Study On The Effect Of VOCs On Ozone Pollution In Atmospheric Background Area In China

To well understand the key scientific issues such as the formation mechanisms and transport processes of ozone(O3)is imperative to support the synergetic control of PM2.5 and O3 and to curb the continuous increase of O3 concentration.Focusing on the large region of ambient air quality background areas with less disturbance by human activities(hereafter referred to as"background areas"),this research selected a number of background areas,rural areas,and urban areas to conduct systematic research on O3 and its precursors,including volatile organics(VOCs)and nitrogen oxides(NOx).Comprehensively applying some methods,including statistical analysis and Weather Research and Forecasting Model coupled to Chemistry(WRF-Chem Model),the temporal and spatial variation characteristics of the O3 concentrations in background areas as well as the influence of biogenic VOCs on O3 formation were systematically analyzed.Then the influences of the human activities in neighboring cities on O3 concentration in different background areas were quantitatively evaluated.Also,the O3 pollution processes several typical regions were simulated,and the contributions of anthropogenic and natural sources to O3 concentration were quantified on a regional scale.The main results are as follows:(1)The annual average and the 90%percentile values of O3 concentration in the background areas from 2016 to 2020 were 89 μg/m3 and 125 μg/m3,respectively 2.3%higher and 9.4%lower than the values in urban areas.The O3 concentrations in the background and urban areas had a similar annual change trend.However,the O3 concentrations in the background areas showed a relatively stable seasonal and daily variation pattern.(2)The influence intensity of human activities in neighboring cities on the changes of O3 concentrations in the background areas were quantitatively analyzed using statistical analysis methods,such as the correlation coefficient(<0.6)of O3 concentrations in the background areas and neighboring cities,and the daily variation of O3 concentrations in the background area(peak-to-valley deviation≤15μg/m3).This finding could provide a scientific basis for the siting of the background stations.(3)The temporal and spatial characteristics of VOCs in the background,rural,and urban areas of East China were compared to assess their influence on the background O3.The results showed that the average concentration of VOCs in the background areas was 39.1%and 46.5%lower than those for rural and urban areas in 2020,respectively.However,the isoprene concentration was 66.9%and 543.4%higher than those in rural and urban areas,respectively.The isoprene concentrations in the background areas showed an obvious seasonal pattern with the highest values in summer,accounting for 17.5%of TVOCs,with the proportion being 14.4 and 16.1 percentage point higher than those in rural and urban areas,respectively.The relative contribution of natural source to O3 formation potential during the summer in the background areas is 44%,34.2 and 38.9 percentage point higher than those in rural and urban areas,respectively.This indicated that the natural emission was an important factor affecting the O3 concentration in the background areas during summer.(4)This research validated the WRF-Chem Model based on the monitoring data in the background areas,and optimized the method of O3 simulation.On this basis,the source apportionment of O3 pollution in East Chin region was performed.The results showed that the contribution of background sources to regional ozone formation was high in the range of 48%to 80%,with obvious influence.The above experimental results showed that there existed significant differences in the temporal and spatial distributions of O3 concentration and their sources between China’s background and urban areas,with the natural sources having a significant impact on O3 in background areas in summer.The background sources are large contributors to the O3 concentration in the whole regions including urban areas.It was suggested that scientific siting and observations of background stations should be further strengthened.And the impact of background O3 should be highlighted in formulating ozone pollution prevention and control policies,and the application of regional synergetic control measures should be strengthened.