AT737 Aerosols

Importance of Aerosols Aerosols directly change the radiation budget Aerosols modify cloud properties (and clouds modify aerosol properties) Aerosols affect atmospheric chemistry Aerosols affect biological systems, including human health AT737 Aerosols

Characteristics of Aerosols Sizes range from 0.01 to 10 or more micrometers Chemical composition: NOTE: VERY CHEMICALLY HETEROGENEOUS ”PHYSICS OF DIRT” o      Sulfate (SO4) o      Nitrate o      Soil and mineral dust (silicates, clays) o      Carbonaceous compounds (elemental and organic carbon) o      Sea-salt (NaCl) SOURCE (of this and next four slides): Dr. Bill Collins, NCAR AT737 Aerosols

Sources Sulfate: Nitrate: Soil and mineral dust: Oxidation of sulfur dioxide from fossil fuel burning Oxidation of DMS released from ocean micro-organisms Volcanic emissions Manmade now 4 times natural (IPCC time series) Nitrate: Combustion Soil and mineral dust: Dry lake beds from prehistoric lakes Desertification Carbonaceous compounds Organic compounds released from forests Natural biomass burning Anthropogenic biomass burning Fossil fuel combustion Sea-salt: oceans, of course AT737 Aerosols

Sinks Lifetime in the atmosphere: about 5-7 days. Stratosphere: x100 Removal mechanisms: Sedimentation (settling) – about 10-20% by mass V = 50 cm/s for large silicates (50 microns) V =0.03 cm/s for small particles (1 micron) “Scavenging” by precipitation – about 80-90% by mass Consequence: aerosol is very uniformly mixed AT737 Aerosols

Properties of Atmospheric Aerosols Type Altitude (km) Horiz scale (km) Freq. Compo-sition Mass loading (mg m−3) Optical depth Mean particle Size Trop. Aerosols 0-10 1000-10000 1 Sulfate, nitrate, minerals 0.01 to 1 ~0.1 0.1-1 Dust storms 0-3 10-1000 Sporadic Silicates, clays <1 to 100 1-10 Volcanic 5-35 Mineral ash, sulfates <1 to 1000 0.1 to 10 Smoke 1-100 Soot, ash, tars 0.1 t 1 0.1 to 1 AT737 Aerosols

Types of Aerosol Continental: sulfate, nitrate, carbonaceous, mineral Marine: sea salt Stratospheric: e.g., sulfate formed from volcanic eruptions AT737 Aerosols

Aerosol Variablility Size spectrum Composition Number density Makes remote sensing difficult, perhaps more difficult than sensing clouds AT737 Aerosols

Stratospheric Aerosols Stratospheric aerosols are few in number The long path length of limb sounding is useful AT737 Aerosols

Solar Occultation Measures transmittance of solar radiation as a function of tangent height Self calibrating AT737 Aerosols

Very peaky weighing functions Abel’s Equation Very peaky weighing functions AT737 Aerosols

Corrections Need to correct for Rayleigh scattering and atmospheric gas absorption AT737 Aerosols

Results AT737 Aerosols

Tropospheric Aerosols If you can see them you can measure them, right? MODIS truecolor 12/17/04 05:20 UTC AT737 Aerosols

Note land/ocean differences! Another Example Note land/ocean differences! MODIS truecolor 3/10/07 AT737 Aerosols

Processes Aerosols scatter solar radiation toward satellite Depends on aerosol properties as well as optical depth AT737 Aerosols

NOAA POES AOD SOURCE: http://www.osdpd.noaa.gov/PSB/EPS/Aerosol/Aerosol.html AT737 Aerosols

NOAA GOES AOD SOURCE: http://www.orbit.nesdis.noaa.gov/smcd/emb/GASP/RealTime.html AT737 Aerosols

Good Paper King et al., 1999: Remote sensing of tropospheric aerosols from space: Past, present, and future. BAMS, 80, 2229-2259. “Reflectance Function” AT737 Aerosols

Aerosols Over Land AT737 Aerosols

Color Color Ratio Angstrom exponent AT737 Aerosols

Forecasts of Aerosols http://www.nrlmry.navy.mil/aerosol_web/loop_html/globaer_world_loop.html AT737 Aerosols

National Park Service http://www.cira.colostate.edu/nps.html AT737 Aerosols

CALIPSO Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) http://www-calipso.larc.nasa.gov/ 532 nm Backscatter AT737 Aerosols