what is a safe level of air pollution?
Medical Studies show no safe level...
One of the landmark studies with air pollution started in 1974. Not long after the EPA was created in 1970, the rigorous Harvard Six Cities Study started following over 8,000 people in 6 different cities spread throughout the East and Midwest US. The study followed people from ages 25 to 74 for 17 years until 1991. Nitrate compounds (NOx), Sulfur compounds (SOx), Particulate Matter (PM) and Ozone (O3) were monitored daily for all 17 years in each city. The cities had different levels of these pollutants. When all other factors were ruled out, mortality followed higher levels of each pollutant. The cities with dirtier air had more lung cancer, more heart attacks, more strokes and more COPD (chronic obstructive pulmonary disease or emphysema).
The Harvard Six Cities Study did not answer the question of what level of pollution was safe. It only showed that more pollution is worse than less pollution. So what is a safe level of pollution? At what level are we as humans safe to be around exhaust from smokestacks, cars and other sources? The answer was recently answered in another New England Journal of Medicine article shown below.
*All images are reprinted with Permission of Massachusetts Medical Society
New England Journal of Medicine June 29, 2017 study
As discussed above, hundreds of air quality studies have been done since 1974. All of these studies continue to show damage to the human body from the byproducts of fossil fuel combustion (our next section "Health Effects" will elaborate on this more). This 2017 study however was important in that it showed that human mortality continued to decrease until there was zero pollution. In other words, no air pollution is safe. The graphs above illustrate this. The top graph is particulate matter (PM) and the bottom graph is ozone. Concentrations of these are on the horizontal axis. Mortality (vertical axis) continued to decline with lower and lower pollution levels. Even levels well below current EPA standards.
This study followed over 60 million US medicare patients from 2000 to 2012 by zip code. The zip code was then linked to that area's air quality over the entire 12 year timeframe. Mortality was higher everywhere (from every cause) where there was higher air pollution, much like the Harvard Six Cities Study. However the study showed that even at what was considered safe levels by the EPA, mortality was still high (recall that acceptable EPA levels are 12mcg/m3 of particulate matter (PM) and 70 ppb of ozone (O3)).
This study demonstrates that we need even more rigorous EPA levels. The only safe level of pollution for humans is no pollution. When there is no air pollution, there is some ozone in the atmosphere naturally (about 20-40 ppb) and some particulate matter naturally (~4mcg/m3). When the atmosphere has these levels of O3 and PM, there is no effect on human health. At DeSmog Denver, we advocate for more stringent EPA levels for all pollutants based on this study.