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 PM, which are particles of coarse granularity, with a particle diameter of 10 micrometers (μm) or less; fine particles, designated PM, with a diameter of 2.5 μm or less; ultrafine particles, PM 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. It is associated with an increased risk of cognitive impairment. There is no safe level for exposure to particulates.
Worldwide, exposure to PM 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 (PM) 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
As of 2023, more than 2.3 billion people worldwide, many of them in developing countries, burn polluting biomass fuels such as wood, dry dung, coal, or kerosene for cooking or heating. This causes harmful household air pollution and contributes significantly to outdoor air pollution. Cooking-related pollution was estimated to cause 3.7 million annual deaths.
Burning biomass emits large amounts of pollutants including PM and PM, black and brown carbon, carbon monoxide, nitrogen oxides (NOx), sulfur dioxide and ozone. The chemical composition of the emitted PM is different for different types of biomass fuels. Less energy dense fuels, such as dung, generate more PM. Dung and wood yield higher organic aerosol emissions, while dung emits more nitrogen content than other biomass fuels.
In the United Kingdom domestic combustion is the largest single source of PM and PM annually. In 2019, domestic wood burning in both closed stoves and open fires was responsible for 38% of PM in the UK. Following the introduction of new laws in 2021 that restricted the sale of wet wood and house coal, particulate levels from domestic use decreased. During 2024, domestic wood burning was responsible for 20% of PM and 11% of PM in the UK. During the winter months, the impact of wood burning is higher and can contribute to half of PM concentrations.
Given the health effects of wood smoke, it is recommended that people only use wood burners or fireplaces if they had no other source of heat. If a stove or open fire is used, the release of particulates may be reduced by using an improved closed wood-burning stove of appropriate size for the space to be heated, maintaining the stove properly, using seasoned wood or kiln-dried wood, and managing the fire appropriately. When cooking, use of improved cooking stoves and better quality fuels may help to reduce particulate exposure.
Waste combustion Composition of particles can vary greatly depending on their sources and production. Particles emitted from fuel combustion are not the same as those emitted from waste combustion. Particulates emitted from the burning of vegetation, incense paper, construction waste, and plastics will all differ. Particulate matter from a fire in a recycling yard or a ship full of scrap metal may contain more toxic substances than other types of burning.
Construction Different types of building activities produce different kinds of dust, that can have different effects on health. The composition of PM generated from cutting or mixing concrete made with Portland Cement would be different from those generated from cutting or mixing concrete made with different types of slag (e.g. GGBFS, EAF slag), fly ash or even EAF dust (EAFD), while EFAD, slag and fly ash are likely to be more toxic as they contain heavy metals. Besides slag cement that is sold and used as an environmental friendly product, fake (adulterated) cement, where different types of slag, fly ash or other unknown substances are added, is also common in some places due to the much lower production cost. To address quality and toxicity problems, some places are starting to ban the use of EAF slag in cement used in buildings.
Composition of welding fumes varies and it depends on the metals in the material being welded and the composition of the coatings, electrode, etc. being used.
Since construction and refurbishment projects are prominent sources of particulate matter, planning and mitigation measures regarding PM emission should be adopted and carefully monitored, particularly when such projects involve actively used health facilities.
Composition
The chemical composition of particulate matter (PM) in atmospheric aerosols varies widely with both time and space. It is affected by emission sources (both natural- and human-caused), geography, weather conditions, and chemical reactions. Atmospheric aerosols can change between liquid, solid, and semisolid states depending on conditions. The particulate matter in an aerosol can be described as primary (directly emitted) or secondary (formed through chemical reactions in the air). PM can include both organic and inorganic components such as minerals.
Both chemical composition and particle size and shape have effects on human health. Inhalable particles are often classified in terms of size as either coarse (PM) with a diameter of 10 micrometers (μm) or less, or fine (PM) with a diameter of 2.5 μm or less. Smaller particulates can penetrate deeper into the lungs and travel through the blood stream to reach other organs. Human-generated particulates are often smaller in size (e.g. PM2.5 or PM1), and pose significant threats to human health.
The chemical composition and size of particulates in an aerosol also determine how the aerosol interacts with solar radiation and affects climate. Chemical constituents within an aerosol change its overall refractive index, determining how much light is scattered or absorbed.
Mineral dust
Wind-blown mineral dust is a major component of particulate matter globally. Most sand and dust storms originate from a dust belt stretching from north Africa through the Middle East into Asia. Dust storms can also arise in arid areas of North and South America and Australia. Particles from dust storms can remain in the atmosphere and travel thousands of km from their source.
Mineral dust is a complex mixture that can be formed from quartz, feldspars, clays, calcites, iron oxides and other material blown from the Earth's crust. It often contains mineral oxides of major crustal elements such as aluminum (Al), silicon (Si), calcium (Ca), iron (Fe), and titanium (Ti). It can also contain alkali metals such as potassium (K), sodium (Na), and lithium (Li); alkaline earth metals such as magnesium (Mg); and heavy metals such as lead (Pb), copper (Cu), nickel (Ni), and zinc (Zn). Mineral dust in particulate matter is light-absorbing. Higher levels of lead in top soil and dust are associated with higher blood levels of lead in people.
Sea salt