the cleaner air.” The air-quality data tell a different story.
According to the EPA’s air-quality monitors, levels of particulate matter — known as PM 2.5 — are not lower now and have, in fact, been higher recently than the median level of the last five years. Consisting of particles smaller than 2.5 microns, PM 2.5 includes natural sources such as smoke or sea salt, as well as human-caused pollution from combustion.
In Philadelphia, a city health commissioner said, “I would expect our air pollution levels will probably go down because the number of vehicles in the streets are less.” Recent particulate-matter levels, however, have been close to the five-year average.
In Dallas, the levels of PM 2.5 are higher than average. In Boston, they are slightly lower.
This counterintuitive result could be due to a number of influences, including weather. The key factor, however, is that in most places, human-caused pollution is small relative to natural sources. Even a significant reduction in the human contribution makes only a small difference.
So, why do so many activists claim the air is ‘physically cleaner’ in the United States?
In part because they want to believe it. Opposition to cars is a major theme in left-wing environmental politics, and it is simply assumed, without looking at the data, that less driving equals cleaner air. The large gap between the political rhetoric and scientific reality is a reminder that costly environmental regulations should be based in real-world data, not ideologically driven assumptions.
Many of the stories focus on far away cities such as Beijing or Delhi where there is, in fact, cleaner air. Those examples may be interesting, but they say nothing about what policy in the United States. Additionally, they highlight that pollution often goes hand in hand with poverty. If the assumption is that shutting down the economy is good for the environment, the fact that poor countries see the biggest improvements is a counterpoint.
There is also some sleight-of-hand in these claims. Articles that cite data focus not on particulate matter, but on NO2, a pollutant associated with driving. They show satellite photos of reductions in NO2 as evidence that air quality is improving.
The satellite photos, however, are not a reliable method of calculating NO2 levels during the shutdown. The European Centre for Medium-Range Weather Forecasts, which operates these satellites, has pointed out that these media reports are based on a flawed analysis, “by comparing too short time periods and/or insufficient filtering of the data” and that, when used correctly, “no marked trend is detected, for example, over the USA for the first three weeks of March.” Dan Goldberg, an atmospheric researcher at Argonne National Laboratory, recently explained that media claims about changes in NO2 levels in the U.S. since COVID-19 have been incorrect, and are driven mostly by the influence of clouds and routine seasonal changes in the angle of the sun.
While exposure to high levels of NO2 can present health effects, all parts of the U.S. attain the most recent national NO2 standards, which were set at a safe level by the Obama administration in 2010, a standard retained by the Trump administration in 2018.
Although it can be harmful, NO2 is a concern primarily because it is a precursor to particulate matter and ozone. Rather than look at just NO2, we should track the actual pollutant that concerns us. Ironically, many of the misleading articles specifically leave out PM 2.5, perhaps because the data tell the wrong story.
One such article in National Geographic notes that NO2 levels in Dallas declined by three percent between March 1 and April 5. Particulate-matter levels, however, were 24 percent higher than the five-year median. In Seattle, NO2 levels fell in March, but the level of particulate matter increased. National Geographic highlighted the health problems associated with PM 2.5, but left out the relevant data.
Many factors over time influence air quality. Looking only at one or two months, or only one factor, is not enough to draw true conclusions. Some may argue that short-term increases in air pollution do not prove anything. That is fine. But it has not stopped political activists from claiming that the air is cleaner — even when it isn’t — and that reducing car travel caused it. Scientific rigor must go in both directions.
All of this is important for three reasons.
First, the economic lockdown has provided a painful, but useful, natural experiment to test the potential benefits of future air-quality regulations. If a policy claims to reduce PM 2.5 by more than we are seeing currently, under a drastic reduction of car travel, we should be very skeptical.
Second, it is a reminder that despite mindlessly repeating the word “science,” politicians and activists do not always check the real-world data, or they cherry-pick the data they think are useful, ignoring what doesn’t fit their narrative. People assume they can use common sense, but the scientific process is designed specifically to identify where reality conflicts with popular assumptions. Science means following the data, especially when it conflicts with your most cherished assumptions.
Finally, even those (or most of those) claiming our air quality is better admit that shutting down the economy is not a good approach. Considering the painful economic impacts of environmental policy is important, not just for our prosperity, but for the environment. Every dollar spent to help the environment should be spent wisely, to yield the greatest environmental benefit, because the recent economic collapse shows us those dollars may not always be there.
During the past five decades, the air quality in the United States has dramatically improved, thanks in part to government regulations. Reducing the impact of air pollution is a goal we should continue to strive for. The small impact from the lockdown on particulate matter, however, reminds us that our air is very clean and dramatically better than in the past, and that adding even more costly regulations would likely provide limited benefit. To successfully identify the best ways to make additional progress, we need to look closely at the data, and not base our efforts on misguided assumptions.