Abstract
The present study analyzes data from total suspended particulate (TSP) samples collected during 3 years (2005–2008) at Nainital, central Himalayas, India and analyzed for carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)) and inorganic species, focusing on the assessment of primary and secondary organic carbon contributions (POC, SOC, respectively) and on source apportionment by positive matrix factorization (PMF). An average TSP concentration of 69.6 ± 51.8 µg m−3 was found, exhibiting a pre-monsoon (March–May) maximum (92.9 ± 48.5 µg m−3) due to dust transport and forest fires and a monsoon (June–August) minimum due to atmospheric washout, while carbonaceous aerosols and inorganic species expressed a similar seasonality. The mean OC/EC ratio (8.0 ± 3.3) and the good correlations between OC, EC, and nss-K+ suggested that biomass burning (BB) was one of the major contributing factors to aerosols in Nainital. Using the EC tracer method, along with several approaches for the determination of the (OC/EC)pri ratio, the estimated SOC component accounted for ~25% (19.3–29.7%). Furthermore, TSP source apportionment via PMF allowed for a better understanding of the aerosol sources in the Central Himalayan region. The key aerosol sources over Nainital were BB (27%), secondary sulfate (20%), secondary nitrate (9%), mineral dust (34%), and long-range transported mixed marine aerosol (10%). The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analyses were also used to identify the probable regional source areas of resolved aerosol sources. The main source regions for aerosols in Nainital were the plains in northwest India and Pakistan, polluted cities like Delhi, the Thar Desert, and the Arabian Sea area. The outcomes of the present study are expected to elucidate the atmospheric chemistry, emission source origins, and transport pathways of aerosols over the central Himalayan region.
Highlights
Deterioration of air quality is a global concern, in South and Southeast Asia, where levels of pollutants frequently exceed the air quality guidelines established by WHO and the National Pollution Control Board of India [1,2,3]
The secondary organic carbon (SOC) concentration was much lower (2.93 ± 2.30 μg m−3 for (OC/EC)min) than that of water-soluble organic carbon (WSOC) (4.91 ± 3.17 μg m−3), most likely corresponding to the soluble nature of biomass burning (BB) aerosols transported from the Indo-Gangetic Plain (IGP) [10,11,40], which have been classified as POC in the current estimates
We examined the chemical composition of total suspended particulate (TSP) samples collected in Nainital, a high-altitude site in the central Himalayan region, for a period of three years, from February 2005 to February 2008
Summary
Deterioration of air quality is a global concern, in South and Southeast Asia, where levels of pollutants frequently exceed the air quality guidelines established by WHO and the National Pollution Control Board of India [1,2,3]. The identification and quantitative characterization of contributing sources and atmospheric processes for aerosol formation are very important to link the emissions with observed levels and develop air pollution control strategies [12,13,14]. For the second major category of receptor models, information on chemical components that are related to specific sources at the receptor site is used for source apportionment. Over South Asia, PMF and PCA techniques have been frequently used for apportioning sources of size-segregated aerosols (PM2.5, PM10, or TSP), with approximately 70% of the total source apportionment studies having been performed using PMF, PCA, or related factor analytic techniques [13]
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