摘要:

To investigate the relative importance of anthropogenic versus marine sources of sulfur in the North Atlantic Ocean troposphere, sulfur species were measured from aircraft, ship, and island based platforms as part of the Global Change Expedition/Coordinated Air‐Sea Experiment/Western Atlantic Ocean Experiment conducted during the summer of 1988. Four synoptic meteorological cases were examined: flow from highly populated North America, lightly populated North America, tropical oceanic regions, and polar oceanic regions. Literature values suggest that 2–10 μmol m−2day−1of (CH3)2S are emitted from the ocean to the atmosphere in marine regions associated with the first three synoptic cases. Data from this experiment indicate that 36, 16, and 14 μmol m−2day−1, for the highly populated North America, lightly populated North America, and tropical oceanic regions synoptic cases, respectively, were deposited to the ocean's surface. Differences between previously estimated natural emissions and calculated deposition suggest that anthropogenic sources of sulfur contribute significantly to sulfur deposition for these cases. The sulfur deposition rate for the polar oceanic regions synoptic case was 20 μmol m−2day−1. Given the larger range of literature values for the corresponding (CH3)2S emission rate (1–14 μmol m−2day−1) , however, the relative importance of the nonmarine S source is

ISSN:0886-6236    

DOI:10.1029/GB004i004p00349

年代:1990

数据来源: WILEY

摘要:

Chemical data derived from air and precipitation samples collected during the Global Change Expedition/Coordinated Air‐Sea Experiment/ Western Atlantic Ocean Experiment (GCE/CASE/WATOX) over the North Atlantic Ocean (NAO) are interpreted using simple box models. Estimated total sulfur (S) deposition fluxes from air masses with tropical oceanic, African, clean North American, and polluted North American origins are 4.4, 16, 33, and 70 μmol m−2day−1, respectively, with associated uncertainties of at least factors of 2 to 3. Crude estimates of the fractions of deposition attributable to marine biogenic versus anthropogenic S sources suggest that the latter may be enhancing the natural NAO atmospheric S cycle by a factor of 0.5 to 0.8. Combination with similar estimates for the North Pacific region [Savoie and Prospero, 1989] yields an overall, area‐weighted enhancement factor of approximately 0.3 for northern hemisphere ocean areas, consistent with estimates by Wigley [1989]based on climate modeling

ISSN:0886-6236    

DOI:10.1029/GB004i004p00367

年代:1990

数据来源: WILEY

摘要:

Sulfur dioxide (SO2) was measured with a pulsed fluorescence analyzer and filter pack system from the instrumented NOAA King Air aircraft. The measurements were part of the GCE/CASE/WATOX project in July 1988 and included a series of eight flights of 4‐hour duration each. During the first four flights the atmosphere was sampled over the Atlantic Ocean within 250 km east of Newport News, Virginia; during the remaining four flights the atmosphere in the vicinity of Bermuda was sampled. SO2data were collected at two elevations: about 750 mbar in the free troposphere (FT), and in the lower part of the boundary layer (BL) at about 1000 mbar. Average BL concentrations were almost 10 times greater near the east coast than near Bermuda (500±800 pptv versus 60±40 pptv). FT concentrations near the east coast also were greater than near Bermuda but by a lesser factor (110±50 pptv versus 70±40 pptv). The data from the continuous analyzer compared favorably with the data obtained from filter samples collected concurrently. SO2data from this study are somewhat lower (factor of 0.6‐0.9) than previous measurements at both sites. Average concentrations of SO2measured near Bermuda (60 pptv) were in the range of those observed in the remote marine atmosphere, although higher SO2concentrations (up to 450 pptv) were also detected on occasion. The SO2removal rate over the western Atlantic Ocean, near the east coast, is estimated empirically at 0.07±0.03 hour−1. Analyses of the known removal mechanisms suggested that the main removal mechanism is dry

ISSN:0886-6236    

DOI:10.1029/GB004i004p00381

年代:1990

数据来源: WILEY

摘要:

A high‐volume sampler and a two‐stage cascade impactor were used aboard the NOAA ship Mt. Mitchell to obtain a fine‐particle‐fraction and two coarse‐particle‐fraction size cuts of atmospheric marine boundary layer aerosol samples. Ion chromatography analysis yielded NO3−, S04=, Na+, and Cl−concentrations and, by calculation, excess sulfate (XSO4) and chloride deficit (Cld) concentrations. Statistical analysis of the July 1988 sample sets from the Bermuda and U.S. east coast areas showed that most of the observed coarse‐particle Cldin the Bermuda‐area samples may be associated with the equivalence sum of NO3−and XSO4. However, the coarse‐particle Cldobserved in the U.S. east coast samples is substantially greater than the equivalence sum of NO3−and XSO4observed at this location. It is concluded that for the east coast sampling, about 13% of the observed 16.9 nmol XSO4m−3displaced Cl−in sea salt aerosol particles. For the Bermuda area, 15‐20% of the observed 11.1 nmol XSO4m−3displaced Cl−in sea salt aerosol particles (nearly 30% of the observed Cld) despite a relatively low sea salt mass concentration under light wind speed conditions. Under more typical sea state and wind speed conditions for the western North Atlantic Ocean, substantially more XSO4may displace chloride

ISSN:0886-6236    

DOI:10.1029/GB004i004p00395

年代:1990

数据来源: WILEY

摘要:

Heterogeneous reactions involving sea‐salt aerosol in the marine troposphere are the major global source for volatile inorganic chlorine. We measured reactant and product species hypothesized to be associated with these chemical transformations as a function of phase, particle size, and altitude over the North Atlantic Ocean during the summer of 1988. Concentrations of HCl were typically less than 1.0 ppbv near the sea surface and decreased with altitude and with distance from the U.S. east coast. Concentrations of Cl volatilized from aerosols were generally equivalent to the corresponding concentrations of HCl and ranged from less than detection limits to 125 nmol m−3STP. Highest absolute and percentage losses of particulate Cl were typically associated with elevated concentrations of anthropogenic combustion products. Concentrations of product nss SO42−and N03−in coarse aerosol fractions indicate that on average only 38% of measured Cl−deficits could be accounted for by the combined effects of acid‐base desorption and reactions involving nonacidic N gases. We hypothesize a mechanism for the Cl loss initiated by reaction of O3at sea‐salt aerosol surfaces, generating Cl2followed by rapid photochemical conversion of Cl2to HCl via Cl atoms (Cl˙) and eventual recapture of HCl by the aerosol. Simulations with a zero‐dimension (0‐D) photochemical model suggest that oxidation by Cl˙ may be an important tropospheric sink for dimethyl sulfide and hydrocarbons. Under low‐NOxconditions, the rapid cycling of reactive Cl would provide a catalytic loss mechanism for O3, which would possibly explain the low O3concentrations often observed abo

ISSN:0886-6236    

DOI:10.1029/GB004i004p00407

年代:1990

数据来源: WILEY

摘要:

Samples for trace metals in precipitation (rain, snow, and fog) and total aerosols were collected at sea as part of the GCE/CASE/WATOX expedition during August and September 1988 in the greater North Atlantic between Bermuda, Iceland, the Azores, and Barbados. The samples were collected using ultra‐clean equipment and methods for the analysis of the trace elements Al, Fe, Mn, Zn, Cu, Ni, Cd, and Pb (including stable isotopes). The samples were analyzed by graphite furnace atomic absorption spectrometry and thermal ionization mass spectrometry. Based on stable lead isotopes and retrospective isentropic air mass analyses, four air mass sources were evidenced including (1) temperate U.S. and (2) boreal Canadian westerlies, and (3) boreal and northern Europe easterlies associated with (4) Mediterranean and Saharan easterlies. Lead isotopic signatures clearly distinguished emission source regions over the North Atlantic with206Pb/207Pb ratios of 1.19–1.22 for North American westerlies, 1.10–1.12 for European boreal easterlies, and 1.15–1.16 for Saharan trade easterlies. Also, the contrasting ratios between precipitation and aerosol demonstrate a vertical mixing of chemical sources in precipitation from contrasting air masses of different origin. The air mass trajectories were independently calculated and are in general agreement with the lead isotopic tracers. The isotopic tracers allowed more confident conclusions on air mass sources, particularly after a few days of oceanic transport. Also, the trajectories appeared to be very useful in explaining the strong variability of the trace metal concentrations during restricted periods of sampling time aboard a moving ship. To a lesser extent, the atmospheric emission sources were characterized by trace element concentrations. The occurrence of large dust loadings in the Saharan trade easterlies contributed abundant crustal elements and were also associated with enriched anthropogenic elements from southern Europe. Scavenging ratios were calculated for lead and cadmium during select periods when aerosol and precipitation were collected under the same meteorological regimes. The cadmium ratio is much greater than that of lead, indicating that cadmium and lead are each transported or scavenged on distinct populations of aerosols. For lead, the ratio is less in the North Atlantic than in the Pacific, suggesting an aerosol concentration dependence. Like the Pacific, the ratios increase for the lead, dust, and sea salt. One may thus conclude that marine scavenging ratios cannot yet be used effectively until factors such as concentration dependency and local conditions of tropospheric processing are better

ISSN:0886-6236    

DOI:10.1029/GB004i004p00431

年代:1990

数据来源: WILEY

摘要:

Rainwater samples from six precipitation events were collected on board ship during legs 3 and 4 of the Global Change Expedition over the North Atlantic Ocean and analyzed for dissolved, particulate (Al and Pb), and acid‐leachable trace metals (Al, Fe, Mn, Cd, Cu, Pb, Zn). Acid‐leachable concentrations of the elements (in 0.4% v/v HNO3) were similar to reported values from the North Atlantic and Pacific oceans which were measured using comparable acidification procedures. Concentrations of dissolved and particulate Al and Pb were determined in rain events concurrently sampled. Comparisons between acid‐leachable and total (dissolved plus particulate) trace metal concentrations suggest that the acid‐leachable fraction of metals can significantly underestimate total concentrations of crustal elements (e.g., Al) in rain). The solubilities of Al and Pb in precipitation were variable and mean solubilities of the elements were 13% and 45%, respectively. Recycled sea salt components were less than 14% for Al, Fe, Mn, Pb, Cd, Cu, and Zn, indicating that the net trace metal flux is from the atmosphere to the oceans. Deep‐sea particle fluxes for these metals through the western tropical North Atlantic exceed atmospheric deposition fluxes by a factor

ISSN:0886-6236    

DOI:10.1029/GB004i004p00445

年代:1990

数据来源: WILEY