基于前体物多情景排放的兰州市2030年夏季臭氧预测

Ozone Simulation of Lanzhou City Based on Multi-scenario Emission Forecast of Ozone Precursors in the Summer of 2030

近年来,兰州市夏季臭氧污染问题日渐凸显,已成为影响当地环境空气质量达标的首要污染因子和制约环境空气质量持续改善的突出短板.解决臭氧污染问题需结合城市经济发展的实际情况定量评估前体物减排量并提出切实可行的减排对策,为环境管理的中长期规划提供科学依据.在2015年本地排放清单的基础上,通过情景分析法预测了兰州市2030年3种梯度城市发展与污染控制情景下臭氧的两类主要前体物氮氧化物(NO_(x))和挥发性有机物(VOCs)的排放量,利用WRF-Chem模型对不同情景下的2030年夏季臭氧污染程度进行了数值模拟,分析了臭氧浓度与生成敏感性的时空变化情况,并提出了兰州市臭氧前体物的总量控制参考和针对不同行政区的减排对策建议.结果表明,3种不同的城市发展与污染控制情景下兰州市2030年NO_(x)排放量为4.57×10^(4)~12.14×10^(4) t,VOCs排放量为5.30×10^(4)~7.69×10^(4) t,NO_(x)排放可通过调整能源结构,加强末端治理和限制机动车排放等措施有效减少;减排VOCs则需从工业源、生活源和移动源多方面同时入手,做好长期治理攻坚的准备.模拟结果显示,兰州市夏季中心城区臭氧浓度高,臭氧生成主要受VOCs控制,郊区浓度略低,受NO_(x)控制.2030年若将兰州市NO_(x)和VOCs的排放量限制在6.25×10^(4) t和5.81×10^(4) t,夏季臭氧1 h平均浓度将全部低于国家二级标准,若限制在4.57×10^(4) t和5.30×10^(4) t,可进一步削减夏季日间臭氧浓度的9.1%,更利于中心城区的臭氧浓度削峰.兰州市目前阶段应着重减排中心城区的VOCs和郊区的NO_(x),同时关注臭氧生成敏感性变化,加强各行政区间的联防联控.

In recent years,summer ozone pollution in Lanzhou has become an increasingly prominent concern and a primary factor causing the air quality of the city to exceed the ambient air quality standard of China.To achieve the city's goal for improving the air quality in Lanzhou,well below the national standard,effective air quality mitigation measures for the next decade must be taken to quantify the reduction in ozone precursor emissions,which would provide scientific support for the long-term outline of local environmental management.Based on the 2015 emission levels issued by the local government,the emission amounts of major ozone precursors(NO_(x) and VOCs)were predicted,and ozone concentration levels subject to three urban development and pollution control scenarios in Lanzhou in 2030 were simulated using a coupled WRF-Chem weather and air quality model.The response and sensitivity of predicted ozone concentration to the changes in precursor emissions was quantified.The results were used to determine the levels and magnitudes of precursor emission reductions in Lanzhou in the next decade and provide guidance for emission mitigation policy.Based on the economic development and pollution control plan in Lanzhou,the emission range of NO_(x) was 4.57×10^(4)-12.14×10^(4) t,and the emission range of VOCs was 5.30×10^(4)-7.69×10^(4)t,under three modeling scenarios.Adjusting the energy structure,tightening up end-treatment,and restricting the vehicle emissions could more effectively reduce NO_(x) emissions,whereas the reduction in VOCs emissions would depend on synergistic emission reduction from industry,residential,and transportation sources,which requires a long-term campaign.The modeling results showed that the ozone concentration in the urban area was higher than that in the suburbs.The urban ozone was formed mainly in a VOCs-limited regime,and the suburban ozone was formed in an NO_(x)-limited regime.If the emissions of NO_(x) and VOCs in Lanzhou were restricted below 6.25×10^(4) t and 5.81×10^(4) t in 2030,respectively,the 1 h average ozone concentration could be well below the secondary level of the national ambient air quality standard in summer.If emissions of these two precursors were further reduced to 4.57×10^(4) t and 5.30×10^(4) t,the summer daytime-ozone concentration could be further reduced by 9.1%,which would be conducive to ozone control in the urban area.By comparing the ozone pollution in different scenarios,the focus to reduce the air quality of the city below the national standard should be on reducing VOCs in urban Lanzhou and NO_(x) in the suburbs of the city.Additional attention should be paid to the sensitivity of ozone formation to the changes in ozone precursor emissions so as to help strengthen regional joint prevention and control for ozone pollution in Lanzhou.