In this study,hygroscopicity of size-segregated ambient submicron particles in urban Hangzhou was studied from 28th December 2009 to 18th January 2010,using a hygroscopicity-tandem differential mobility analyzer(H-TDMA).The submicron particles in Hangzhou showed a minor hygroscopic growth at 73%relative humidity(RH),and then grew significantly between 77%and 82%RH.Monomodal distribution accounted for 90%for 30 nm particles,17%for 50 nm particles,and less than 7%for particles larger than 50 nm at 82%RH.Deconvolution of the bimodal distribution indicated a less hygroscopic group and a more hygroscopic group,with the fraction of the more hygroscopic group increasing with the initial dry particle size and then remaining almost constant for accumulation mode particles.Our results imply that submicron particles in urban Hangzhou were almost entirely externally mixed,and the hygroscopic properties of ambient particles in urban Hangzhou were mainly a function of their size and chemical composition.
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） x 10^-17 cm^3/（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 KH 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, H2SO4-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 a-pinene consumption during daytime.
