Atmospheric trace gas measurements by PTR-MS over western Pacific during late winter in 2003 (MR03K01 cruise)

Atmospheric measurements were conducted on R/V Mirai from February 20 to March 30 in 2003 over western Pacific. The ship left from Sekinehama, northern Japan, and went to 51° N 165° E, and then cruised down to south on 155° E line to 17° N. Then the ship cruised up to 40° N on 155° E line and returned to Japan. Data on northern Pacific during winter time were obtained during this cruise. Also there was an opportunity to get information about latitudinal gradient of atmospheric species at west Pacific in winter time. Concentrations of CO, O₃, SO₂, NO, NO₂, and JNO₂ value were measured continuously. VOCs were measured by Proton Transfer Reaction Mass Spectrometry (PTR-MS). Air was also sampled into canisters for VOC measurements (total 42 samples). The sampled air was analyzed by GC-FID and GC-MS in the laboratory in Tokyo after the cruise. At the northern Pacific, the concentration of CO and O₃ were almost constant. And only slight concentration gradient was observed between in 45° N and in 17° N on the 155° E line in this season. This was quite different from the similar observation in May in 2002; at that time quite lower concentration was observed at lower latitude and the latitudinal gradient was very clear. About longitudinal variation, the concentrations were almost same at high latitude and did not dependent on the distance from the continent. Even short life species in the atmosphere such as pentane showed similar concentration along with distance from the land. The concentration of DMS was relatively low in this season. But DMS tended to become higher concentration at lower latitude. Sporadic high peaks of DMS were observed at lower latitude. Concomitantly, acetone became lower concentration. This would be related to the upwelling of sea water. CH₃CN was higher in lower latitude. There was no clear evidence of transport of air plume influenced by biomass burning. But the higher concentration at low latitude is probably related to the enhanced biomass burning at low latitude because lifetime of CH₃CN is relatively long.