Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The term aerosol commonly refers to the particulate/air mixture, as opposed to the particulate matter alone.[1] Sources of particulate matter can be natural or anthropogenic.[2] They have impacts on climate and precipitation that adversely affect human health, in ways additional to direct inhalation.

This diagram shows types, and size distribution in micrometres (μm), of atmospheric particulate matter.

Types of atmospheric particles include suspended particulate matter; thoracic and respirable particles;[3] inhalable coarse particles, designated PM10, which are coarse particles with a diameter of 10 micrometers (μm) or less; fine particles, designated PM2.5, with a diameter of 2.5 μm or less;[4] ultrafine particles, with a diameter of 100 nm or less; and soot.

The IARC and WHO designate airborne particulates as a Group 1 carcinogen.[5] Particulates are the most harmful form (other than ultra-fines) of air pollution[6] due to their ability to penetrate deep into the lungs, blood streams and brain, causing health problems including heart attacks, respiratory disease, and premature death.[7] In 2013, a study involving 312,944 people in nine European countries revealed that there was no safe level of particulates and that for every increase of 10 μg/m3 in PM10, the lung cancer rate rose 22% (95% CI [1.03–1.45]). The smaller PM2.5, which can penetrate deeper into the lungs, were associated with an 18% increase in lung cancer per 5 μg/m3; however, this study did not show statistical significance for this association (95% CI [0.96–1.46])[8] Worldwide exposure to PM2.5 contributed to 4.1 million deaths from heart disease and stroke, lung cancer, chronic lung disease, and respiratory infections in 2016.[9] Overall, ambient particulate matter ranks as the sixth leading risk factor for premature death globally.[10]

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