Strategic control of combustion-induced ammonia emissions: A key initiative for substantial PM2.5 reduction in Tianjin, North China Plain

Hao Xiao; Chuanwen Ji; Shiyuan Ding; Xiaodong Li

doi:10.1016/j.scitotenv.2024.172328

Strategic control of combustion-induced ammonia emissions: A key initiative for substantial PM_2.5 reduction in Tianjin, North China Plain

Sci Total Environ. 2024 Jun 10:928:172328. doi: 10.1016/j.scitotenv.2024.172328. Epub 2024 Apr 11.

Authors

Hao Xiao¹, Chuanwen Ji², Shiyuan Ding², Xiaodong Li³

Affiliations

¹ School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China; Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
³ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China. Electronic address: xiaodong.li@tju.edu.cn.

PMID: 38614324
DOI: 10.1016/j.scitotenv.2024.172328

Abstract

Information on the temporal and spatial variations in the sources of ammonium salts (NH₄⁺), a crucial alkaline component in PM_2.5, is limited. Here, we simultaneously collected PM_2.5 and gaseous ammonia (NH₃) samples in both summer and winter from two sites in Tianjin: an urban site (Tianjin University, TJU) and a suburban site (Binhai New-region, BH). NH₃ concentrations, the contents of major water-soluble inorganic ions in PM_2.5, and the compositions of ammonium‑nitrogen isotopes (δ¹⁵N-NH₄⁺) were measured. As a result, (NH₄)₂SO₄ and NH₄NO₃ were the predominant forms of NH₄⁺ in PM_2.5 during summer and winter, respectively. However, the NH₄NO₃ concentrations were notably greater at TJU (6.2 ± 7.3 μg m^-3) than at BH (3.8 ± 4.7 μg m^-3) in summer, with no regional differences observed in winter. Both sites displayed almost half the contribution of c-NH₃ (combustion-related NH₃) to NH₄⁺_, differing from the finding of previous isotope-based studies. This discrepancy could be attributed to the combined effects of NH_x isotope fractionation and seasonal δ¹⁵N value variations in NH₃ sources. The contribution fractions of v-NH₃ (volatile NH₃) and c-NH₃ exhibited similar patterns at both sites seasonally, probably caused by coal combustion for heating in winter and temperature fluctuations. However, the contribution fraction of c-NH₃ was lower at BH than at TJU in summer but greater in winter than at TJU. In summer, NH₄NO₃ was unstable and limited its delivery to TJU from BH, and the high contribution of c-NH₃ to NH₄⁺ at TJU could be attributed to local vehicle emissions. In winter, the stable particulate NH₄NO₃ that formed from the c-NH₃ in the upwind area could be transported to the downwind area, increasing the NH₄⁺ concentration at BH. Our study provides valuable insights for devising emission mitigation strategies to alleviate the increasing burden of NH₃ in the local atmosphere.

Keywords: Ammonium; Combustion-related NH(3); Nitrogen isotope; Source identification; Spatiotemporal variations.