Particulate matter

Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. The combination of particulates and air is called an aerosol. Sources of particulate matter can be either natural or occur as a result of human activities. Particulates may adversely affect human health and impact climate and precipitation. Categories of atmospheric particles include inhalable coarse particles, designated PM10, which are particles of coarse granularity, with a particle diameter of 10 micrometers (μm) or less; fine particles, designated PM2.5, with a diameter of 2.5 μm or less; ultrafine particles, PM.10 with a diameter of 100 nanometers (nm) or less; and soot (fine or ultrafine particles primarily made up of carbon). Airborne particulate matter is a IARC Group 1 carcinogen. Particulate matter is considered the most dangerous type of air pollution because particulates can penetrate deep into the lungs and travel through the blood stream to multiple organs, such as the brain. Particulate matter contributes to health problems such as stroke, cardiovascular disease, respiratory disease, many types of cancer, and preterm birth. There is no safe level for exposure to particulates. Worldwide, exposure to PM2.5 contributed to 7.9 million deaths in 2023; of those, 4.9 million had outdoor air pollution as a contributing factor, and 2.8 million had household air pollution as a contributing factor. Fine particulate matter (PM2.5) is considered the leading environmental risk factor for earlier death worldwide. Because many sources of particulates result from human actions, it is a modifiable risk factor which can be addressed. Many countries have established standards for particulate matter and are improving air quality.

Sources

Approximately 90 percent of the total mass of particulate matter in the atmosphere (as estimated in 2010) comes from natural sources such as volcanoes, dust storms, forest and grassland fires, living vegetation and sea spray, emitting particulates such as volcanic ash, desert dust, soot and sea salt. Human-contributed (anthropogenic) particulate matter accounts for the remaining 10 percent of the total mass of aerosols. Human activities that generate particulates include:

Burning of fossil fuels (coal, oil, and natural gas) for electricity, heat and transportation, biomass fuels (plants, wood, crop residue and manure) for heating and cooking, waste, joss paper, and firecrackers. Construction and renovation (including earthwork and foundation, demolition and rehabilitation). Dusty materials that are not properly stored, cleaned up or disposed of (from construction sites, landfills, industrial facilities, and households). Waste incineration. Concrete. Metalworking (grinding, cutting, welding). Woodworking (sawing, sanding, and planing). Industrial processes such as quarrying, mining, smelting and oil refining. Wet cooling towers in cooling systems. Exhaust gas from motor vehicles, including diesel exhaust from heavy equipment used in construction, road building, and other industries. Road dust from unpaved roads and from the wearing down of tires, brakes, and paved road surfaces. Microplastics (as a type of airborne PM) of which vehicle-related microplastics from road and tire wear are a major part. Agricultural activities (e.g. wind erosion, ploughing, soil tilling, grain harvesting, and livestock management). Cooking (frying, boiling, grilling). Smoking Disasters (e.g. wildfires, which may be human- or naturally-caused, wars, and the 11 September attacks.)

Worldwide and seasonal sources Human-generated particulates are often smaller in size (e.g. PM2.5 or PM1), and pose significant threats to human health. Globally, major contributors to PM2.5 include residential energy use (40%), industrial processes (11.7%), and energy generation (10.2%), all of which involve fuel combustion. The types of emissions that contribute to particulate matter vary widely across countries and local regions, reflecting regional characteristics, seasonal variation, human activities, and types of fuels used. A worldwide analysis in 2021 reported that of anthropogenic fuels, coal was the highest contributor to PM2.5-related mortality in China; oil and natural gas dominated in Egypt, Russia, and the United States; and solid biofuels had the highest impact in Pakistan, Bangladesh, Indonesia, India, and Nigeria. Contributions due to residential fuel use varied from 4.0% in Egypt to 33.1% in Indonesia. Contributions from energy and industry sectors ranged from 3.2% in Nigeria to 27.3% in India. The most common PM2.5-related causes of death were ischemic heart disease (IHD) and stroke. The impact of windblown dust ranged from 1.5% in Bangladesh to 70.6% in Nigeria, where lower respiratory tract infections (LRIs) in childhood were the largest PM2.5-related cause of mortality.

An examination of PM2.5 concentrations using data from 2000 to 2019 showed that during those two decades, PM2.5 concentrations in Europe and northern America decreased, due to reductions in fossil fuel emissions. However, exposures increased in southern Asia, Australia, New Zealand, Latin America and the Caribbean. Distinct seasonal patterns were seen in many parts of the world. There were regular high regional PM2.5 concentrations in the Amazon rainforest in August and September. Sub-Saharan Africa showed higher levels from June to September. Levels in eastern North America were higher in their summer months. Levels in China and north India were high in their winter months, as are levels in South Korea.

Domestic combustion

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