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

Gyanesh Kumar Singh; Pradhi Rajeev; Debajyoti Paul; Tarun Gupta

doi:10.1016/j.scitotenv.2020.143032

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

Sci Total Environ. 2021 Apr 1:763:143032. doi: 10.1016/j.scitotenv.2020.143032. Epub 2020 Oct 20.

Authors

Gyanesh Kumar Singh¹, Pradhi Rajeev², Debajyoti Paul³, Tarun Gupta²

Affiliations

¹ Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India; APTL at Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Kanpur, Kanpur 208 016, India. Electronic address: gyanesh@iitk.ac.in.
² Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India; APTL at Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Kanpur, Kanpur 208 016, India.
³ Department of Earth Sciences, Indian Institute of Technology Kanpur, Kanpur 208 016, India; APTL at Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Kanpur, Kanpur 208 016, India.

PMID: 33131840
DOI: 10.1016/j.scitotenv.2020.143032

Abstract

Measurements of water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), water-soluble organic nitrogen (WSON) and ẟ¹⁵N_TN (total N) was carried out on PM_2.5 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⁺/SO₄^2- average equivalent mass ratio = 3.1 ± 0.7), suggesting complete neutralization of SO₄^2- 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 (SO₄^2-, 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 SO₄^2-) suggests a strong impact of biomass burning activities. Multi-linear regression (MLR) analysis shows a strong dependence of ẟ¹⁵N on NO₃^-_N, SO₄^2- and WSON in night-1 (10:00 pm to 2:00 am) and on NO₃^-_N and SO₄^2- in night-2 (2:00 am to 6:00 am) depicting different formation and removal mechanism of aerosols during both the time-periods. ẟ¹⁵N_TN in PM_2.5 varied from +8.8 to +15.5‰ (10.8 ± 1.3), similar to the variability observed for many urban locations in India and elsewhere. NH₄⁺_N and WSON control the final ẟ¹⁵N 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 ẟ¹⁵N by ~48‰ to 51‰ (at T of 5.4 °C to 15.4 °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.

Keywords: Atmospheric processing; Biomass burning; Fractionation; Nitrogenous aerosols; Stable isotope.