Influence Of Aromatic And Olefin Content On Tailpipe VOCs And PM_2.5 Emissions From Gasoline Vehicle

The fuel quality,as one of the key elements in the pollution prevention and control system of"vehicle-fuel-road",has become a key factor affecting the progress of atmospheric pollution control in China.The contents of aromatics and olefins in gasoline in China are higher than those in Europe,United States and Japan,which are key indices for vehicular exhaust.However,it’s not clear yet about their impacts on exhaust PM_2.5 and VOCs emissions from vehicles,so it is difficult to clarify the relevance between fuel quality and the formation/transformation of airborne particulate matter.In this study,two typical gasoline vehicles with different technologies of gasoline direct injection（GDI）and port fuel injection（PFI）are selected for emission tests.Firstly,emission characteristics of traditional gaseous pollutants（CO,NOx,THC and CO₂）,PM_2.5 and VOCs were analyzed from the test vehicles fueled with different contents of aromatics（20%and 40%）and olefins（4%and 24%）according to the standards of“Light Vehicle Pollutant Emission Limits and Measurement Methods（China VI）”（GB18352.6-2016）with the globally unified light vehicle test cycle（WLTC）.Secondly,the ozone generation potential（OFP）and secondary organic aerosol generation potential（SOAFP）were calculated.Finally,the emission reduction scenarios were set up to quantitatively evaluate the emission reduction effects of reducing the content of aromatics and olefins.The main conclusions were as follows:（1）The content of aromatics in gasoline increased from 20%to 40%,which significantly increased vehicle exhaust particulate matter and VOCs emission.With the increased of aromatics content,vehicle fuel consumption,NOx and CO₂ emissions increased slightly,while CO and THC had no consistent change.PM and PN emission factors increased by 11.5%～57.2%and 73.5%～132.5%respectively,especially in the medium speed+high speed stage of WLTC.The emission factor of VOCs in the exhaust increased to 2.0～2.3 times,but different components were affected differently（aromatics>olefins>aldehydes and ketones≈alkane）.After calculation,OFP and SOAFP increased to about 2 times and 4 times respectively,of which aromatic VOCs were the largest contributor to OFP and the most significant component affected by gasoline aromatics content.（2）The olefin content of gasoline increased from 4%to 24%,which reduced the emission of volatile organic compounds in vehicle exhaust,but had no consistent effect on particulate matter.With the increase of olefin content,vehicle fuel consumption and CO₂ increased slightly,THC emission decreased,and CO and NOx had no obvious effect;PM and PN emission factors for GDI vehicles increased by 42.4%and 9.3%respectively,but PFI vehicles decreased by 47.3%and 5.4%respectively;VOCs in the tested vehicle exhaust decreased by 29.8%～39.4%,of which alkanes were greatly affected,with a reduction of 61.6%～70.7%;It is estimated that OFP of the two tested vehicles decreased by 9.6%～12.2%,and the SOAFP also had a downward trend,especially the PFI vehicles.（3）In this study,four fuel quality improvement schemes were designed,which reduced vehicle exhaust particulate matter and volatile organic compound emission to different degrees.,and PM and VOCs emissions in exhaust and the corresponding OFP and SOAFP were reduced by 1.2%,2.7%,2.3%and 3.7%respectively when aromatic content in gasoline reduced by 1%;and the corresponding results of the four emission reduction objects increased slightly when olefin content deceased by 1%.The reduction rates of PM_2.5,VOCs,OFP and SOAFP of cumulative newly registered gasoline vehicles in Zhengzhou will reach 8.2%～15.2%,6.8%～39.1%,13.3%～31.1%and16.7%～51.4%,respectively in 2030 under the four prediction scenarios based on the baseline scenario.