Airborne particulates
Airborne particulates are tiny particles suspended in the air, which can vary widely in size, composition, and origin. They include visible materials like dust and soot, as well as microscopic particles that can only be detected with specialized equipment. The inhalation of these particles poses significant health risks, particularly to the respiratory and cardiovascular systems, leading to conditions such as asthma, chronic obstructive pulmonary disease, and increased risk of heart attacks. Airborne particulates are categorized into primary particles, which are directly emitted from sources like construction sites and fires, and secondary particles, which form through chemical reactions involving gases emitted from vehicles and industrial processes.
The U.S. Environmental Protection Agency (EPA) has established health-based air quality standards for two main types of particulate matter: PM10 and PM2.5. PM10 refers to particles with a diameter of 10 micrometers or smaller, while PM2.5 consists of even finer particles, 2.5 micrometers or smaller. Due to their size, PM2.5 particles can penetrate deeply into the lungs and enter the bloodstream, leading to more severe health outcomes. Over the years, the EPA has revised the standards for these pollutants to reflect new scientific research, aiming to reduce exposure and protect public health.
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Subject Terms
Airborne particulates
DEFINITION: Tiny particles found in the air
Some airborne particulates, such as dust, dirt, soot, and smoke, are large enough to be visible to the naked eye, while other forms are so small that they require electron microscopes for detection. The inhalation of microscopic particles can have serious adverse effects on human respiratory and cardiovascular health.
Airborne particulate matter (PM) represents a complex mixture of organic and inorganic substances and varies in size, composition, and origin. Some particles, known as primary particles, are emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, and fires. Secondary particles are formed by reactions of gases, such as sulfur dioxide and nitrogen oxides, that are emitted from power plants, industrial plants, and automobiles. Secondary particles make up most of the fine-particle pollution in the United States.
Particle pollution contains microscopic solids or liquid droplets that are small enough to travel deep into the lungs and cause serious health problems. Breathing such pollution can lead to respiratory symptoms such as coughing and difficult breathing; it can decrease lung function and aggravate existing asthma. Also associated with exposure to particle pollution are chronic obstructive pulmonary disease and emphysema, chronic bronchitis, irregular heartbeat, nonfatal heart attacks, and premature death in people with heart or lung disease.
The size of airborne particulates is directly linked to their potential for causing health problems. The US Environmental Protection Agency (EPA) has established air-quality standards concerning two sizes (or fractions) of particles: PM10 and PM2.5. PM10 particles (coarse particles) are those with a diameter of 10 micrometers or smaller (10 micrometers is equal to 0.004 inch, or one-seventh the width of a human hair); they include both coarse and fine particles. PM10 particles smaller than 10 micrometers can settle in the bronchi and lungs and cause health problems. PM2.5 particles (fine particles) are 2.5 micrometers in diameter or smaller. Particles in this fraction tend to penetrate further, reaching the gas exchange regions of the lung, and even smaller particles (0.1 micrometer or smaller) may pass through the lungs into the bloodstream and affect other organs, particularly the cardiovascular system. These particles can also adsorb harmful gases or other components (such as iron, carcinogens, or ozone) and release them within lung cells. Particles emitted from modern diesel engines are typically 0.1 micrometer or smaller. PM2.5 inhalation can lead to high plaque deposits in the arteries, causing vascular inflammation and atherosclerosis (hardening of the arteries that reduces elasticity and can lead to heart attacks).
The federal Clean Air Act requires the EPA to review the latest scientific information every five years and promulgate the National Ambient Air Quality Standards for six pollutants, among them PM. US air-quality standards for PM were first established in 1971 and were not significantly revised until 1987, when the EPA changed the indicator of the standards specifically to regulate PM10 levels. Ten years later, the agency set a separate standard for PM2.5 particles based on new research findings regarding their link to serious health problems. The 1997 standards also retained but slightly revised the PM10 standards, which were intended to regulate inhalable coarse particles ranging from 2.5 to 10 micrometers in diameter. The EPA revised the air-quality standards for airborne particle pollution in 2006, lowering the acceptable level of PM2.5 over a 24-hour period from 65 micrograms per cubic meter to 35 micrograms per cubic meter (1 cubic meter is roughly equivalent to 35 cubic feet). It retained the 24-hour PM10 standard of 150 micrograms per cubic meter. In 2012 the standard for acceptable levels of PM2.5 exposure averaged over the course of a year (annual mean) was set at 12 micrograms per cubic meter. In 2024, the EPA again lowered the national ambient air quality standard for PM2.5 exposure to 9 micrograms per cubic meter. This change was based on evidence of the impact of exposure to PM2.5 on human health.
Bibliography
"Air Pollution: The Invisible Health Threat." World Health Organization, 12 July 2023, www.who.int/news-room/feature-stories/detail/air-pollution--the-invisible-health-threat. Accessed 12 July 2024.
"Air Quality Index." American Lung Association, 2 Nov. 2023, www.lung.org/clean-air/outdoors/air-quality-index. Accessed 12 July 2024.
Hilgenkamp, Kathryn. “Air.” In Environmental Health: Ecological Perspectives. Sudbury, Mass.: Jones and Bartlett, 2006.
National Research Council. Research Priorities for Airborne Particulate Matter, IV: Continuing Research Progress. Washington, D.C.: National Academies Press, 2004.
"Particulate Matter (PM) Pollution." Environmental Protection Agency, 25 June 2024, www.epa.gov/pm-pollution. Accessed 12 July 2024.
Peters, Annette, and C. Arden Pope III. “Cardiopulmonary Mortality and Air Pollution.” The Lancet 360 (October 19, 2002): 1184-1185.
Rasmussen, Niels, and Henrik Knudsen. Particulate Matter: Sources, Emission Rates, and Health Effects. New York: Nova Science, 2012. eBook Collection (EBSCOhost). Web. 14 Jan. 2015.
Vallero, Daniel A. Fundamentals of Air Pollution. Waltham: Elsevier, 2014. eBook Collection (EBSCOhost). Web. 14 Jan. 2015.