Particulate matter (PM) air pollution is a product of modern civilization and poses a serious health hazard to the mankind.
According to the WHO, ambient (outdoor) air pollution, in both cities and rural areas, caused about 4.2 million premature deaths worldwide in 2016; the cause of mortality was exposure to the fine particulate matter (PM2.5).
Particulate matter (PM) is the term that refers to a mixture of solid and liquid particles of organic and inorganic substances suspended in the air. PM10 refers to the particles having diameters of 10 micrometers (microns or µm) or lesser. PM10 is also known as coarse particulate matter (coarse PM). PM2.5 refers to the particles having diameters of 2.5 micrometers or lesser. PM2.5 is also known as fine particulate matter (fine PM). Particles having a diameter of less than 0.1 micrometer are known as ultrafine particles.
To have an idea of how small PM10 and PM2.5 are, a comparison can be made with the size of an average human hair, which is about 70 micrometers in diameter.
Composition of Particulate Matter (PM)
The physical and chemical characteristics of particulate matter vary by location. Common chemical constituents of PM include sulphates; nitrates; ammonium; other inorganic ions such as ions of sodium, potassium, calcium, magnesium and chloride; metals (including cadmium, copper, nickel, vanadium and zinc); organic and elemental carbon; crustal material (Si, Al); particle-bound water; and polycyclic aromatic hydrocarbons (PAH). In addition, biological components such as allergens and microbial compounds are found in PM.
Sources of Particulate Matter (PM)
Particles can either be directly emitted into the air (primary PM), or be formed in the atmosphere through chemical reactions of precursor gases such as sulphur dioxide, oxides of nitrogen, ammonia and non-methane volatile organic compounds (secondary PM). Secondary particles are mostly found in fine PM.
Primary PM and the precursor gases can have both anthropogenic (man-made) and non-anthropogenic (natural) sources.
Anthropogenic sources of PM include burning of liquid and solid fuels (diesel, petrol, kerosene, coal, lignite, heavy oil, biomass, etc.) for energy production, other industrial activities (mining; manufacture of cement, ceramic and bricks; smelting; etc.), construction work, agriculture, burning of waste, burning of stubble, erosion of roads and pavements by road traffic, abrasion of brakes and tires, etc.
Natural sources of PM include –
Wind-blown desert dust: It contains natural particulate matter transported from dry regions, i.e. resuspended and transported (wind-blown) desert dust particles. In the European Union, arid zones in North Africa are the major source of this kind of particulate matter, for example, long-range transportation of dust occurs from the Sahara Desert to Southern Europe. African dust consists mainly of silicate minerals and carbonates, with the precise composition dependent on the geographical origin.
Sea spray aerosols: These contain finely dispensed particles formed by the action of wind on the sea and emitted into the air. Sodium chloride (NaCl) is the main component in sea spray aerosols.
Volcanoes and seismic activities: Particulate matter emitted directly during a volcanic eruption (primary PM) often has a characteristic composition. Mercury is amongst the most toxic elements emitted by volcanic eruptions. The main compounds emitted include water vapour, ash, carbon dioxide (CO2), sulphur dioxide (SO2), hydrogen chloride, fluoride and bromide (HCl, HF and HBr), and a long list of other components emitted in lower abundances.
Wild-land fires: Wild-land fires are caused by burning of non-managed and managed forests and other vegetation, excluding agricultural burning of stubbles, etc. The fire must have a natural cause, e.g. lightning, in order to be considered a natural source. During wild-land fires, mainly, fine particulate matter (PM2.5) is emitted directly into the air. Further, non‑methane volatile organic compounds (NMVOC) are emitted by such fires, and they participate in chemical reactions, which lead to the formation of organic particulate matter (secondary organic aerosols).
Other sources: These include primary biological aerosols such as spores (very small in size and part of PM10) or pollen (typically larger in size than PM10) derived from biological processes, secondary organic biogenic aerosols (these constitute the organic fraction of PM formed in the atmosphere through a chain reaction of volatile organic compounds emitted by soils and vegetation), resuspended particles from erosion of roads and pavements by wind, etc.
Harmful Effects of PM on Health
The size of particles is directly linked to their potential for causing health problems. PM10 and PM2.5 are inhalable and respirable particles, and can cause serious health problems. While PM10 can penetrate and lodge deep inside the lungs, PM2.5 particles are even more damaging to health as they can penetrate the lung barrier and enter the bloodstream. Exposure to particulate matter can cause cardiovascular diseases, respiratory diseases, lung cancer, and premature death. Furthermore, there is no evidence of a safe level of exposure or a threshold below which no adverse health effects occur.
Studies have also shown association between particulate matter (PM) air pollution and other diseases such as hypertension (high blood pressure), diabetes and kidney disease. Maternal exposure to ambient air pollution is associated with adverse birth outcomes, such as low birth weight, preterm birth and small for gestational age (SGA) births.
People suffering from heart disease and/or respiratory disease, children, and older adults are much more likely to be affected by the particulate matter air pollution. For example, exposure to PM affects lung development in children, including reversible deficits in lung function as well as chronically reduced lung growth rate and a deficit in long-term lung function. Ambient air pollution affects neurological development in children, and causes neural, behavioral and cognitive changes in children.
According to the WHO, PM is a common proxy indicator for air pollution. It affects more people than any other pollutant. WHO estimates that in 2016, 58% of outdoor air pollution-related premature deaths were due to ischemic heart disease and stroke, 18% of deaths were due to chronic obstructive pulmonary disease (COPD), 18% were due to acute lower respiratory tract infections respectively, and 6% of deaths were due to lung cancer.
According to a study published in July 2018 in the journal “The Lancet Planetary Health”, the global toll of diabetes attributable to PM2·5 air pollution is substantial. The burden of diabetes attributable to PM2·5 air pollution is more heavily skewed towards low-income and lower-to-middle-income countries, and countries with a lower socio-demographic index (SDI).
According to the study, in 2016, globally, ambient PM2·5 contributed to –
- About 3·2 million incident cases of diabetes, representing 14% of total cases of incident diabetes
- About 8·2 million years of healthy life lost due to diabetes, representing 14·4% of total years of healthy life lost due to diabetes.
- 206,105 deaths from diabetes