| 17 Oct 2025
Measurement report: Assessing the ammonia characteristics over a high-altitude mountain site in Shanxi province, China: a comparison with the observations in the North China Plain
Abstract. Ammonia (NH3) acts as the dominant alkaline gas and plays a crucial role in atmospheric chemistry, thereby influencing air quality and ecological systems. Previous NH3 measurement studies have primarily focused on near-ground environments or relied on passive sampling methods; however, continuous, high-resolution NH3 observations at high-altitude sites remain scarce. This study investigated NH3 characteristics at a high-altitude mountain site (WTM) in northern China, using high-resolution and real-time measurement data spanning a full annual cycle. It further conducted comparative analyses with a regional background site (SDZ) and an urban site (BMS) to better understand the regional features of NH3 in northern China. A multi-method approach was employed, integrating in situ NH3 measurements, meteorological data analyses, Convergent Cross Mapping (CCM), Potential Source Contribution Function (PSCF), and WRF-Chem modeling, to identify NH3 source regions and clarify underlying transport mechanisms. The results indicated that NH3 emissions from the North China Plain (NCP) can reach WTM and SDZ through distinct circulation patterns: mountain-plain circulations for WTM and mountain-valley circulations for SDZ. Notably, despite significant differences in altitude, geography, and pollutant transport mechanisms between WTM and SDZ, regional agricultural emissions in the NCP were the dominant factor driving the similarity in NH3 levels at the two sites. This study enhances the understanding of how surface emissions influence NH3 concentrations at high-altitude mountain site and highlights the critical role of NCP emissions in influencing regional NH3 levels, thereby providing insights for formulating strategies to mitigate regional NH3 pollution.
Pu et al. reports valuable year-long measurements of NH3 simultaneously captured at 3 distinct site types at different locations in the North China Plain, respectively representing high altitude background in the western North China Plain , regional background of the northern part of the Plain and urban pollution within the Plain area. These data were used to reveal similarities and differences within NH3 measurements at distinct locations as well as uncover the influences of emissions, local circulations and transport. Overall, the manuscript presented valuable insights into the homogeneity of NH3 pollution in the North China Plain, and the impact of geographical circulations. However, the manuscript still needs to be further improved before it can be accepted for publication. Below are some detailed comments:
1. P1 L22-23: Grammar issue:"It further conducted comparative analyses"
2. P1 L30: Basically mountain-plain and mountain-valley circulations are caused by similar phyisical processes, they only differ in spatial scale. Is it accurrate to say that the SDZ station is only influenced by mountain-valley circulations? Although the altitude of SDZ is not that high, it is still located within the Yan mountains, therefore must be also subjected to mountain-plain circulations.
3. P3 L73-82: What scientific findings did previous measurements at high altitude sites present? How did these high altitude measurements compare to those in nearby urban sites? What was still unexplained by these studies and needs to be further studied in this one?
4. P4 L115: Should be "by various land use types" instead of "varied".
5. P8 L210-227: Regional air pollution occurs typically throughout the entire North China Plain under favorable meteorological conditions. Typically, there is a appromimate cycle of 7 days in synoptic pattern variations, which might be mainly responsible for the observed "similarities" between observations at the two background sites.
6. P8 L228-229: What are the possible influences of micriobial soil activities on NH3 at WTM and SDZ?Â
7. What kind of data were used in the CCM analysis? Daily averages? How are intercorrelations among meteorological factors considered within this methodology (e.g.: intercorrelation between RH，T and P)
8. L274: "NH3 intensity emission regions" should be revised as "intense NH3 emission regions"
9. P11, L285: NCP is a region and cannot act like a potential emission "hotspot"
10. P15, L342: Might this be because cold and shallow wintertime BLH might trap pollutants over the plain region, preventing it from reaching SDZ? While during the other seasons the BLH was high enough for pollutants to mix up to the height of SDZ, under such context higher BLH would only result in more dilution and lower pollution levels.
11. P15 L353: There seems to be two sources influencing NH3 at the WTM site, one that is closer to the site, that influences the WTM earliear during the day and another later peak seems to be similar to that of SDZ, possibly more linked to moutain-plain circulation induced transport from the plain region. How do wind speed and wind directions vary diurnally at WTM and SDZ during distinct seasons?
12. P17 L 398-399 grammar issue.
13. While the case studies help understanding the role of topography and transport, the authors should fully exploit their long-term data and answer some critical questions such as: how does the regional background concentration vary with season, how does urban emissions add to the NH3 burden over the NCP, how much influence do agricultural emissions contribute during distinct seaons? How frequent are morning peaks and how often are they linked to dew emissions?Â
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