Reactive Organic Gases from Vehicle Evaporative Emissions: Rates, Compositions, and Temperature Effects

This study quantifies evaporative volatile organic compound emissions from China 3 to China 6 standard vehicles using a variable temperature sealed housing evaporative determination system. Total hydrocarbon (THC) emission factors during diurnal breathing losses (DBL) exhibited distinct temporal trends: the averages were 0.58, 0.87, 0.40, and 0.18 g·day^-1 for DBL day 1 (0-24 h) escalating to 2.97, 2.88, 0.41, and 0.21 g·day^-1 for DBL day 2 (24-48 h) across emission standards. Proton Transfer Reaction Time-of-Flight Mass Spectrometry identified 197 reactive organic gases (ROGs), with oxygenated and nitrogen-containing compounds contributing 20% ± 11%, 18% ± 9%, and 13% ± 9% to hot soak losses, DBL day 1, and DBL day 2, respectively. Alkanes, alkenes, aromatics, and carbonyls/ketones dominated ROG emissions (44%-99% combined). The emission composition shifted significantly across high-, normal-, and low-emitting vehicles: traditional hydrocarbons decreased progressively, while carbonyls/ketones increased, attenuating hydroxyl radical reactivity (OHR) reduction. Temperature-dependent experiments revealed proportional increases in THC and key ROG emissions per unit temperature increase, well-characterized by exponential functions. Controlling evaporative emissions by regulating oxygenated species and adopting near-zero emission vehicles reduces aerosol/ozone formation, while reactive carbonyl/ketone shifts in modern fleets highlight evolving atmospheric impacts, requiring tailored control strategies.