Prashant Rajput

Chemical characterisation and source apportionment of PM1 during massive loading at an urban location in Indo-Gangetic Plain: impact of local sources and long-range transport

This study assesses temporal variability and source contributions of PM1 (particles with aerodynamic diameter ≤ 1.0 µm) samples (n=51; November 2009–February 2010) from an urban location at Kanpur (26.30°N; 80.13°E; 142 m above mean sea-level) in the Indo-Gangetic Plain (IGP). A study period from November to February is preferred owing to massive loading of particulate matter in entire IGP. PM1 varies from 18 to 348 (Avg±SD: 113±72) µg m−3 in this study. A total of 11 trace metals, five major elements and four water-soluble inorganic species (WSIS) have been measured. Mass fraction of total metals (∑metals=trace+major) centres at 18±14 %, of which nearly 15 % is contributed by major elements. Furthermore, ∑WSIS contributes about 26 % to PM1 mass concentration. Abundance pattern among assessed WSIS in this study follows the order: ≈ > > Cl−. The K-to-PM1 mass fraction (Avg: 2 %) in conjunction with air-mass back trajectories (AMBT) indicates that the prevailing north-westerly winds transport biomass burning derived pollutants from upwind IGP. A recent version of positive matrix factorisation (PMF 5.0) has been utilised to quantify the contribution of fine-mode aerosols from various sources. The contribution from each source is highly variable and shows a strong dependence on AMBT. Events with predominant contribution from biomass burning emission (>70 %) indicate origin of air-masses from source region upwind in IGP. One of the most interesting features of our study relates to the observation that secondary aerosols (contributing as high as ~60 % to PM1 loading) are predominantly derived from stationary combustion sources ( / ratio: 0.30±0.23). Thus, our study highlights a high concentration of PM1 loading and atmospheric fog prevalent during wintertime can have a severe impact on atmospheric chemistry in the air-shed of IGP.

The diurnal variability of sulfate and nitrate aerosols during wintertime in the Indo-Gangetic Plain: implications for heterogeneous phase chemistry

We have conducted this study (November 09–February 10) during the daytime (average PM1: 113 μg m−3; n = 51) and nighttime (average PM1: 159 μg m−3; n = 49) in the Indo-Gangetic Plain (IGP). Air-mass back trajectories suggest the impact of local emission and long-range transport (predominantly from the north–west direction). Mass fractions of SO42− and NO3− in PM1 are significantly (p < 0.05) different during both the daytime and nighttime, whereas NH4+/PM1 were similar during the day and night. The relatively high concentration of SO42− observed during the daytime was explained based on heterogeneous-phase reactivity due to the positive response of Fe and Mn species (inferred from correlation and multi-linear regression analysis: MLRA). Likewise, the lower concentration of NO3− was explained based on the negative response of Fe during heterogeneous phase formation. The role of wet-bulb temperature and solar flux has also been studied. From the field-based measurements our study shows that heterogeneous formation of SO42− (involving Fe and Mn) and NO3− occur via selective endothermic pathways. The proposed mechanism for sulfate and nitrate formation via heterogeneous phase reactivity is in good agreement with the field-based measurements obtained during this study (IGP). The impact of the heterogeneous-phase reactivity via endothermic pathways relates to the uptake of various reactive species during the winter in IGP. This, in turn, has implications for fog-formation and tropospheric oxidative cleansing. Furthermore, the uptake of various species will lead to altered size, morphology and optical properties of aerosols. This would have impact on regional scale radiative forcing estimates and future climate projections.

Water soluble organic aerosols in indo gangetic plain (IGP): Insights from aerosol mass spectrometry

Filter samples collected during winter of 2015-16 from two polluted urban locations (Allahabad and Kanpur) residing within Indo-Gangetic plain (IGP) showed high levels of water-soluble organic aerosols (WSOA). Total organic aerosols (OA) in submicron fraction, measured at Kanpur in real time via Aerosol Mass Spectrometer also showed substantially high concentration levels. WSOA to OA contribution in Kanpur was found to be very high (around 55%) indicating significant contributions from secondary OA (SOA). On average, WSOA oxidation ratio (O/C) was found to be higher (15-20%) in Kanpur than at Allahabad. WSOA from Allahabad was found to be following a much shallower slope (-0.38) in Van Krevelen diagram (H/C vs O/C plot) than Kanpur (-0.58). These differences suggest different composition and chemistry of WSOA at these two different locations. O/C ratios of WSOA were found to be much higher (~40%) than that of OA and independent of WSOA loading. Higher OA loadings were found to be associated with less oxidized primary OAs (POA) and culminated into lower WSOA/OA ratios. The presence of organo sulfate in filter samples from both locations indicate a significant amount of aqueous processing of organics. Concentrations and characteristics of water insoluble OA (WIOA) in Kanpur revealed that although they are present in significant quantity, their oxidation levels are much (almost 3 times) lower than that of WSOA. This finding indicates that less oxidized OAs are less soluble in line with the conventional wisdom. This study provides the first insight into oxidation levels and evolution of WSOA from India and also explores the interplay between WSOA and OA characteristics based on AMS measurements.

Dicarboxylic acids and levoglucosan in aerosols from Indo-Gangetic Plain: Inferences from day night variability during wintertime

This study assesses daytime and nighttime atmospheric abundance and molecular distribution of dicarboxylic acids (DCA: C2-C10) and biomass burning tracers (levoglucosan and biomass burning derived potassium: K+BB) in PM10 (particulate matter with aerodynamic diameter≤10μm) from an urban location, Kanpur (in central Indo-Gangetic Plain: IGP) during wintertime (December 2015-February 2016). In this study, PM10 varied from 130 to 242 and 175-388μgm-3 during daytime and nighttime, respectively. The average ratios of OC/EC (day: 12.3; night: 9.3) and WSOC/OC (day: 0.74; night: 0.48) were relatively high during daytime (OC: organic carbon; EC: elemental carbon; WSOC: water-soluble organic carbon). Strong linear correlations (R2≥0.6; p<0.05) of OC with levoglucosan and K+BB suggest biomass burning emission as predominant source of organic aerosols over the IGP. The measured concentrations of total DCA (ΣC2-C10) showed pronounced diurnal variability with a higher concentration during nighttime (2510±1025ngm-3) as compared to that in daytime (1499±562ngm-3). Concentrations of oxalic acid (C2), succinic acid (C4) and malonic acid (C3) were predominantly high as compared to other congeners of DCA (C2-C10) over central IGP. Relatively higher mass fraction (73.4%) of C2 in total DCA during nighttime than that in daytime (61.5%) indicates role of secondary organic aerosols (SOAs) formation involving aqueous-phase chemistry. Strong linear correlations of C2 with C3 and C4 plausibly suggest that C2 can have predominant formation pathways via decomposition of higher congeners of DCA. Overall, strong linear correlations of C2 with levoglucosan and sulphate suggest that biomass burning emission and secondary transformations are predominant sources of DCA over IGP during wintertime.

Risk assessment of submicron PM-bound hexavalent chromium during wintertime

ABSTRACT This study reports health risk assessment of PM1-bound carcinogenic hexavalent chromium [Cr(VI)] from central part of Indo-Gangetic plain (IGP) (PM1: particulate matter with aerodynamic diameter ≤1µm). Cr(VI) concentration has been estimated utilizing spectrophotometer with a modified novel method. Average ratio of Cr(VI)/CrT was 0.39 ± 0.07 (CrT: Total chromium) in the central IGP (Kanpur). Our study reports that mass fraction of Cr(VI) averaging at 0.39 is ∼3 times higher than that assumed conventionally [Cr(VI)/CrT: 1/7]. Cancer risk assessment has been performed by assessing excess cancer risk (ECR) for the Cr(VI). ECR determined due to Cr(VI) was 57 and 14.3 (in one million) for adults and children, respectively. Our study suggests that risk due to Cr(VI) reported in previous studies were being underestimated by a factor of three. The Cr(VI)/CrT average ratio of 0.39 determined in this study was utilized to calculate risk assessment due to Cr(VI) from other locations in the IGP. Owing to large population of India (∼125 million), the cancer risk due to Cr(VI) inhalation itself would become very significant. Thus, future research should focus on metal speciation of PM-bound samples from different locations to better constraint the toxicological risk assessment on a regional-to-global scale.

Stable Carbon Isotope and Bulk Composition of Wintertime Aerosols from Kanpur

This study assesses stable carbon isotopic composition (δ13C) of total carbon (TC) in ambient aerosols (PM2.5) during wintertime (December 2014) from Kanpur (26.30 °N, 80.14 °E) in northern India. Chemical constituents viz organic carbon (OC), elemental carbon (EC) and water-soluble ions in PM2.5 have also been measured. Back trajectories of air masses arriving at the sampling site (Centre for Environmental Science and Engineering, IIT Kanpur) have been utilized to infer the air-mass transport. Most of the trajectories showed their origin from northwestern region during the study period. Average PM2.5 and TC concentrations were centered around 240 μg m−3 and 91 μg m−3, respectively. The OC + EC concentrations averaged at 58 ± 15 μg m−3. Significant linear correlation between OC and EC in conjunction with high OC/EC ratio (9 to 12) suggests dominance of anthropogenic combustion sources of organic aerosols. Concentration of anthropogenic ionic species (SO4 2− + NO3 − + NH4 +) averaged at 46.74 μg m−3. The average δ13C values of TC in the integrated 24-h samples were centered around −25‰. Integrated data analyses of chemical constituents and stable C isotope suggests the influence of mixed emission sources. Future studies are required to better constraint the observations.

Bioaerosols Over the Indo-Gangetic Plain: Influence of Biomass Burning Emission and Ambient Meteorology

Bioaerosols (particles of biological origin) can be produced from living or dead plants and animals. They can potentially serve as the cloud condensation and ice nuclei (CCN and IN). Their role in global carbon cycle further highlights importance of studying their variability to link up with climate relevance parameters. Focusing on tropical region reveals that it holds wealthy number of human population and has massive vegetation cover-area. From Indian region, production estimates of bioaerosols from human population (current: ~1.25 billion; of which over 45% resides in Indo-Gangetic Plain: IGP) and Wildlife Sanctuaries and National Parks (100 in numbers, situated from north to south and east to west) is not known. Most of the forest fires in India occur during March–June (hot and drier season). The detailed information on chemical composition, fingerprinting and radiative forcing from regional forest fires is also lacking. Unlike natural sources (forest cover and fires), the seasonal variability of pollutants emission characteristic and chemical, optical and radiative forcing are relatively well studied from anthropogenic biomass (post-harvest paddy- and wheat-residue and biofuels) burning emission in India. However, the abundance of bioaerosols and their variability over a large stretch of IGP (north-west to north-east) was not well documented. Towards this, we have undertaken a year-long campaign to study and document (first-attempt) bioaerosols variability over a complete annual cycle from central IGP. We observed a parallel enhancement in concentrations of fine-particulate matter (PM2.5 in October–November: 158 ± 89 µg m−3 as compared to June–September months: 40 ± 18 µg m−3; two-tailed t = 8.2, p < 0.05) and bioaerosols (particularly Gram-negative bacteria: GNB, a source of endotoxin in ambient air; 186 ± 87 CFU/m3 during October-November as compared to 114 ± 58 CFU/m3; t = 4.0, p < 0.05) with the biomass burning emissions intensification period. The abundance of bioaerosols exhibits influence of ambient meteorology, for example GNB exhibited negative correlations with T, wind speed and heavy (>4 mm daily) precipitation, whereas it showed positive correlations with RH and low precipitation amount (<4 mm). Studying bioaerosols and establishing its linkage to health and climate appear to be of utmost importance.