You have probably been hearing the word aerosol a lot. This word basically means very small bits of stuff in the air. You may have first heard aerosol meaning stuff that you spray out of a can (like hairspray) that forms small droplets in the air. In the news right now, people are talking about the stuff being saliva and virus coming from people’s breath. Atmospheric scientists use the word aerosol frequently. For them, the stuff would be small bits of pollution floating around in the air.
Previous posts on Envirobites (A, B, C) have discussed how the small bits of stuff, called either aerosols or particulate matter, can make people sick when they breathe it. Breathing aerosols can damage your lungs and cause respiratory diseases. Particulate Matter less than 2.5 microns in diameter is called PM2.5. For reference, a grain of table salt is 40 microns across. PM2.5 can be especially harmful because it is small enough to get into your lungs.
So What’s New?
There is a research group at Harvard that studies where people get sick and how that correlates with pollution levels. The people in this group noticed that many of the pre-existing conditions that make COVID-19 more dangerous are also the conditions that are caused or made worse by air pollution. They hypothesized that places that typically have high levels of PM2.5 would have worse outcomes from COVID-19 cases, since both have negative effects on the respiratory (breathing) and cardiovascular (blood) systems.
The researchers used a similar method to that described in this post , with the addition of the new data on COVID-19. Because the researchers had already done a lot of hard work to get local pollution values across the country, they were able to also use that to do this timely analysis with new health data. For all counties that had confirmed COVID-19 cases, they compared deaths in that county to levels of PM2.5 pollution.
PM2.5 pollution is measured in a unit of micrograms per cubic meter. This means a weight of “stuff” in millionths of a gram in each cubic meter of air. The scientists found that a long-term reduction in PM2.5 concentrations of just 1 microgram per cubic meter could reduce deaths from COVID-19 by 15%. Although social media has shown photos of clean air in locations where people are no longer driving to work, this is not what was studied here. People already have weaker lungs due to years of living in this pollution, and that is what is tested in this study. These results are preliminary as deaths are expected to continue from COVID-19, but these results are also in line with analyses done after the SARS outbreak.
The researchers also looked at other things that might affect the correlation, such as poverty and smoking rates, number of hospital beds, and number of tests performed. They found that the results were true even after accounting for most of these effects, but they noted that the number of hospital beds has a strong effect on deaths as well. Both pollution and hospital beds seem to affect the deaths in a county, and we don’t yet know the exact value of each effect.
This work shows the importance of scientists doing their work all the time, even if it is in the background. They are then more prepared to provide vital knowledge quickly when required. It also shows that working to reduce pollution has high benefits. In addition to the previously known benefits that reducing pollution reduces the number of people with illnesses, a population with fewer illnesses can be more resilient to new threats. So keep listening to scientists, wash your hands, and keep physical distance between yourself and people outside your household. When scientists say you can reduce the distance, remember that clean air (and hand washing) are important all the time.
Citation: Exposure to air pollution and COVID-19 mortality in the United States. Xiao Wu, Rachel C. Nethery, Benjamin M. Sabath, Danielle Braun, Francesca Dominici. medRxiv 2020.04.05.20054502; doi: https://doi.org/10.1101/2020.04.05.20054502
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