Carbonaceous and inorganic species in atmospheric aerosols during wintertime over urban and high‐altitude sites in North India

Abstract

[1] Synchronous sampling of bulk-aerosols, carried out during wintertime from the two strategically located sites in North India, reveals that total suspended particulates (TSP) over an urban site (Hisar: 29.2°N 75.7°E; 219 m asl) ranged from 67 to 396 mg m À3 ; in contrast, TSP at Manora Peak (a high-altitude station: 29.4°N 79.5°E; 1950 m asl) was relatively low (range: 13.7 to 42.7 mg m À3 ). At Hisar, on average, water-soluble ionic species (WSIS, range: 14.1 to 78.3 mg m À3 ) contribute nearly one-fourth by weight to TSP, with dominant contribution from SO 4 2À , NO 3 À and NH 4 + . The time series analysis over a span of 30 days shows somewhat uniform distribution of organic carbon/elemental carbon (OC/EC) ratio centering around 8.5 ± 2.2 at this urban site; and the water-soluble organic components (WSOC range: 6.7 to 42.0 mg m À3 ) account for 11.5 % to the TSP concentration. Both WSOC and OC exhibit significant positive correlation with water-soluble K + (r = 0.88 and 0.79 respectively), suggesting their dominant contribution from biomass burning. At Manora Peak, the chemical composition of ambient aerosols show characteristically lower abundances of WSIS (range: 2.0 to 9.9 mg m À3 ) and WSOC (range: 1.4 to 6.0 mg m À3 ); together they account for one-third of the TSP. The characteristic low abundances of OC (range: 2.8 to 6.9 mg C m À3 ) and EC (range: 0.34 to 1.4 mg C m À3 ) at this high-altitude site and their significant correlation with K + and SO 4 2À suggest contribution from long-range transport of anthropogenic species. This study represents a first comprehensive data set for documenting the chemical characteristics of ambient aerosols and source apportionment of EC, OC, WSIS and mineral dust over urban and high-altitude sites in north India, an important data set required for the south Asian region. If the observed OC/EC ratios far greater than $2 (unlike reported values in the literature for urban sites) and the semi-empirical estimates of secondary OC are typical of the annual average abundances in the ambient aerosols over north India, then the temporal and regional analyses of primary and secondary OC using the existing emission models require reassessment for this region.Citation: Rengarajan, R., M. M. Sarin, and A. K. Sudheer (2007), Carbonaceous and inorganic species in atmospheric aerosols during wintertime over urban and high-altitude sites in North India,

Carbonaceous and Secondary Inorganic Aerosols during Wintertime Fog and Haze over Urban Sites in the Indo-Gangetic Plain

“…The contribution of unidentified matter (UM), estimated by taking difference of OM, EC and inorganic constituents from the TSP, is of the order of 40% at Hisar and ~50% at Allahabad. The unidentified matter mainly consists of mineral dust with dominant contribution from carbonate-rich minerals (such as CaCO 3 , MgCO 3 , dolomite [CaMg(CO 3 ) 2 ]), calcium sulphate (or Gypsum), and alumino-slilicates (Krueger et al, 2004;Rengarajan et al, 2007;. The high-level of Ca 2+ concentration in our samples (Table 2) and neutralization of acidic species by mineral aerosol (Table 3 and section 4.5) further attests our inference.…”

“…OM/OC ratio) is highly variable (range: 1.4-2.1) (Turpin and Lim, 2001) and depends on the sources of organic aerosol, location and environment (urban, rural or high-altitude). In this study, we have used a value of 1.6 to estimate the OM concentration at the urban sites (Rengarajan et al, 2007;Ram et al, 2010;Turpin and Lim, 2001). SO 4 2− contributes ~7% to the TSP mass at both sites, followed by NO 3 − (8% at Hisar and 4% at Allahabad) and NH 4 + (4% at Hisar and 2.5% at Allahabad).…”

“…The particulate matter (PM) mass (μg/m 3 ) was ascertained gravimetrically by weighing full-filter before and after the aerosol sampling, and dividing the aerosol mass (in μg) by the total volume of air sampled (in units of m 3 ). The mass concentrations of elemental and organic carbon (EC and OC) in ambient aerosol were assessed on the EC-OC analyzer (Sunset Laboratory, USA) using thermo-optical transmittance (TOT) protocol (Rengarajan et al, 2007;Ram et al, 2008). The transmittance signal measured using a laser source (at 678 nm) was used to define the split-point between EC-OC and to correct for the pyrolyzed carbon.…”

“…Among the major sources of aerosol, emissions from agricultural-waste and biomass burning dominate during the wintertime (Dec-Feb) (Venkataraman et al, 2005;Rengarajan et al, 2007;Gustafsson et al, 2009;Ram et al, 2010a;Shakya et al, 2010;Rajput et al, 2011;Ram and Sarin, 2011). The transport of mineral aerosol from arid and semiarid regions of western India, during the summer (Aprilearly June), imparts strong temporal variability in the chemical composition and optical properties of aerosol (Jethva et al, 2005;Chinnam et al, 2006).…”

“…The formation of fog and haze is associated with high aerosol loading from anthropogenic sources as well as formation of secondary aerosols via gas-to-particle conversion under favorable meteorological conditions (Reilly et al, 2001;Husain et al, 2004;Sun et al, 2006;Fang et al, 2011;). Recent studies suggest that a significant fraction of atmospheric particulate matter (PM) in the Indo-Gangetic Plain are comprised of carbonaceous aerosol (~30-35% of the PM) and water-soluble inorganic species (~10-20% of the PM) over IGP and other locations in India Rengarajan et al, 2007;Ram et al, 2010a;Deshmukh et al, 2011;Kothai et al, 2011). During the wintertime, low ambient temperatures (range: ~10-20°C, at times dipping as low as 5°C) and weak winds (< 2 m/s) and boundary layer height (~500-800 m) favour stable atmosphere, leading to poor convective mixing and accumulation of pollutants in the lower atmosphere (Nair et al, 2007;Ram et al, 2010a).…”