the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Spatial-temporal variations of atmospheric NH3 concentration and its dry deposition across China based on one decade of satellite and ground-based observations
Abstract. Ammonia (NH3), a key alkaline gas in the atmosphere, significantly influences ecosystem nitrogen cycling and the formation of fine particulate matter (PM2.5). However, limited ground-based monitoring hinders understanding of NH3’s spatial and temporal dynamics and its dry deposition across China, which is ranked as one of global largest NH3 emission hotspots. This study integrated 2013–2023 satellite-derived NH3 column concentrations from the Cross-track Infrared Sounder (CrIS) with ground in-situ observations. We used the GEOS-Chem transport model and a random forest algorithm to simulate NH3 dry deposition fluxes and explore the driving forces behind observed trends. Our results show that NH3 concentrations were the highest in the North China Plain (>10 ppb), with notable annual and seasonal increases. NH3 concentration in 2023 were 14–31 % higher than in 2013. CrIS retrievals aligned well with in-situ data, though were generally about twice as high. Dry deposition fluxes exhibited a clear east-west gradient, with maxima in the North China Plain and Sichuan Basin. Increases in NH3 concentrations and deposition were most pronounced in urban, cropland, and forest regions, with urban areas experiencing the fastest growth and grasslands the highest total deposition. The national mean NH3 concentration and dry deposition flux were 4.98 ppb and 0.51 g m⁻2 yr⁻1, respectively. Anthropogenic emissions explained 77 % of the variability in NH3 concentration trend, while meteorological factors accounted for the remainder. 70 %–80 % of deposition trend was governed by atmospheric NH3 concentration changes. This study highlights growing ammonia pollution and informs nitrogen management strategies in China.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-3090', Anonymous Referee #1, 07 Sep 2025
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RC2: 'Comment on egusphere-2025-3090', Anonymous Referee #2, 09 Sep 2025
The manuscript attempts to investigate spatial-temporal variations of atmospheric NH3 concentration and its dry deposition across China in 2013-20123 by combining satellite-based, ground-level observational data in publica domain and 3-D modeling results. The analysis sounds scientific, but it needs a substantial revision on potential uncertainty and modeling accuracy. The major comments are listed as below:
1) Key scientific questions are too general to be valuable by considering the uncertainties associated and previous studies published in the literature. The authors are encouraged to deeply think the issues.
2) Figure 4, the size of data is too small by considering one decade observations, what happens?
3) Modleing results always suffer from the errors. However, most of air quality modeling results in China well reproduce PM2.5 in approximately 1/3 days in each year. However, it is not case in other times because of the poor prediction of one or several meteorological conditions. The authors should select the 1/3 days with good prediction performance for machine learning.
4) Line 399-400, “Elevated temperatures further enhance volatilization from manure and urban waste, intensifying atmospheric NH3 levels.”. The reviewer has much concern on the statement, i.e., the authors might not know what exactly happen for agriculture emissions of NH3 in China? With a large population moving from the country land to the city in the last decade, the sources are negligible.
Minor comments:1)The effective number through the manuscript are total off and needs to be corrected. Principally, it should be consistent with the analytic error, i.e., 5-10% analytic errors correspond two effective numbers.
2)Abstract, lines 37, “our results”, what does it means? Modeling results? Observations from CrIS ,AMoN-China or NNDMN?
3)Abstract, line 40-42, “Dry deposition fluxes exhibited a clear east-west gradient, with maxima in the North China Plain and Sichuan Basin. “ The sentence is problematic. Sichuan Basin should be located in southwestern China, correct?Citation: https://doi.org/10.5194/egusphere-2025-3090-RC2
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General comments
This manuscript addresses an important topic, spatial–temporal variability of atmospheric NH3 and its dry deposition across China, which has not been jointly studied before, especially for using CrIS in China, as far as I know. However, the main problem is that the logical connection between derived surface-level/near-surface NH3 concentrations and the derived NH3 dry-deposition fluxes is not sufficiently explained. In its current form, it is difficult to follow the storyline between concentrations and dry depositions and contains several conceptual and presentation problems in figures and tables that must be resolved before publication. The title (“one decade of satellite and ground-based observations”) is misleading because the text does not make clear which data sources (RF-derived GEOS-Chem simulations, satellite, or ground obs) dominate the results and how they are linked. Suggest alternatives, something like, “Decadal changes in atmospheric ammonia and dry deposition across China inferred from space-ground measurements, and model simulations". The manuscript frequently mixes satellite, ground, reanalysis, and inventory products without a clear, reproducible workflow.
Specific comments