Gas-phase ammonia and PM2.5 ammonium in a busy traffic area of Nanjing, China

The gas-phase ammonia (NH3) and fine particle PM2.5 ammonium (pNH4+) (collectively, NHx) were monitored between July 2013 and August 2014 in a busy traffic area of Nanjing, China. Results showed that PM2.5 concentration was 66.7 μg m−3, and NH3 concentration was 6.66 μg m−3. In the PM2.5, the concentration of pNH4+ was 3.04 μg m−3, SO42− (pSO42−) was 10.16 μg m−3, and NO3− (pNO3−) was 1.60 μg m−3. The significant correlation curves from the tests of PM2.5 revealed that molar ratio of pNH4+ and pSO42− was approximately 2, which could be (NH4)2SO4. Particulate NH4+ primarily associated with pSO42−, which accounted for 4.54 % of total PM2.5 mass. The PM2.5 observed acidic and the NH3 in the atmosphere neutralized acidic species, mainly in a sulfate form. The traffic intensity in the region was partially related to the formation of PM2.5 and NH3, suggesting that traffic pollution may be an important source of PM2.5. The reaction between NHx and acidic species was assumed to the secondary PM2.5. The neutralization and photochemical property of NHx were discussed.