The cars are parked. Can we breathe safely now?
By Susan Anenberg and Dan Goldberg
Scientists around the world are hard at work understanding how the composition of the air we breathe has changed during COVID-19 physical distancing. Last month, NASA reported that nitrogen dioxide levels, an indicator of urban air pollution, have declined by about 30 percent on average across the Eastern United States, when comparing March 2020 to a typical March. Satellite data indicate that China and Italy also experienced massive improvements in air quality during COVID-19 lockdowns.
Two things happened during the COVID-19 lockdowns that can explain the air pollution levels we are seeing. Activity levels of major emission sources dropped, on the order of about 50 percent for passenger vehicles, over the course of a few days. At the same time, much of the U.S. experienced a windy and rainy transition period from winter to spring, which kept air pollution low. The combination of favorable weather and emissions reductions during the lockdowns has pushed air pollution down to some of the lowest levels seen in recent decades. Our preliminary analyses using satellite data indicate that nitrogen dioxide in Washington, DC, dropped 31 percent, about two-thirds of which can be attributed to less fossil fuel burning, primarily from less passenger vehicle traffic, and the remaining one-third due to favorable weather conditions.
However, these emissions declines are only temporary. They will go back to pre-COVID-19 levels once we open back up, and potentially even worsen if people are less inclined to pack into subways and buses or if enforcement of environmental regulations loosens.
Unfortunately, these large changes in nitrogen dioxide pollution have not necessarily translated into large improvements in levels of fine particulate matter and ozone, two ubiquitous pollutants that are associated with a range of cardiovascular and respiratory health outcomes, and even early death. While passenger vehicle traffic has been down, other emissions sources are continuing — including trucks and buses, power generation, agriculture, manufacturing, and shipping. Combined with shifting weather patterns and the complexity of atmospheric chemistry, these continuing emissions have muted the impact of the nitrogen dioxide reductions on overall air pollution levels.
Perhaps most importantly, any emissions reductions have come at an enormous public health and economic cost. The right way to reduce air pollution is by strengthening and enforcing regulations that keep emissions low without damaging the economy. In fact, even before the lockdowns, air pollution levels were already among the lowest we have experienced in the last half a century. We have the Clean Air Act of 1970 and its 1990 Amendments to thank for a 74 percent decline in air pollutant emissions, even while gross domestic product increased by 275 percent.
But we still have a way to go. Mounting evidence indicates that even low levels of pollution can make people sick. The natural experiment we are experiencing can shed light on some important questions for designing future emissions policies: How much can policies that reduce emissions from transportation and other sources influence local air quality? What are the impacts of different types of vehicles, such as passenger cars, trucks, and buses in different cities and countries? With the unprecedented and sudden drop in emissions from passenger vehicles in cities globally, we can observe a signal that may otherwise be impossible to isolate.
At GW, we will be spending the next year or more pouring through satellite images to address these questions. With support from NASA, we are using the OMI and TROPOMI satellite instruments, along with ground measurements of air pollution, traffic and mobility data, and atmospheric modeling to estimate pollution levels in various cities worldwide. We will try to understand why we are seeing variations in the post-social distancing air pollution levels in different cities globally and will work with key stakeholders to use this information to develop more effective and efficient policies.
While it may seem like the air is getting cleaner because of the traffic reductions, reality is more complicated. Our air quality problems have not been solved. In fact, this public health crisis is yet another reason why we need long-term policy solutions that steadily reduce emissions over time. Reducing air pollution will improve overall population health, making people and communities more resilient to unforeseen risk factors, like viruses. In fact, by improving U.S. air quality over the past half a century we have already seen massive public health gains, which we can and should build on for the future.
Susan Anenberg, PhD, MS, is an Associate Professor of Environmental and Occupational Health at the George Washington University Milken Institute School of Public Health.
Dan Goldberg, PhD, is a Research Scientist in the Environmental and Occupational Health Department at the George Washington University Milken Institute School of Public Health.
