Abstract
A study on atmospheric fine (less than 2.0 µm) particulate matter was performed for the first time over the eastern Himalayas in India in order to investigate the formation and sources in two different seasons, pre-monsoon (Mar–May) and winter (Dec–Feb), for three consecutive years, 2008, 2009 and 2010. Fine mode aerosols were further segregated into three modes: ultrafine (less than 0.32 µm), superfine (0.32–1.0 µm) and fine (1.0–2.0 µm). The study was carried out at a high altitude hill station Darjeeling (2200 m asl) in the eastern Himalayas, India, using an aerosol spectrometer (GRIMM) to measure aerosol number concentrations. It was found that the ultrafine and superfine aerosol (less than 1.0 µm) concentrations were higher in the pre-monsoon period compared to winter, whereas the concentrations of fine mode aerosols were comparable during these two seasons. Meteorological conditions like sunny/non-cloudy days with higher radiative fluxes and lower humidity favored the formation of ultrafine aerosols from their precursor gases, and the initiation of this formation were observed during 0900–1000 hours LT. Superfine aerosols were mainly found to be aerosols transported from long distances during the pre-monsoon period, and showed peak levels during late morning till late afternoon. In contrast, higher concentrations were seen at night in winter. The fine mode aerosols were mainly locally generated anthropogenic aerosols, mostly emitted from vehicular sources during the pre-monsoon period, and from biomass burning during winter, with sharp diurnal peaks during morning and evening. The long-term study on size segregated aerosol concentrations carried out in this work is of considerable importance, and can be helpful for the validation of several regional and global aerosol models, and for other climate related studies that focus on the Himalayan region.
Highlights
The study of atmospheric aerosols especially in fine mode is gaining importance in scientific community as numerous studies have demonstrated their association with healthrelated (Pekkanen et al, 1997; Oberdorster et al, 1990; Laden et al, 2000) and climate change (Tegen et al, 1996; Ramanathan et al, 2001) issues
Due to increased vertical mixing, boundary layer air could reach at Darjeeling supplying precursor gases necessary for the particle formation
The meteorological conditions were favourable for the particle formation over Darjeeling during premonsoon
Summary
The study of atmospheric aerosols especially in fine mode is gaining importance in scientific community as numerous studies have demonstrated their association with healthrelated (Pekkanen et al, 1997; Oberdorster et al, 1990; Laden et al, 2000) and climate change (Tegen et al, 1996; Ramanathan et al, 2001) issues. The regional and synoptic characteristics of size-segregated fine mode aerosol and their significance are required to be investigated (Moorthy et al, 1998, 2007, 2008), while this kind of study has been done at fewer stations over Himalayan regions of India (Sellegri et al, 2010). Various studies have been carried out on the characterization of total fine mode aerosols, the size segregated fine mode aerosol characteristics specially the formation of ultra fine particles through nucleation of their gaseous precursors is not well documented in India especially over eastern Himalayan region. New particle formation is a complex process that depends on the nature of gaseous precursor species, which differ according to the environment; on meteorological factors such as UV-radiation, temperature, and relative humidity; and on boundary layer dynamics
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
