Trace gas measurements over the northwest Pacific during the 2002 IOC cruise

[1] The R/V Melville cruised from Osaka ( Japan) on 1 May and reached Hawaii on 5 June on a project for the Intergovernmental Oceanographic Commission (IOC) in 2002. During this cruise, the concentrations of atmospheric trace gases (O(3), CO, DMS, hydrocarbons, and halocarbons) were measured. Air at high latitudes and low latitudes exhibited starkly different characteristics regarding their chemical composition. The concentrations of anthropogenic species clearly decreased from high latitude to low latitude. On the other hand, biogenic species such as DMS and alkenes were highly abundant at lower latitudes. Backward air trajectories show that the northwestern continental air mass was dominant at higher latitudes and the eastern marine air mass was dominant at lower latitudes. However, the long-range transport of pollutants to clean regions near Hawaii was also observed. The ratios of ethane to CO decreased from high latitude to low latitude. On the basis of a VOC ratio analysis, the benzene concentration is relatively higher at low latitudes. DMS concentrations and wind speed at low latitudes have good correlation. This indicates that at low latitudes, the DMS concentration at the ocean surface is roughly uniform.