Vertical distributions of particles and sulfur gases (volatile sulfur compounds and SO2) over East Asia: Comparison with two aircraft-borne measurements under the Asian continental outflow in spring and winter

We have presented the vertical distributions, between 0.5 and 5.5 km, of particles, volatile sulfur compounds, sulfur dioxide, O3, and fractions of sulfur over the Japan Sea coast, Wakasa Bay, on 23 April 1996 and 28 December 1995. Comparison of these measurements showed that free tropospheric concentrations of particles and short-lived sulfur gases (CS2, H2S, SO2) on 23 April 1996 were significantly higher than those on 28 December 1995. Clustered isentropic backward trajectory analysis and meteorological data indicated that the difference was associated with air mass transport routes and meteorological conditions. On 23 April 1996, coarse size particles (mineral dust particles) were injected over the arid region associated with dust storms. During transport by westerly winds, these coarse size particles were mixed with short-lived sulfur gases injected by convection over an industrial region. The presence of DMS, confined to the boundary layer, indicated that Asian continental outflow can be modified during long-range transport through mixing with marine air in the boundary layer over the Japan Sea. On the other hand, on 28 December 1995, low concentrations of particles and short-lived sulfur gases, measured at altitudes above 3.0 km, were due to air mass subsidence. It is likely that some photochemical processing was also due to low concentrations of short-lived sulfur gases. Vertical distributions of O3 concentrations and values of sulfur fraction (SO42−/(SO42−+SO2)) supported this interpretation. There was no significant difference in concentrations of long-lived COS, except for one sample on 23 April 1996. The low COS concentration coincided with significantly high concentrations of CS2, suggesting rapid upward transport of COS depleted air masses from the surface.