Marked impacts of transient conditions on potential secondary organic aerosol production during rapid oxidation of gasoline exhausts

Abstract

Vehicle emission is a major source of atmospheric secondary organic aerosols (SOA). Driving condition is a critical influencing factor for vehicular SOA production, but few studies have revealed the dependence on rapid-changing real-world driving conditions. Here, a fast-response oxidation flow reactor system is developed and deployed to quantify the SOA formation potential under transient driving conditions. Results show that the SOA production factor varies by orders of magnitude, e.g., 20–1500 mg kg-fuel−1 and 12–155 mg kg-fuel−1 for China V and China VI vehicles, respectively. High speed, acceleration, and deceleration are found to considerably promote SOA production due to higher organic gaseous emissions caused by unburned fuel emission or incomplete combustion. In addition, China VI vehicles significantly reduce SOA formation potential, yield, and acceleration and deceleration peaks. Our study provides experimental insight and parameterization into vehicular SOA formation under transient driving conditions, which would benefit high time-resolved SOA simulations in the urban atmosphere.

Secondary Organic Aerosol Formation Potential from Vehicular Non-tailpipe Emissions under Real-World Driving Conditions

“…This significantly affected the gas-particle partitioning and reduced the loss of aged low-volatile organic compounds. 15 Considering the neutral property, NaCl material was used as the seed aerosol, generated by an aerosol atomizer (model 3076, TSI Inc.).…”

“…A detailed description of the methods can be found in our previous study. 15 The SOA production factors within the bin of 30−40 km/h were extracted to compare with tunnel experimental results. The schematic of the enclosure study combined with tunnel and laboratory experiments is shown in Figure S3.…”

“…Among the species, benzene, toluene, ethylbenzene , and m/p-xylene (BTEX) are found to be the dominant contributors to SOA, similar to the results of previous dynamometer tests. 15 These species generally come from the unburned fuel exhaust, from both the tailpipe and evaporative emissions. 47,48 Considering that VOC emissions were 3.6 times higher than those of IVOCs, this result underscores the relative efficiency with which IVOCs from vehicle exhaust lead to SOA formation.…”

“…13,14 For example, dynamometer tests showed that driving conditions can lead to order magnitude variation in SOA formation potential. 15 Also, the update of emission standards highly decreases the nonmethane organic gas exhaust from the tailpipe and associated SOA formation. 16 These discrepancies drive the SOA research under city-scale vehicle fleets with a wide range of types to obtain more representative SOA measurements.…”

“…A wide variation in the SOA formation from tailpipe exhaust has been found in previous laboratory oxidation flow reactor (OFR) studies. Several internal influencing factors drive the variability of vehicle SOA precursor emissions, including emission standards, fuel types, and driving conditions. , For example, dynamometer tests showed that driving conditions can lead to order magnitude variation in SOA formation potential . Also, the update of emission standards highly decreases the nonmethane organic gas exhaust from the tailpipe and associated SOA formation .…”