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. 2025 Sep 25:127159.
doi: 10.1016/j.envpol.2025.127159. Online ahead of print.

Impacts of Uncertainties in Chinese NH3 Emissions on PM2.5 Concentrations over Mainland China and Downwind Regions

Hyeonsik Choe  1 , Chae-Yeong Yang  1 , Yunsoo Choi  2 , Jincheol Park  2 , Dongjin Kim  1 , Jeonghyeok Moon  3 , Min Heo  1 , Jaehyeong Park  4 , Cheol-Hee Kim  5 , Wonbae Jeon  6
Affiliations

Impacts of Uncertainties in Chinese NH3 Emissions on PM2.5 Concentrations over Mainland China and Downwind Regions

Hyeonsik Choe et al. Environ Pollut. .

Abstract

Uncertainties in ammonia (NH3) emissions can influence ambient fine particulate matter (PM2.5) concentrations through atmospheric chemical reactions. In this study, we performed numerical simulations using the Community Multiscale Air Quality (CMAQ) model to assess how uncertainties in Chinese NH3 emissions affect PM2.5 concentrations over mainland China and its downwind regions. We designed perturbation scenarios for spring and summer 2019 by increasing NH3 emissions by 75.7%, reflecting values reported in previous studies. Although the emission increase was larger in summer (2.00 moles/s) than in spring (1.05 moles/s), PM2.5 concentration changes were more pronounced in spring (2.54 μg/m3) than in summer (1.99 μg/m3). The greater PM2.5 response in spring is attributed to the nitrate (NO3-) production-loss mechanism (NH3 + HNO3 ⇌ NH4+ + NO3-). Despite the larger increase in NH3 emissions during summer, the net rise in NO3- was lower than in spring because the dominant NO3- decomposition rate of -1.229 μg/m3/h under higher temperatures offset production. Concurrently, seasonal shifts in synoptic wind patterns were found to significantly modulate downwind PM2.5 concentration variations attributable to emission heterogeneity. Springtime atmospheric circulation facilitated efficient transboundary transport of NO3- towards the Korean Peninsula, consequently elevating PM2.5 concentrations in downwind Seoul by 3.07 μg/m3, surpassing the 2.75 μg/m3 increase observed in upwind Beijing. In stark contrast, summertime circulation impeded NO3- advection, resulting in a mere 0.15 μg/m3 PM2.5 change in Seoul compared to 2.42 μg/m3 in Beijing. These findings underscore that variations in NH3 emissions from China can profoundly influence regional PM2.5 levels, and that meteorological conditions, particularly wind patterns, play a pivotal role in dictating East Asian air quality.

Keywords: Ammonia; CMAQ; Emission; PM(2.5); Transboundary transport.

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Conflict of interest statement

Declaration of Competing Interest ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.