Understand Air Pollution

Particulate matter (PM) refers to solid and liquid particles—soot, smoke, dust, and others—that are suspended in the air.

When the air is polluted with PM, these particles enter the respiratory system along with the oxygen that the body needs.

When PM is breathed into the nose or mouth, each particle’s fate depends on its size: the finer the particles, the farther into the body they penetrate. PM⏨, particles with diameters smaller than 10 micrometers (μm), are small enough to pass through the hairs in the nose. More deadly is an even smaller classification: PM₂.₅, or particles with diameter less than 2.5 μm—just 3 percent the diameter of a human hair.

After PM⏨ and PM₂.₅ pass through the nose, they travel down the respiratory tract and into the lungs, where the metal elements on the surface of the particles oxidize lung cells, damaging their DNA and increasing the risk of cancer.[1]

The particles’ interactions with lung cells can also lead to inflammation, irritation, and blocked airflow, increasing the risk of or aggravating lung diseases that make breathing difficult, such as chronic obstructive pulmonary disorder (COPD), cystic lung disease, and bronchiectasis. [2]

In addition to contributing to risk of lung disease, PM₂.₅ particles pass even deeper into the lungs’ alveoli, the blood vessel-covered air sacs in which the bloodstream exchanges oxygen for carbon dioxide. Once PM₂.₅ particles enter the bloodstream via the alveoli, they inflame and constrict blood vessels or dislodge fatty plaque, increasing blood pressure or creating clots. This can block blood flow to the heart and brain, and over time, lead to stroke or heart attack.

In recent years, researchers have even begun to observe that PM pollution is associated with lower cognitive function. They speculate that PM₂.₅ in the bloodstream may cause the brain to age more quickly due to the inflammation. In addition, it may damage the brain’s white matter, which is what allows different regions of the brain to communicate.[3] White matter damage, such as due to the decreased blood flow that PM₂.₅ may cause, has been linked to Alzheimer’s and dementia.[4]

The tiny size of PM₂.₅ particles allows these particles to stay in the air potentially for weeks and to travel hundreds or thousands of kilometers.[5] This increases the likelihood that the particles will end up inhaled by humans before depositing onto the ground.

The Air Quality Life Index reveals that ambient particulate pollution is consistently one of the world’s greatest risks to human health. As of 2023, particulate pollution is set to reduce global average life expectancy by 1.9 years. That means the impact of particulate pollution on life expectancy is comparable to that of tobacco use, 4 times that of alcohol use and unsafe water sanitation and handwashing, 5 times that of transport injuries, 7 times that of HIV/AIDS.[6]

The key difference is that residents of polluted areas can do very little to avoid particulate pollution, since everyone breathes the air. In contrast, it is possible to quit smoking and take precautions against diseases. Thus, air pollution affects many more people than any of these other conditions. So, although other risks such as HIV/AIDS, tuberculosis etc. have a larger impact among the affected, they affect far fewer people.