10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Contributions of the N2O5 Heterogeneous Hydrolysis Reaction to the Nitrate Formation in the North China Plain (NCP) During Wintertime: A Case Study
LANG LIU, Guohui Li, Institute of Earth Environment, Chinese Academy of Sciences
Abstract Number: 214 Working Group: Air Quality in Megacities: from Sources to Control
Abstract Although stringent emission mitigation strategies have been implemented in China since 2013 to improve the air quality, heavy haze with high levels of fine particulate matters (PM2.5) still frequently engulfs the North China Plain (NCP), China. Observations show that the nitrate aerosol has played an increasingly important role in the heave haze formation, constituting a major component of PM2.5. The N2O5 heterogeneous hydrolysis reaction is the most important pathway of the nitrate formation during nighttime or even dominates the nitrate formation during heavy haze episodes with weak sunlight and high humidity. The reaction is dependent on temperature, relative humidity, and aerosol constituents, including sulfate and organic matters. In the present study, the WRF-CHEM model is applied to quantify the contribution of the N2O5 heterogeneous hydrolysis reaction to the nitrate formation and investigate the effect of organic coating on the hydrolysis reaction during persistent haze pollution episodes from 10 to 27 February 2014 in NCP. The WRF-CHEM model generally performs well in simulating the temporal variations and spatial distributions of air pollutants concentrations against observations at ambient monitoring sites in NCP. The simulated diurnal variations of inorganic aerosol species are also well consistent with the measurements in Beijing. Simulations show that on average during the episodes, the nitrate aerosol contributes around 25% of PM2.5 mass concentrations in NCP. The N2O5 heterogeneous hydrolysis reaction accounts for about 34% of nitrate concentrations, playing an important role in the nitrate formation and contributing appreciably to PM2.5 mass concentrations. The organic coating effect on the N2O5 hydrolysis reaction considerably suppresses the nitrate formation, reducing the nitrate concentration by more than 10% during heavy haze days and also improving the nitrate simulation against the measurement. Our results highlight the importance of the nitrate aerosol to the heavy haze formation in NCP and the N2O5 heterogeneous hydrolysis reaction to the nitrate formation. Further studies need also to been conducted to evaluate the organic coating effect on the nitrate formation.