Air Pollution and PM2.5: The Deadly Result of Burning Things

There are many well-known health consequences of the climate crisis we are facing. These come from excessive heat and heat waves, drought, and natural disasters like floods and hurricanes. There is one consequence of burning fossil fuels, however, that is killing people right now on a daily basis. That is a type of air pollution called fine particulate matter or PM2.5.

         Many types of particles constitute air pollution, but perhaps the nefarious are the microscopic particles called fine particulate matter or PM2.5. The number 2.5 comes from the fact that these particles are 2.5 microns or smaller in diameter. To put that in perspective, a human hair is about 70 microns in diameter (a micron is one millionth of a meter or about one twenty-five thousandth of an inch). PM2.5 is released into the air when we burn things—it comes from car exhausts, power plants, indoor cooking, smokestacks, fires, the use of certain types of fertilizers in agriculture, and a variety of other sources. Living near a highway confers long-term exposure to PM2.5and may account for higher premature mortality rates among people who live in areas near heavily trafficked roads.

PM2.5 Is a Serious Health Risk

         PM2.5 is the sixth leading cause of death in the world, responsible for about four million deaths every year. Not surprisingly, it causes or worsens lung and cardiovascular disease because it gets deep into lungs and into the circulating blood. In the respiratory system, it is a cause of and worsens asthma, chronic obstructive pulmonary disease (COPD), and possibly cancer.  Studies show it is associated with a wide variety of cardiovascular disorders including hypertension, arrhythmias, heart attacks, and stroke. It also plays a role in neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease. PM2.5 easily slips across the blood-brain barrier, the physical system that protects the brain from toxic substances floating in the bloodstream, and therefore increases the risk for a variety of neurological diseases.

Smoke from burning fossils fuels causes air pollution, including a type called fine particulate matter of PM2.5. PM2.5 has been shown to be a serious health risk and to cause premature death (image: Shutterstock).

         In one interesting recent study, investigators used positron emission tomography (PET) scanning to measure the amount of a protein that is found in increased amounts in people with Alzheimer’s disease. The protein, called amyloid, forms plaques in affected individuals’ brains. All of the participants already had evidence of cognitive impairment at the time of the scans. The amount of PM2.5 in the patients’ home neighborhoods was taken from existing databases both for 2002-2003 and 2015-2016. They found that higher levels of PM2.5 exposure both thirteen years before the scans and more recently was associated with the presence of brain amyloid plaques. This finding confirmed a number of other epidemiological and animal studies showing a link between dementia and PM2.5 pollution.

         Most recently, PM2.5 exposure has been linked to increased death rates for patients with COVID-19. After adjusting for 20 possible confounders, authors of one study concluded that “A small increase in long-term exposure to PM2.5 leads to a large increase in the COVID-19 death rate.” This is one of the many ways that the current pandemic is linked to the ongoing climate crisis caused by burning fossil fuels like release carbon dioxide and to agricultural practices that release nitrous oxide into the atmosphere.

         The issue of setting appropriate air pollution standards is clearly one of environmental justice. People of color are exposed to significantly more air pollution than white Americans and this may partially account for higher rates of respiratory and cardiovascular disease and shorter lifespan. A Brookings report noted that a new administration could help address the “persistent inequity of air pollution exposure in low income neighborhoods and communities of color.”

PM2.5 particles present in air pollution cause adverse health effects involving many organs of the body including lungs, heart, blood vessels, and brain (image: Shutterstock).

EPA Refuses to Budge

         The U.S. Environmental Protection Agency (EPA) monitors PM2.5 levels throughout the country and sets a maximum concentration for average annual PM2.5 at 12.0 µg/m3 (that’s 12 micrometers per cubic meter). On December 7, 2020 the EPA disappointed many scientists and environmental activists by announcing its final rule against lowering that standard. EPA had convened one of its Clean Air Scientific Advisory Committees (CASAC) in 2015 to study the current standards for PM2.5 and make recommendations for revisions. This CASAC was composed of 20 experts from a variety of relevant scientific fields. But in 2018 EPA Administrator Andrew Wheeler dismissed the PM2.5 CASAC. The committee met on its own anyway  in 2019. Its members reviewed the literature on air pollution’s health effects and concluded that concentrations lower than the current standard of 12.0 µg/m3 should be instituted to between 8 and 10 µg/m3. It was clear from their review of the available science that lower concentrations of PM2.5 still have an adverse effect on lung and cardiovascular disease. EPA ignored that recommendation in its decision last month.

         Scientists, both in and out of EPA, have consistently pointed to solid research showing that much lower concentrations of PM2.5 are responsible for adverse health effects, including higher rates of COVID-19 mortality. These are especially prevalent among communities of color and low-income neighborhoods, places where decades of structural racism have resulted in the disproportionate placement of factories, highways, and warehouses with idling trucks. We can only hope that under a new administration this matter will get swift attention and the recommendation to lower the PM2.5 standard be addressed.

         Ultimately, it is up to our society to do what is really needed to eliminate the PM2.5 health risk: eliminate the production of greenhouse gasses like carbon dioxide, methane, and nitrous oxide. Climate change is already killing people in many ways—it is not just a concern for the future. Air pollution is one of those ways. It is time to face it.

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