Air Pollution: Dynamics, Effects, and Mitigation
Factors Influencing Pollutant Dispersion
Pollutant dispersion and concentration are influenced by emission characteristics, weather conditions, and geographical/topographical features. The pollutant’s nature, concentration, temperature, and physicochemical properties play a crucial role. When gas emissions exceed the average, weather conditions facilitate dispersion.
Atmospheric Conditions
The atmosphere’s state determines air mass movement and stability, influencing pollution spread. Key factors include:
- Air temperature and vertical gradients: These affect air mass movement and atmospheric stability, potentially leading to thermal inversions that hinder dispersion.
- Wind: Direction, velocity, and turbulence impact pollutant dispersion. Direction indicates potential movement, while velocity relates to dispersal ability.
- Precipitation: This has a flushing effect, dragging pollutants to the ground. Low-pressure conditions often accompany diffusive precipitation.
- Lightning: This promotes reactions between secondary pollutant precursors, increasing their concentration.
Geographical and Topographical Influences
Geographical location and relief influence breezes, which can either wash away or accumulate pollutants. Coastal systems experience sea breezes that shift pollutants inland during the day and towards the sea at night. Mountain breezes, caused by differential heating of slopes and valleys, create varying effects throughout the day. Daytime temperature inversions in valleys hinder dispersion, while nighttime downdrafts move air into the valley.
Vegetation and Urbanization
Plant mass reduces pollution by facilitating particle deposition on leaves and absorbing CO2. Urban areas influence air mass movement, decreasing speed, creating turbulence, and generating a “heat island” effect, where city temperatures are higher than surrounding areas due to combustion-generated heat.
Effects of Air Pollution
Changes in normal air composition cause adverse effects in living organisms, ranging from local to global scales. The type and degree of impact depend on the pollutant, its concentration, and exposure duration. Effects manifest in plants, animals, human health, and materials.
Local Effects: Smog Formation
Significant local effects arise from individual pollutants and smog formation, highlighting the relationship between weather and pollution. Wet sulfur dioxide smog, exemplified by the London incident, results from high particulate matter concentrations, causing respiratory problems. Photochemical smog, a brownish-gray haze, originates from atmospheric oxidants produced by photochemical reactions of nitrogen oxides, hydrocarbons, and oxygen, exacerbated by anticyclonic conditions, sunlight, and light winds.
Photochemical oxidant production involves complex reactions, including:
- Ozone formation from the NO2 photolytic cycle.
- Active free radical formation from hydrocarbon radicals, oxidizing NO to NO2.
- PAN formation. Free radicals react with primary pollutants or other air constituents, creating a complex oxidant mixture.
Regional Effects: Acid Rain
Pollutants can return to the surface near emission sources or in remote areas, causing transboundary pollution like acid rain. This involves sulfur and nitrogen oxides from fossil fuel combustion being deposited on Earth. The process begins with the release of sulfur and nitrogen during combustion, followed by atmospheric transport and deposition through:
- Dry deposition: In gaseous or aerosol form.
- Wet deposition: Atmospheric oxidation forms sulfuric and nitric acids.
Acid rain intensity depends on chemical reaction rates, atmospheric moisture, and atmospheric dynamics, influencing ion transport distances. Acid rain impacts various aspects of the environment.