Heterogeneous nitrate production mechanisms in intense haze events

Abstract

The importance of heterogeneous (multi-phase) reactions between trace gases and particulates in controlling the tropospheric chemistry of reactive nitrogen oxides and driving the production of nitrate has long been recognized. However, less is known about how different chemical mechanisms contribute to nitrate production in intense haze events. I analyze the wintertime observations of reactive nitrogen oxides and isotopic composition of nitrate in Beijing, China, where intense haze events frequently occurred in the first two decades of the 21st century. The observation data are compared to predictions from the GEOS-Chem 3-D chemical transport model. The analysis shows that the mechanism that involves N2O5 most likely dominates nitrate production in wintertime Beijing, while the mechanism that involves NO2 is a major source of uncertainty in the model. I conduct a critical review of previous laboratory studies of NO2 uptake on different surfaces and explain the origins of the model uncertainty.