Abstract
Abstract. The winter haze is a growing problem in North China, but the causes are not well understood. The chemistry version of the Weather Research and Forecasting model (WRF-Chem) was applied in North China to examine how PM2.5 concentrations change in response to changes in emissions (sulfur dioxide (SO2), black carbon (BC), organic carbon (OC), ammonia (NH3), and nitrogen oxides (NOx)), as well as meteorology (temperature, relative humidity (RH), and wind speeds) changes in winter. From 1960 to 2010, the dramatic changes in emissions lead to +260 % increases in sulfate, +320 % increases in nitrate, +300 % increases in ammonium, +160 % increases in BC, and +50 % increases in OC. The responses of PM2.5 to individual emission species indicate that the simultaneous increases in SO2, NH3, and NOx emissions dominated the increases in PM2.5 concentrations. PM2.5 shows more notable increases in response to changes in SO2 and NH3 as compared to increases in response to changes in NOx emissions. In addition, OC also accounts for a large fraction in PM2.5 changes. These results provide some implications for haze pollution control. The responses of PM2.5 concentrations to temperature increases are dominated by changes in wind fields and mixing heights. PM2.5 shows relatively smaller changes in response to temperature increases and RH decreases compared to changes in response to changes in wind speed and aerosol feedbacks. From 1960 to 2010, aerosol feedbacks have been significantly enhanced due to higher aerosol loadings. The discussions in this study indicate that dramatic changes in emissions are the main cause of increasing haze events in North China, and long-term trends in atmospheric circulations may be another important cause since PM2.5 is shown to be substantially affected by wind speed and aerosol feedbacks. More studies are necessary to get a better understanding of the aerosol–circulation interactions.
Highlights
PM2.5 is a main air pollution concern due to its adverse effects on public health (Gao et al, 2015; Pope et al, 2009). Pope et al (2009) estimated that a decrease of 10 μg PM2.5 is related to about 0.6-year mean life expectancy increase
The main objective of this study is to investigate the responses of PM2.5 and its major species to changes in emissions, including SO2, black carbon (BC), organic carbon (OC), NOx, and NH3, and temperature, relative humidity (RH), and wind speed in North China region
A fully online-coupled meteorological and chemical transport model, WRF-Chem was used to study responses of winter PM2.5 concentrations to changes in emissions of SO2, BC, OC, NH3, and NOx and to meteorology changes in North China region, where people suffer due to severe winter haze pollution
Summary
PM2.5 (particulate matter with diameter equal to or less than 2.5 μm) is a main air pollution concern due to its adverse effects on public health (Gao et al, 2015; Pope et al, 2009). Pope et al (2009) estimated that a decrease of 10 μg PM2.5 is related to about 0.6-year mean life expectancy increase. PM2.5 (particulate matter with diameter equal to or less than 2.5 μm) is a main air pollution concern due to its adverse effects on public health (Gao et al, 2015; Pope et al, 2009). Pope et al (2009) estimated that a decrease of 10 μg PM2.5 is related to about 0.6-year mean life expectancy increase. PM2.5 is associated with visibility reduction and regional climate (Cheung et al, 2005). Many cities in North China are experiencing severe haze pollution with exceedingly high PM2.5 concentrations. In January 2010, a regional haze occurred in North China and maximum hourly PM2.5 concentration in Tianjin was over 400 μg m−3 (Zhao et al, 2013). In January 2013, another unprecedented haze event happened, and the daily PM2.5 concentrations in some areas of Beijing and Shijiazhuang reached over 500 μg m−3
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