Abstract
Abstract. Information on the aerosol intensive properties like Single Scattering Albedo (SSA) and asymmetry parameter are very limited, particularly over the peninsular India, though extensive reports are available on the aerosol bulk properties. In view of the importance of these parameters in evaluating the aerosol radiative forcing, we present for the first time the temporal variation in SSA with measurements on aerosol absorption and scattering coefficients over Visakhapatnam (17.72° N, 83.32° E; located on the east coast of India) for the year 2007. The inferred SSA was in the range of 0.65 and 0.9 with an annual mean of 0.76 ± 0.013 and with a probable value of 0.80, indicating a marginal atmospheric warming over the region. The mixed layer contribution to column Aerosol Optical depth is found to be 35 % in summer while it is well above 35 % in winter, indicating the confinement of aerosol within the boundary layer during winter. The asymmetry parameter which represents the angular scattering in radiative forcing estimation is found to be around 0.65 ± 0.1 for the location. The day to day variability in SSA is found to be well correlated with the variations in surface BC mass concentrations and/or the relative dominance of the fine/coarse mode aerosol. The results are discussed in light of the aerosol physical and optical properties and the asymmetry parameter.
Highlights
Characterization of aerosol radiative effects has been a challenging task due to large spatial and temporal variability of aerosol species on regional as well as global scales
Though losses within the Nephelometer instrument for super micron particles could be slightly higher, they are relatively insignificant since the present measurements relate to a coastal urban location, where the sub-micron particles dominate as seen from the aerosol near surface mass size distribution
The measurements included: (i) aerosol optical depths (AOD) at 5 wavelengths centered about 380, 440, 500, 675, and 870 nm using a Microtops II Sun Photometer (Solar Light Co, USA), with a Global Positioning System (GPS) receiver attached to the Photometer to provide information on the location, altitude, and pressure; and (ii) near surface aerosol mass concentrations using a ten channel Quartz Crystal Microbalance (QCM) Impactor (California Measurements Inc., USA), whose 50 % aerodynamic cutoff diameters are 25, 12.5, 6.4, 3.2, 1.6, 0.8, 0.4, 0.2, 0.1, and 0.05 μm, respectively, with an air inlet at a flow rate of 0.24 liters per minute and sampled for duration of 300 s
Summary
Characterization of aerosol radiative effects has been a challenging task due to large spatial and temporal variability of aerosol species on regional as well as global scales. Due to the importance of characterizing the aerosol intensive parameters in the outflow regions from the Indian sub-continent, we present here results of comprehensive investigations carried out on temporal characteristics of the aerosol SSA and the asymmetry parameter at Visakhapatnam, a coastal urban environment representative of the aerosol characteristics over eastern peninsular India. It is usual to derive the SSA both from column integrated optical measurements from ground based and satellite data and it is important to assess whether the in-situ measured SSA is applicable to column integrated estimation In view of these aspects we have presented here the temporal characteristics of SSA during the year 2007 and its relation to the surface and column integrated aerosol physical and optical properties at Visakhapatnam
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