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The winter haze is a growing problem in North China, but the causes are not well understood. The chemistry version of the Weather Research andForecasting model (WRF-Chem) was applied in North China to examine howPM2.5 concentrations change in response to changes in emissions (sulfurdioxide (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 % increasesin OC. The responses of PM2.5 to individual emission species indicatethat the simultaneous increases in SO2, NH3, and NOx emissionsdominated the increases in PM2.5 concentrations. PM2.5 shows morenotable increases in response to changes in SO2 and NH3 as comparedto increases in response to changes in NOx emissions. In addition, OCalso accounts for a large fraction in PM2.5 changes. These resultsprovide some implications for haze pollution control. The responses ofPM2.5 concentrations to temperature increases are dominated by changesin wind fields and mixing heights. PM2.5 shows relatively smallerchanges in response to temperature increases and RH decreases compared tochanges in response to changes in wind speed and aerosol feedbacks. From 1960to 2010, aerosol feedbacks have been significantly enhanced due to higheraerosol loadings. The discussions in this study indicate that dramaticchanges in emissions are the main cause of increasing haze events in NorthChina, and long-term trends in atmospheric circulations may be anotherimportant cause since PM2.5 is shown to be substantially affected bywind speed and aerosol feedbacks. More studies are necessary to get a betterunderstanding of the aerosol–circulation interactions

Response of winter fine particulate matter concentrations to emission and meteorology changes in North China