Tracking ammonia morning peak, sources and transport with 1 Hz measurements at a rural site in North China Plain

The North China Plain has been identified as a global hotspot for ammonia (NH3). To date, NH3 surface observations in the region have mostly been obtained by passive samplers with a time resolution of weeks (e.g., AMoN-China), and few studies have been performed with fast-response instruments. Thus, the detailed temporal variations of NH3 concentrations are still unclear in the region. From December 2017 to February 2018, NH3 concentrations were observed at a high-temporal resolution of 1 Hz by using the Picarro online instrument at the Xianghe, a rural site between the megacities of Beijing and Tianjin. During the campaign, the hourly NH3 concentrations ranged from 0.8 to 483.3 ppb, with an overall mean of 16.7 ± 19.7 ppb, which was considerably higher than those reported at other sites. In addition, the diurnal profile showed a notable increase of NH3 concentrations in the morning, which was likely due to dew evaporation. While the monthly difference of NH3 concentrations in winter was most likely driven by temperature, the elevated biomass burning may have also a considerable effect. The presented observations could provide insights into the dynamic characteristics of NH3 during haze pollution and provide a unique dataset to validate atmospheric chemistry and transport models at high-temporal resolutions.