Heterogeneous chemistry: a mechanism missing in current models to explain secondary inorganic aerosol formation during the January 2013 haze episode in North China

摘要

Severe regional haze pollution events occurred in eastern and central Chinain January 2013, which had adverse effects on the environment and publichealth. Extremely high levels of particulate matter with aerodynamicdiameter of 2.5 μm or less (PM) with dominant components ofsulfate and nitrate are responsible for the haze pollution. Althoughheterogeneous chemistry is thought to play an important role in theproduction of sulfate and nitrate during haze episodes, few studies havecomprehensively evaluated the effect of heterogeneous chemistry on hazeformation in China by using the 3-D models due to of a lack of treatments forheterogeneous reactions in most climate and chemical transport models. Inthis work, the WRF-CMAQ model with newly added heterogeneous reactions isapplied to East Asia to evaluate the impacts of heterogeneous chemistry andthe meteorological anomaly during January 2013 on regional haze formation.As the parameterization of heterogeneous reactions on different types ofparticles is not well established yet, we arbitrarily selected the uptakecoefficients from reactions on dust particles and then conducted severalsensitivity runs to find the value that can best match observations. Therevised CMAQ with heterogeneous chemistry not only captures the magnitudeand temporal variation of sulfate and nitrate, but also reproduces theenhancement of relative contribution of sulfate and nitrate to PMmass from clean days to polluted haze days. These results indicate thesignificant role of heterogeneous chemistry in regional haze formation andimprove the understanding of the haze formation mechanisms during theJanuary 2013 episode.