VOCs measurement at Tomakomai research forest, Japan

Intensive atmospheric field measurement was held on at Tomakomai research forest during summer in 2006. The purpose of the measurement was to observe the atmospheric chemistry at enhanced biogenic emission area influenced by urban polluted air, especially in the view point of OH reactivity. Tomakomai research forest is located by city area. Several VOCs including both anthropogenic and biogenic VOC were observed by different methods, canister grab sampling (GC-FID, and GC-MS), on site GC-FID measurement, and PTR-MS measurement. Also general atmospheric species (O3, CO, NOx, SO2) were observed. From the results of anthropogenic species, influence of urban air nearby and of long-range transport was both expected. Also influence of volcano was expected by SO2. The comparison of biogenic VOCs by different methods showed good agreement. The problem during the canister storage was not observed. Observed terpenes (alfa-pinene, camphene, limonene, and beta-pinene) showed higher concentration during night and lower during daytime. The maximum concentration was about 900 ppt as the sum of terpenes. On the other hand, isoprene showed higher concentration during daytime and low during night. The maximum concentration was about 1.5 ppb. There concentrations were not high as expected as a forest atmosphere. Since the temperature during the campaign was 27 C at maximum, the emission from the plants was not very enhanced. The comparison with directly observed OH reactivity and calculated OH reactivity from various species showed some difference during daytime. The difference has good correlation between isoprene. The difference would be caused by unmeasured species, which should have similar concentration variation as isoprene. The signal of m/z=71 observed by PTR-MS, corresponding to VMK and MACR, showed quite similar variation of isoprene. They ware produced by the oxidation of isoprene. Even if their very high concentrations were assumed, the difference of the OH reactivity can not be explained.