text: Particulate pollution is observed around the globe in varying sizes and compositions and is the focus of many epidemiological studies.  Particulate matter (PM) is generally classified into two main size categories: PM and PM. PM, also known as coarse particulate matter, consists of particles 10 micrometers (μm) and smaller, while PM, also called fine particulate matter, consists of particles 2.5 μm and smaller. Particles 2.5 μm or smaller 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. Particulate exposure has been associated with adverse respiratory symptoms ranging from irritation of the airways, aggravated asthma, coughing, and difficulty breathing from acute exposure 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 chronic exposure. The severity of health effects generally depends upon the size of the particles as well as the health status of the individual exposed; older adults, children, pregnant women, and immunocompromised populations are at the greatest risk for adverse health outcomes. Short-term exposure to particulate pollution has been linked to adverse health impacts.
  As a result, the US Environmental Protection Agency (EPA) and various health agencies around the world have established thresholds for concentrations of PM and PM that are determined to be acceptable. However, 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/m) for PM increases the all-causes daily mortality rate by 0.2-0.6% and the cardiopulmonary mortality rate by 6-13%.
  Worldwide, PM concentrations of 70μg/m and PM concentrations of 35μg/m 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. Of these premature deaths, 58% were 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/m to 12μg/m in 2012. As a result, U.S. annual PM averages have decreased from 13.5 µg/m to 8.02 µg/m, between 2000 and 2017.
  Microplastics prove to be particularly concerning as particulate matter for their reactivity and ability to become contaminated. Microplastic particles, depending on their composition, can form carbonyl bonds on the surface, causing contaminants such as heavy metals to be adsorbed by the particle. When microplastic particles are inhaled, they persist in the lungs and cause inflammation. More research is needed to understand the long-term health effects of microplastics in the human body.