Particulates

Particulates or atmospheric particulate matter (see below for other names) 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. Sources of particulate matter can be natural or anthropogenic. They have impacts on climate and precipitation that adversely affect human health, in ways additional to direct inhalation. Types of atmospheric particles include suspended particulate matter; thoracic and respirable particles; inhalable coarse particles, designated PM_10, which are coarse particles with a diameter of 10 micrometers (μm) or less; fine particles, designated PM_2.5, with a diameter of 2.5 μm or less; ultrafine particles, with a diameter of 100 nm or less; and soot. The IARC and WHO designate airborne particulates as a Group 1 carcinogen. Particulates are the most harmful form (other than ultra-fines) of air pollution due to their ability to penetrate deep into the lungs and brain from blood streams, causing health problems such as heart disease, lung disease, and premature death. 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/m^3 in PM_10, the lung cancer rate rose 22% (95% CI [1.03–1.45]). The smaller PM_2.5, which can penetrate deeper into the lungs, were associated with an 18% increase in lung cancer per 5 μg/m^3; however, this study did not show statistical significance for this association (95% CI [0.96–1.46]). Worldwide, exposure to PM_2.5 contributed to 4.1 million deaths from heart disease, stroke, lung cancer, chronic lung disease, and respiratory infections in 2016. Overall, ambient particulate matter ranks as the sixth leading risk factor for premature death globally. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation and sea spray. Human activities also generate significant amounts of particulates.