Emission Characteristics Of Volatile Organic Compounds (VOCs) From Motor Vehicles In The Pearl River Delta Region

With the continuous strengthening of governance efforts,the PM_2.5concentration in the Pearl River Delta has been declining year after year,and can stably meet the standard,and ozone（O₃）has become an important factor affecting air quality.Volatile organic compounds（VOCs）,as important precursors of O₃generation,are the key to alleviating O₃pollution.Motor vehicles are an important man-made source of VOCs emissions.As the number of motor vehicles continues to rise,the impact of motor vehicle VOCs emissions on the prevention and control of air pollution has become more and more critical.However,the existing vehicle emission factors and source profiles not only lack localized data,but also lack attention to the composition of oxygenated VOCs（OVOCs）,which leads to underestimation of the total VOCs.The lack of dynamic vehicle data makes it difficult to clarify the influencing factors of vehicle VOCs.In addition,the current control of VOCs is still based on total control,while ignoring the important impact of highly active VOCs components on secondary pollution.Therefore,this study selected the main types of in-used motor vehicles in the Pearl River Delta region on the basis of traditional offline sampling methods（DNPH cartridges and SUMMA canisters）,and additionally employed ion molecular reaction mass spectrometry（IMR-MS）and proton transfer reactions-time-of-flight mass spectrometry（PTR-To F-MS）with other instruments to perform high-time resolution tests on key VOCs components.The influence of different factors on emission factors was analyzed,and the Ozone Formation Potential（OFP）of motor vehicles was evaluated based on the reactivity of VOCs components.On the basis of online data,the high time resolution characteristics of key VOCs components were identified,and the real-time distribution of each component was analyzed.The VOCs emission factors under different cycles were obtained,and the impacts of cold start on the VOCs components were studied.Finally,based on the data on the activity level of motor vehicles in the Pearl River Delta,combined with the emission factor data obtained in this paper,a rough calculation of the VOCs emission inventory of motor vehicles in the Pearl River Delta region has been made.The main conclusions are as follows:With the strengthen of emission standards,the VOCs of light-duty gasoline vehicles showed that the high contribution of CHINAⅠvehicles of alkanes,alkenes,and aromatics was gradually decreasing,while the contribution of OVOCs was gradually increasing.The VOCs emission factors of light-duty gasoline vehicles from CHINAⅠto CHINAⅥwere862.1±712.8,873.7±607.4,199.2±236.6,115.0±102.6,42.3±20.7 and 30.3±13.4 mg/km,respectively.While diesel vehicles with different emission standards are dominated by OVOCs,followed by alkenes.OVOCs gradually decrease with the rise of emission standards,while alkenes showed the different emission trends.Emission factors of VOCs for diesel vehicles from CHINAⅢto CHINAⅤwere 256.1±180.4,246.6±175.4 and57.6±27.3 mg/km,respectively.Exhaust form LPG vehicles was mainly occupied by C₂-C₄alkanes,which accounted for more than 80%.Emission factors of CHINA IV and CHINA V LPG vehicles were 140.62 and 53.53 mg/km,respectively.The emission characteristics of VOCs in the exhaust of light-duty gasoline vehicles with high time resolution are as follows:the highest VOCs concentration of exhaust occurred during vehicular starting,and the duration of cold start gradually decreases with the upgrade of emission standards.The cold start of the latest CHINA VI light-duty gasoline vehicles continues about 40～60s.In addition,the importance of cold-start emissions of different VOCs species was different,and the emissions of formaldehyde was still not apparently decrease during hot-stabilized period.The average commuting distance in urban areas showed that the majority of in-use vehicle emissions are dominated by cold-start emissions.In 2019,the emission of VOCs in motor vehicle exhaust in the Pearl River Delta region was 51093.46t,from which the contribution rates of diesel vehicles,light gasoline vehicles and LPF vehicles were 30.63%,68.13%and 1.24%,respectively.The VOCs emissions of different cities in the Pearl River Delta are sorted as follows:Shenzhen>Guangzhou>Dongguan>Foshan>Huizhou>Zhongshan>Jiangmen>Zhuhai>Zhaoqing.Light-duty gasoline vehicles with CHINAⅣemission standards have the highest contribution of VOCs.The OFP of VOCs emitted by motor vehicles in the Pearl River Delta was 28.63×10⁴t.Highly active alkenes and OVOCs have the highest contribution rate to OFP,which can add up to as high as 66.62%.In conclusion,eliminating old vehicles,strengthening vehicle maintenance,paying attention to the impact of cold start on VOCs emission,striving to shorten the cold start time and strengthening the control of high active VOCs components play an important role in the emission reduction of VOCs emissions from motor vehicles.