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 (Mountain Wutai, WTM) in northern China, using high-resolution and real-time measurement data spanning a full annual cycle. It also compared a regional background site (Shangdianzi, SDZ) with an urban site (Beijing Meteorological Service, 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 primary 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.