Characteristics of inorganic aerosol formation over ammonia-poor and ammonia-rich areas in the Pearl River Delta region, China. (March 2018)

• Record Type: Journal Article
• Authors: Yin, Shasha; Huang, Zhijiong; Zheng, Junyu; Huang, Xiaobo; Chen, Duohong; Tan, Haobo
• Is Part Of: Atmospheric environment. Volume 177(2018)
• Page Start: 120
• Page End: 131
• Publication Date: 2018-03
• Subjects: Secondary inorganic aerosol -- Ammonia -- Nitrate -- Adjusted gas ratio -- Emission control; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2018.01.005
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: A well-evaluated Comprehensive Air quality Model with extensions (CAMx) was used to simulate concentrations of secondary inorganic aerosols in fine particulate matter (PM2.5 ) over Pearl River Delta (PRD) region during two separate months (April and October) in 2013. An indicator of adjusted gas ratio (AdjGR) was used to characterize PM chemistry under both NH3 -poor (NP) and NH3 -rich (NR) conditions as well as to identify their respective spatiotemporal patterns at different PM2.5 levels. The results were as follows: (1) Based on both observed molar ratio of [NH4 + ]/[SO4 2− ] and modeled AdjGR, NR and NP conditions exhibited diurnal, daily, and seasonal variations. (2) A larger area in PRD had NP conditions over the two months when pollution was apparent; this NP region tended to occur downwind of PRD in October and the central region of PRD in April, with high PM2.5 concentrations in both. (3) This wider NP distribution could be related to higher nitrogen oxidation ratio (NOR), with more NOx converting to nitrate. Under conditions of higher pollution, there were relative lower degree of sulfate neutralization (DSN) and particle neutralization ratio (PNR). This supports the claim that NH3 may not be fully neutralized by SO4 2− . (4) Modeled AdjGR displayed clear hourly variations, with the lowest levels occurring in the afternoon. Reducing NH3 emission is not as efficient as NOx at increasing evening nitrate concentrations. (5) To mitigate PM2.5 pollution even further, a greater reduction of NH3 should be suggested in chemical regions transiting to NR condition when there are lower SO2 and NOx emissions. Highlights: Seasonal, diurnal, and episodic chemical aerosol condition of NH3 -rich or NH3 -poor are characterized. NH3 -poor region tends to occur at downwind area of PRD in October and central PRD in April. Increased NOR in PM episode affects the shift of free ammonia regime. Indicator of AdjGR has clearly hourly variations along with PM2.5 levels.