Air Pollution 1 Grangemouth oil refinery, ~20 miles west of Edinburgh 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 Primary and Secondary APs Primary air pollutants are directly emitted, e.g., Soot (a primary aerosol AP) SO 2 Secondary APs form in-situ from precursors, via chemical transformation, e.g.: Ozone (O 3 ) is a gaseous secondary AP formed from the NO x -catalysed oxidation of precursors such as CO (carbon monoxide) and hydrocarbons Sulphuric acid aerosol is an aerosol secondary pollutant, formed by the oxidation of SO 2 to H 2 SO 4, which then condenses to form liquid aerosols Sources of Air pollution Anthropogenic Urban and Industrial mainly from fossil fuel combustion Power generation (CO 2, SO 2, NO x, 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 Desert dust Forest fires Volcanoes (particles, SO 2, ) Indoor air pollution is the 2 nd largest contributor to the global burden of disease (after poor water and sanitation) kills 1.6 million people annually (WHO, 2002) 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. 1
Particulate matter less than 10m Air in Quality diameter (PM 10 ) concentrations (g m -3 ) 1993-2008 PM 10 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, 1955-2005 China: 1.3-1.7 years US: 0.6 yrs per 10g/m 3 CA Pope et al (2009) New England Journal of Medicine 360 www.euphix.org/object_class/euph_airborne_particulate_matter.html Rosenfeld et al., 2007 Observed relationship between visibility and PM in Shanghai Mortality and visibility Huang et al., 2009 2
Air Quality Ground level ozone concentrations in rural Scotland: 1990-2008 Time and space scales Global 10 3-10 4 km Climate change due to greenhouse gases/aerosols; ozone depletion Regional 10 2-10 3 km Regional acid rain/deposition; ozone exposure; vegetation fires Larger scale Air pollution: Next lecture Local 1-100 km Exposure to urban NO 2 PM pollution Source: UK National Air Quality Archive minutes -hours hours -days days -years Understanding air pollution Sources Dispersion Transformation Sinks Concentrations Deposition Impacts Buncefield oil depot fire, 2005 3
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 Top of BL 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 Diurnal variation of the Boundary Layer (idealised: sunny day, light winds) # $ # $ " # " #" $# # #%''" 4
( ( " " # #$ % )# '% #%#% %# $ '''' '# '' '# *" #''' # +,-.%/ ' 0 ' 1# 2 1 # % # Buncefield oil depot fire, 2005 Top of BL Buoyant thermal plume rose to ~3 km Very high concentrations of soot, or black carbon aerosol Turbulent mixing on many scales Settling out of largest aerosol particles Summary Understanding air pollution requires knowledge of the: 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 5