Abstract
AbstractAtmospheric NH3 plays a vital role not only in the environmental ecosystem but also in atmosphere chemistry. To further understand the effects of NH3 on the formation of haze pollution in Beijing, ambient NH3 and related species were measured and simulated at high resolutions during the wintertime Air Pollution and Human Health‐Beijing (APHH‐Beijing) campaign in 2016. We found that the total NHx (gaseous NH3+particle NH4+) was mostly in excess of the SO42−‐NO3−‐NH4+‐water equilibrium system during our campaign. This NHx excess made medium aerosol acidity, with the median pH value being 3.6 and 4.5 for polluted and nonpolluted conditions, respectively, and enhanced the formation of particle phase nitrate. Our analysis suggests that NH4NO3 is the most important factor driving the increasing of aerosol water content with NO3− controlling the prior pollution stage and NH4+ the most polluted stage. Increased formation of NH4NO3 under excess NHx, especially during the nighttime, may trigger the decreasing of aerosol deliquescence relative humidity even down to less than 50% and hence lead to hygroscopic growth even under RH conditions lower than 50% and the wet aerosol particles become better medium for rapid heterogeneous reactions. A further increase of RH promotes the positive feedback “aerosol water content‐heterogeneous reactions” and ultimately leads to the formation of severe haze. Modeling results by Nested Air Quality Prediction Monitor System (NAQPMS) show the control of 20% NH3 emission may affect 5–11% of particulate matter PM2.5 formation under current emissions conditions in the North China Plain.
Highlights
Ammonia (NH3) is an alkaline gas that plays a very important role in the atmosphere
Our analysis suggests that NH4NO3 is the most important factor driving the increasing of aerosol water content with NO3− controlling the prior pollution stage and NH4+ the most polluted stage
The APHH‐Beijing winter campaign was performed from 10 November to 10 December 2016 at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (39°58′28′′N, 116°22′16′′E), which is located between the north 3rd and 4th Ring Road in Beijing
Summary
Ammonia (NH3) is an alkaline gas that plays a very important role in the atmosphere. It may react with acidic species such as sulfuric and nitric acids to form ammonium salts (Walker et al, 2004), which are the major inorganic components of fine particles and contribute to regional haze (Cao et al, 2009; Fu et al, 2017; Meng et al, 2018). Warner et al (2017) reported an increased trend of NH3 vertical column density over agricultural regions across China (2.3%/year) based on satellite observation between 2002 and 2013. Warner et al (2017) reported an increased trend of NH3 vertical column density over agricultural regions across China (2.3%/year) based on satellite observation between 2002 and 2013. Fu et al (2017) found an obvious increase of NH3 vertical column density in recent years (from 2011 to 2014) over magecity clusters of the North China Plain
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