Abstract
PM2.5 samples were collected at traffic, rural and campus sites in Agra during Nov 2010 to Feb 2011 and characterized for carbonaceous aerosols. The average mass concentrations of PM2.5 were 308.3 ± 51.8 μg/m3, 91.2 ± 17.3 μg/m3 and 140.8 ± 22.3 μg/m3 at the traffic, rural and campus sites, respectively. The 24-h mass concentrations of PM2.5 were significantly higher than the limit of 60 μg/m3 prescribed in the National Ambient Air Quality Standards (Indian NAAQS) and 25 μg/m3 of those of the WHO (World Health Organization). The average concentrations of OC (organic carbon) and EC (elemental carbon) were 86.1 ± 5.2 and 19.4 ± 2.4 at the traffic site, 30.3 ± 12.9 and 4.0 ± 1.5 at the rural site and 44.5 ± 18.5 μg/m3 5.0 ± 1.4 μg/m3 at the campus one. The contributions of TCA (Total Carbonaceous Aerosol) at the traffic, campus and rural sites were found to be 52, 54 and 58% of PM2.5 mass, respectively. A significant correlation was observed between water soluble K+ and OC at the rural (R2 = 0.63) and campus (R2 = 0.53) sites compared to the traffic one (R2 = 0.35). This may be attributed to increased biomass burning emissions at the rural and campus sites. The concentrations of SOC (Secondary Organic Carbon) were estimated based on the minimum OC/EC ratio, and were found to be 15.3 ± 6.3, 8.2 ± 5.8 and 28.8 ± 15.8 μg/m3, accounting for 18, 24.7 and 60.7% of total OC at the traffic, rural and campus sites, respectively. The surface morphology of the particles was analyzed by scanning electron microscopy and energy- dispersive X-ray spectroscopy (SEM/EDX). The results indicated branched chain-like aggregates of carbon bearing spheres at the traffic and rural sites, while at the campus site carbon-rich and minerogenic (mineral dust) particles were the dominant ones.
Highlights
Atmospheric aerosols play an important role in regional air quality, public health, atmospheric chemistry and climate change especially over East Asia (Jacobson, 2001)
A wind rose (WR) plot of winter months with 46.8% calm conditions showed low and steady wind speed. These climatic conditions i.e. less dispersion and low mixing heights or lower boundary layer height, typically 500–1000 m (Nair et al, 2007) during winter months help the ambient particles to remain for longer time in the atmosphere. These stagnant meteorological conditions is supported by the results of back trajectory analysis that shows that the site is under the influence of different local emissions and account for increased levels of particulate mass (Fig. 3(a) and 3(b))
24 h average mass concentrations ranged from 210–381 μg/m3, 101–163 μg/m3 and 72–118 μg/m3 at traffic, campus and rural sites, respectively
Summary
Atmospheric aerosols play an important role in regional air quality, public health, atmospheric chemistry and climate change especially over East Asia (Jacobson, 2001). They are produced from various natural and anthropogenic sources and have significant direct radiative impact through absorption and scattering of incoming radiation (Haywood and Boucher, 2000; Tare et al, 2006). It comprises a mixture of sulfates, nitrates, carbonaceous particles, sea salt, and mineral dust (Hansen et al, 2000). Elemental carbon is a primary pollutant emitted from anthropogenic combustion sources and does not undergo chemical transformations, while OC can be either released directly into the atmosphere
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