Formation, radiative forcing, and climatic effects of severe regional haze
- 1Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843, USA
- 2Joint Institute for Regional Earth System Science and Engineering (JIFRESSE), University of California at Los Angeles, Los Angeles, CA 90064, USA
- 3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- 4Department of Atmospheric Science, Colorado State University, Fort Collins, CO, 80521, USA
- 5Cooperative Institute for Mesoscale Meteorological Studies, NOAA/OAR National Severe Storms Laboratory, Norman, OK, USA
- 6State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 10087, P.R. China
- 7Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe St., Baltimore, MD 21205, USA
- 8Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, P. R. China
- 9Water Management & Hydrological Science, Texas A&M University, College Station, TX 77843, USA
- 10Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China
- 11Department of Chemistry, Texas A&M University, College Station, TX 77843, USA
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, and climate. The occurrence of the haze extremes involves a complex interplay between primary emissions, secondary formation, and conducive meteorological conditions, and the relative contributions of the various processes remains unclear. Here we investigated severe regional haze episodes in 2013 over the Northern China Plain (NCP), by evaluating the PM production and the interactions between elevated PM and the planetary boundary layer (PBL). Analysis of the ground-based measurements and satellite observations of PM properties shows nearly synchronized temporal PM variations among the three megacities (Beijing, Baoding, and Shijiazhuang) in this region and a coincidence of the aerosol optical depth (AOD) hotspots with the three megacities during the polluted period. During the clean-to-hazy transition, the measured oxygenated organic aerosol concentration ([OOA]) well correlates with the odd-oxygen concentration ([Ox] = [O3] + [NO2]), and the mean [OOA]/[Ox] ratio in Beijing is much larger than those in other megacities (such as Mexico City and Houston), indicating highly efficient photochemical activity. Simulations using the Weather Research and Forecasting (WRF) model coupled with an explicit aerosol radiative module reveal that strong aerosol-PBL interaction during the polluted period results in a suppressed and stabilized PBL and elevated humidity, triggering a positive feedback to amplify the haze severity at the ground level. Model sensitivity study illustrates the importance of black carbon (BC) in the haze-PBL interaction and the aerosol regional climatic effect, contributing to more than 30 % of the PBL collapse and about half of the positive radiative forcing on the top of the atmosphere. Overall, severe regional haze exhibits strong negative radiative forcing (cooling) of −63 to −88 W m−2 at the surface and strong positive radiative forcing (warming) of 57 to 82 W m−2 in the atmosphere, with a slightly negative net radiative forcing of about −6 W m−2 on the top of the atmosphere. Our work establishes a synthetic view for the dominant regional features during severe haze events, unraveling rapid in-situ PM production and inefficient transport, both of which are amplified by atmospheric stagnation. On the other hand, regional transport sufficiently disperses gaseous aerosol precursors (e.g., sulfur dioxide, nitrogen oxides, volatile organic compounds, and ammonia) during the clean period, which subsequently result in rapid in-situ PM production via photochemistry during the transition period and via multiphase chemistry during the polluted period. Our findings also highlight the co-benefits for reduction in BC emissions, which not only improve local and regional air quality by minimizing air stagnation, but also mitigate the global warming by alleviating the positive direct radiative forcing.
Yun Lin et al.
Yun Lin et al.
Yun Lin et al.
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