Formation, radiative forcing, and climatic effects of severe regional haze

Abstract. Severe regional haze events, which are characterized by exceedingly high levels of fine particulate matter (PM), occur frequently in many developing countries (such as China and India), with profound implications for human health, weather, climate. The occurrence the extremes involves a complex interplay between primary emissions, secondary formation, conducive meteorological conditions, relative contributions various processes remain unclear. Here we investigated severe episodes 2013 over Northern Plain (NCP), evaluating PM production interactions elevated planetary boundary layer (PBL). Analysis ground-based measurements satellite observations properties shows nearly synchronized temporal variations among three megacities (Beijing, Baoding, Shijiazhuang) this region coincidence aerosol optical depth (AOD) hotspots during polluted period. During clean-to-hazy transition, measured oxygenated organic concentration ([OOA]) well correlates odd-oxygen ([Ox]=[O3]+[NO2]), mean [OOA] / [Ox] ratio Beijing is much larger than those other Mexico City Houston), indicating highly efficient photochemical activity. Simulations using Weather Research Forecasting (WRF) model coupled an explicit radiative module reveal that strong aerosol–PBL interaction period results suppressed stabilized PBL humidity, triggering positive feedback to amplify severity at ground level. Model sensitivity study illustrates importance black carbon (BC) haze–PBL climatic effect, contributing more 30 % collapse about half forcing on top atmosphere. Overall, exhibits negative (cooling) ?63 ?88 W m?2 surface (warming) 57 82 atmosphere, slightly net ?6 Our work establishes synthetic view dominant features unraveling rapid situ inefficient transport, both amplified atmospheric stagnation. On hand, transport sufficiently disperses gaseous precursors (e.g., sulfur dioxide, nitrogen oxides, volatile compounds, ammonia) clean period, subsequently result via photochemistry transition multiphase chemistry findings highlight co-benefits reduction BC not only improve local air quality minimizing stagnation but also mitigate global warming alleviating direct forcing.