Changes in the elemental ratios of Cl/Na and S/Na in sea‐salt particles are expected from the atmospheric reactions of sulfuric and nitric acids with these particles. Chloride depletion is expected to occur upon the liberation of HCl to the gas phase, with the particles remaining enriched in sulfate or nitrate. The elemental ratios of Ca/Na, Mg/Na and K/Na should remain constant during this process. Analysis of chloride depletion and sulfur enrichment was obtained for individual sodium‐containing particles from the remote marine Pacific atmosphere in both the accumulation mode (0.06 ≤ Dp ≤ 1.0 μm, where Dp is the particle diameter) and the coarse mode (Dp > 1.0 μm) size range. Sodium‐containing particles comprised close to 100% of the coarse mode and 11 to 31% of the accumulation mode by number. Aerosols were collected with a low‐perssure impactor and examined with a transmission electron microscope (TEM) coupled with an energy‐dispersive X ray (EDX) detector. The elemental ratios obtained from the atmospheric particles were determined by comparison with values obtained from laboratory‐generated sea‐salt, sodium chloride, and sodium sulfate particles of known size and chemical composition, which served as a calibration set. The elemental ratios of Ca/Na, Mg/Na, and K/Na were found to remain fairly constant between individual sea‐salt particles of various sizes for more than 85% of the particles examined. Deviations in the ratio of Cl/Na and S/Na from that of reference seawater values were observed most commonly for the submicrometer sea‐salt aerosol. The Cl/Na ratio was significantly (Student's t test, 99.9%) lower than that of reference seawater for 89% of the particles examined, while the S/Na ratios were higher for 100% of the particles. The Cl/Na ratio measured in 48% of the coarse sea‐salt particles (1.0 < Dp ≤ 2.5 μm) reflected the ratio in bulk seawater, while the remaining particles had statistically lower ratios and qualitatively different morphologies. All but 3% of these coarse particles had enhanced S/Na ratios over that of bulk seawater. Estimates of non‐sea‐salt (nss) sulfate mass ranged from 216 to 1422 fg for particles of 0.50 μm in diameter to 861 and 5235 fg for particles of 0.80 μm in diameter, corresponding to 74 to 96% of the sea‐salt particle mass. These values are compared with the recent measurements of Mouri and Okada [1993] as well as predictions from the atmospheric chemistry models of in‐cloud sulfate production of Hegg et al., [1992] and estimations of S(IV) oxidation in sea‐salt aerosol water by Chameides and Stelson [1992].
The regional deposition of an inhaled aerosol of 1.0-micron diameter fluorescent microspheres (FMS) was used to produce high-resolution maps of regional ventilation. Five anesthetized, prone, mechanically ventilated pigs received two 10-min inhalations of pairs of different FMS labels, accompanied by intravenous injection of 15.0-micron radioactive microspheres. The lungs were air dried and cut into 1.9-cm3 pieces, with notation of the spatial coordinates for each piece. After measurement of radioactive energy peaks, the tissue samples were soaked in 2-ethoxyethyl acetate, and fluorescent emission peaks were recorded for the wavelengths specific to each fluorescence label. The correlation of fluorescence activity between simultaneously administered inhaled FMS ranged from 0.98 to 0.99. The mean coefficient of variation for ventilation for all 10 trials (47.9 +/- 8.1%) was similar to that for perfusion (46.2 +/- 6.3%). No physiologically significant gravitational gradient of ventilation or perfusion was present in the prone animals. The strongest predictor of the magnitude of regional ventilation among all animals was regional perfusion (r = 0.77 +/- 0.13).
Correlated measurements of dimethylsulfide (DMS), gas phase dimethylsulfoxide (DMSO), methanesulfonic acid (MS A)(g), sulfuric acid (H2804), and cloud condensation nuclei (CCN) were conducted in April 1991 at a Pacific coastal site in northern Washington. Measurements of SO 2, aerosol methanesulfonate (MS A)(p), and non-seasalt sulfate (nss-SO4) concentrations were also included. Maximum DMS concentrations between 100 and 240 pptv were observed when the measurement site (480 m above sea level) was embedded in clouds and air from the marine boundary layer was flowing upslope to the site. DMS levels measured in continental air and/or above the mixed layer were typically less than 20 pptv. The sulfur gases DMSO, H2804, and MSA(g) were measured in real time on a continuous basis (once every 60-150 s) using selected ion chemical ionization mass spectrometry. Corresponding concentrations ranged between <0.5-3.2 pptv, 0.001-1.19 pptv, and 0.002-0.19 pptv, respectively. All three sulfur gases showed significant diel variations mostly in phase with each other. Their corresponding lifetimes in the marine atmosphere are estimated to be of the order of a few hours. The results in connection with recent laboratory studies and model calculations suggest that dimethylsulfone (DMSO 2) was the dominant end product of DMS oxidation under the present conditions. CCN concentrations measured in marine air ranged roughly between 10-200 cm -3 and 200-400 cm -3 at 0.3% and 0.9% supersaturation, respectively. A statistical analysis using only data obtained in predominantly marine air and during non-fog/non-precipitation periods showed significant correlations between individual sulfur species and between CCN (0.3% ss) and H2SO 4, and CCN (0.3% ss) and nss-SO 4. The results indirectly support a relationship between DMS and CCN concentrations. However, other observations also suggest that at higher supersaturations (0.9%), compounds less soluble than sulfate may become important in marine CCN formation. Institute of Technology, Atlanta 3Department of Chemistry, University of Washington, Seattle 4joint Institute for the Study of Atmosphere and Ocean, University of Washington, Seattle 5Departments of Environmental Health and Atmospheric Sciences, University of Washington, Seattle atmosphere represents a crucial component in the DMScloud-climate hypothesis [Chadson et al., 1987; Bigget al., 1984; Shaw, 1983]. Although recent studies have shown indirect evidence for such a link [Hegg et al., 199 la, 199 lb; Ayers and Gras, 1991; Ayers et al., 1991], the intricate mechanisms involved in each of these processes are still poorly understood. As discussed by Bates et al. [1989] and Quinn et al. [1993], a variety of factors control the relationships among the DMS sea-to-air flux, atmospheric DMS chemistry, and CCN formation making an experimental verification of the above hypothesis extremely difficult. In particular, large uncertainties still exist with respect to the relative yields of the end products of DMS oxidation, i.e., dimethylsulfone (CH3S...
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