Atmospheric pollution

Main sources of smoke

• combustion of fossil fuels in urban areas

• combustion of organic wastes in rural areas

Impacts of smoke pollution on organisms

• causes respiratory diseases in humans, can kill cilia and be carcinogenic (cause asthma and lung cancer)

• may block sunlight needed for photosynthesis

• may contain toxic substances

Impacts of smoke pollution on climate

• increased albedo causing cold temperatures (risk of nuclear winter)

• high persistence and therefore remain in the atmosphere for a long time period and can deplete stratospheric ozone

Impacts of smogs

• high albedo can increase the length of a temperature inversion, allowing a greater accumulation of pollutants e.g the London Smog of 1952 which lead to 12000 deaths

Legislation for control of smoke pollution

Clean Air Act (1956) - restricts use of fossil fuels in large urban areas like London - direct result of the 1952 smog

Technology for control of industrial smoke

• cyclone separator

• electrostatic precipitator

• bag filter

• scrubber

• coal treatment

Cyclone separator

waste air and smoke drawn into the tank, forced to rotate in a cyclical shape - suspended solids are thrown to the edge of the tanks where they fall and can be collected

Electrostatic precipitator

effluent gases passed through a tank with charged plates, smoke particles are attracted to these plates and are collected together as ‘fly ash’

Scrubbers

use of fine water sprays which wash out suspended particulate matter and soluble gaseous pollutant from an effluent gas

Coal treatment

heating coal which allows the removal and drainage of tar and therefore creates smokeless coal

Formation of photochemical smogs

• nitrous oxides, unburnt hydrocarbons and tropospheric ozone undergo a reaction to form Peroxyl Acteyl Nitrates (PANs) in the presence of sunlight

Impacts of photochemical pollutants

• nitrous oxides increase risk of respiratory infections like asthma or bronchitis

• PANs are toxic at very low concentrations and can cause eye irritation, breathing difficulties and increased risk of heart attacks

• tropospheric ozone is toxic and causes asthma, bronchitis and heart disease

Areas most at risk of photochemical smogs

• highly populated areas with heavy traffic and nitrous oxide pollution

• areas around the equator with sunny climates

• suitable topography (where temperature inversions are common)

Control of photochemical smog

Control of hydrocarbon release:

• use of catalytic convertors to oxidise hydrocarbons to co2 and h2o and nitrous oxides to nitrogen and water

• collection and condensing of hydrocarbon vapours at filling stations

• use of active carbon filtration to filter effluent gases

Formation of acid rain

• sulfur oxides dissolving to produce sulphurous acid (sulfur dioxide) and sulfuric acid (sulfur trioxide)

• nitrous oxides dissolving to produce nitrous or nitric acid

• hydrogen chloride dissolving to form hydrochloric acid

Main sources of sulfur dioxide

combustion of materials containing sulfur like coal and the smelting of sulfide ores

Sources of hydrogen chloride

combustion of coal and the incineration of wastes like PVC plastics containing chlorine

Source of sulfur trioxide

sulfur dioxide is oxidised in the atmosphere by ozone or other gases

Impacts of acid rain on non-living things

• acid can corrode metals, which can cause damage to railway lines, metal railings, water pipes, pylons and powerlines

• limestone buildings and statues are damaged as acids dissolve surface layers and weaken the structure

Direct impacts of acid rain on organisms

• change conditions out of species’ range of tolerance, denature proteins on cell membranes altering permeability and inhibit enzyme action

• exposed tissues like plant stomata, fish gills, plant root hairs, germinating seeds and fish eggs may be damaged

• organisms with an exoskeleton may be killed as acids dissolve the calcium carbonate compounds

• species like lichen are more sensitive due to their size, state of health and abundance - biotic indices

Indirect effects of acid rain on organisms

• may alter the solubility of minerals like metals, causing leaching out of soils (particularly for magnesium and calcium)

• toxic ions like aluminium and lead normally adsorbed by clays may be mobilised which may inhibit enzyme action of detritovores

• toxic ions may be leached into water sources, impacting aquatic life and entering the human food chain

Factors affecting severity of acid rain

• soil lime content may neutralise acids, reducing impacts on soil pH

• fog may cause the longer-term suspension of acidic water droplets in the environment, increasing damage to plant leaves

• fall as snow may cause a greater accumulation of acids, when this melts very quickly, the water may have much greater impacts on soils and river due to lower pH

Control methods for acid rain

• control of sulfur oxides (natural gas desulfurisation, crude oil desulfurisation, coal desulfurisation, flue gas desulfurisation (wet and dry))

• control of nitrous oxides (lower temp combustion, catalytic convertors and urea sprays)

Natural gas desulfurisation

• removal of hydrogen sulfide after extraction by dissolving in amine solutions or reacting with iron

• to prevent corrosion damage to refinery and pipeline equipment

• prevents the formation of sulfur oxides during combustion

Crude oil desulfurisation (aka hydrodesulfurisation)

• sulfur compounds removed during distillation by molybdenum catalysts