The haze pollution that frequently occurred in winter in cities of North China has aroused widespread concern. Since the implementation of Air Pollution Prevention and Control Action Plan in 2013, the atmospheric concentration of acidic gases such as sulfur dioxide and nitrogen oxides have significantly decreased in this region. However, the concentration of ammonia gas (NH3) and inorganic ammonium (NH4+) salts such as ammonium sulfate and ammonium nitrate in atmospheric aerosol particles were still increasing.
Click here for original story, Vehicle exhaust emission and ammonia slip are the main sources of atmospheric ammonia and ammonium in North China cities
Source: Phys.org