A Multi-scenario Simulation Based Framework Development Of Air Pollution Control Strategies And Its Efficacy Evaluation

In recent years,the atmospheric compound pollution characteristics in China were severe.Haze and ozone pollution occurred frequently,which had threaten the public health and environmental safety.Under the severe air pollution situation,how to put forward feasible control strategies and improve the air quality have become one of the major challenges for the cities.Besides,although governments at all levels have issued a series of air pollution control measures,and air quality has been improved.However,what is the real effect of these measures,and how to perform quantitative evaluation have been emergent tasks to study.In view of this,this paper studied the the methodology system of atmospheric pollution control strategy and its efficacy evaluation,which can provide practical support for air quality improvement,and have important scientific value and real significance.The atmospheric compound pollution in Sichuan province were also severe with complex emission sources and unique meteorological conditions.There were typical representation for taking the Sichuan province as a case study.Therefore,the thesis developed a multi-scenario simulation based framework of air pollution control strategies and its efficacy evaluation for Sichuan province,using a common emission-meteorology-air quality coupled modelling system with the local emissions and meteorology conditions.The followings are the key results and findings:（1）Due to the different pollutant emissions and the changes of weather conditions,air pollution characteristics in different areas or cities will certainly be in vary.This thesis established a framework of air pollution control strategies and its efficacy evaluation based on multi-scenario simulations.The framework consisted of air quality analysis,emission inventory development and spatial-temporally allocation,meteorological condition analysis and simulation,air quality modeling system,control strategies development based on multi-scenario simulation,and efficacy evaluation based on simulation and actual measured data.（2）The PM_2.5pollution is the major problem for the atmospheric environment in Sichuan province.Though annual concentration of PM_2.5has been decreased in recent years,air quality improvement in Autumn and winter were relatively limited.The annual concentration of PM_2.5in each region decreased by 8%-19%in the year of 2015-2017,while increased by 10%-22%in December.Meanwhile,about 15cities in Sichuan failed to meet the PM_2.5national standards,and PM_2.5had the maximum frequency as the primary pollutant.In addition,particulate matter pollution had higher spatial agglomeration than other gaseous pollutants,and high PM_2.5concentration were mainly located in the South Sichuan area and Chengdu Plain area.The regional air pollution characteristics suggested that joint control and prevention measures should be implemented to relieve the PM_2.5pollution.（3）Emission inventory of Sichuan province were developed with five-level source classification,in order to meet the requirements of air pollution control strategies.The results showed that stationary combustion sources,industry processes,on-road mobile sources,off-road mobile sources,fugitive dust sources,solvent utilization and agricultural sources were the major emission sources.The source contribution for each pollutant was different.Taking the year of 2017 as an example,PM_2.5emissions were mainly from industry processes（45%）and fugitive dust sources（29%）,while PM₁₀emissions came from fugitive dust source（52%）.NOx emissions came from on-road mobile sources（36%）and off-road mobile sources（24%）.VOCs emissions were mainly from solvent utilization（35%）and on-road mobile sources（27%）.SO₂emissions were mainly from industrial sources,and NH₃came from agricultural sources.Pollutant emissions were mainly concentrated on the area of Chengdu plain and South Sichuan.Additionally,the source contributions characteristics in different regions were different.The mobile sources emissions in Chengdu Plain were relatively high,while that in South Sichuan were dominated by industrial emissions.Besides,the domestic combustion and biomass burning had important emission contributions in the Northeast Sichuan.Source-specific temporal and spatial surrogates were adopted to prepared model-ready emission inventories for air quality modelling system.The spatial-temporal characteristics of emission inventory were also identified in this research.In addition,the emission reduction potential for each emission source were analyzed in order to support the design of emission control scenarios.（4）The regional meteorological characteristics and the relation with air quality were investigated using historical meteorological data,which can provide basis for meteorological scenarios design.The results showed that the ground wind speed in Sichuan Basin was relatively small.The annual wind speed for each city in the year of 2015-2017 were between 0.92-1.89 m/s,and the frequency of calm wind was high,approximately 39.9%-85.9%.The water vapor conditions inside basin were sufficient.The monthly average rainfall reached 47.93-117.00 mm,and the relative humidity were approximately 69.78%-81.85%.The meteorological conditions in South Sichuan were particularly unfavorable.Annual wind speed in South Sichuan was approximately 1.39 m/s,and total annual rainfall was approximately 865.60 mm,both of which were lower than other regions.Also,annual relative humidity in South Sichuan reached 80.4%,and was higher than other regions.Additionally,meteorological simulation results suggested that there was a gas flow vortex in South Sichuan,resulting in the gathering of pollutants here.The weather conditions in autumn and winter were poor,such as that the wind speed and rainfall were lower than other seasons,while the calm wind frequency and relative humidity were higher than others.The meteorological conditions had important impact on air pollution.For example,wind speed,rainfall and temperature in non-attainment days were significantly lower than that in days with clean air.Besides,PM_2.5concentration was much easily to exceed the standard when the wind speed was low and the relative humidity was high in winter.In sum,the frequency of PM_2.5pollution can reach more than 30%,when the following weather conditions were met:the wind speed was less than 1.35 m/s,the temperature was between 5.75-11.75°C,the relative humidity was between 72%-90%,and without visible rainfall.The land use and terrain elevation data were updated in the WRF model.Meanwhile the model parameterization schemes were also screened.With a comparison of modelling results before and after optimization,the correlation coefficient between simulated data and monitoring data for the air pressure,relative humidity and wind speed were increased by 0.06,0.15 and 0.09,respectively,and can provide a more reliable meteorological simulation input for the air quality model.（5）With the use of WRF-SMOKE-MEGAN-CMAQ air quality modelling system,the air quality improvement database under different emission reductions and meteorological conditions were developed in this study and can support the formulation of emission reduction scheme aimed to different control targets.The simulation results of emission scenarios showed that emission reductions can significantly reduce the concentration of pollutants with the unchanged weather conditions.However,due to the regional differences,the required emission reduction for each city were also different.Take the reaching of basic goal in 2020 for example,the city of Zigong,Mianyang and Yibin had the highest reduction pressure,SO₂,NO_Xand PM emissions should be reduced by 60%,40%,40%or more.While the city of Ziyang,Suining,Guangan and Nanchong did not need to reduce emission and then reached the set goal.However,the decline rates of PM_2.5concentration were below 25%for most cities,and that in Southern Sichuan were below 20%under the present emission reduction scenarios,which were insufficient for the target of national Grade II standard.Thus,the control strategies should be optimized according to the actual emission characteristics and reduction potential.On the basis of the original control scenario,VOCs and NH₃emissions reduction should be added,and the control of off-road mobile sources,domestic combustion and catering sources should be enhanced.Taking the city of Leshan as an example,when the emission reduction rates reaching approximately 23%-58%,the declining rate of PM_2.5concentration increased approximately 11%comparing with original control,and the predicted PM_2.5concentration was approximately 34.3μg/m³.The simulation results of meteorology scenarios suggested that the deterioration of meteorological conditions had an important contribution to the increase of pollutant concentrations when the emissions were stable.Weather conditions in December were the worst throughout the year of 2017.The simulated PM_2.5concentration in December inside basin was approximately 1.19 times of that in November when the emissions were equal.Meteorological changes in short term had more significant influence on the air quality.The average PM_2.5concentrations in December 22th-28th was 1.38 times of that in November 3rd-9th with the fixed emissions.Meanwhile,if the weather conditions were unfavorable,more emission reduction were required under the same air quality target.According to the simulation results,when equivalent to the basic goal in 2020,cities under the weather conditions of December need more than 15%of the emission reduction compared with the weather conditions in November.Generally,the air pollution control strategies should be developed on the basis of actual emission characteristics for each region,and the coordinated control of multi-pollutants and multi-emission sources must be implemented to achieve the concentration goal for PM_2.5.In addition,special weather conditions such as poor weather diffusion in winter,were needed to be taken into account.（6）Due to the uncertainties in the emission inventory and meteorological simulation,the efficacy evaluations of control measures should be carried out with the model simulation and actual monitoring data.This thesis took the Environmental Protection Inspection in the year of 2017 as an example to evaluate the efficacy of relevant control measures in Chengdu Plain.The research found that the air quality improved significantly during the inspection period,and the average concentration of PM_2.5decreased by 37%-66%compared with the year of 2016.The simulation results showed that the contributions of emission reductions to the decreased of PM_2.5concentration were estimated to be approximately 24%-40%,and the contributions of meteorological changes to PM_2.5improvement were approximately 11%-22%.When combined the monitoring air quality data analysis and the model simulation results,some interesting findings can be concluded.For example,if pollution reduction measures were not implemented,the PM_2.5concentration will increase by 27%-127%compared with the actual values.In addition,the actual PM_2.5concentration declining rates for cities were larger than the simulated sum of emission reductions contribution and meteorological contribution,except for Deyang and Mianyang.The results suggested that the real control effect in the inspection period for most of cities were better than expected,and the related measures were effectively executed.Generally,air quality improvement during the inspection period were dominated by emission reduction.Emissions control measures can effectively reduce PM_2.5concentration.Moreover,the improved meteorological conditions further increase the declining rate of PM_2.5.In summary,with the use of air pollution characteristics analysis,emission inventory,meteorology simulation,air quality modelling and scenario analysis,a multi-scenario simulation based framework of air pollution control strategies and its efficacy evaluation were developed in this thesis.The research results can improve the pertinence and effectiveness of the pollution emission reduction plan,and can be an important reference for the efficacy evaluation of control measures.