Problems caused by atmospheric pollutants
Chemistry of the atmosphere • Atmospheric pollutants
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Definition and limiting factors
An atmospheric pollutant denotes any gas, particle or aerosol present at concentrations that cause harm to health, ecosystems or materials. Limiting factors include pollutant concentration, exposure time, particle size, chemical form and local meteorology. Weather and topography influence pollutant dispersal and chemical transformation, so identical emissions produce different effects in different locations. Short-term peaks cause acute health impacts; long-term elevated concentrations cause chronic environmental change.
Sulfur dioxide (SO2) → Acid rain and respiratory irritation
Sulfur dioxide forms from combustion of fossil fuels containing sulfur. SO2 reacts with water and oxidants in the atmosphere to produce sulfuric acid, which falls as acid rain. Acid rain lowers the pH of soils and freshwater, causing loss of biodiversity, damage to buildings and corrosion of metal and stone. Sulfur dioxide and its acidic products also irritate the respiratory system and worsen asthma and bronchitis symptoms.
Nitrogen oxides (NOx) → Photochemical smog and acid deposition
Nitrogen oxides originate from high-temperature combustion in vehicles and power stations. NOx gases participate in sunlight-driven reactions that form ground-level (photochemical) ozone and secondary nitrate aerosols. Photochemical smog reduces air quality and visibility, damages plant tissues, and increases respiratory disease. NOx also contributes to acid deposition, which disrupts aquatic ecosystems and mobilises toxic metals in soils.
Carbon monoxide (CO) → Reduced oxygen transport
Carbon monoxide forms during incomplete combustion of carbon-containing fuels. CO binds strongly to haemoglobin in the blood, reducing the capacity to carry oxygen to tissues. Reduced oxygen delivery produces headaches, dizziness and, at high concentrations, unconsciousness or death. Vulnerable groups such as infants and those with heart disease experience greater risk at lower exposures.
Particulate matter (soot and aerosols) → Respiratory disease and visibility reduction
Particulate matter consists of solid and liquid particles suspended in air; particles smaller than 10 micrometres penetrate deep into lungs. Fine particles cause inflammation, aggravate cardiovascular and respiratory diseases, and increase premature mortality. Particulates scatter and absorb sunlight, reducing visibility and contributing to so-called global dimming. Deposition of particulates on plant leaves reduces photosynthesis and damages surfaces and materials.
Ground-level ozone (O3) → Respiratory and plant damage
Ground-level ozone forms when NOx and volatile organic compounds react in sunlight. Ozone is a highly reactive oxidant that damages lung tissue and reduces lung function, increasing respiratory symptoms. Ozone also damages plant cells, reducing crop yields and ecosystem productivity, and accelerates deterioration of rubber and some plastics.
Greenhouse gases and climate impacts
Increased concentrations of greenhouse gases such as carbon dioxide and methane trap outgoing infrared radiation and lead to global warming. Climate change produces indirect air-quality impacts by changing weather patterns that affect pollutant dispersal. Climate change triggers sea-level rise, altered rainfall patterns and increased frequency of extreme weather, which in turn cause ecosystem loss, agricultural disruption and health risks linked to heat and infectious disease spread.
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