Winter aerosol and trace gas characteristics over a high-altitude station in the Western Ghats, India

This paper presents spectral distribution of aerosol optical depth (and derived size distribution), water vapor and ozone in total atmospheric column; in conjunction with particulate mass concentration in the size range from 0.3 to 20 μm and black carbon mass concentration at the surface-level during four different campaigns, conducted in months of December-January-2006-2007 (Campaign I), February-2007 (Campaign II), January-2008 (Campaign III) and November-2008 (Campaign IV) at a high-altitude station, Sinhgad (18°22'N, 73°45'E, 1450 m AMSL) in the Western Ghats of Indian Peninsula. Aerosol optical depth (AOD) measured within the spectral range 440-1020 nm is found lower as compared to that measured over a nearby urban station, Pune; but relatively higher than that over other remote high-altitude stations in India. The columnar Angstrom exponent derived within the 440-870 nm spectral range showed maximum values close to 1 indicating relatively higher contribution from fine-mode particles to aerosol size spectrum. Interestingly, this parameter shows lower values when the total aerosol mass concentration exhibits higher values during afternoon hours. Both columnar water vapor (CWV) and ozone (TCO) exhibit lower values in the morning hours and higher in the afternoon hours. The mass concentration of black carbon shows an association with AOD during the study period over the station. The measured surface aerosol particle number concentrations are used to reconstruct AOD spectra using the Optical Properties of Aerosols and Clouds (OPAC) software package and compared with simultaneously available columnar AOD spectra