Chemical and isotopic characteristics of PM2.5 over New Delhi from September 2014 to May 2015: Evidences for synergy between air-pollution and meteorological changes.

The capital city of India, New Delhi, is experiencing serious PM2.5 pollution in the form of recurrent hazy skies and smoky fog (SMOG) episodes in recent years. Besides source-emission strengths, frequency and time-spans of these air-pollution episodes are uncertain due to variable urban meteorological influences, preventing the formation of a cohesive policy to tackle air-quality degradation. About 70% mass of PM2.5 particle is composed of Carbon (C), Nitrogen (N), and Sulphur (S) and, hence, their mass concentrations along with their stable isotopic imprints (viz. δ13CPM2.5, δ15NPM2.5 and δ34SPM2.5) provide powerful tools to gain insights into complex aerosol chemistry. This study presents the aforementioned data generated for PM2.5 collected from New Delhi covering full post-monsoon, winter, and summer months of 2014-15. Temporal variability in the generated dataset was analyzed with variabilities in atmospheric concentrations of key gaseous species (NH3, NOx, and SO2) and meteorological indices. The highest PM2.5 concentrations were observed in winter months with enhanced aerosol N and S concentrations. Active biomass (crop-residue) burning in the northwest Indo-Gangetic Plains (IGP) appears to be the major source of aerosol TC for post-monsoon and winter months in addition to emission sources from the combustion of bio- and fossil- fuels. Aerosol TN contents appear to be largely impacted by ambient ammonia emissions, especially during winter. Aerosol TS contents could be manifested by emissions from coal combustion, road dust, and biogenic sulphur. Total C + N + S contents of PM2.5 showed significant negative correlations with surface solar radiation and air-visibility. Both δ15NPM2.5 and δ34SPM2.5 values show remarkable correlations with air-quality and meteorological parameters during winter months demonstrating considerable secondary cycling. Cluster analysis and concentrated weighted wind trajectories over New Delhi for the study-period showed ~64% and ~58% of air mass trajectories from the northwest (Punjab-Haryana) region during post-monsoon and winter months respectively.

Chemical and isotopic characteristics of PM10 over the Bay of Bengal: Effects of continental outflow on a marine environment.

Pollutants transport from South and Southeast Asia can profoundly affect the marine atmospheric boundary layer (MABL) over the Bay of Bengal (BoB). This study presents chemical and stable isotopic composition of PM10 collected at Port Blair Island (11.6°N, 92.7°E) located in the middle of the BoB during the late northeast monsoon (February-April), a period when the BoB receives considerable continental outflow. These samples (n = 50) were analysed for major ions, carbonaceous species, trace metals, and isotopic composition of total C, N, and S components. Mass concentration of PM10 ranged from 24 to 65 µg m-3 during the study period. The dominance of continental inputs over a marine realm was evident by a significant amount of non-sea-salt (nss)-SO42- (range: 1.8 to 16.9 µg m-3), which accounts for ~65% of the total water-soluble inorganic constituents. The impact of anthropogenic emissions was further evident from the widespread depletion of chloride (range: 57-100%, avg.: 98 ± 7%) from sea-salt aerosols. Carbonaceous species (elemental carbon and organic matter) contributed nearly 35% to PM10. Further, average δ13C (-25.6‰ ± 0.5) and δ34S (4.5‰ ± 1.3) values observed over the marine study region were similar to those found in typical urban environments. δ15N values (13.7‰ ± 5.1) show the significant presence of combustion sources along with the effect of atmospheric processing. Aerosol δ13C values correlate positively with the ratio of water-soluble organic carbon to total organic carbon, indicating the aging of organic aerosols during the transport. Chemical and isotopic data suggest that both biomass burning (BB) and fossil fuel burning (FFB) contributed to ambient PM10 with relatively more contribution of BB during February to early March and that of FFB during late March to middle of April. In aggregate, this study provides newer insights into sources of carbonaceous species and their chemical processing in MABL of BoB.

Delineating sources of groundwater recharge and carbon in Holocene aquifers of the central Gangetic basin using stable isotopic signatures.

Stable isotopes of water (δ2H, δ18O) and δ13CTIC were used as a tool to trace the recharge processes, natural carbon (organic and inorganic) source and dynamics in the aquifers of the central Gangetic basin, India. Stable isotope (δ2H, δ18O) record of groundwater (n = 105) revealed that the groundwater of Piedmont was recharged by meteoric origin before evaporation, while aquifers of the older and younger alluvium were recharged by water that had undergone evaporation loss. River Ganges and its tributaries passing through this area have very little contribution in recharging while ponds play no role in the recharging of adjacent aquifers. The connectivity of shallow aquifers of aquitard formation (comprised of clay/sandy clay with thin patches of fine grey sand), i.e. 25-60 m below ground level (bgl) with the main upper aquifer (at a depth of >120 m bgl) was found to be higher in older and younger alluvium. Negative values of δ13CTIC (median -9.6 ‰; range -13.2 to -5.4 ‰) and high TIC (median 35 mM; range 31-46 mM) coupled with low TOC (median 1.35 mg/L; range 0.99-1.77 mg/L) indicated acceleration in microbial activity in the younger alluvium, especially in the active floodplain of river Ganges and its proximity.