Masahiko Hayashi

Chemical characteristics of free tropospheric aerosols over the Japan Sea coast: aircraft-borne measurements

Abstract Atmospheric aerosol particulate matter was directly collected in the free troposphere over the Japan Sea coast between 1992 and 1994 using an aircraft-borne nine-stage cascade impactor (particle size range: 0.1–8xa0μm). The water-soluble components in the aerosol particulate matter were analyzed by ion chromatography. Particulate sulfate and ammonium were detected in most of the samples and their size distributions showed noticeable peaks below the 1xa0μm particle size range. Water-soluble calcium (Ca 2+ ) was detected in half of the samples; the size distribution showed that the maximum particle size was larger than 1xa0μm. Highly concentrated Ca 2+ in larger particles was possibly due to transport of Kosa aerosols from the Asian continent in the free troposphere. The concentration of fine particulate sulfate and ammonium tended to increase whenever Ca 2+ was detected, which suggests possible mixing of Kosa aerosols and non-Kosa aerosols during long-range transport of air masses containing Kosa particles.

Reactive nitrogen, ozone, and nitrate aerosols observed in the Arctic stratosphere in January 1990

Total reactive nitrogen (NOy), nitrate aerosols, and ozone were measured between 12 and 30 km on board balloons launched from Esrange, near Kiruna, Sweden (68°N, 20°E), on January 18 and 31, 1990. A series of ozone measurements were performed using small balloons in addition to the measurements made simultaneously with NOy on the large gondola. On January 18, Kiruna was located inside the polar vortex, while it was outside the vortex on January 31. The NOy mixing ratio inside the vortex was 5 ± 1 parts per billion by volume (ppbv) at the altitudes between 20 and 22 km. This value is considerably smaller than the value of about 13 ppbv that is expected from gas phase chemistry, indicating that a degree of denitrification had occurred by mid-January in 1990. On the other hand, the NOy mixing ratio outside the vortex in the same altitude region ranged between 6 and 13 ppbv, suggesting less denitrification outside the vortex. The cause of the denitrification is interpreted in terms of the very cold stratospheric temperature that prevailed from December 1989 to January 1990. The mixing ratios of nitric acid in gas phase (Schlager et al., 1990) and particulate phase (Hofmann et al., 1990) were measured on January 31, but not on the same gondola. The HNO3/NOy ratio was close to unity in a polar stratospheric cloud but decreased to 0.75 ± 0.05 outside the cloud. Assuming this ratio, HNO3 has been found to be highly supersaturated over nitric acid trihydrate particles.

Depletion of Arctic ozone in the winter 1990

Ozone mixing ratios were measured by ozonesondes on board balloons launched from Esrange, near Kiruna, Sweden (68{degree}N, 20{degree}E) from January 11 to February 9, 1990. The data obtained prior to a sudden warming on February 7, 1990 show that at potential temperatures between 460 and 640 K, the ozone mixing ratio just inside the polar vortex was systematically smaller than that outside, the largest difference being 29% at around 525 K. The ozone mixing ratio at 525 K inside the vortex decreased at a rate of about 1.5% per day between January 25 and February 4. The temperatures simultaneously observed were quite often low enough to allow for formation of nitric acid trihydrate (NAT) particles around this altitude. Depletion of ozone due to highly perturbed chemical conditions in late January and early February is strongly suggested.

Spatial distributions of volatile sulfur compounds in surface seawater and overlying atmosphere in the northwestern Pacific Ocean, eastern Indian Ocean, and Southern Ocean

[1]xa0Distributions of volatile sulfur compounds (carbonyl sulfide (COS), carbon disulfide (CS2), hydrogen sulfide (H2S), dimethyl sulfide (DMS)) in surface seawater and overlying atmosphere were measured in the northwestern Pacific, eastern Indian, and Southern Oceans (40°N–66°S, 40°E–140°E) in November–December 1996 during the 38th Japanese Antarctic Research Expedition cruise. Seawater measurements revealed that DMS was the dominant sulfur compound, with concentrations of 0.5–15.8 nM. High values were found in the Southern Oceans marginal ice zone (84°E–63°E, 59°S–63°S), suggesting that the area during the bloom acts as an important source of atmospheric DMS. Atmospheric concentrations were 456–471 pptv for OCS, n.d. (not detected level) −13 pptv for CS2, n.d. −17 pptv for H2S, and n.d. −755 pptv for DMS. Concentrations of OCS were nearly constant. Concentrations of CS2 and H2S were high in terrigenic air masses and low in those of oceanic origin. Comparison of atmospheric DMS data and a steady state box model using sea-to-air fluxes of DMS and assumed OH radical concentrations revealed that atmospheric DMS concentrations in the equatorial region and most of the Southern Ocean were balanced with local oceanic emission residues and photochemical oxidation. Simultaneous measurements in the atmosphere showed DMS was the dominant sulfur gas that was oxidized rapidly to sulfate aerosols in the marine atmosphere.