Source Characteristics Of VOCs And PM_2.5 For Vehicle Exhausts In The Pearl River Delta Region

With the rapid increasing of motor vehicles, the vehicle exhaust has becomemain source of air pollution in many cities in recent years, especially in the PearlRiver Delta （PRD） region. Frequent ozone episode and haze days in the PRD region isclosely related to volatile organic compounds （VOCs） and fine particulate matter(PM_2.5) emitted from motor vehicle. Establishing source profiles of VOCs and PM_2.5are the fundamental research of regional air quality model and source apportionmentmodel, which are very important for studying complex regional air pollution. Forbetter understanding the characteristic of VOCs and PM_2.5composition and localizedthe VOCs and PM_2.5source profiles for motor vehicles, VOCs and PM_2.5sourceprofiles for different vehicles in the PRD region were developed in this study.Light-duty gasoline vehicle, light-duty diesel vehicle, LPG taxi and motorcyclewere tested at chassis dynamometer and on-road measurement to investigate differentmobile emission characteristics, the emission characteristics of VOCs emitted frmlight-duty gasoline vehicle at cold start and different speed were also analysed. Thetailpipe VOCs samples were collected by evacuated2-liter electro-polished andstainless steel canister. The results indicated that （1） on chassis dynamometer,aromatics were the major compound from the gasoline exhaust, while toluene,1,2,4-trimethylbenzene, ethene, m/p-xylene and isopentane were the dominant speciesfrom gasoline exhaust. Alkanes were the most abundant species of light-duty dieselemissions and LPG taxi emissions, n-undecane, ethene, propylene and n-dodecanewere the major species from diesel exhaust while propane,1,2,4-trimethylbenzene andn-butane were the major species from taxi exhaust.（2） Similar source profile patternswere found for light-duty gasoline vehicles and motorcycle during on–roadmeasurement, with aromatics as the most abundant species, followed by alkanes andalkenes. Toluene, m/p-xylene,1,2,4-trimethylbenzene and m-ethyltoluene were thedominant components emitted from light-duty gasoline vehicles, while acetylene,toluene, m/p-xylene and isopentane were the major components emitted frommotorcycle.（3） Higher VOCs emission was emitted during the cold start period and aromatics hydrocarbons were the major compound, while toluene,1,2,4-trimethylbenzene, m/p-xylene and isopentane were the dominant species duringthe cold start.（4） With the increase of driving speed, the emissions of alkanes showeda decreasing pattern, and the emissions of aromatics had a slight increasing trend. Forindividual VOCs, the emissions of different species showed different relationshipswith the driving speeds.（5） α-Pinene and β-Pinene were found in light-duty gasolinevehicle, light-duty diesel vehicle and motorcycle, indicating that the vehicle exhaustmight be one source of ozone episode and secondary organic aerosol.On-road measurement was used to study the PM_2.5characteristic of heavy-dutydiesel vehicles. The source profile was developed after using chemical mass balancemodel （CMB） to eliminate the influence from road dust. The results showed that totalcarbon （TC） was the dominant compound from heavy-duty vehicle, followed by watersoluble ions and element. The main component of total carbon was organic carbon,the main components of water soluble ions were SO₄^2-，Na⁺and NH₄⁺, while S，Na，Fe and Ca were the major components of element.