Aerosols Why are we interested in them? Health problems Decrease visibility Reduce (normally) the amount of solar radiation that reach the ground Affects surface energy balance Plant growth Provide cloud condensation nuclei Provide surface area for heterogeneous chemical reactions
OZONE AND PARTICULATE MATTER (PM): THE TOP TWO AIR POLLUTANTS IN THE U.S. # millions of people living in areas exceeding national ambient air quality standards (NAAQS) in 2007 75 ppb (8-h average) 15 mg m -3 (day), 65 (annual) 65 mg m -3 (24-h), 15 (annual)
Potential impact of BC reductions (UNEP, 2011)
A general view of the CCTV towers, headquarters of China Central Television, in Beijing on January 12, 2013 Illustrasjon av redusert siktbarhet. Elektronisk manipulert. http://www.marketplace.o rg/topics/sustainability/w hat-would-your-city-lookbeijings-air-smogsimulator
VISIBILITY IN U.S. WILDERNESS AREAS 2001 observations Natural Background; includes transboundary pollution Deciviews 300 150 80 40 20 Visual range (km) Park et al. [2006]
Høy relativ fuktighet i luften i grenselaget gjør at partiklene sveller mer spredning av lys.
The aerosol lifecycle
Forurenset byluft Kontinental bakgrunn Marin bakgrunn Aerosol surface area distribution Principle sources for aerosols
Strålingspådriv (radiative forcing)
Strålingspådriv (radiative forcing)
Fra IPCC 2007
Typical aerosol size distribution Red: Continental air Blue: Marine air Black: Urban (polluted) Number of aerosols falls off very rapidly with diameter
AOD (Aerosol Optical Depth) Fra Myhre et al., ACP, 2009. AOD (δ): F t =F s e -δ Ulike observasjonsbaserte estimater spriker Modellene avviker omtrent like mye som forskjellen mellom observasjonene
Strålingspådriv pga. spredende aerosoler (sulfat, nitrat, organisk karbon, mineral støv). Finner da ΔF=-0.9 Wm -2
Composition of aerosols Fine Mode (d < 1.0 μm) Sulphate Organics (Primary and secondary) Nitrate Ammonium Black carbon Coarse mode (d > 1.0 μm) Sea salt Mineral dust Biological material Fly ash
WORLDWIDE MEASUREMENTS OF FINE AEROSOL COMPOSITION
ANNUAL MEAN PM 2.5 CONCENTRATIONS (2002) derived from MODIS satellite instrument data
GLOBAL SULFUR BUDGET [Chin et al., 1996] (flux terms in Tg S yr -1 ) cloud 42 SO4 2-4 18 SO 2 t = 1.3d OH 8 H 2 SO 4 (g) t = 3.9d NO 3 OH (CH 3 ) 2 S (DMS) t = 1.0d 10 64 dep 27 dry 20 wet dep 6 dry 44 wet 22 Phytoplankton Volcanoes Combustion Smelters
U.S. SO 2 EMISSIONS Main source is coal combustion GLOBAL Industrial UNITED STATES Sulfur emissions, Tg a -1 Volcanoes Biomass burning Oceans 78 8.3
FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS HO 2 2 H SO ( g) SO 2H 2 4 4 HO 2 NH ( g) NH OH 3 4 HO 2 HNO ( g) NO H 3 3 NH ( g) HNO ( g) NH NO ( aerosol) 3 3 4 3 Highest concentrations in industrial Midwest (coal-fired power plants) Thermodynamic rules: Sulfate always forms an aqueous aerosol Ammonia dissolves in the sulfate aerosol totally or until titration of acidity, whichever happens first Nitrate is taken up by aerosol if (and only if) excess NH 3 is available after sulfate titration Condition aerosol ph Low RH High RH [S(VI)] > 2[N(-III)] acid H 2 SO 4 nh 2 O, NH 4 HSO 4, (NH 4 ) 2 SO 4 [S(VI)] 2[N(-III)] neutral (NH 4 ) 2 SO 4, NH 4 NO 3 HNO 3 and excess NH 3 can also form a solid aerosol if RH is low (NH 4 +, H +, SO 4 2- ) solution (NH 4 +,NO 3 - ) solution
AMMONIA EMISSIONS Ammonia, Tg N a -1 GLOBAL Livestock Fertilizer Humans Industry Biofuels Soils/vegetation UNITED STATES Oceans 55 Biomass burning 2.8
What is black carbon aerosols? Product of incomplete combution Fossil fuels or biomass
ng/g Annual BC concentration in snow Ice-core location D4 Greenland McConnell et al. (Science, 2007) 6 5 BC concentration in snow 1 st Aug ICEC-D4 FFC BIO 4 3 2 1 0 1850 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 38
INTERCONTINENTAL TRANSPORT OF DESERT DUST Glen Canyon, Arizona clear day April 16, 2001: Asian dust! Asia Annual mean PM 2.5 dust (mg m -3 ), 2001 Sahara Most fine dust in the U.S. (except in southwest) is of intercontinental origin
WILDFIRES: A GROWING AEROSOL SOURCE S. California fire plumes, Oct. 25 2004 Total carbonaceous (TC) aerosol averaged over U.S. IMPROVE sites Interannual variability is driven by wildfires
Geoengineering. En mulighet er å øke albedoen ved å øke aerosolmengden. SRM: Solar radiation management kan nøytralisere globalt midlet temperaturøkning, men ser ut til å redusere nedbør. Katharine L. Ricke, M. Granger Morgan & Myles R. Allen Nature Geoscience 3, 537-541 (2010)