基于观测模型的成都市臭氧污染敏感性研究

Sensitivity analysis of atmospheric ozone formation to its precursors in Chengdu with an observation based model

2019年4—8月,在成都市城区开展了O3、NOx、VOCs及气象参数的连续在线观测,基于观测数据OBM模拟的方式,对O3超标日的敏感性及收支进行了分析.研究发现,成都市城区O3超标日对应的绝大部分前体物的浓度均有所上升,基于VOCs的组分变化分析推断工业源排放在超标日可能存在较大幅度的增加.相对增量反应活性(RIR)值结果表明,成都市城区O3超标日对人为源VOCs(AVOCs)敏感性最强,其次为天然源(BVOCs)和CO,而对NOx为负敏感性,控制AVOCs对站点超标日的O3浓度下降最为有利;逐月变化来看,O3对AVOCs和NOx的敏感性逐月差异较小,对BVOCs的敏感性在6—7月最强,对CO的敏感性在4—5月最强.观测点位处于典型的VOCs控制区,以O3浓度为等值线的EKMA曲线显示4—5月脊线比例约为13,6—7月及8月的脊线比例约为8.建议在开展O3防控时,VOCs的减排比例应远大于NOx,且春季的减排比例应大于夏季.典型O3污染日的日最大O3小时生成速率为10×10-9~18×10-9·h-1,上午存在O3输入,下午O3本地生成占主导,其余时段O3输出影响较强.

From April 2019 to August 2019,on⁃line measurements of ozone(O3)and its precursors were conducted in Chengdu,China.An observation based model was used to study the in situ O3 formation of and sensitivity of O3 production to its precursors in O3⁃unattainment days.The results showed that the concentrations of most O3 precursors increased on episode days(days with maximum daily 8⁃hour O3>160μg·m-3)relative to those on non⁃episode days,with significant enhancement of industrial emissions as indicated by the variations of corresponding tracers.The relative incremental reactivity(RIR)analysis revealed that O3 formation was most sensitive to anthropogenic Volatile Organic Compounds(AVOCs),followed by biogenic VOCs(BVOCs)and CO,which however had negative sensitivity to NOx.It meant that controlling AVOCs was most effective in reducing in situ O3 production in the study period.The monthly average RIR values of AVOCs and NOx were relatively stable,in contrast to the significant variations in RIRs of BVOCs and CO,which peaked in June—July and April—May,respectively.The localized Empirical Kinetic Modeling Approach(EKMA)curve again confirmed the generally VOC⁃limited regime governing O3 formation,with the VOCs/NOx dividing ratio of^13 in April—May,and of^8 in June—August.It was therefore suggested that the cutting percentages of VOCs should be much higher than those of NOx for effective control of local O3 production,and the cutting ratios of VOCs/NOx in spring should be higher than in summer.During the study period,the maximum hourly O3 production rate varied between 10×10-9 and 18×10-9·h-1 on episode days.It was implied that net O3 input generally occurred in the morning,while O3 was dominated by in situ production in the afternoon and could be exported at other times.