Characteristics of dimethylsulfide, ozone, aerosols, and cloud condensation nuclei in air masses over the northwestern Pacific Ocean

Long-term measurements of several trace gases and aerosols were carried out from December 1994 to October 1996 at Ogasawara Hahajima Island over the n orthwestern Pacific Ocean. The continental impact on the concentrations of sulfur compounds, ozone (O-3), and cloud condensation nuclei (CCN) was esti mated on the basis of the classification of air mass into seven types by is entropic trajectory analysis. From May to October, the air mass originating from the central North Pacific Ocean is predominant and regarded as the cl ean marine air for the concentrations of sulfur compounds and CCN. From the results of the molar ratio of methane sulfonic acid to non-sea-salt sulfat e (NSS) and the positive correlation between dimethylsulfide (DMS) and CCN in this air mass it can be concluded that DMS largely contributes to the pr oduction of NSS and CCN. On the other hand, continental and anthropogenic s ubstances are preferably transported to the northwestern Pacific Ocean by t he predominant continental air mass from November to March. The enhancement of concentrations by the outflow from the Asian continent are estimated by a factor of 2.8 for O-3, 3.9 for SO2, 3.5 for CCN activated at 0.5% supers aturation (0.5% CCN), 4.7 for 1.0% CCN, and 5.5 for NSS. Moreover, the CCN supersaturation spectra are also affected by the continental substances res ulting in factor 2 of enhancement of cloud droplet number concentration. Th e diurnal variations of DMS and O-3 for each air mass show a pattern of day time minimum and nighttime maximum, which are typically found in remote oce an, even though those amplitudes are different for each air mass. Consequen tly, it can be concluded that the influence of nitric oxides (NOx) for the daytime O-3 production and nitrate (NO3) radical for the nighttime oxidatio n of DMS are small even in the continental air mass.