For years, Americans have been breathing increasingly cleaner air. However, according to a new analysis of Environmental Protection Agency (EPA) data, particle matter pollution has increased in 2017 and 2018. The findings may signal a trend reversal after decades of generally positive environmental accomplishments.

Air pollution is responsible for a fifth of all deaths around the world, killing around 5.5 million annually.

People suffer both short-term and long-term health effects from air pollution, causing diseases and complications in nearly every system of the body. Some of these include:

• Respiratory and cardiovascular diseases,
• Neuropsychiatric complications (i.e., seizures, attention deficits, palsies, migraine headaches, and mood disorders),
• Eye irritation,
• Skin diseases,
• Cancer,
• Infertility,
• Birth defects,
• Premature death.

Studies have even associated air pollution with damage to short-term memory and IQ, as well as even increases in violent crime rates.

Some of the most dangerous air pollutants include nitrogen oxides, sulfur oxides, carbon monoxide, lead, or ground-level ozone. The main component of air pollution, however, is particulate matter smaller than 2.5 micrometers, often labeled as PM2.5. This fine dust or soot particles are small enough to travel through a person’s respiratory tract, causing illness and premature death.

Since the U.S. Congress passed the Clean Air Act in 1963, air quality at the national level has tended to improve. More recently, between 2009 and 2016, PM2.5 concentrations in the air dropped by 24%.

However, according to a new report authored by two Carnegie Mellon economists, PM2.5 concentrations have increased by 5.5% in 2017 and 2018.

“The increase was associated with 9,700 additional premature deaths in 2018. At conventional valuations, these deaths represent damages of $89 billion,” the authors wrote.

The researchers identified three potential factors that may be responsible for the recent uptick in air pollution: increased economic activity, wildfires, and EPA enforcement actions. It is important to note that the authors haven’t traced any causal links between the three factors and worsening air quality.

Since 2017, economic activity in the U.S. has increased significantly, which means more factories are producing goods (along with emissions) and there are more vehicles on the road.

Air pollution may have increased because of soot from wildfires, particularly in the West where such events have become more common since 2016.

And, finally, the authors found that EPA enforcement activity of the Clean Air Act has been declining since 2009. That’s nothing particularly wrong with that because there are now more compliant businesses and organizations than ever so it makes sense that there now fewer inspections and reports. The authors note, however, that EPA enforcement actions have not matched the rate of air pollution increase. Why this may be happening is the subject of a new study the authors have planned for in the future.