Post-evaluation Of PM_2.5 Improvements From Local Control Measures In A City

A series of control measures released in recent years had mitigated the air pollution in China.Assessing the effectiveness of control measures and identifying the key measures are beneficial to guide future control measure development.Previous control measures assessment studies,most of them applied observations,statistical model,sensitivity analysis and numerical model simulations,typically focused on the national or regional scale other than the city scale.Unlike the national or regional scale,city air quality is largely affected by the regional and even super-regional transportation,making the traditional control measure assessment methods are less reliable.Therefore,in this study,we developed a city-based control measure assessment method using source apportionment technique and sensitivity analysis.A case study in Zhaoqing city,located in the PRD region,was used to demonstrate the feasibility of the proposed method.According to the study of emission reductions of SO₂,NO_X,PM₁₀,PM_2.5,VOCs and NH₃driven by the local control measures implemented in Zhaoqing during 2014–2016 were25.3%,10.5%,13.1%,14.2%,4.2%and 9.1%,respectively.Most of these emission reductions came from combustion sources(NOx,SO₂,PM_2.5,and PM₁₀),dust sources(PM_2.5 and PM₁₀),on-road mobile sources（NOx and VOCs）,biomass combustion sources(PM_2.5,PM₁₀,and VOCs)and agriculture sources（NH₃）.However,the control-driven emission reductions in Zhaoqing were crippled by the rapid growth of industrial activities and vehicle populations.Therefore,compared with 2014,Zhaoqing’s emission in 2016 decreased by 18.8%for SO₂,0.2%for PM₁₀,6.5%for PM_2.5 and 1.5%for NH₃.NO_X and VOCs emissions even increased by 1.5%and 2.9%,respectively.We assessed the air quality benefits of local control measures using numerical simulations.In January 2016,the ambient PM_2.5 level in Zhaoqing dropped by-74.4μg/m³compared with the same period in 2014.48.8%of the PM_2.5 level decrease was associated with the change of regional transport and 51.2%comes from the changes in local emission and meteorological condition.In fact,emission reduction driven by the local control measures brought 1.88μg/m³ PM_2.5 concentration decreases,but nearly 50%of the benefits were covered by the activity level rises.Among all the local control measures during 2014-2016,setting the no-burn zone and upgrading coal-burned quality,delimiting incineration zones,removing highly polluted fuel boilers,and reforming desulfurization and denitrification of cement plants were the key control measures,which contributed 45.2%,14.7%,12.0%and 9.4%respectively to the total PM_2.5 concentration decreases（1.88μg/m³）.The post-evaluation method proposed in this study can identify the most effective control measures and thus is beneficial to guiding the government policy-making.Also,this method can be adopted in other cities in China.