Aerosol optical properties from the Himalayan foothills site during GVAX

Description

Aerosol at the GVAX Manora Peak site emanates from local vegetation, biofuel burning, and pollution from the Ganges River Valley as well as long-range transport, especially during downslope periods. Source and seasonal variability of the aerosol optical and cloud-forming properties are presented for the summer monsoon season and fall transition to the dry season. Aerosol loading has a seasonal low during the summer with an average June–August aerosol scattering coefficient at 550 nm of 74 Mm-1 and a mid-September–mid-November average value of 205 Mm-1. As evidenced by changes in the aerosol single-scatter albedo and Ångstrom exponent, the aerosol is slightly smaller and darker during the summer and may reflect wet scavenging of larger, more hygroscopic aerosol. A strong diurnal trend is apparent with higher loading around solar noon. The most remarkable feature of the GVAX aerosol during both seasons is its relatively large size. The average Ångstrom exponent for the 450/700 nm wavelengths is ~ 1.0. The large size persists through both seasons and during upslope and downslope conditions.