Characteristics Of VOCs Emission From Plant Sources In Tropical Islands And Its Contribution To Regional Ozone

In this study,the hourly VOCs emission from plants in Hainan was estimated by using MEGAN V3.1 model and some local parameters in January,April,July and October,2019.Then,with the establishment of VOCs emission inventory of plants in Hainan,an in-depth analysis on the spatial-temporal variation rules of VOCs from such plants has been conducted.Online measurement of isoprene in VOCs at National Center for Atmospheric Research in Wuzhishan city was made to assess the accuracy of MEGAN V3.1 model estimation.In July,2019,based on the estimation of VOCs emission from plants along with WRF-CAMx air quality model,the baseline scenario(S_a+b)and control scenario(S_a)were adopted to simulate the regional ozone concentration.Ultimately,VOCs emission's effect on the production of ozone was calculated and a quantitative analysis on how VOCs emission from Hainan plants helps generate local ozone was also made.The result shows that the annual VOCs emission from plants in Hainan in 2019 is about 551,000 t,among which,isoprene emission is 173,000 t(31.3%),monoprene emission 170,000 t(30.9%),and other VOC emission 208,000 t(37.8%).In terms of the spatial distribution of emission and Danzhou city had the highest annual VOCs emission,followed by Qiongzhong,Sanya nd Wenchang.The annual VOCsemission fromplants in Hainan 40,000 t.With regard to emission intensity,the emission intensity of VOCs fromplants in Hainan in 2019 is 16.02 t·km^-2·a^-1,the highest of which is 21.48t·km^-2·a^-1in Sanya and the lowest 12.53t·km^-2·a^-1in Changjiang.According to time distribution,VOCs emission from plants in Hainan showed obvious seasonal changes in 2019,with total emissions of 148,000 t(26.9%),232,000 t(42.1%),125,000 t(22.6%),and 47,000 t(8.5%)respectively.The overall seasonal emission rule was:in summer,>in spring,>in autumn,and>in winter.In winter,the emission intensity of the whole island is the lowest of the whole year,which is basically below 800kg·km-2.In summer,theemission is at arelatively high level,with the emission intensity reaching more than 3000kg·km^-2.The emissions in spring and autumn are similar,with the emission intensity basically above 1000kg·km^-2.VOCs from plants in Hainan are also characterized by diurnal variation,and theconclusion is as follows:the emission rategoes up with the increase of temperature and solar radiation.The rate in the daytime is higher.And it reaches the highest at noon and drops to the lowest before dawn.After the analysis on the effect of VOCs emission from plants in Hainan on the production of ozone,it can be concluded that the high-concentration ozone area is mainly located in northeast Hainan,and the concentration gradually decreases from the northeast to the southwest.The average monthly ozone concentration is 1.23 ppb,with an average contribution rate of 3.67%.The average monthly ozone concentrationin each city and county of Hainan ranges from 0.23 ppb to 3.43 per hour,and the average monthly ozone contribution rate from 0.68%to 9.89%.Among them,the contribution rates of 5 cities are higher than 5%.In particularly,Haikou,Wenchang and Dinga have achieved the3 highest contribution rates(9.89%,6.35%and 6.29%respectively).