Hardly a day passes without hearing about an “airpocalypse,” often occurring in a developing country. It’s difficult not to feel for the people in the smog-filled images from places like New Delhi, Ulaanbaatar, or Kathmandu, usually wearing masks as they make their way to school or work through the thick haze. A study from last year revealed that over 8 million people die prematurely each year due to air pollution exposure. This surpasses deaths from diarrheal diseases, tuberculosis, and HIV/AIDS combined. As someone researching air pollution and its health impacts, I realize that even if you don’t reside in these areas, air pollution still likely impacts your quality of life. Here’s what you should know. Air pollution generally refers to a mix of various chemicals present in the air. Invisible gases such as ozone or carbon monoxide, along with tiny particles or liquid droplets, combine in the atmosphere.
Each molecule is too small to see with the eye, but when enormous quantities come together, they form visible haze. These chemicals are almost always combined in varying amounts. Scientists are still figuring out how these different combinations affect us. Individuals react differently to air pollution exposure—some have minimal effects while others, such as children with asthma, could become severely ill. Moreover, air pollution mixtures in any given area change over time, sometimes rapidly over hours or slowly over months. Short-term surges in air pollution from something like heavy traffic during rush hour can make us unwell and occur throughout the year. Seasonal pollutants, such as ozone, tend to appear only during the sunniest and warmest times of the year. Additionally, ozone levels fluctuate throughout the day, generally peaking in the afternoon and dipping in the early morning.
These fluctuations make it challenging for environmental health scientists and epidemiologists to pinpoint precisely how air pollution affects humans. You might visualize air pollution as smoke pouring out from a factory chimney or a car exhaust. While these are significant sources, many others contribute as well. Air pollution includes both chemicals introduced into the atmosphere by humans and those released by natural events. For instance, forest fires are a major source of air pollutants affecting numerous communities. Dust carried by the wind can also worsen air quality. Ronald Reagan famously remarked that “trees cause more pollution than automobiles do.” While this myth has been debunked, he was partially correct. Trees release certain gases, like volatile organic carbon, which contribute to air pollution chemistry.
When mixed with emissions from cars and industry, these gases increase other pollution types, such as ozone. There isn’t much scientists can or should do about emissions from trees. Public health researchers, like myself, focus primarily on emissions from human activities—such as burning petroleum or controlling emissions from industrial sites—since these are typically close to where people live and work. There are also numerous chemical reactions happening in the air itself, creating what are called secondary pollutants, some of which are quite toxic. It’s crucial to understand that air pollution doesn’t respect borders.
A pollutant released in one spot can easily travel across regions or national boundaries to other areas. In New Delhi, for example, seasonal pollution results from extensive agricultural field burning occurring roughly 200 miles away. New Delhi is an extreme case, but even if you reside in a less polluted zone, pollutants emitted elsewhere frequently journey to where other people reside and work, as displayed by recent wildfires in California. This is a complex issue because air pollution is an unseen problem that triggers many health conditions. Many individuals suffer from asthma and lung ailments, heart attacks, and cancer, all linked to particulate matter exposure. The best evidence suggests that the higher the air pollution dose, the worse our response. Unfortunately, other factors also lead to these diseases: poor diet, genetic predispositions, access to quality healthcare, or smoking.
This complexity makes identifying the exact cause of a disease linked to air pollution exposure more challenging. Every health study yields slightly different results because each observes different groups of people and usually various types of air pollution. Scientists typically report findings based on any change in disease development risk from air pollution or whether the odds of developing a particular disease change. For instance, a study from Taiwan examined average particulate matter concentrations over two years. The researchers found that a 10 micrograms per cubic meter increase in particulate matter raised the odds of developing high blood pressure by about 3 percent. This suggests that a rise in particulate matter in any community might lead to more cases of high blood pressure.
On the other hand, scientists generally expect that reducing air pollution decreases disease occurrence. An average adult takes around 20,000 breaths daily. Whether you fall ill due to air pollution depends on the amount and type of chemicals you inhale and whether you are vulnerable to these diseases. For someone living in heavily polluted New Delhi, those 20,000 breaths might include approximately 20 grains of table salt worth of particulate matter deposited in their lungs each day. While it might not seem substantial, remember that this particulate matter isn’t harmless table salt—it’s a mix of chemicals from burning materials, unburned oils, metals, and even biological materials. This excludes gaseous pollutants like ozone, carbon monoxide, or nitrogen oxides. The United States and Europe have significantly reduced air pollution concentrations in recent decades by implementing effective air quality regulations.
However, in the U.S. today, where environmental laws are being methodically dismantled, there’s a growing concern that policymakers are ignoring scientific evidence. One new member of the Environmental Protection Agency’s science advisory board, Robert Phalen from the University of California, Irvine, claimed that “modern air is too clean for optimum health.” This contradicts thousands of research papers and is certainly untrue. While some air pollution components have minimal health effects, this shouldn’t be used to obscure our understanding of air pollution exposure. Confusing the public with irrelevant statistics to cause uncertainty is a common tactic, likely intended to influence policy.