Zhanqing Li& R. Dickerson

Dept. of Atmos. & Oceanic Science University of Maryland

Remote Sensing of Aerosols

What are aerosols and where are they from ?

Pollution over IndiaThe view from Tibet Sea of pollution Over India

Image from the Shuttle

Aerosol Types and OriginAerosol particles larger than about 1 mm in size are produced by windblown dust and sea salt from sea spray and bursting bubbles. Aerosols smaller than 1 m are mostly formed by condensation processes such as conversion of sulfur dioxide (SO2) gas (released from volcanic eruptions) to sulfate particles and by formation of soot and smoke during burning processes. After formation, the aerosols are mixed and transported by atmospheric motions and are primarily removed by cloud and precipitation processes.

Pollution/dust in IndiaSea SaltSaharan dustSmokePollution?Pollution/dust in ChinaDust and smoke are Transported to the North-East Atlantic. From MODIS

photos from Gunther Helas, MPICNatural biogenic aerosol particles Wherever you have trees or vegetation, these particles are there. These are from Brazil.P.S.: Are these particles spherical? Are they Sulfates? Soil Dust? Sea Salt?

0.010.11.010.0 It presents 3 modes :

- nucleation: radius is between 0.002 and 0.05 mm. They result from combustion processes, photo-chemical reactions, etc.

- accumulation: radius is between 0.05 mm and 0.5 mm. Coagulation processes.

- coarse: larger than 1 mm. From mechanical processes like aeolian erosion.

fine particles (nucleation and accumulation) result from anthropogenic activities, coarse particles come from natural processes.

Aerosol Size Distribution

Aerosol Observations

Aerosol Observation Programs In recent years, a great deal of effort has gone into improving measurements and data sets:It is feasible to shift the estimate of aerosol radiative effects from largely model-based to increasingly measurement-based.

MISR

Aerosol Observation Programs AERONET

The AERONET (AErosol RObotic NETwork) program: a federation of ground-based remote sensing aerosol networks.

AERONET provides global observations of spectral aerosol optical depth (AOD), inversion products, and precipitable water.

Quality levels: Level 1.0 (unscreened), Level 1.5 (cloud-screened), and Level 2.0 (cloud-screened and quality-assured).

NASAs AERONET

NASAs AERONET

The Cimel Electronique 318A spectral radiometer is a solar-powered, weather-hardy, robotically-pointed sun and sky spectral sun photometer.

A sensor head points the sensor head at the sun according to a preprogrammed routine.

The Cimel controller, batteries, and Vitel satellite transmission equipment are usuallydeployed in a weatherproof plastic case.InstrumentationCimel Spectral Radiometer

Which of the three levels would you use to have the highest confidence in your data set? Which has the most data?Sun photometer system

The radiometer makes two basic measurements-either direct sun or sky-both within several programmed sequences.

The direct sun measurements are made in eight spectral bands requiring approximately 10 seconds at wavelengths of 340, 380, 440, 500, 670, 870, 940 and 1020 nmthe 940 nm channel is used for column water abundance determination

A preprogrammed sequence of measurements is taken by these instruments from 7 am-7pm daily.Spectral Radiometer

http://aeronet.gsfc.nasa.gov/

http://aeronet.gsfc.nasa.gov/cgi-bin/type_one_station_opera_v2_new?site=GSFC&nachal=2&level=1

http://aeronet.gsfc.nasa.gov/new_web/DRAGON-USA_2013_Houston.htmlhttp://calipsooutreach.hamptonu.edu/sunphoto-sim/photometer.htmlSun Photometer Tutorial

On NASA AERONET site

Find a nearby Cimel sun photometerDetermine the annual average AOD and seasonal cycleLook at a few individual days.July 2011 was dry and hot; August 2011 was rainy. Can you see a difference?Pick a polluted location and a pristine one examine the differences. Repeat for water vapor, Angstrom exp.

256 citationsAerosol Climatology from AERONETCoolingHeatingHansen et al. (1997)Dubovik, O., B. Holben, T. F. Eck, A. Smirnov, Y. J. Kaufman, M. D. King, D. Tanr, and I. Slutsker, 2002: Variability of absorption and optical properties of key aerosol types observed in worldwide locations. J. Atmos. Sci., 59, 590608.

SummaryRemote sensing with sun photometers is a powerful tool for monitoring AOD and other aerosol properties.Industrial aerosols tend to be small and highly reflective in developed countries.Mineral dust is larger and absorbs more radiation.Biomass burning can be sootier and absorb even more radiation.

AERONET provides a world-wide network.Only works when you can see the sun.This is ok for satellite validation

MISR Provides New Angle on HazeSeptember 7, 2000Nadir46 Forward70 Forward60 Forward

Aerosol Retrieval over the AppalachiansSeptember 7, 2000Nadir70 ForwardAerosol optical thickness

***********Sun photometers are spectral radiometers*Dubovik, O., B. Holben, T. F. Eck, A. Smirnov, Y. J. Kaufman, M. D. King, D. Tanr, and I. Slutsker, 2002: Variability of absorption and optical properties of key aerosol types observed in worldwide locations. J. Atmos. Sci., 59, 590608.**