Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Analysis of optical properties of atmospheric aerosols inferred from spectral AODs and Ångström wavelength exponent
Abstract Aerosol measurements over a tropical semi-arid site in Anantapur (14.62°N, 77.65°E, 331 m asl), India, provide the variabilities of aerosol characteristics for the period of January 2007–December 2008. The mean values of aerosol optical depth at 500 nm (AOD500 nm) over 2-year period are found to be 0.37 ± 0.11, 0.39 ± 0.13 and 0.30 ± 0.10 during winter, summer and monsoon seasons, respectively. A rather systematic variation is seen with AOD peaking in the month of March, falling off gradually to the lowest value in June and increasing slowly superposed with some modulations, which show a weak secondary peak in October. The mean and standard values of the Ångström exponent, α (turbidity coefficient, β), are found to be 1.06 ± 0.33 (0.17 ± 0.05) during winter, 0.97 ± 0.35 (0.22 ± 0.04) during summer and 0.85 ± 0.26 (0.16 ± 0.06) during monsoon. The frequency distribution of α is relatively broad with two modes for dusty (α < 1) and non-dusty (α > 1) situations. This frequency distribution of α reveals a great dispersion of a values in all seasons thus denoting variability in the aerosol-size distribution. In this study, spectral AOD and Ångström exponent data are analyzed to obtain information about the adequacy of the simple use of the Ångström exponent and its variation for characterizing optical properties of aerosols, and exploring possibilities for a more efficient characterization of them. Using the least-squares fit method, the Ångström parameter, α, is calculated in the spectral interval 380–850 nm, along with coefficients a1 and a2 of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The correlations between the coefficients a1 and a2 with months and α are discussed in the paper.
Research highlights ► AOD showed large and small values during summer and monsoon seasons. ► Alpha is low (high) in summer (winter) indicates abundance of coarse (fine) aerosol. ► WVC varies with maximum (minimum) during monsoon (summer). ► The frequency distribution of α denotes variability in the aerosol-size distribution. ► a2<0 (a2>0) is characteristic of ASD dominated by fine (coarse) aerosols.
Analysis of optical properties of atmospheric aerosols inferred from spectral AODs and Ångström wavelength exponent
Abstract Aerosol measurements over a tropical semi-arid site in Anantapur (14.62°N, 77.65°E, 331 m asl), India, provide the variabilities of aerosol characteristics for the period of January 2007–December 2008. The mean values of aerosol optical depth at 500 nm (AOD500 nm) over 2-year period are found to be 0.37 ± 0.11, 0.39 ± 0.13 and 0.30 ± 0.10 during winter, summer and monsoon seasons, respectively. A rather systematic variation is seen with AOD peaking in the month of March, falling off gradually to the lowest value in June and increasing slowly superposed with some modulations, which show a weak secondary peak in October. The mean and standard values of the Ångström exponent, α (turbidity coefficient, β), are found to be 1.06 ± 0.33 (0.17 ± 0.05) during winter, 0.97 ± 0.35 (0.22 ± 0.04) during summer and 0.85 ± 0.26 (0.16 ± 0.06) during monsoon. The frequency distribution of α is relatively broad with two modes for dusty (α < 1) and non-dusty (α > 1) situations. This frequency distribution of α reveals a great dispersion of a values in all seasons thus denoting variability in the aerosol-size distribution. In this study, spectral AOD and Ångström exponent data are analyzed to obtain information about the adequacy of the simple use of the Ångström exponent and its variation for characterizing optical properties of aerosols, and exploring possibilities for a more efficient characterization of them. Using the least-squares fit method, the Ångström parameter, α, is calculated in the spectral interval 380–850 nm, along with coefficients a1 and a2 of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The correlations between the coefficients a1 and a2 with months and α are discussed in the paper.
Research highlights ► AOD showed large and small values during summer and monsoon seasons. ► Alpha is low (high) in summer (winter) indicates abundance of coarse (fine) aerosol. ► WVC varies with maximum (minimum) during monsoon (summer). ► The frequency distribution of α denotes variability in the aerosol-size distribution. ► a2<0 (a2>0) is characteristic of ASD dominated by fine (coarse) aerosols.
Analysis of optical properties of atmospheric aerosols inferred from spectral AODs and Ångström wavelength exponent
Balakrishnaiah, G. (Autor:in) / Raghavendra kumar, K. (Autor:in) / Suresh Kumar Reddy, B. (Autor:in) / Rama Gopal, K. (Autor:in) / Reddy, R.R. (Autor:in) / Reddy, L.S.S. (Autor:in) / Nazeer Ahammed, Y. (Autor:in) / Narasimhulu, K. (Autor:in) / Krishna Moorthy, K. (Autor:in) / Suresh Babu, S. (Autor:in)
Atmospheric Environment ; 45 ; 1275-1285
01.12.2010
11 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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