English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

Extreme haze events have occurred frequently over China in recent years.Although many studies have investigated the formation mechanisms associatedwith PM2.5 for heavily polluted regions in China based on observationaldata, adequately predicting peak PM2.5 concentrations is stillchallenging for regional air quality models. In this study, we evaluate theperformance of one configuration of the Weather Research and Forecastingmodel coupled with chemistry (WRF-Chem) and use the model to investigate thesensitivity of heterogeneous reactions on simulated peak sulfate, nitrate,and ammonium concentrations in the vicinity of Beijing during four extremehaze episodes in October 2014 over the North China Plain. The highestobserved PM2.5 concentration of 469 µg m−3 occurred inBeijing. Comparisons with observations show that the model reproduced thetemporal variability in PM2.5 with the highest PM2.5 values onpolluted days (defined as days in which observed PM2.5 is greater than75 µg m−3), but predictions of sulfate, nitrate, and ammoniumwere too low on days with the highest observed concentrations. Observationaldata indicate that the sulfur/nitric oxidation rates are strongly correlatedwith relative humidity during periods of peak PM2.5; however, the modelfailed to reproduce the highest PM2.5 concentrations due to missingheterogeneous/aqueous reactions. As the parameterizations of thoseheterogeneous reactions are not well established yet, estimates ofSO2-to-H2SO4 and NO2/NO3-to-HNO3 reaction ratesthat depend on relative humidity were applied, which improved the simulationof sulfate, nitrate, and ammonium enhancement on polluted days in terms ofboth concentrations and partitioning among those species. Sensitivitysimulations showed that the extremely high heterogeneous reaction rates andalso higher emission rates than those reported in the emission inventory werelikely important factors contributing to those peak PM2.5concentrations

Simulations of sulfate–nitrate–ammonium (SNA) aerosols during the extreme haze events over northern China in October 2014