Aerosol characteristics at a high‐altitude location in central Himalayas: Optical properties and radiative forcing

Abstract

[1] Collocated measurements of the mass concentrations of aerosol black carbon (BC) and composite aerosols near the surface were carried out along with spectral aerosol optical depths (AODs) from a high-altitude station, Manora Peak in central Himalayas, during a comprehensive aerosol field campaign in December 2004. Despite being a pristine location in the Shivalik Ranges of central Himalayas and having a monthly mean AOD (at 500 nm) of 0.059 ± 0.033 (typical to this site), total suspended particulate (TSP) concentration was in the range 15-40 mg m À3 (mean value 27.1 ± 8.3 mg m À3 ). Interestingly, aerosol BC had a mean concentration of 1.36 ± 0.99 mg m À3 and contributed $5.0 ± 1.3% to the composite aerosol mass. This large abundance of BC is found to have linkages to the human activities in the adjoining valley and to the boundary layer dynamics. Consequently, the inferred single scattering albedo lies in the range of 0.87 to 0.94 (mean value 0.90 ± 0.03), indicating significant aerosol absorption. The estimated aerosol radiative forcing was as low as À4.2 W m À2 at the surface, +0.7 W m À2 at the top of the atmosphere, implying an atmospheric forcing of +4.9 W m À2 . Though absolute value of the atmospheric forcing is quite small, which arises primarily from the very low AOD (or the column abundance of aerosols), the forcing efficiency (forcing per unit optical depth) was $88 W m À2 , which is attributed to the high BC mass fraction.

Aerosol optical properties and radiative forcing in the high Himalaya based on measurements at the Nepal Climate Observatory-Pyramid site (5079 m a.s.l.)

“…In particular, the diurnal variation of anthropogenic species such as BC regularly exhibits very low night-time concentrations and daytime values peaking in the middle of the afternoon. Consequences of local circulation on aerosol dynamics are discussed by Venzac et al (2008) and Panday et al (2009). Local circulation is not considered in the cluster analysis of Bonasoni et al (2010).…”

Similarities and differences of aerosol optical properties between southern and northern sides of the Himalayas

“…Black carbon (BC) reaching the Himalayas and the Tibetan Plateau (HTP) has increased in recent years, and South Asia and East Asia appear to be the two main source regions . Over the Indian Himalayan foothills, high concentrations of BC were related to the boundary layer dynamics and to human activities in the adjoining valley (Pant et al, 2006). Although the high peaks of the Himalaya appear to block the transport of BC particles to the TP, the Yarlung Tsangpo River valley acts as a "leaking wall" to contaminate the southeast TP (Cao et al, 2011).…”

A long-term study of aerosol modulation of atmospheric and surface solar heating over Pune, India

“…In recent years, many studies have been undertaken to assess the impact of aerosols on the climate in the Indian region Ramanathan et al, 2001b;Moorthy et al, 2005;Ramachandran, 2005aRamachandran, , 2005bTripathi et al, 2005;Pant et al, 2006;Niranjan et al, 2007;Babu et al, 2007;Sreekanth et al, 2007;Dey and Tripathi, 2008). However, a few long-term (5-yr or so) studies have been carried out, whereas most of the other studies are limited in observations span.…”