Chemical characterization and stable nitrogen isotope composition of nitrogenous component of ambient aerosols from Kanpur in the Indo-Gangetic Plains

Measurements of water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), water-soluble organic nitrogen (WSON) and delta N-15(TN) (total N) was carried out on PM2.5 aerosol samples during wintertime to understand the major sources of ambient nitrogenous species at a heavily polluted location of Kanpur in north India. During the nighttime sampling campaign, WSON and NH4+_N contributed dominantly to the WSTN. Ammonium-rich condition persisted during sampling (NH4+/SO42- average equivalent mass ratio = 3.1 +/- 0.7), suggesting complete neutralization of SO42- and formation of NH4NO3, which is stable in winter due to low temperature and high relative humidity (RH). Stagnant atmospheric conditions during wintertime enhanced concentrations of ionic species (SO42-, NH4+, and NO3-) at this location. Good correlations between NO3-_N, NH4+_N and biomass burning tracer K-BB(+) (and also between NO3-_N, NH4+_N and SO42-) suggests a strong impact of biomass burning activities. Multi-linear regression (MLR) analysis shows a strong dependence of delta N-15 on NO3-_N, SO42- and WSON in night-1 (10:00 pm to 2:00 am) and on NO3-_N and SO42- in night-2 (2:00 am to 6:00 am) depicting different formation and removal mechanism of aerosols during both the time-periods. delta N-15(TN) in PM2.5 varied from +8.8 to +15.5 parts per thousand (10.8 +/- 1.3), similar to the variability observed for many urban locations in India and elsewhere. NH4+_N and WSON control the final delta N-15 value of nitrogenous aerosols. High relative humidity during nighttime enhanced the secondary organic aerosols formation due to aqueous-phase formation and gas to particle-phase partitioning. Isotopic fractionations associated with multi-phase reactions during gas to particle conversion of NH3 would result in an increase in delta N-15 by similar to 48 parts per thousand to 51 parts per thousand (at T of 5.4 degrees C to 15.4 degrees C) than that of the emission source(s), which indicates the most likely N-emission sources at Kanpur to be from agriculture activities and waste generation. (C) 2020 Elsevier B.V. All tights reserved.

Automated summary

Measurements of nitrogenous species in winter PM2.5 aerosol samples were conducted in a heavily polluted area in Kanpur, north India. Results showed NH₄⁺_N and WSON dominated WSTN, with stagnant atmospheric conditions enhancing concentrations of ionic species. Isotopic analysis indicated likely sources of nitrogen emissions in the area to be agriculture activities and waste generation.