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<p>This study conducted online observations of atmospheric ammonia (NH<sub>3</sub>) concentrations from 20 February to 5 March, 2025, during which the “Two Sessions” were held in Beijing and emission control measures were typically implemented in surrounding regions. An unexpected heavy pollution episode occurred during this period, with NH<sub>3</sub> concentrations reaching 59.7 ppb, significantly higher than those observed on clean days (17.8 ± 4.5 ppb). During the development of the pollution episode, NH<sub>3</sub> concentrations exhibited synchronous variations with PM<sub>2.5</sub>, indicating that NH<sub>3</sub> played a crucial role in the formation of secondary inorganic aerosols. Additionally, NH<sub>3</sub> concentrations displayed a distinct morning peak, primarily attributed to temperature-driven natural emissions, traffic emissions during morning rush hour, and re-mixing of residual layers. NH<sub>3</sub> was significantly correlated with SO<sub>2</sub> and CO, suggesting contributions from fossil-fuel combustion. Furthermore, the overlap of concentration-weighted trajectory analysis and MODIS fire-point data indicated that biomass burning in south-eastern Beijing likely contributed additional NH<sub>3</sub> emissions. Overall, this study highlights the importance of reducing combustion-related NH<sub>3</sub> sources to mitigate heavy air pollution and improve air quality through cross-regional collaborative control measures.</p>

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Combustion Sources Dominated Ammonia Concentrations During Severe Air Pollution Episodes During “Two Sessions” 2025 in Beijing

  • 期刊论文

  • 发表日期：

    2026年7月8日

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  • Yifei Lu,
  • Mengna Gu,
  • Xingru Li,
  • Shili Tian,
  • Qian Sun,
  • Yuepeng Pan

摘要

This study conducted online observations of atmospheric ammonia (NH3) concentrations from 20 February to 5 March, 2025, during which the “Two Sessions” were held in Beijing and emission control measures were typically implemented in surrounding regions. An unexpected heavy pollution episode occurred during this period, with NH3 concentrations reaching 59.7 ppb, significantly higher than those observed on clean days (17.8 ± 4.5 ppb). During the development of the pollution episode, NH3 concentrations exhibited synchronous variations with PM2.5, indicating that NH3 played a crucial role in the formation of secondary inorganic aerosols. Additionally, NH3 concentrations displayed a distinct morning peak, primarily attributed to temperature-driven natural emissions, traffic emissions during morning rush hour, and re-mixing of residual layers. NH3 was significantly correlated with SO2 and CO, suggesting contributions from fossil-fuel combustion. Furthermore, the overlap of concentration-weighted trajectory analysis and MODIS fire-point data indicated that biomass burning in south-eastern Beijing likely contributed additional NH3 emissions. Overall, this study highlights the importance of reducing combustion-related NH3 sources to mitigate heavy air pollution and improve air quality through cross-regional collaborative control measures.