Measurement report: Emissions of intermediate-volatility organic compounds from vehicles under real-world driving conditions in an urban tunnel

Abstract

Abstract. Intermediate-volatility organic compounds (IVOCs) emitted from vehicles are important precursors to secondary organic aerosols (SOAs) in urban areas, yet vehicular emission of IVOCs, particularly from on-road fleets, is poorly understood. Here we initiated a field campaign to collect IVOCs with sorption tubes at both the inlet and the outlet in a busy urban tunnel (>30 000 vehicles per day) in south China for characterizing emissions of IVOCs from on-road vehicles. The average emission factor of IVOCs (EFIVOCs) was measured to be 16.77±0.89 mg km−1 (average ±95 % CI, confidence interval) for diesel and gasoline vehicles in the fleets, and based on linear regression, the average EFIVOCs was derived to be 62.79±18.37 mg km−1 for diesel vehicles and 13.95±1.13 mg km−1 for gasoline vehicles. The EFIVOCs for diesel vehicles from this study was comparable to that reported previously for non-road engines without after-treatment facilities, while the EFIVOCs for gasoline vehicles from this study was much higher than that recently tested for a China V gasoline vehicle. IVOCs from the on-road fleets did not show significant correlation with the primary organic aerosol (POA) or total non-methane hydrocarbons (NMHCs) as results from previous chassis dynamometer tests. Estimated SOA production from the vehicular IVOCs and VOCs surpassed the POA by a factor of ∼2.4, and IVOCs dominated over VOCs in estimated SOA production by a factor of ∼7, suggesting that controlling IVOCs is of greater importance to modulate traffic-related organic aerosol (OA) in urban areas. The results demonstrated that although on-road gasoline vehicles have much lower EFIVOCs, they contribute more IVOCs than on-road diesel vehicles due to its dominance in the on-road fleets. However, due to greater diesel than gasoline fuel consumption in China, emission of IVOCs from diesel engines would be much larger than that from gasoline engines, signaling the overwhelming contribution of IVOC emissions by non-road diesel engines in China.

Oxidation Flow Reactor Results in a Chinese Megacity Emphasize the Important Contribution of S/IVOCs to Ambient SOA Formation

“…The updated emission inventory shows that ambient S/IVOCs in Guangzhou was mainly contributed by vehicle emissions (45%) and industry (38%) . A recent local tunnel study in Guangzhou suggested the ambient IVOCs from vehicle emission was dominated by gasoline vehicles (80%) . If we assume that ambient cyclic and linear alkane concentrations in Guangzhou are present in similar ratios as emitted by gasoline vehicles, then the total SOA contribution from linear and cyclic alkanes increases from 8 to 20% (linear only) to 17.5–46%.…”

“…84 A recent local tunnel study in Guangzhou suggested the ambient IVOCs from vehicle emission was dominated by gasoline vehicles (80%). 85 If we assume that ambient cyclic and linear alkane concentrations in Guangzhou are present in similar ratios as emitted by gasoline vehicles, then the total SOA contribution from linear and cyclic alkanes increases from 8 to 20% (linear only) to 17.5−46%. The updated IVOC contribution to SOA is comparable to the traditional VOCs (13−68%) when different SOA yields were applied, as shown in Figure 4c.…”

Evolution of source attributed organic aerosols and gases in a megacity of central China

“…The produced species are oxygenated SecVOC2 and OOA2, showing enhancement with O x , peaking at midday to the afternoon. This process was rapid, as the SOA production increased by a factor of 2.5 and the oxygenated VOCs production increased by a factor of 1.7 within 6 h. The traffic VOCs are widely observed to contribute to SOA production, with aromatic compounds serving as key precursors (Fang et al, 2021). The semi-volatile nature of HOA means it could be evaporated to the gas phase and further oxidized to recondense as SOA (Robinson et al, 2007).…”

Evolution of source attributed organic aerosols and gases in a megacity of central China

“…This process was rapid as the SOA production by a factor of 2.5 and the oxygenated VOCs production by a factor of 1.7 within 6 hours. The traffic VOCs are widely observed to contribute to SOA production, with aromatic compounds serving as key precursors (Fang et al, 2021).…”