Post on 28-Aug-2018
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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)
– 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
Sources of Air pollution• Anthropogenic
– Urban and Industrial – mainly from fossil fuel combustion• 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• 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…
Indoor air pollution isthe 2nd largest contributorto the global burden ofdisease (after poor waterand sanitation) –kills 1.6 million people
annually (WHO, 2002)
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London smog, 1952Estimated 12,000total excess deaths
High levels ofSulphuric 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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Air Quality
Source: UK National Air Quality Archive
www.scotland.gov.uk/stats/envonline
PM10 in Scottish cities 1993-2008
Particulate matter less than 10�m in diameter (PM10) concentrations (�g m-3)
1993-2008
Current exposure to PM from anthropogenic
sources leads to the loss of 8.6 months of life expectancy, as an average for Europe.
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 visibility trends at a site in China, Observed visibility trends at a site in China,
19551955--20052005
Rosenfeld et al., 2007
Observed relationship between visibility and PM in Shanghai Mortality and visibilityMortality and visibility
Huang et al., 2009
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Air Quality
Ground level ozone concentrations in rural Scotland: 1990-2008
Source: UK National Air Quality Archive
Time and space scales
Local1-100 km
Regional102-103 km
Global103-104 km
minutes-hours
hours-days
days-years
Exposure tourban NO2 &PM pollution
Regional acidrain/deposition; ozone exposure;vegetation fires
Climate change dueto greenhouse gases/aerosols;
ozone depletion
Larger scaleAir pollution:Next lecture
SourcesDispersion
TransformationSinks
Concentrations Deposition
Impacts
Understanding air pollution
Buncefield oil depot fire, 2005
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Satellite image at 1045 GMT,~5 hours after start of fire
Nottingham Skew T-log P on day of
Buncefield Fire (12Z, 11 Dec 2005)
Top of BL
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
Diurnal variation of the Boundary Layer(idealised: sunny day, light winds)
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Buncefield oil depot fire, 2005
Top of BL
Buoyantthermal
plume roseto ~3 km
Very high concentrations
of soot, or ‘black carbon’
aerosol
Turbulent mixing on many scales
Settling outof largestaerosol
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