Particle Characterization of European and Indo-Asian Pollution Plumes With Six-Wavelength Lidar
Abstract
The institute's scanning six-wavelength aerosol lidar allows a comprehensive characterization of atmospheric particles on a vertical scale. The system provides highly accurate profiles of the spectrum of the particle backscatter coefficient between 355 and 1064 nm, and of extinction coefficients and extinction-to-backscatter (lidar) ratios at 355 and 532 nm. Effective radius, volume and surface-area concentration, and complex refractive index of the particle ensembles are retrieved from the optical properties with an inversion scheme. The profile of the single-scattering albedo may be calculated with high accuracy. European pollution plumes were observed during the Aerosol Characterization Experiment 2 (ACE 2; North Atlantic/Portugal) in June/July 1997. Indo-Asian pollution was observed in the framework of the Indian Ocean Experiment (INDOEX; Indian Ocean/Maldives) in February/March 1999 and March 2000. In both cases a great share of columnar optical depth was contributed by particles above 1000 m height. In the first case it was approximately 59% for the monthly-mean values. In the second it ranged from 30% to 55% for the different months. During ACE 2 the lidar ratio at 532 nm mostly ranged from 30 to 50 sr, with peak values of 80 sr. During INDOEX the lidar ratio mostly was 50-80 sr, with peak values of 110 sr. The mean Angstrom exponent in the wavelength range from 400 to 532 nm was ~1.34 for ACE 2 and for INDOEX. In contrast, in the wavelength-range from 532 to 800 nm the mean value of 1.41 for ACE 2 was larger than the INDOEX value of 1.17, which indicates a higher contribution from large particles. Effective radii in both cases mostly were below 0.2 μ m. Significant differences were found for the complex refractive index. For ACE 2 real parts were ~1.55, and imaginary parts were <0.03i. INDOEX showed considerably larger values above 1.6 in real part and maximum values of 0.07i in imaginary part. Accordingly the single-scattering albedo at 532 nm was 0.9-1 for ACE 2. For INDOEX values were between 0.8 and 0.93. In summary the parameters for ACE 2 indicate non-absorbing ammonium-sulfate-like material as the main contributor to the observed pollution. In contrast, highly absorbing carbon-like material from coal and diesel combustion, and from biomass burning was responsible for the particle properties observed during INDOEX.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.A41B0032M
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0305 Aerosols and particles (0345;
- 4801);
- 0345 Pollution: urban and regional (0305);
- 1630 Impact phenomena;
- 1640 Remote sensing