Particulate matter

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. The particulate matter in an aerosol can be described as primary (directly emitted) or secondary (formed through chemical reactions in the air). and inorganic components such as minerals. Both chemical composition and particle size and shape have effects on human health. 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. 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), 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 Sea salt particles are another leading contributor to global particulate matter. Sea salt aerosols (SSAs) can develop over both open water and pack ice. and the average concentration of SSAs is generally higher there than in the Northern Hemisphere. The production of sea salt aerosols is affected by aspects of the air-sea interface including wind speed, seawater temperature, surface tension, density, and viscosity. Sea salt aerosols reflect the composition of sea spray and evaporated sea water, consisting mainly of inorganic salts like sodium chloride (NaCl), along with magnesium, sulfate, calcium, bromine and potassium. Sea salt aerosols can include biological and organic matter such as bacteria, viruses, proteins, enzymes, dissolved organic carbon, fatty acids and sugars. They are relatively large compared to other aerosols. Burning of living or once-living matter, whether natural or human-caused, releases black carbon (BC) and organic carbon (OC), both of which are part of smoke and soot. Approximately 85% of the world's population lives in the Northern Hemisphere, where human activities are the dominant sources of organic matter and fine particulate matter (PM25). and contains mostly pure (elemental) carbon. Organic matter can influence the atmospheric radiation field by both scattering and absorption. Black carbon is the most strongly light-absorbing aerosol component, while organic carbon tends to be less absorptive, depending on its structure. In addition to carbon compounds, the burning of petroleum and oil also releases sulfur oxides and many other chemicals into the atmosphere. Secondary organic aerosols Secondary organic aerosols (SOA) are major components of PM2.5, small inhalable particulate matter that is linked to health problems. Secondary organic aerosols form when gaseous vapors in the atmosphere (e.g. SO2, NO and NO2, NH3, VOCs) react chemically to produce compounds that then form particles. Precursor gases may be anthropogenic (e.g. from biomass and fossil fuel combustion) or natural (e.g. from dust, forest fires, or sea salt aerosols) in origin. Aerosols can mix rapidly in ambient air, forming new chemical compounds as well as diluting their concentration with distance from an emissions source. The smallest class of particulates, PM1 frequently contains sulfate, ammonium, and nitrate. Primary gases such as sulfur and nitrogen oxides can oxidize to form secondary particles of sulfuric acid (liquid) and nitric acid (gaseous). In the presence of ammonia, they often form ammonium salts such as ammonium sulfate and ammonium nitrate (both can be dry or in aqueous solution). Haze, particulate matter that generally causes visual effects, tends to consist of sulfur dioxide, nitrogen oxides, carbon monoxide, mineral dust, and organic matter in dry air. The particles are hygroscopic due to the presence of sulfur, and SO is converted to sulfate when high humidity and low temperatures are present. This causes reduced visibility and red-orange-yellow colors. == Measurement ==

Particulates have been measured in increasingly sophisticated ways since air pollution was first systematically studied in the early 20th century. The earliest methods included relatively crude Ringelmann charts, which were grey-shaded cards against which emissions from smokestacks could be visually compared, and deposit gauges, which collected the soot deposited in a particular location so it could be weighed. , Germany Modern air pollution measurement techniques characterize ambient air quality using data from three main sources: direct measurements of on site sources, computer models, and remote sensing platforms such as satellites. Direct methods of measuring particulates can determine the total mass of particles per unit volume of air (particle mass concentration) using techniques such as gravimetric air quality analysis, beta attenuation monitoring, tapered element oscillating microbalances, and aethalometers (for black carbon). Sometimes it is more useful to measure the total number of particles per unit volume of air (particle number concentration). This can be done with optical particle counters and condensation particle counters. To measure the atomic composition of particulate samples, techniques such as X-ray spectrometry can be used. Special filters and detection techniques can be used to select samples of a particular size (e.g. PM or PM) or chemical composition (e.g. black carbon) and to track their distribution over time. Human-generated particulates are often smaller in size (e.g. PM2.5 or PM1) than naturally formed ones. Satellite-based estimates of PM2.5 are important tools. Satellite measurements of aerosols are based on the fact that particles change the way the atmosphere reflects and absorbs visible and infrared light. Satellites measure aerosol optical depth (AOD) and other factors that indicate the concentration and distribution of particulates in the atmosphere. PM2.5 concentrations are then inferred from the satellite data by using models or ground-based monitoring data. Combining these approaches can enhance the spatial coverage of PM2.5, to show patterns of distribution and movement in space and time. Such information can be used to create smoke forecasts and pollution advisories. ==Movement and deposition==

Satellite data has shown that volcanic eruptions can send ash and particles high into the atmosphere, with fine particulates remaining in the air for long periods, traveling over long distances, and affecting global climate. Particulate matter from wildfires in the western United States and Canada can travel to the United Kingdom and northern France in a few days. Dust thrown into the air by sandstorms in the Sahara travels from North Africa to North America. Particles are transported globally and locally via characteristic atmospheric and oceanic currents, transitioning between air and water at the air-sea interface. Particles move between land, water and air through mechanisms such as emission, suspension, and deposition. Circulation models take into account the release of particulates into the air, conditions under which they remain in air, their physical transport, and their removal from the atmosphere. Wet deposition or precipitation scavenging is the removal of particulate matter from the atmosphere through interactions with clouds, precipitation, and other particles that lead to settling. Particles may act as cloud condensation nuclei to create cloud droplets or collide with already-formed raindrops. Sedimentation (settling due to gravity) and evaporation are influenced by physical and chemical factors including temperature, humidity, particle radius, particle volume, and height at which an emission is released. Solubility and evaporation significantly affect the size, phase, and behavior of particles and aerosols. == Health effects ==

Size, shape, and solubility matter Health effects of particulate matter are influenced by factors such as particle size, shape, solubility, charge, chemical composition, and concentration and rate of exposure. Toxicity of particles tends to increase with smaller size, larger surface area, accumulation of material on particle surfaces, and other physical characteristics of particles. Particles of different sizes deposit in different regions of the respiratory tract, leading to various health effects. • Coarse particles (PM), with diameters between 2.5 and 10 micrometers, can be inhaled and can deposit in the upper airways, including the nose, throat, and bronchi. and cardiovascular effects (e.g. heart attacks and arrhythmias due to systemic inflammation and oxidative stress). • Fine particles (PM), with diameters less than 2.5 micrometers, can penetrate deep into the lungs, reaching the bronchioles and alveoli. Ultrafine particles contribute to health issues including neurodegenerative diseases (e.g. Alzheimer's) • PM: Annual mean not to exceed 15 μg/m3; 24-hour mean not to exceed 45 μg/m3. Irregularly shaped particles are more likely to be deposited in airways than spherical ones of similar size. Geometrically angular shapes have more surface area than rounder shapes, increasing the area available for binding to other substances, which can increase toxicity. Respiration and diffusion bring particulate matter into the airways, where particles can be deposited onto airway surfaces such as epithelial tissue and dissolved into the bronchial and pulmonary circulation. Particles that are deposited on airway surfaces can be cleared through respiration, move to other locations within the respiratory tract, or remain trapped and cause irritation or toxicity. From the respiratory system, particulate matter can travel through veins and arteries to the heart, brain, muscle, skin, kidneys, gastrointestinal tract, spleen, liver, bone, and fat. The fate of a specific contaminant is dependent upon the form in which it exists (aerosol or particle). Water-soluble organic compounds include alcohols, carboxylic acids, keto acids, phenols and hydroxylamines, while insoluble organic compounds include aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and polycyclic aromatic ketones. Water-soluble inorganic ions account for 30% to 50% of PM2.5 mass concentration, with sulfate, nitrate, and ammonium salts being the most abundant. Alveoli have a fluid-coated surface that helps them to inflate properly and maintain their shape. Immune cells called macrophages protect tissues through innate immune responses, detecting, surrounding and digesting inhaled particulate matter and cellular debris. Alveolar macrophages adapt to environmental cues by managing inflammatory responses. They react in ways that can be either pro-inflammatory (M1) to fight infections or anti-inflammatory (M2) to promote tissue repair. They also manage adaptive immune responses involving future recognition and response to harmful substances. This can lead to either increased immune response or increased tolerance of challenges. Alveolar macrophages are crucial in maintaining a stable environment to support gas exchange in the alveoli, attempting to balance attacks on pathogens with prevention of cell damage. PM10 is related to increases in upper respiratory tract symptoms such as runny nose, cough and sneezing. It increases susceptibility to respiratory infections and inflammatory respiratory disorders of the nasal cavity (e.g. allergic rhinitis and chronic rhinosinusitis). Fine particulate matter (PM2.5 and ultrafine particulates) can reach the lower lungs and alveoli. Long-term damage to lung tissues can result from accelerated cell death, tissue scarring (fibrosis), reduced lung elasticity, and structural remodeling. Some PM2.5 and ultrafine particulates can cross the air-blood barrier to enter the bloodstream. From there, they can travel throughout the body. Particulate matter that is caught by the mucociliary system and removed from the lungs can be swallowed and reach the intestines, affecting the gastrointestinal system. Particulate matter has been linked to inflammatory bowel disease (IBD), colorectal cancer, appendicitis, and chronic kidney and liver diseases. Toxic components in PM2.5 disrupt the activity of macrophages and are associated with the development of cancers. Quantity and duration of exposure affect processes and outcomes. Adverse effects may occur at exposure levels lower than those recommended in published air quality standards. Impacts on health Exposure to particulate matter, a modifiable risk factor, is linked to diseases throughout the body. It affects the respiratory system (asthma, chronic obstructive pulmonary disease, lung cancer, pulmonary fibrosis, pneumonia, acute respiratory distress syndrome), the cardiovascular system (heart attacks, hypertension, arrhythmias, and atherosclerosis), the nervous system (cognitive decline, neurodegenerative diseases such as Alzheimer's disease, mental disorders,), the gastrointestinal system (inflammatory bowel disease, colorectal cancer, appendicitis, kidney and liver diseases), metabolic syndrome), and the reproductive system. The effects of particulate matter have been studied in connection with premature delivery, birth defects, low birth weight, Air pollution has also been linked to a range of psychosocial problems including violence and crime. Death According to the State of Global Air 2025 report, air pollution (including particulate matter from both outdoor and household sources) is the leading environmental risk factor for death world-wide. and has been reproduced many times since. Both short-term exposure (hours to a few days) and long-term exposure (months to years) to PM10 and PM2.5 have negative effects. Over all causes of mortality, PM2.5 has more severe health effects than PM10. The 2021 Global Burden of Disease Study (GBD) reported that outdoor fine particulates with diameter less than 2.5 microns (PM2.5) accounted for 7.83 million deaths and 231.51 million disability-adjusted life-years lost (DALYs) globally in 2021. PM2.5 was identified as a major health risk factor globally. In 2023, PM2.5 contributed to an estimated 182,000 premature deaths in the European Union. This was a decrease of 57% compared to the effects of PM2.5 in 2005. The decrease is attributed to changes in policies that led to a 38% decline in total emissions of primary PM2.5 between 2005 and 2023. In China, passage of the Air Pollution Prevention and Control Action Plan (APPCAP) in 2013 led to a one-third decrease in annual average PM2.5 concentrations and fewer deaths between 2013 and 2017. However PM2.5 continues to be a major environmental health risk in China, responsible for 2.27 million deaths and 46.68 million disability-adjusted life years (DALYs) in 2021. In the United States, amendments to the Clean Air Act in 1970 resulted in decreases in PM2.5 levels and increases in life expectancy, as was shown by the Harvard Six Cities Study and others. In 2017, pollution was estimated to account for nearly 197,000 deaths in the United States. A 2022 study in GeoHealth concluded that eliminating energy-related fossil fuel emissions in the United States would prevent premature deaths each year and provide in benefits from avoided PM-related illness and death. There are interactions between particulate matter, exercise, and mortality. The health benefits of physical exercise may be affected by air quality. A 2025 cross-national study involving 1.5 million adults demonstrated that high levels of ambient PM2.5 can significantly diminish the protective effects of leisure-time physical activity against all-cause and cause-specific mortality. Below an annual average concentration of 25 μg/m³, regular exercise reduces all-cause mortality by approximately 30%. This benefit is halved (to 12–15%) when concentrations exceeded 25 μg/m³. In addition, the protective effects of exercise against cancer-related mortality become statistically non-significant when PM2.5 levels reach 35 μg/m³ or higher. Respiratory system Particulate matter is associated with respiratory diseases including asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, pneumonia, acute respiratory distress syndrome, and lung cancer. PM10 rarely travels beyond the upper airway, while finer particulates such as PM2.5 and PM0.1 can go deeper into the lungs and cause greater harms to respiratory health. Similar results are reported by other studies. The IARC and WHO designate particulates as a Group 1 carcinogen. Short-term exposure is also associated with increased emergency room visits and hospitalizations relating to asthma, COPD, upper respiratory infections (URI), and pneumonia. Airborne particulate matter can carry microbes into the respiratory system and increase the risk of respiratory infections and allergic reactions. PM2.5 suppresses immune responses and worsens inflammation, increasing severity and mortality of bacterial and viral infections in the respiratory system. PM2.5 has been found to promote allergic reactions and cytokine storms during respiratory viral infections. PM2.5 has been shown to increase both oxidative stress and inflammation. Oxidative stress decreases availability of nitric oxide, needed to maintain the elasticity of blood vessels. Chronic inflammation damages blood vessel walls, interfering with their ability to relax and regulate pressure. In 2022, a systematic review and analysis of 27 studies with approximately 42 million participants reported that each 10 µg/m³ increase in long-term PM2.5 exposure was associated with a 21% higher risk of developing hypertension over time. Nervous system The effects of air pollution and particulate matter on cognitive performance are an active area of research. Meta-analysis and reviews indicate that exposure to PM, PM, and SO are associated with decreases in global cognitive function and with cognitive decline. PM2.5 is associated with reduced cognitive function in children, as measured by IQ scores. Improved air quality has been found to have a protective effect on cognitive function. Risk of Alzheimer's disease is associated with PM, and is higher in heavily polluted regions than in lightly polluted regions. There is also a strong association between Parkinson's disease and PM. Higher rates of Parkinson's disease are generally associated with higher levels of PM. Air pollution may increase the risk of mental disorders such as depression, anxiety,, bipolar disorder and psychosis Increases in symptoms and behaviors may be related to underlying changes in neurotransmitters and neuromodulators. Relationships between depression, suicide, and air pollution are complicated. For example, daily increases in both temperature and air pollution have been found to increase the risk of death from suicide, with stronger effects for women than men. Air pollution is also associated with increased levels of violence and crime. A review and meta-analysis including 20 studies reports an increased risk of autism spectrum disorders (ASD) in children following exposures to PM prenatally and for the first year and second years after birth. ASD and Attention Deficit Hyperactivity Disorder (ADHD) have been linked to early-life exposures to both PM and NO. While mechanisms connecting PM exposure and cognitive decline are not fully understood, research suggests that particulate matter may reach the brain via multiple pathways, including inhalation, ingestion, and the olfactory system. Respiratory inflammation can lead to systematic inflammation, interfering with the blood–brain barrier and enabling toxins and other materials to enter the brain. There, particulate matter causes damage as a result of neuroinflammation, oxidative stress, buildup of misfolded proteins, and neuronal cell death. Reproductive system Particulate matter and PM exposure have been studied with respect to the reproductive system. and higher rates of infertility in both men and women have been correlated with exposure to particulates. PM has been shown to disrupt hormone levels and decrease the supply of eggs in a woman's ovaries. PM accumulates in the reproductive organs and can cause male infertility. Overall epidemiologic and toxicological evidence suggests causal relationships between long-term exposure to fine and ultrafine particulate matter and adverse outcomes in offspring. Smaller forms of particulate matter, including black carbon and microplastics, can cross the placental barrier and cause harms during placental development. Particulate matter from wildfire smoke leads to alterations in placental function and negative outcomes in pregnancy. Wildfire smoke effects Smoke from wildfires may more seriously affect sensitive groups such as the elderly, children, pregnant women, and people with lung, and cardiovascular disease. Particulate matter from wildfires can be a triggering factor of acute coronary events such as ischemic heart disease. Evidence also suggests that wildfire smoke reduces mental performance. Racial disparities There have been many studies linking race to increased proximity to particulate matter emissions sources and adverse health effects such as asthma. Black populations are located disproportionately closer to areas of high PM output than White populations. Residential proximity to particulate emitting facilities increases exposure to PM2.5 and rates of illness and death. Multiple studies confirm that the burden of PM emissions is higher among populations that are non-White or living in poverty. Socioeconomic conditions are not sufficient to explain these differences: disparities for Blacks are more pronounced than disparities on the basis of income. a longstanding environmental justice problem linked to the practice of historic redlining. Health effects are further worsened because "health care occurs in the context of broader historic and contemporary social and economic inequality and persistent racial and ethnic discrimination in many sectors of American life". One example is an area of Southeastern Louisiana, colloquially dubbed 'Cancer Alley' for its high concentration of cancer related deaths due to neighboring chemical plants. Cancer Alley is a majority African American community, with the neighborhood nearest to the plant being 90% Black. Long-term health effects of living in high PM concentrations have increased both illness and mortality rates, which were further worsened by COVID-19. Such outcomes reflect a history of racism. == Vegetation effects ==

The release of particulate matter into the environment affects both terrestrial and aquatic ecosystems. Particulate matter can settle from the air onto plants, ground, and water. Ultrafine particles can enter plants via both leaves and root systems, travel throughout plants, and affect their physical and chemical processes. The deposition of trace elements from pollution into the rings of trees can be used by dendrochronologists to reconstruct a pollution history, a historical record of changes in soils, sediments and the atmosphere. Particulate matter can physically block sunlight from entering leaves, preventingh photosynthesis. It can clog stomatal openings of plants and interfere with photosynthesis and transpiration functions. Particulate matter can damage plant cells and stunt or kill some plant species. Plants can absorb and retain particulate matter, removing it from the air and improving the quality of the air we breathe. However, this also means that particulate matter such as heavy metals can contaminate plants such as leafy vegetables above safe levels for human consumption. == Climate effects ==

Atmospheric aerosols affect the climate of the Earth by changing the amount of incoming solar radiation and outgoing terrestrial longwave radiation retained in the Earth's system. This occurs through several distinct mechanisms which are split into direct, indirect and semi-direct aerosol effects. The aerosol climate effects are the biggest source of uncertainty in future climate predictions.While the radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modeling studies that are difficult to verify at the present time. Aerosol radiative . The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight. (MODIS) on NASA's Terra satellite. Direct during sunset The direct aerosol effect consists of any direct interaction of radiation with atmospheric aerosols, such as absorption or scattering. It affects both short and longwave radiation to produce a net negative radiative forcing. The magnitude of the resultant radiative forcing due to the direct effect of an aerosol is dependent on the albedo of the underlying surface, as this affects the net amount of radiation absorbed or scattered to space. For example, if a highly scattering aerosol is above a surface of low albedo it has a greater radiative forcing than if it was above a surface of high albedo. The converse is true of absorbing aerosol, with the greatest radiative forcing arising from a highly absorbing aerosol over a surface of high albedo. The interaction of an aerosol with radiation is quantified by the single-scattering albedo (SSA), the ratio of scattering alone to scattering plus absorption (extinction) of radiation by a particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, the sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber. Indirect The Indirect aerosol effect consists of any change to the Earth's radiative budget due to the modification of clouds by atmospheric aerosols and consists of several distinct effects. Cloud droplets form onto pre-existing aerosol particles, known as cloud condensation nuclei (CCN). Droplets condensing around human-produced aerosols such as found in particulate pollution tend to be smaller and more numerous than those forming around aerosol particles of natural origin (such as windblown dust). For any given meteorological conditions, an increase in CCN leads to an increase in the number of cloud droplets. This leads to more scattering of shortwave radiation i.e. an increase in the albedo of the cloud, known as the cloud albedo effect, First indirect effect or Twomey effect. and biomass burning on cloud albedo compared to ambient clouds. The Cloud albedo aerosol effect is a first order effect and therefore classified as a radiative forcing by the IPCC. and inhibited precipitation in biomass burning plumes. This cloud lifetime effect is classified as a climate feedback (rather than a radiative forcing) by the IPCC due to the interdependence between it and the hydrological cycle. Semi-direct The Semi-direct effect concerns any radiative effect caused by absorbing atmospheric aerosol such as soot, apart from direct scattering and absorption, which is classified as the direct effect. It encompasses many individual mechanisms, and in general is more poorly defined and understood than the direct and indirect aerosol effects. For instance, if absorbing aerosols are present in a layer aloft in the atmosphere, they can heat surrounding air which inhibits the condensation of water vapour, resulting in less cloud formation. Additionally, heating a layer of the atmosphere relative to the surface results in a more stable atmosphere due to the inhibition of atmospheric convection. This inhibits the convective uplift of moisture, which in turn reduces cloud formation. The heating of the atmosphere aloft also leads to a cooling of the surface, resulting in less evaporation of surface water. The effects described here all lead to a reduction in cloud cover i.e. an increase in planetary albedo. The semi-direct effect classified as a climate feedback) by the IPCC due to the interdependence between it and the hydrological cycle. which are mainly produced when sulfur dioxide reacts with water vapor to form gaseous sulfuric acid and various salts (often through an oxidation reaction in the clouds), which are then thought to experience hygroscopic growth and coagulation and then shrink through evaporation.) or geological via volcanoes or weather-driven from wildfires and other natural combustion events, but in the recent decades anthropogenic sulfate aerosols produced through combustion of fossil fuels with a high sulfur content, primarily coal and certain less-refined fuels, like aviation and bunker fuel, had dominated. By 1990, global human-caused emissions of sulfur into the atmosphere became "at least as large" as all natural emissions of sulfur-containing compounds combined, and were at least 10 times more numerous than the natural aerosols in the most polluted regions of Europe and North America, where they accounted for 25% or more of all air pollution. and also contributed to heart and lung conditions and even the risk of preterm birth and low birth weight. Sulfate pollution also has a complex relationship with NOx pollution and ozone, reducing the also harmful ground-level ozone, yet capable of damaging the stratospheric ozone layer as well. Once the problem became clear, the efforts to remove this pollution through flue-gas desulfurization measures and other pollution controls were largely successful, reducing their prevalence by 53% and causing healthcare savings valued at $50 billion annually in the United States alone. Yet, around the same time, research had shown that sulfate aerosols were affecting both the visible light received by the Earth and its surface temperature, and as the so-called global dimming) began to reverse in the 1990s in line with the reduced anthropogenic sulfate pollution, climate change accelerated. As of 2021, state-of-the-art CMIP6 models estimate that total cooling from the currently present aerosols is between to ; the IPCC Sixth Assessment Report uses the best estimate of , with the uncertainty mainly caused by contradictory research on the impacts of aerosols of clouds. Some are certain that they cool the planet, though, and this led to solar geoengineering proposals known as stratospheric aerosol injection, which seeks to replicate and enhance the cooling from sulfate pollution while minimizing the negative effects on health through deploying in the stratosphere, where only a fraction of the current sulfur pollution would be needed to avoid multiple degrees of warming, but the assessment of costs and benefits remains incomplete, even with hundreds of studies into the subject completed by the early 2020s. Instances Volcanoes are a large natural source of aerosol and have been linked to changes in the Earth's climate often with consequences for the human population. Eruptions linked to changes in climate include the 1600 eruption of Huaynaputina which was linked to the Russian famine of 1601–1603, leading to the deaths of two million, and the 1991 eruption of Mount Pinatubo which caused a global cooling of approximately 0.5 °C lasting several years. Research tracking the effect of light-scattering aerosols in the stratosphere during 2000 and 2010 and comparing its pattern to volcanic activity show a close correlation. Simulations of the effect of anthropogenic particles showed little influence at present levels. Aerosols are also thought to affect weather and climate on a regional scale. The failure of the Indian monsoon has been linked to the suppression of evaporation of water from the Indian Ocean due to the semi-direct effect of anthropogenic aerosol. Recent studies of the Sahel drought and major increases since 1967 in rainfall in Australia over the Northern Territory, Kimberley, Pilbara and around the Nullarbor Plain have led some scientists to conclude that the aerosol haze over South and East Asia has been steadily shifting tropical rainfall in both hemispheres southward. Energy industry knowledge and response to adverse health effects use in power plants exceed those caused by production of renewable energy. Major energy companies understood at least since the 1960s that use of their products causes widespread adverse health effects and death but continued aggressive political lobbying in the United States and elsewhere against clean air regulation and launched major corporate propaganda campaigns to sow doubt regarding the causative link between the burning of fossil fuels and major risks to human life. Internal company memoranda reveal that energy industry scientists and executives knew that air pollutants created by fossil fuels lodge deep in human lung tissue, and cause birth defects in children of oil industry workers. The industry memos acknowledge that automobiles "are by far the greatest sources of air pollution" and also that air pollution causes adverse health effects and lodges toxins, including carcinogens, "deep into the lungs which would otherwise be removed in the throat". In response to mounting public concern, the industry eventually created the Global Climate Coalition, an industry lobby group, to derail governments' attempts to regulate air pollution and to create confusion in the public mind about the necessity of such regulation. Similar lobbying and corporate public relations efforts were undertaken by the American Petroleum Institute, a trade association of the oil and gas industry, and the climate change denier private think tank, The Heartland Institute. "The response from fossil-fuel interests has been from the same playbook – first they know, then they scheme, then they deny and then they delay. They've fallen back on delay, subtle forms of propaganda and the undermining of regulation," said Geoffrey Supran, a Harvard University researcher of the history of fossil-fuel companies and climate change. These efforts have been compared, by policy analysts such as Carroll Muffett of the Center for International Environmental Law, to the tobacco industry strategy of lobbying and corporate propaganda campaigns to create doubt regarding the causal connection between cigarette smoking and cancer and to forestall its regulation. In addition, industry-funded advocates, when appointed to senior government positions in the United States, have revised scientific findings showing the deadly effects of air pollution and have rolled back its regulation. == Control ==

Technologies Hepa effect: without (outdoor) and with filter (indoor) Particulate matter emissions are highly regulated in most industrialized countries. Due to environmental concerns, most industries are required to operate some kind of dust collection system. These systems include inertial collectors (cyclonic separators), fabric filter collectors (baghouses), electrostatic filters used in facemasks, wet scrubbers, and electrostatic precipitators. Cyclonic separators are useful for removing large, coarse particles and are often employed as a first step or "pre-cleaner" to other more efficient collectors. Well-designed cyclonic separators can be very efficient in removing even fine particulates, and may be operated continuously without requiring frequent shutdowns for maintenance. Fabric filters or baghouses are the most commonly employed in general industry. They work by forcing dust-laden air through a bag-shaped fabric filter leaving the particulate to collect on the outer surface of the bag and allowing the now clean air to pass through to either be exhausted into the atmosphere or in some cases recirculated into the facility. Common fabrics include polyester and fiberglass and common fabric coatings include PTFE (commonly known as Teflon). The excess dust buildup is then cleaned from the bags and removed from the collector. emitted and rising up from a building under rehabilitation on a Saturday afternoon, Treasure Garden, Tai Po, Hong Kong. The rehabilitation scheme is subsidised by the government and contract like this can worth up to a hundred million. People are living inside the building throughout the whole period of the renovation work, which usually lasts for over a year, and it can be foretold that the residents' exposure to construction dust is even more serious than the occupational exposure of the workers. The possible presence of asbestos and lead paint dust is also worth worrying. This type of rehabilitation works are very common (over 3000 buildings in the first 6 years of the scheme), especially in some older districts. With such a large amount of dust emitted, it was obvious that neither water was being sprayed nor dust extraction device was in use, which was a violation of the local law. Wet scrubbers pass the dirty air through a scrubbing solution (usually a mixture of water and other compounds) allowing the particulate to attach to the liquid molecules. Electrostatic precipitators electrically charge the dirty air as it passes through. The now charged air then passes through large electrostatic plates which attract the charged particle in the airstream collecting them and leaving the now clean air to be exhausted or recirculated. Measures For general building construction, some places that have acknowledged the possible health risks of construction dust for decades legally require the relevant contractor to adopt effective dust control measures, although inspections, fines and imprisonments are rare in recent years (for example, two prosecutions with a total fines of in Hong Kong in the year 2021). Some of the mandatory dust control measures include load, unload, handle, transfer, store or dispose of cement or dry pulverized fuel ash in a completely enclosed system or facility, and fit any vent or exhaust with an effective fabric filter or equivalent air pollution control system or equipment, enclose the scaffolding of the building with dust screens, use impervious sheeting to enclose both material hoist and debris chute, wet debris with water before it is dumped into a debris chute, have water sprayed on the facade surface before and during grinding work, use grinder equipped with vacuum cleaner for facade grinding work, spray water continuously on the surface for any pneumatic or power-driven drilling, cutting, polishing or other mechanical breaking operation that causes dust emission, unless there is the operation of an effective dust extraction and filtering device, provide hoarding of not less than 2.4 m in height along the whole length of the site boundary, have hard paving on open area and wash every vehicle that leaves the construction sites. Use of automatic sprinkler equipment, automatic carwash equipment and installation of video surveillance system for the pollution control facilities and retain the videos for one month for future inspections. Besides removing particulates from the source of pollution, they may also be cleaned in the open air (e.g. smog tower, moss wall, and water truck), while other control measures employ the use of barriers. ==Regulation==

Most governments have created regulations both for the emissions allowed from certain types of pollution sources (motor vehicles, industrial emissions etc.) and for the ambient concentration of particulates. Particulates are the deadliest form of air pollution due to their ability to penetrate deep into the lungs and blood stream, contributing to premature death from a wide variety of causes including respiratory diseases and cardiovascular diseases. Limits / standards set by governments Canada The Canadian Ambient Air Quality Standard (CAAQS) for particulate matter is set nationally by the federal-provincial Canadian Council of Ministers of the Environment (CCME). In 2025, more stringent national standards were endorsed to take effect as of 2030. The 2030 CAAQS for PM are 23 μg/m (calculated using the 3-year average of the annual 98th percentile of the daily 24-hr average concentrations) and 8.0 μg/m3 (3-year average of annual mean). China Air pollution in China is a long-standing public health issue. In 2013, China introduced an Air Pollution Prevention and Control Action Plan to reduce pollution levels, which has led to improvements in air quality. On February 24, 2026, China's Ministry of Ecology and Environment further updated its ambient air quality standards, to be implemented in two phases. During a transitional phase, from March 1, 2026 through December 31, 2030, the annual PM limit will be 30 μg/m and the PM limit will be 60 μg/m. European Union The European Union has established air quality legislation through the passage of Ambient Air Quality Directives (AAQD), National Emission Ceilings Directives (NECD), and various source-specific directives. First introduced in 1980, AAQDs have defined limits for sulfur dioxide, particulate matter, lead, nitrogen dioxide, PM and PM. Changes to EU standards have been passed and will be phased in beginning in 2026. The Euro 7 vehicle emissions standards will be phased in beginning 29 November 2026. They will cover petrol, diesel, and electric vehicles. Euro 7 will be the first standard to regulate sources of pollution such as dust from tires and brakes, not just exhaust fumes. As of December 10, 2024, the European Union updated its Ambient Air Quality Directive (AAQD), giving EU member states until December 11, 2026 to implement the updated directive in their national laws and achieve interim targets, with stricter values to be attained by January 1, 2030. United Kingdom The Clean Air Act of 1956 was a pivotal act of the Parliament of the United Kingdom for UK pollution control policies. Enacted in response to 1952's Great Smog of London, it allowed local authorities to declare smoke control areas and laid the foundation for future pollution control measures. Wood sold in volumes of less than 2m3 must be certified as 'Ready to Burn', which means it has a moisture content of 20% or less. Manufactured solid fuels must also be certified as 'Ready to Burn' to ensure they meet sulfur and smoke emission limits. Starting from January 2022, all new wood burning stoves must meet new EcoDesign standards (Ecodesign stoves produce 450 times more toxic air pollution than gas central heating. Older stoves, which are now banned from sale, produce 3,700 times more). As of 2023, the amount of smoke that burners in "smoke control areas" – most England's towns and cities – can emit per hour was reduced from 5g to 3g. Violations can result in an on-the-spot fine of up to £300 and a possible criminal record. United States As required by the Clean Air Act, the United States Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health and the environment. The six criteria air pollutants are particulate matter (PM and PM), carbon monoxide, lead, ozone, nitrogen dioxide, and sulfur dioxide. Target levels are designated as either primary (protecting public health) or secondary (protecting "public welfare" due to harms against animals, crops, vegetation, buildings and decreased visibility). NAAQS for PM and PM are: California The California Environmental Protection Agency and its department, the California Air Resources Board (CARB) have repeatedly taken action to set stricter ambient air quality standards. In some cases, such as PM, California ambient air quality standards (CAAQS) are more stringent than national standards. Regional initiatives such as the 2006 California Goods Movement Plan have been linked to improvements in air quality and health outcomes. Colorado Colorado generally follows National Ambient Air Quality Standards (NAAQS) for criteria air pollutants. Its State Implementation Plan (SIP) outlines the steps to be taken to enforce the NAAQS. Counties that exceed thresholds for criteria air pollutants are designated as "nonattainment areas." The Air Quality Control Commission (AQCC), appointed by the Governor and confirmed by the Senate, oversees Colorado's air quality program. The Air Pollution Control Division (APCD) of the Colorado Department of Public Health and Environment (CDPHE) monitors the air quality index (AQI) and reports daily air quality and health alerts. The Regional Air Quality Council (RAQC) has been the lead air quality planning agency for the metro Denver area since 1989. The metro area of Denver, Colorado's capital, is of particular concern due to ozone and particulate pollution from industry, vehicles, power plants, refineries, and airports. Hot and dry conditions during the summer time put the area at risk for forest fires. As of April 2026, the Colorado Air Quality Control Commission adopted new emission standards for five toxic air contaminants in addition to those covered by the NAAQS: Hydrogen sulfide, Benzene, Formaldehyde, Ethylene oxide, and Hexavalent chromium compounds. == Particulate matter worldwide ==

PM by city To analyse the air pollution trend, 480 cities around the world (Ukraine excluded) was mapped by air experts Average levels of PM were measured using aqicn.org's World Air Quality Index data, and a formula developed by AirNow was used to convert the PM figure into micrograms per cubic meter of air () values. Among the 70 capital cities investigated, Baghdad, Iraq is the worst performing one, with PM levels going up . Ulan Bator (Ulaanbaatar), the capital city of Mongolia, is performing the best, with PM levels dropping by . Previously it was as one of the most polluted capital cities in the world. An air quality improvement plan in 2017 appears to be showing positive results. Out of the 480 cities, Dammam in Saudi Arabia is performing the worst with PM levels going up . The city is a significant center for the Saudi oil industry and home to both the largest airport in the world and the largest port in the Persian Gulf. It is currently the most polluted city surveyed. In Europe, the worst performing cities are located in Spain. They are Salamanca and Palma, with PM levels increase by and respectively. The best performing city is Skopje, the capital city of North Macedonia, with PM levels dropping by . It was once the most polluted capital city in Europe and still has a long way to go to achieve clean air. In the U.S., Salt Lake City, Utah and Miami, Florida are the two cities with the highest PM level increases (). Salt Lake City suffers from a weather event known as 'inversion'. Located in a valley, cooler, polluted air is trapped close to ground level under the warmer air above when inversion occurs. On the other hand, Omaha, Nebraska is performing the best and has a decrease of in PM levels. The cleanest city in this report is Zürich, Switzerland with PM levels of just '''''', placed first in both 2019 and 2022. The second cleanest city is Perth, with and PM levels dropping by since 2019. Of the top ten cleanest cities, five are from Australia. They are Hobart, Wollongong, Launceston, Sydney and Perth. Honolulu is the only U.S. city in the top ten list, ranking tenth with levels of , with a tiny increase since 2019. Almost all of the top ten most polluted cities are in the Middle East and Asia. The worst is Dammam in Saudi Arabia with a PM level of ''''''. Lahore in Pakistan is the second worst with . The third is Dubai, home to the world's tallest building. In the bottom ten are three cities from India, Muzaffarnagar, Delhi and New Delhi. Here is a list of the 30 most polluted cities by PM, Jan to Sep 2022: According to National Pollutant Inventory data, PM10, PM2.5, metals and nitrogen oxide emissions increased alongside rising coal production between 2008 and 2018. Coal mines accounted for 42.1% of national PM10 emissions, of which 19.5% was PM2.5. Australia is also being affected by severe wildfires. The fire season of 2019–20 was known in Australia as Black Summer. Massive wildfires burned over 186,000 square kilometers of land, producing plumes of smoke and particulate matter. This increased concentrations of ice crystals, resulting in as much as 270% more lightning activity and 240% more rainfall in lightning storms over the Tasman Sea. Mineral dust and smoke particles from the fire emissions altered particulate composition on the surface of the ocean. China Air pollution in China has long been a public health issue, estimated to contribute to 1.67 million premature deaths nationally in 2020. Exposure to particulate matter is the nation's fourth leading risk factor for mortality. PM2.5 has been identified as the primary contributor to atmospheric particulate pollution in China. Pollution levels in Chinese cities were extreme between 2010 and 2014. In 2011, in Beijing, a "Crazy Bad" air quality index (AQI) was reported that exceeded 500: 500 is the hypothetical maximum on the scale. On January 12, 2013, Beijing reported a "jaw-dropping" all-time high AQI of 755, In 2013, China introduced an Air Pollution Prevention and Control Action Plan to reduce pollution levels. Since then, air quality in China has shown substantial improvements thanks to clean air actions. From 2013-2017, annual average PM concentrations declined by 33.3% across 74 major Chinese cities. Reductions in PM are associated with decreases in mortality rate. Europe Europe continues to experience poor air quality. In 2021, the World Health Organization strengthened its guideline levels on annual PM2.5, lowering its recommended guideline from 10 μg/m3 to 5 μg/m3. According to a study conducted by NASA and NIER, 52% of PM measured in Olympic Park, Seoul in May and June 2016 came from local emissions. The rest was trans-boundary pollution coming from China's Shandong Province (22%), North Korea (9%), Beijing (7%), Shanghai (5%), and a combined 5% from China's Liaoning Province, Japan and the West Sea. In December 2017, the environmental ministers from South Korea and China signed the China-Korea Environmental Cooperation Plan (2018–22), a five-year plan to jointly solve issues in the air, water, soil and waste. An environmental cooperation centre was also launched in 2018 to aid cooperation. Thailand PM and PM pose serious health risks and are linked to high mortality rates in Thailand. They show seasonal variation: in urban areas of Thailand such as its capital, Bangkok, concentrations and PM exposure risk are higher during the cool dry season (December to February). PM levels and associated health risks tend to be worse in northern areas such as Chiang Mai. The mountains that surround Chiang Mai interfere with air flow and cause temperature inversions that trap pollution. In 2023, Chiang Mai, a popular tourist destination, was ranked as the most polluted of 100 cities worldwide by a Swiss air quality company. In March and April 2026, Chang Mai smog reached dangerous PM levels as a result of fires during the burning season (January through April), with dense haze and reduced visibility across the region. Particulate matter levels in southern Thailand are also increasing as a result of open crop residue burning in Thailand and nearby Southeast Asian countries. Mongolia Mongolia's capital city Ulaanbaatar has an annual average mean temperature of about 0 °C, making it the world's coldest capital city. Ulaanbaatar is located in the Tuul River Valley, surrounded by the Khentii Mountains, conditions which tend to cause temperature inversions and trap air pollution. Temperature inversions are strongly correlated with particulate matter concentrations. Heating mainly comes from coal. Coal is burned in power stations, heating the apartments of about 40% of the population, and in stoves in traditional Ger housing, home to the other 60% of the population. Ger districts or shantytowns have developed due to the country's new market economy and the very cold winter seasons. The poor in these districts cook and heat their wood houses with indoor stoves fueled by wood or coal. The resulting air pollution is characterized by extremely high levels of particulate matter, carbon, sulfur dioxide, nitrogen oxide, iron, arsenic, lead, zinc, and nickel. Burning coal also produces fly ash, which contains fine dust particles in the PM2.5 size range. Pollution in Ulaanbaatar is 4–11 times higher during the winter than other seasons, with primary emissions from combustion contributing prominently to winter air pollution. PM2.5 levels are elevated during the heating season, starting to rise in October and dropping by April. During peak heating season, November to February, hourly averaged PM2.5 concentrations can exceed , an extremely dangerous level. Since 2010, rapid growth and uneven patterns of economic development have worsened poverty and air pollution. Mongolia has introduced a number of initiatives to improve availability of heating sources, fuels, and stoves. United States Following implementation of the Clean Air Act in 1970, air quality in the U.S. improved, with a reduction of 79% in combined emissions of criteria and precursor pollutants from 1970-2024. From 2000-2024, PM levels have decreased by 46% (Annual) and 45% (24-Hour), while PM has decreased by 36% (24-Hour). Since 2018, wildfires have been a source of large amounts of particulate matter and ozone. In 2020, 1.7 million hectares burned in California. In 2023, wildfires in Canada contributed to large numbers of "smoke days" across the continental United States. File:Naaqs-concentrations-averages-data-1990-2024.png|Declining National Air Pollutant Concentration Averages in the United States, 1990-2024 File:Naaqs-emissions-categories-data.png | National Emissions of Pollutants By Source Category, United States, 2024 File:US-PM25-nonattainment-2026-02.pdf|U.S. counties violating national PM standards, February 2026 File:US-PM10-nonattainment-2018-06.png|U.S. counties violating national PM standards, June 2018 == See also ==