Quantifying the formation pathways of nitrate in size-segregated aerosols during winter haze pollution

Nitrate (NO3-) is an important acidic component in haze pollution. The NO3- formation pathways for bulk aerosols have been studied thoroughly, leaving the size-segregated NO3- formation mechanisms under -explored. By coupling nitrate dual isotopes with aerosol chemical compositions, we studied size -segregated aerosols collected during winter haze pollution events at Chengdu, China. Different formation mechanisms for the size-segregated NO3- were analyzed. For fine particles (0.43-2.1 lm), NO3- was dominantly formed under NH4+ enriched conditions, during which the SIAR (stable isotope analysis in R) model suggested that N2O5 hydrolysis, NO3 + VOCs (volatile organic compounds) and NO2 + OH homo-geneous reactions contributed 38-42 %, 32-38 %, and 22-30 % of NO3- production, respectively. For coarse particles (>3.3 lm), majority of NO3- was produced through the reaction of gas-phase HNO3 with CaCO3 (63-71 %). This work revealed differential formation pathways of size-segregated NO3- and pro-vided quantitative insights on information on NO3- formation during the haze pollution.CO 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.