Smog Chamber Study on the Ozone Formation Potential of Acetaldehyde

Acetaldehyde is one of the important VOC species of O 3 precursors in the atmospheric environment. The influences of relative humidity (RH) and initial VOC/NO x ratio ( R CN ) on the formation of O 3 are studied in smog chamber experiments, and the MCM v3.3.1 mechanism of acetaldehyde is modified based on the experimental results. In low-RH conditions (RH = 11.6%±1.1%), the O 3 concentration at 6 h increases first and then decreases with the increase of R CN , and the R CN at the inflection point of O 3 concentrations is 3.2. In high-RH experiments (RH = 78.8%±1.0%), variation of the O 3 concentration at 6 h with R CN is similar to that in low-RH experiments, but the R CN at the inflection point is 2.8. RH has no significant effect on the O 3 concentrations under low R CN (< 3), whereas it has a negative effect under high R CN (> 3). Compared with the experimental results, original MCM v3.3.1 greatly underestimates the O 3 concentrations. Addition of both the photolysis process of peroxyacetyl nitrate and the photolysis process of HNO 3 on the reactor surface into the original MCM can reduce the difference between the simulated O 3 concentrations and the experimental results at 6 h from 24%−35% and 17%−49% to 6%−26% and 10%−42% under low- and high-RH conditions, respectively. The maximum incremental reactivity (MIR) of acetaldehyde simulated with the modified MCM is 4.0 ppb ppb −1 without considering the effect of other VOCs.