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Epidemiology of Particulate Pollution
Airborne particulate pollution is observed around the globe in varying sizes and compositions and is the focus of many epidemiological studies. Particulate matter, or PM for short, is generally classified into two main size categories: PM10 and PM2.5. PM10, also known as coarse particulate matter, consists of particles 10 micrometers (μm) and smaller, while PM2.5, also called fine particulate matter, consists of particles 2.5 micrometers (μm) and smaller. Particles 2.5 micrometers (μm) or less in size are especially notable as they can be inhaled into the lower respiratory system, and with enough exposure, absorbed into the bloodstream. Particulate pollution can occur directly or indirectly from a number of sources including, but not limited to: agriculture, automobiles, construction, forest fires, chemical pollutants, and power plants.

Exposure to particulates of any size and composition may occur acutely over a short duration, or chronically over a long duration, and has been associated with adverse respiratory symptoms ranging from irritation of the airways, aggravated asthma, coughing, and difficulty breathing to symptoms such as irregular heartbeat, lung cancer, kidney disease, chronic bronchitis, and premature death in individuals who suffer from pre-existing cardiovascular or lung diseases; due to acute and chronic exposure, respectively. The severity of health effects generally depends upon the size of the particles as well as the health status of the individual exposed, and older adults, children, pregnant women, and immunocompromised populations are at the greatest risk for adverse health outcomes.

As a result, the EPA and various health agencies around the world have established thresholds for concentrations of PM2.5 and PM10 that are determined to be acceptable. Although, there is no known safe level of exposure and thus, any exposure to particulate pollution is likely to increase an individual's risk of adverse health effects. In European countries, air quality at or above 10 micrograms per cubic meter of air (μg/m3) for PM2.5, increases the all causes daily mortality rate by 0.2-0.6%, and the cardiopulmonary mortality rate by 6-13%, in locations experiencing at or above 10 micrograms per cubic meter (μg/m3) of PM2.5 pollution.

Worldwide, PM10 concentrations of 70μg/m3 and PM2.5 concentrations of 35μg/m3 have been shown to increase long-term mortality by 15%. More so, approximately 4.2 million of all premature deaths observed in 2016 occurred due to airborne particulate pollution, 91% of which occurred in countries with low to middle socioeconomic status with 58% of the premature deaths having been attributed to strokes and ischaemic heart diseases, 8% attributed to COPD (Chronic Obstructive Pulmonary Disease), and 6% to lung cancer.  

In 2006 the EPA conducted air quality designations in all 50 states, denoting areas of high pollution based on criteria such as air quality monitoring data, recommendations submitted by the states, and other technical information; and reduced the National Ambient Air Quality Standard for daily exposure to particulates in the 2.5 micrometers and smaller category from 15μg/m3 to 12μg/m3 in 2012. As a result, U.S. annual PM2.5 averages have decreased from 13.5µg/m3 to 8.02µg/m3, between 2000 and 2017.