Particulate matter

Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. The combination of particulates and air is called an aerosol. Sources of particulate matter can be either natural or occur as a result of human activities. Particulates may adversely affect human health and impact climate and precipitation. Categories of atmospheric particles include inhalable coarse particles, designated PM10, which are particles of coarse granularity, with a particle diameter of 10 micrometers (μm) or less; fine particles, designated PM2.5, with a diameter of 2.5 μm or less; ultrafine particles, PM.10 with a diameter of 100 nanometers (nm) or less; and soot (fine or ultrafine particles primarily made up of carbon). Airborne particulate matter is a IARC Group 1 carcinogen. Particulate matter is considered the most dangerous type of air pollution because particulates can penetrate deep into the lungs and travel through the blood stream to multiple organs, such as the brain. Particulate matter contributes to health problems such as stroke, cardiovascular disease, respiratory disease, many types of cancer, and preterm birth. It is associated with an increased risk of cognitive impairment. There is no safe level for exposure to particulates. Worldwide, exposure to PM2.5 contributed to 7.9 million deaths in 2023; of those, 4.9 million had outdoor air pollution as a contributing factor, and 2.8 million had household air pollution as a contributing factor. Fine particulate matter (PM2.5) is considered the leading environmental risk factor for earlier death worldwide. Because many sources of particulates result from human actions, it is a modifiable risk factor which can be addressed. Many countries have established standards for particulate matter and are improving air quality.