基于中国四大城市群计算的最大增量反应活性

Calculation of maximum incremental reactivity scales based ontypical megacities in China

我国臭氧污染呈逐年加重的趋势,已有研究显示我国大部分城市地区处于臭氧生成的挥发性有机物(volatile organic compound, VOCs)控制区,因此准确计算VOCs对臭氧生成潜势的贡献是对于臭氧污染采取科学有效防控措施的前提条件.本研究使用基于二代区域大气化学机理(the second regional atmospheric chemistry mechanism,RACM2)的盒子模型,建立我国四大城市群(京津冀、长三角、珠三角以及成渝地区)的基准情景以及最大增量反应活性(MIR)情景,计算了适用于我国大气复合污染条件下的VOCs最大增量反应活性(MIR_CHN).与Carter基于美国39个城市所计算的MIR相比,我国最活跃VOCs与最惰性VOCs之间的最大增量反应活性差异范围更大.若使用基于美国39个城市所计算的MIR对我国城市地区的臭氧生成潜势进行预判,容易造成对于我国城市地区臭氧污染控制过程中特征VOCs的误判.因此本研究计算得到的MIR_CHN能够更准确地评估我国大气条件下VOCs的臭氧生成潜势,且对臭氧生成过程中关键VOCs物种的判定更为准确.

Ozone pollution is becoming increasingly serious in China,the accurate calculation of the volatile organic compounds(VOCs)contributions to ozone formation potential is the precondition for scientific and effective ozone control strategies.Maximum incremental reactivity(MIR)is an effective tool to evaluate VOCs’reactivities,which may vary significantly because of different atmospheric conditions,VOCs compositions,and the relative abundances of VOCs and NOx.Nevertheless,the most widely used MIR calculated by Carter based on 39 urban areas in the United States reflected the ozone formation potential of each VOCs species under atmospheric conditions in US.Whether their MIR values are appropriate under atmospheric conditions in China or not is still under discussion.In order to calculate the real contribution of VOCs to ozone formation,we firstly calculated the indigenized MIR values for Chinese megacities.Box model based on the second Regional Atmospheric Chemistry Mechanism(RACM2)was used to calculate the indigenized MIR for China.Observed data of four megacities(Beijing-Tianjin-Hebei,Yangtze River Delta,Pearl River Delta and Chengdu-Chongqing)which represent the typical atmospheric conditions in China were used as input parameters in calculation.We set two scenarios(Base scenarios and MIR scenarios)for MIR calculation,where Base scenarios were established by selecting the fourth highest ozone day during three years’observed data,MIR scenarios were set by adjusting the NOxavailability to obtain the scenarios where ozone formation was most sensitive to VOCs.MIR values were calculated via the ratio of the change in ozone concentration due to the change in VOCs concentration divided by the change of VOCs concentrations in MIR scenarios.MIR_CHN(MIR values for four megacities)was obtained by averaging the normalized MIR values of all sites,with an uncertainty of 25%.Compared to the MIR calculated by Carter(MIR_USA in this study),our results showed a larger range values between the most active VOCs and the most inert VOCs.The MIR_CHN values of highly reactive VOCs(such as internal alkenes,butadiene,anthropogenic dienes,terminal alkenes,isoprene and o/m/p-xylene)were higher than MIR_USA values.Whereas MIR_CHN values of low reactive VOCs(HC5 and acetylene)were lower than MIR_USA values.Values of MIR_CHN and values of MIR_UAS were comparable for the moderate reactive VOCs.The differences between MIR_CHN and MIR_USA may be caused by differences in simulation time,reaction mechanism,and proportion of ozone precursors,NOxavailability,and VOCs compositions.Ozone formation potential of four megacities calculated by the MIR_CHN were much higher than that calculated by the MIR_USA,which meant that using MIR_USA may not only underestimate ozone formation potential,but also miss the key VOCs species in ozone formation in China.The key VOCs were isoprene,internal alkenes and m/p-xylene in ozone formation in China based on MIR_CHN calculation.