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.

Automated summary

By coupling nitrate dual isotopes with aerosol chemical compositions, this study investigated the size-segregated formation mechanisms of nitrate (NO3-) during winter haze pollution events in Chengdu, China. Different formation pathways were identified for fine particles and coarse particles, with N2O5 hydrolysis, NO3 + VOCs, and NO2 + OH homogeneous reactions being major contributors for fine particle NO3- production, and the reaction between gas-phase HNO3 and CaCO3 dominating coarse particle NO3- formation. This research provides quantitative insights and a better understanding of NO3- formation during haze pollution.