Effect of Ambient Temperature on Total Organic Gas Speciation Profiles from Light-Duty Gasoline Vehicle Exhaust

Total
organic gases (TOG) emissions from motor vehicles include
air toxic compounds and contribute to formation of ground-level ozone
and secondary organic aerosol (SOA). These emissions are known to
be affected by temperature; however previous studies have typically
focused only on the temperature dependence of total emission factors
and select toxic compounds. This study builds on the previous research
by performing an evaluation of a comprehensive set of gas-phase organic
compounds present in gasoline motor vehicle exhaust. A fleet of five
vehicles using port fuel injection engine technology and running on
E10 fuel was tested. Overall, three temperatures (0, 20, and 75 °F;
or −18, −7, and 24 °C), two driving conditions
(urban-FTP75 and aggressive driving-US06) and 161 compounds were evaluated;
the emissions distributions were used to construct speciation profiles
for each driving cycle and temperature. Overall, the speciation results
indicated a significant increase in alkane and methane content, and
decrease in alcohol, aldehyde and ketone content with decreasing temperature.
These were verified using a statistical significance test. The fraction
and composition of Mobile Source Air Toxics (MSATs) were significantly
affected by temperature for both driving cycles. The ozone forming
potentials of these profiles were evaluated using the maximum incremental
reactivity (MIR) scale. Aromatic content was predicted to be a major
driver behind the ozone forming potentials. Additionally, the decreasing
ozone potential could be attributed to increased methane fractions
with increasing temperature.