Air Pollution: Understanding Particulate Matter's Impact

Air pollution is a major environmental health problem that affects people in low-, middle-, and high-income countries. Outdoor air pollution in both cities and rural areas was estimated to cause 4.2 million premature deaths worldwide per year in 2019, with 89% of these occurring in low- and middle-income countries. Particulate matter (PM) is a proxy indicator for air pollution and is made up of a complex mixture of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. PM is categorized by size, with PM10 referring to particles with a diameter of 10 micrometres or less, and PM2.5 referring to particles with a diameter of 2.5 micrometres or less. These fine particles can be inhaled and cause serious health problems, including heart disease, respiratory issues, and lung cancer. While particle pollution comes from both outdoor and indoor sources, human activities such as combustion in mechanical and industrial processes, vehicle emissions, and tobacco smoke are major contributors.

Particulate matter is a complex mixture of solids and aerosols, composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings

Particulate matter is categorised by size, with PM2.5 comprising particles 2.5 microns or less in diameter, and PM10 for particles 10 microns or less

Particulate matter, also known as particle pollution or soot, is a mix of tiny solid and liquid particles in the air. These particles vary widely in size, shape, and chemical composition. They may contain inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the Earth's crust.

PM2.5 and PM10 often derive from different sources and have different chemical compositions. PM2.5 is primarily produced by the combustion of gasoline, oil, diesel fuel, or wood, as well as industrial processes and motor vehicle exhaust. PM10 includes dust from construction sites, landfills, agriculture, wildfires, industrial sources, wind-blown dust, pollen, and fragments of bacteria. Natural sources of both PM2.5 and PM10 include bushfires, dust storms, pollen, and sea spray.

The sources and composition of particulate matter contribute to its impact on human health. Particles smaller than 2.5 microns may be associated with more adverse effects as they can be inhaled more deeply into the lungs. The duration of exposure is also a factor, with both short-term and long-term exposure having negative consequences. While air quality has improved in recent decades due to stricter regulations, many people still live with unhealthy levels of particle pollution, and fine particles are increasingly understood to be more dangerous than previously thought.

Sources of particulate matter include human activities like combustion of carbon-based fuels, and natural sources like dust storms and wildfires

Particulate matter, also known as particle pollution, refers to a mixture of solid particles and liquid droplets found in the air. These particles can be large or dark enough to be seen, such as dust, dirt, soot, or smoke, or they can be so small that they require an electron microscope for detection.

Sources of particulate matter include human activities, such as the combustion of carbon-based fuels, and natural sources, like dust storms and wildfires. Human activities that contribute to particulate matter include transportation, electricity generation, and industrial processes that burn fossil fuels. This combustion releases pollutants such as carbon dioxide, nitrogen oxides, sulfur dioxide, volatile organic compounds (VOCs), and particulate matter. In addition, human activities like cooking, heating with dirty technologies, and lighting with kerosene also contribute to indoor air pollution.

The combustion of carbon-based or fossil fuels is a significant source of particulate matter, particularly fine particles known as PM2.5. These particles have a diameter of 2.5 micrometers or less and can be harmful to human health. They are produced through the incomplete combustion of fossil fuels, biofuels, and biomass, which can be emitted from diesel vehicles, biomass cookstoves, and wildfires.

Natural sources of particulate matter include dust storms, wildfires, volcanoes, and aerosolized sea salt. Even with the removal of anthropogenic emissions, natural sources of particulate matter, such as dust, sea salt, and organics from vegetation, can still pose challenges for air quality. For example, regions like India and Northern Africa, which are exposed to large amounts of fine dust, may struggle to reduce PM2.5 exposures below the recommended guidelines.

Particulate matter can also form indoors through complex reactions of gaseous pollutants emitted from household cleaning products and air fresheners. Additionally, indoor activities such as smoking tobacco, cooking, and burning wood, candles, or incense contribute to indoor particulate matter.

Particulate matter can cause serious health issues, especially for vulnerable groups like children, older adults, and those with pre-existing health conditions

Particulate matter is a widespread air pollutant that poses serious health risks, especially to vulnerable groups such as children, older adults, and those with pre-existing health conditions. It refers to a mix of tiny solid particles, liquid droplets, and aerosols in the air we breathe. These particles can be emitted through human activities, such as combustion in industrial processes and vehicle emissions, or natural sources like volcanoes and dust storms.

The health effects of particulate matter on vulnerable groups are significant. Research has identified older adults with chronic heart or lung disease, children, and asthmatics as the most susceptible to the adverse consequences of exposure to particulate matter. Children, for instance, inhale more air per pound of body weight than adults due to their faster breathing rates, smaller body sizes, and the tendency to spend more time outdoors. Their immature immune systems also make them more vulnerable to the harmful effects of particulate matter.

Studies have linked particulate matter exposure to a range of health issues. It is a contributing factor to cardiovascular and respiratory diseases, as well as cancers. The World Health Organization (WHO) estimates that particulate matter air pollution leads to approximately 800,000 premature deaths each year, with a more recent estimate placing the figure at 4.2 million premature deaths worldwide in 2019. The major components of particulate matter, such as sulfates, nitrates, black carbon, and mineral dust, have been associated with negative health impacts.

Vulnerable groups are particularly susceptible to the health risks associated with particulate matter. Older adults, especially those with pre-existing heart or lung conditions, are at an increased risk of experiencing adverse health effects. Children, too, are vulnerable, as evidenced by the Children's Health Study, which found that children exposed to high levels of particulate matter had slower lung growth and smaller lungs at age 18 compared to those living in less polluted areas. Additionally, people of colour and low socioeconomic status populations are at higher risk of suffering from the consequences of particulate matter pollution.

While particulate matter pollution is a pressing issue, it is reassuring to note that air quality has improved in many regions. The implementation of protective standards, such as the Clean Air Act, has helped reduce emissions and drive down the levels of particulate matter in the atmosphere. However, it is crucial to recognize that many people still live with unhealthful levels of particle pollution, and the emerging evidence underscores the heightened dangers associated with fine particles.

Efforts to reduce particulate matter pollution include regulatory actions, such as the Clean Air Act, and the adoption of air quality standards and guidelines.