https://ourworldindata.org/data-review-air-pollution-deaths> Particulate matter – often abbreviated as PM – is everything in the air that is not a gas. These are very small particles made up of sulfate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water that are suspended in the air that we breathe.
> Particles with a diameter of 10 micrometers (10 millionth of a metre) or less can enter deep inside a person’s lungs. But the most health-damaging particles are even smaller. Those with a diameter of 2.5 micrometers or less – abbreviated as PM2.5 – can penetrate the lung barrier and enter a person’s blood system. These are extremely fine particles: 2.5 micrometers is about one-thirtieth of the diameter of a human hair.1
> All studies of the mortality impacts of air pollution consider our exposure to particulate matter. Some studies also consider the impact of ground-level ozone. The death toll from ozone is much lower than that of PM, but it is still considerable: it’s responsible for hundreds of thousands of premature deaths every year. Other air pollutants are rarely considered in global studies.