| China is affected by severe air pollution with increasing air pollutants emission and activity sectors due to rapid economic growth and urbanization.Numerous studies have investigated air pollution in economic developed regions,such as North China Plain,the Yangtze River Delta and the Pearl River Delta,but the characteristics and sources of pollutants are not well understood in northwest China.Firstly,the air quality and pollution characteristics,including the differences in pollutants concentration caused by terrain and synergy among pollutants,were analyzed in Shaanxi,a major province in northwest China.Secondly,a high-resolution pollutant inventory and its projections were built for the coal-fired power plants in Shaanxi,which could help to acknowledge the pollutant emission in each city and provide insights into the method to build pollutant inventory for other sources.Thirdly,source-oriented versions of Community Multi-scale Air Quality(CMAQ)was conducted to study the biogenic source contribution to secondary organic aerosol(SOA)in summertime and the anthropogenic sources contribution to primary and secondary fine particulate matter(PM2.5)in wintertime in Shaanxi.The results are as follows:(1)Based on real-time hourly ambient monitoring of PM2.5,inhalable particulate matter(PM10),CO,SO2,NO2,and O3 in the ten cities in 2015.Shaanxi cities were affected by severe air pollution and CAAQS Grade II was exceeded on 16–28%days.PM2.5 and PM10 were the dominant pollutants in all cities,and their annual concentrations exceeded the Grade II standards by 9.4–68.6%and 6.0–73.9%,respectively.PM2.5,PM10,CO,SO2,and NO2concentrations had similar seasonal trends with highest values in winter and lowest values in summer,whereas O3 concentrations exhibited the opposite trend.Cities in Guanzhong Plain had higher PM2.5,PM10,NO2,and SO2 concentrations but lower CO,1–hour peak O3,and8–hour peak O3(8h–O3)compared to other regions.PM2.5,PM10,and 8h–O3 were the three main dominant pollutants.The nonattainment rate was highest in winter(30-60%)and lowest in summer or autumn(<10%).Pollution also exhibited synergy,especially in the North region and Guanzhong Plain.PM2.5 was significantly correlated with PM10.NO2 and SO2were positively correlated with PM2.5 and PM10,while 8h–O3 generally had significant negative correlations with other pollutants,especially in the winter.(2)A high-resolution inventory of primary atmospheric pollutants,including SO2,NOx,PM2.5,PM10,organic carbon(OC),elemental carbon(EC),carbon mo NOxide(CO)and non-methane volatile organic compounds(NMVOCs)from coal-fired power plants in Shaanxi in 2012 was built based on a detailed database compiled at unit level of 72 power plants.The estimated annual emissions of SO2,NOx,PM2.5,PM10,EC,OC,CO and NMVOCs were 152.4,314.8,16.6,26.4,0.07,0.27,64.9 and 2.5 kt,respectively.Small units(<100 MW),which accounted for?60%of total unit numbers,had less coal consumption but higher emission rates compared to medium and large units.Main factors affecting SO2,NOx,PM2.5 and PM10emissions were decontamination efficiency,sulfur content and ash content of coal.Weinan and Xianyang were the two cities with the highest emissions,while Guanzhong plain had the largest emission density.Despite the projected growth of coal consumption,emissions would decrease in 2030 due to improvement in emission control technologies and combustion efficiencies.SO2and NOx emissions would experience significant reduction of?81%and?84%,respectively.PM2.5,PM10,EC and OC would all decrease by?43%and both CO and NMVOCs would reduce by?16%.(3)The emissions of biogenic volatile organic compounds(BVOCs)were simulated using MEGAN(Model of Emissions of Gases and Aerosols from Nature)in Shaanxi in summertime.A revised CMAQ model with updated SOA yields and a more detailed description of SOA formation from isoprene oxidation was applied to study the spatial distribution of SOA and its precursors BVOCs in Shaanxi in July of 2013.Emissions of isoprene and monoterpene mostly emitted by forest were two highest with 1.73×109and1.82×108 mol in Shaanxi,respectively.Diurnal variation of BVOCs emissions had the similar trend of inverted‘U'shape.The emission distribution was significantly correlated with the vegetation coverage distribution in Shaanxi,i.e.highest around Qinlin and Qinba Mountains,and lowest in Loess Plateau region,especially in Yulin.VOCs from biogenic sources in the ambient were mainly ISOP and their semi-volatile compounds,and highest concentration were about 7.0,1.0 and 1.4 ppb,respectively,indicating that ISOP has the highest potential contribution to SOA.Besides,HCHO from biogenic sources contributed?3 ppb in the South region.Predicted SOA was generally 2–6?g/m3,and biogenic SOA(BSOA)accounted for approximately 75%of total SOA.The Guanzhong Plain had the highest BSOA concentrations of 3-5?g/m3,and the North region had the lowest with 2-3?g/m3.More than half of the BSOA was mainly due to reactive surface uptake of isoprene epoxide(0.2-0.7?g/m3),glyoxal(GLY)(0.2–0.5?g/m3)and methylglyoxal(MGLY)(0.4–1.4?g/m3),while the remaining was due to the traditional equilibrium partitioning of semivolatile components(0.1-1.2?g/m3)and oligomerization(0.2-0.4?g/m3).Overall,BSOA was mainly contributed by isoprene with province average about 60%(1-3?g/m3),of which GLY+MGLY was made up?50%.Contributions of monoterpene BSOA was relatively constant(6–14%).(4)Extremely high PM2.5 concentrations prevailed many parts of China in January 2013,including Guanzhong Plain.The source-oriented versions of CMAQ were used to study the source contributions to primary and secondary inorganic PM2.5(nitrate and sulfate components)during this severe wintertime PM2.5 pollution episode with a high spatial resolution of 4km.Concentrations of major components of EC,organic aerosol(OA),sulfate,nitrate and ammonium were 3.6,11.8,7.2,9.4 and 5.1?g/m3 in the north region,and they were 5.3,46.1,12.4,18.7 and 10.0?g/m3 in the Guanzhong Plain and they were 5.2,18.4,10.9,12.5 and 9.6?g/m3 in the south region,respectively.In Guanzhong Plain,industrial and residential activities combined are the dominating sources for EC,primary organic aerosol(POA),and other primary PM2.5 components(PM2.5 Other),contributing 85%,95%and 83%,respectively.Energy production industries(mainly coal combustion)are the dominating source for secondary nitrate,contributing 46%,and other local sources and upwind sources are also important,contributing 43%and 11%of total nitrate,respectively.Secondary sulfate formed by SO2 emitted from local sources was dominated by energy production.The contributions of different sources to PM2.5 total mass in Xi'an during the extremely polluted period are:energy 5%,industries 58%,transportation 2%,residential activities 16%,dust 4%,and other sources(including other components,inexplicit sources,and upwind sources)15%?... |
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