Effect of relative humidity and the presence of aerosol particles on the α-pinene ozonolysis.

The α-pinene ozonolysis under the different environmental conditions were observed in a smog chamber. The second-order rate constant (k) was determined to be (7.25±0.06)×10-17 cm3 /(molecule·sec) under 20% of relative humidity (RH) and room temperature. RH showed a marked influence on the α-pinene ozonolysis. The value of k increased with RH increase, which was 1.6 times faster at RH=80% than that at RH=20%. Additionally, the value of k apparently changed in the presence of the aerosol particles. The diesel soot increased the k value. The fly ash prohibited the reaction, however, H2 SO4 -treated fly ash promoted the reaction. The information of products gained using FT-IR and SPAMS showed that pinonic acid, 10-hydroxy-pinonic acid and pinic acid could be generated during the α-pinene ozonolysis. Water molecules could take part in the formation of the products, and play a vital role in the degradation of α-pinene. The atmospheric residence time calculation showed that the ozonolysis in the atmosphere is an important way of the α-pinene consumption as compared to that reacted with OH during daytime. The results suggested that the degradation of α-pinene via the ozonization in the atmosphere may be affected greatly by RH, as well as the presence of aerosol particles. The ozonolysis reaction may be an important way of the α-pinene consumption during daytime.