Development And Assessment Of The City-scale Emission Inventory Of Anthropogenic Air Pollutants

Emission inventory of air pollutants is an important basis for policy making of pollution abatement and key input of chemistry transport modeling for pollution mechanism study.Facing the big challenges of improving air quality in most cities in eastern China,there is strong need to develop and to evaluate the city-scale emission inventory,which can be better applied in the emission control and chemistry transport modeling.A high-resolution emission inventory of air pollutants and CO₂ for Nanjing,a typical city in Yangtze River Delta,is developed combining the best available information of local sources.The unit-/facility-based emission factors and activity level data are compiled through a thorough onsite survey on major emission sources.Totally 704 individual plants,which account for 97%of the city’s total coal consumption,are identified as point sources,and all the emission-related parameters including combustion technology,fuel quality,and removal efficiency of air pollution control devices（APCD）,are carefully investigated and analyzed.New data and approaches including CEMS（continuous emission monitoring systems）and real-time traffic flow monitoring are applied to improve spatiotemporal distribution of emissions.Based on the above work,an emission inventory of 10 air pollutants and CO₂ for Nanjing is established at the spatial resolution of 3×3km,from 2010 to 2012.In 2010,the emissions of SO₂,NO_x,CO,VOC（volatile organic compounds）,NH3,PM2.5,PM10,TSP（total suspended particulate）,BC（black carbon;or EC,elemental carbon）,OC（organic carbon）and CO₂ for Nanjing are estimated at 165,216,800,224,21.4,71,93,158,6.2,6.7 and 79975 kt（kiloton）,respectively.Even with a fast growth of energy consumption and output of industrial products between 2010 and 2012,relatively small inter-annual variability in emissions is found for most air pollutants,attributed mainly to increased APCD application and removal efficiencies.Large point sources dominate the levels and spatial distributions of the emissions.The ten largest point sources are estimated to account for 54%,43%,75%and 52%ofthe total SO₂,NO_x,PM2.5（excluding fugitive dust）and VOC emissions in Nanjing.The improvement of this city-level emission inventory is tested through comparisons with observation and other inventories at larger spatial level.The inter-annual variability and spatial distribution of NO_x emissions are evaluated and confirmed with the NO₂ vertical column density（VCD）measured by Ozone Monitoring Instrument（OMI）.In particular,the city-scale emission inventory correlates better with OMI observation than MEIC（Multi-resolution Emission Inventory for China）when the emissions from power plants are excluded.It thus confirms the improvement of current work on emission estimation for sectors other than power generation,e.g.,industry and transportation.Relatively good spatial correlations are found for SO₂,NO_x and CO between the city-scale emission estimates and concentrations at the 9 state-operated monitoring sites（R=0.58,0.46 and 0.61,respectively）."Top-down" constraints are developed based on the ground observation inNanjing and compared with "bottom-up" emission inventory to analyze the correlation between specific pollutants（including BC to CO,OC to EC,and CO₂ to CO）.Among them,the emission and observation ratio of BC to CO is 0.0097 and 0.0079,and that of OC to EC is 1.38 and 1.59,that of CO₂ to CO is 76.1 and 66.8,respectively.With it assessed by observation,the high-resolution emission inventory can also provide a perspective to rethink the quality of ground observation.In this study,"top-down" constraints from ground observation are used to analyze the improvement of city-scale emission inventory comparing with regional emission inventory.To further improve the emission eatimation and evaluation,more measurements on both emission factors and ambient levels for non-criterion pollutants are suggested.The uncertainty of emission inventory at city scale should also be fully quantified and compared with that at national level to further improve emission inventory study in China.