Air Pollution 1
What is Air Pollution? • Latin pollutus – foul, unclean, dirty • Definition: ‘Air pollution is when a substance (an air pollutant) is present in the atmosphere at higher than ambient (clean) levels and produces significant effects on humans, animals, vegetation or materials’ • Air pollutant may be man-made or natural, gaseous, or suspended liquid/solid particles (aerosols) • Some typical effects: foul odours, irritation of senses, sickness, death, vegetation damage, damage to materials, obscuration of visibility, adverse weather or climate changes
Grangemouth oil refinery, ~20 miles west of Edinburgh
Primary and Secondary APs
Sources of Air pollution • Anthropogenic – Urban and Industrial – mainly from fossil fuel combustion
• Primary air pollutants are directly emitted, e.g., – Soot (a primary aerosol AP) – SO2
• Secondary APs form in-situ from precursors, via chemical transformation, e.g.: – Ozone (O3) is a gaseous secondary AP – formed from the NOx-catalysed oxidation of precursors such as CO (carbon monoxide) and hydrocarbons – Sulphuric acid aerosol is an aerosol secondary pollutant, formed by the oxidation of SO2 to H2SO4, which then condenses to form liquid aerosols
• • • •
Power generation (CO2, SO2, NOx, particles…) Industry Transport (land, sea, air) Waste disposal (landfills, incineration…)
– Agricultural and Rural • • • •
Dust Slash and burn agriculture/waste burning Soil emissions (fertilizer) Livestock emissions – Domestic (e.g. local heating/cooking)
• Natural • • • • • • •
Indoor air pollution is the 2nd largest contributor to the global burden of disease (after poor water and sanitation) – kills 1.6 million people annually (WHO, 2002)
Desert dust Forest fires Volcanoes (particles, SO2,…) Biogenic emissions – from vegetation and wetlands (incl. pollen) Sea spray & ocean emissions Soils and decaying matter (natural microbial activity) Lightning…
London smog, 1952 Estimated 12,000 total excess deaths High levels of Sulphuric acid aerosol from burning high-S coal. Trapped under inversion. Eventually led to the clean air act and other pollution control measures.
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Particulate matter less than 10 mAir in Quality diameter (PM10) concentrations ( g m-3) 1993-2008
PM10 in Scottish cities 1993-2008 www.scotland.gov.uk/stats/envonline
Source: UK National Air Quality Archive
Current exposure to PM from anthropogenic sources leads to the loss of 8.6 months of life expectancy, as an average for Europe.
Observed visibility trends at a site in China, 19551955-2005
China: 1.3-1.7 years
US: 0.6 yrs per 10 g/m3 CA Pope et al (2009) New England Journal of Medicine 360
www.euphix.org/object_class/euph_airborne_particulate_matter.html
Observed relationship between visibility and PM in Shanghai
Rosenfeld et al., 2007
Mortality and visibility
Huang et al., 2009
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Air Quality
Ground level ozone concentrations in rural Scotland: 1990-2008
Time and space scales Global 103-104 km
Climate change due to greenhouse gases/aerosols; ozone depletion Regional acid rain/deposition; ozone exposure; vegetation fires
Regional 102-103 km
Local 1-100 km
Larger scale Air pollution: Next lecture
Exposure to urban NO2 & PM pollution minutes -hours
hours -days
days -years
Source: UK National Air Quality Archive
Understanding air pollution
Sources
Dispersion Transformation
Sinks
Concentrations
Deposition
Impacts
Buncefield oil depot fire, 2005
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Nottingham Skew T-log P on day of Buncefield Fire (12Z, 11 Dec 2005)
Satellite image at 1045 GMT, ~5 hours after start of fire
The Atmospheric Boundary Layer • Layer of atmosphere next to surface • Typically 1-2 km deep • Strongly influenced by the surface (including friction), on timescales < 1 hour; diurnal cycle • Dominated by turbulence, so well mixed; capped by an inversion or very stable layer Top of BL
Diurnal variation of the Boundary Layer (idealised: sunny day, light winds)
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Buoyant thermal plume rose to ~3 km Top of BL
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Very high concentrations of soot, or ‘black carbon’ aerosol
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Turbulent mixing on many scales
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Buncefield oil depot fire, 2005
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Summary • Understanding air pollution requires knowledge of the:
Settling out of largest aerosol particles
1. Sources (man-made, natural; gases, aerosols; primary, secondary) 2. Dilution, dispersion, and transformation processes 3. Sinks (removal mechanisms) 4. Impacts
• Meteorology is all important for (2), and can also affect the others • Next time: (less obvious) air pollution on larger scales
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