Altitude variation of aerosol properties over the Himalayan range inferred from spatial measurements

Abstract

Altitude variations of the mass concentration of black carbon, number concentration of composite aerosols are examined along with the columnar spectral aerosol optical depths using state of the art instruments and the Ångström parameters are inferred from the ground based measurements at several altitude levels, en route from Manora Peak, Nainital (∼1950 m above mean sea level) to a low altitude station Haldwani (∼330 m above mean sea level) at its foothill within an aerial distance of <10,000 m. The measurements were done during the winter months (November–February) of 2005, 2006 and 2007 under fair weather conditions. The results show a rapid decrease in all the measured parameters with increase in altitude, with >60% contribution to the AOD coming from the regions below ∼1000 m. The Ångström wavelength exponent remained high in the well mixed region, and decreased above. The normalized AOD gradient was used to estimate aerosol mixing height, which was found to be in the altitude range 1000–1500 m, above which the particle concentrations are slowly varying as a function of altitude. The heating rate at the surface is found to be maximum but decreases sharply with increase in altitude. Analysis of the wavelength dependence of absorption aerosol optical depth (AAOD) showed that the aerosol absorption over the site is generally due to mixed aerosols.