Aerosol Chemistry over a High Altitude Station at Northeastern Himalayas, India

Abstract

BackgroundThere is an urgent need for an improved understanding of the sources, distributions and properties of atmospheric aerosol in order to control the atmospheric pollution over northeastern Himalayas where rising anthropogenic interferences from rapid urbanization and development is becoming an increasing concern.Methodology/Principal FindingsAn extensive aerosol sampling program was conducted in Darjeeling (altitude ∼2200 meter above sea level (masl), latitude 27°01′N and longitude 88°15′E), a high altitude station in northeastern Himalayas, during January–December 2005. Samples were collected using a respirable dust sampler and a fine dust sampler simultaneously. Ion chromatograph was used to analyze the water soluble ionic species of aerosol. The average concentrations of fine and coarse mode aerosol were found to be 29.5±20.8 µg m−3 and 19.6±11.1 µg m−3 respectively. Fine mode aerosol dominated during dry seasons and coarse mode aerosol dominated during monsoon. Nitrate existed as NH4NO3 in fine mode aerosol during winter and as NaNO3 in coarse mode aerosol during monsoon. Gas phase photochemical oxidation of SO2 during premonsoon and aqueous phase oxidation during winter and postmonsoon were the major pathways for the formation of SO4 2− in the atmosphere. Long range transport of dust aerosol from arid regions of western India was observed during premonsoon. The acidity of fine mode aerosol was higher in dry seasons compared to monsoon whereas the coarse mode acidity was higher in monsoon compared to dry seasons. Biomass burning, vehicular emissions and dust particles were the major types of aerosol from local and continental regions whereas sea salt particles were the major types of aerosol from marine source regions.Conclusions/SignificanceThe year-long data presented in this paper provide substantial improvements to the heretofore poor knowledge regarding aerosol chemistry over northeastern Himalayas, and should be useful to policy makers in making control strategies.

Atmospheric Fine Mode Particulates at Eastern Himalaya, India: Role of Meteorology, Long-Range Transport and Local Anthropogenic Sources

“…A high background of larger particulate matter also acts as a condensation sink for the nucleating vapours and initially formed nm-sized particles (Neitola et al, 2011). We observed higher fine mode aerosol (PM 2.5 ) concentration than coarse mode (PM of diameter larger than 2.5 microns) aerosol over the same study location in the year of 2005 (Chatterjee et al, 2010) and 2008 (Chatterjee et al, 2012) throughout the entire dry season. During premonsoon, fine mode aerosol concentration was found to be maximum and much higher than coarse mode aerosol.…”

“…The increasing dustiness has also been reported from other indirect studies using isotopically inferred temperatures from ice-cores in the Himalayan-Tibetian plateau (Thomson et al, 2000). Our earlier study (Chatterjee et al, 2010) also identified two distinct source regions; Thar deserts and Arabian deserts for the long range transport of dust aerosols reaching over Darjeeling during premonsoon. It was found that 45% dust loading was from Thar deserts and 32% was from Arabian deserts during premonsoon.…”

“…This has been performed during two important seasons, premonsoon (March-May i.e., before the onset of Asian summer monsoon) and winter (December-February), over three consecutive years 2008, 2009 and 2010. Our earlier study (Chatterjee et al, 2010) carried out over the same location has shown that during premonsoon, aerosols are transported from arid and semi-arid regions of India and beyond to the Himalaya driven by the westerly pre-monsoon winds. Due to enhanced convection and the steep pressure gradient across the Himalayan-Gangetic region, these aerosols are transported to the higher altitudes.…”

“…The eastern frontier lies along two rivers, locally called Tista and Rangeet. The map of the experimental site is given in our earlier paper (Chatterjee et al, 2010).…”

“…The anthropogenic activities such as increasing vehicular traffic due to increased tourism-related activities, biomass burning and fuel wood burning for cooking and heating are the causes of concern for most of the Himalayan high altitude hill stations in India which apparently look like pollution-free regions as situated far away from the Indian mega-cities. Most of the studies on physical and chemical characterization of aerosols have been made over western and north-western Himalaya but as far as the eastern Himalaya is concerned, ours was the first study (Chatterjee et al, 2010) on a thorough chemical characterization of aerosol at a high altitude station, Darjeeling.…”