Air Pollutants Emission Inventory For The Main Urban Area Of Tianshui City Based On Verification By WRF-Chem Simulation

Numerical simulation of ambient air quality is one of the effective methods to carry out ambient air quality forecasting,analyze the causes of regional air pollution,and conduct research on atmospheric environmental problems.Accurate simulation of spatial and temporal distribution characteristics of pollutants are the basis for scientific formulation of pollution prevention and control measures,and then improve regional air quality.Emission inventories,meteorological conditions,initial conditions,and chemical transformation processes all have important effects on air quality simulation,and the emission inventory of pollution sources is one of the main uncertainties of air quality models.The construction of local high-resolution emission source inventories is important to accurately characterize air pollutant emission information,identify key pollution sources,and thus improve the accuracy of air quality simulation.Tianshui city is located in southeastern Gansu,the middle reaches of Weihe River,bordering Shanxi in the east,and is an important city in the Guanzhong Plain city cluster.Tianshui city is susceptible to particulate pollution in winter due to local source emissions,external source transport and unfavorable dispersion conditions in the complex river valley topography.In this paper,we obtained the activity level data of air pollution sources in the main urban area of Tianshui City based on departmental research,field survey and remote sensing interpretation,estimated the emissions of 9 pollutants from 10 types of sources in the main urban area of Tianshui City using the emission factor method,constructed a high-resolution（1 km×1 km）emission inventory for the main urban area of Tianshui City in 2019,quantitatively analyzed the uncertainty of the key sources,and assessed the reasonableness of this emission inventory by the cross-sectional comparison method and model.The reasonableness of this emission inventory was evaluated by the cross-sectional comparison method and the model verification method.The article also developed emission reduction plans for industrial sources,mobile sources and dust sources in the main urban area under different warning levels during heavy pollution according to the requirements of the"Guidance on Strengthening Emergency Emission Reduction Measures in Response to Heavy Pollution Weather",and provided data support for the construction of the emergency emission reduction inventory for heavy pollution in Tianshui City in the later period.The main conclusions obtained are as follows:（1）Construction of emission inventory of air pollution sourcesThe emissions of SO₂,NOx,CO,VOCs,NH₃,PM₁₀,PM_2.5,BC and OC in the main urban area of Tianshui City in 2019 are 2702,8829,82670,10460,7551,14221,8252,1682 and 2814 tons,respectively.Fossil fuel stationary combustion sources are the main contributors of SO₂,CO and particulate matter,mobile sources are the main contributors of NOx and VOCs,and NH₃emissions are mainly from agricultural sources.Temporal characteristics of pollutant emissions show that high emission values of SO₂,CO,PM₁₀and PM_2.5occur mainly from November to March;high emission periods of NOx and VOCs occur in summer and winter,and high emission values of NH₃occur in May-June when agricultural activities are more frequent.daily emission peaks of SO₂,CO,VOCs and particulate matter occur at 7:00 a.m.and 17:00 p.m.NO_Xmaintains high emission intensity during all hours of the day,with peak values at9:00 a.m.and 17:00 p.m.The emission trend of NH₃shows a single-peak characteristic,with the highest emission time at about 12:00 noon.The spatial characteristics of pollutant emissions show that the high value areas of SO₂,NOx,particulate matter,CO and VOCs emissions in the main urban area of Tianshui City are mainly concentrated in the river valley terrain with high population density,dense road networks and concentrated workers,and the high value areas of NH₃emissions are distributed in the arable land areas around the river valley range.The spatial allocation scheme of civil scattering sources has an important influence on the simulation results,and it is reasonable to determine the spatial allocation scheme of civil scattering sources by dividing the main urban area into zones and then identifying the location of civil scattering sources in each small area outside the centralized heating range of the river valley terrain.（2）Verification of emission inventoryThe results of quantitative uncertainty analysis show that the uncertainties of NO_Xand VOC_Sof important sources in the main urban area of Tianshui City are high,among which the uncertainty ranges of NO_Xand VOC_Semission factors of road mobile sources are large,and it is necessary to carry out an empirical study on the emission factors of road mobile sources in the main urban area in the future to reduce the uncertainties of the inventory.The daily average concentrations of pollutants in the main urban area of Tianshui City simulated by the WRF-Chem model are more consistent with the distribution of pollutant concentrations monitored during the same period,and the correlation coefficients of six conventional pollutant concentrations are high（0.767,0.502,0.618,0.462,0.647,and 0.654）,indicating that the emission source inventory constructed in this study is reasonable and can be used as a management and ambient air quality management.（3）Construction of heavy pollution weather emergency emission reduction inventoryThe emission reduction amounts of particulate matter,SO₂,NO_X,and VOCs under the red warning are 10609,1174,8726,and 2741 kg/d,respectively;the total emission reduction amounts of four pollutants under the orange warning are 10609,1174,8650,and 2474 kg/d;the total emission reduction amounts of four pollutants under the yellow warning are 3598,1022,1403,and 766 kg/d,respectively 766 kg/d.