Atmospheric Environment. Part A. General Topics最新文献

Comparison of ice-core nss sulfate records (two sites in Greenland and one in the North Pacific) with temperature change records for the regions including these core sites provides further confirmation that change in the concentration of anthropogenic sulfate has had a significant effect on regional temperature during at least the period ∼ad1940–1970 over at least the Atlantic portion of the Arctic. Using the ad1880–1985 portion of our ice-core records as an analog, we provide a test of the potential temperature depression caused by non-seasalt (nss) sulfate aerosols over Greenland during the period ∼ad700–1900 concluding that the anthropogenic era is unique by comparison. Statistical examination of this record allows a determination of the relative contributions of volcanic vs biogenic source nss sulfate during this period plus a characterization of the variability in these two sources.

A suite of 14 individual debris and silt-laden samples were selected from teh bottom 30 m increment of 2035 m deep Dye-3 Greenland ice core. Concentrations of trace elements in these samples were measured by instrumental neutron activation analysis (INAA). The results show characteristics elemental patterns for the embedded particles and debris from two different sources. The upper samples contain trace element marker species identifying atmospherically transported material; the lower samples contain marker species identifying particles originating from continental crustal lithologies from two different sub-ice source areas. This study supports the theory that bedrock scouring is the origin of particles in the bottom 23.6 m of the Dye-3 core, and atmospheric transport and deposition is the origin of the particles above this depth; some particles may be of volcanic origin.

The limitations of air trajectory models are reviewed, and suggestions are made regarding their appropriate use in interpreting atmospheric chemistry measurements. Single trajectories are shown to be potentially unrepresentative in the presence of large wind shears.

The optical properties of Arctic Haze were studied using a total-direct-diffuse radiometer as part of the Arctic Gas Aerosol Sampling Project, part III (AGASP III). The radiometer was installed on the NOAA WP-3D research aircraft and measured solar downwelling irradiance in seven narrow-band channels in the visible and near-infra-red. Haze optical depths had maximum values near 0.1 in the mid-visible for AGASP flights 310 and 311. An inferred particle size spectrum from flight 311 extinction measurements showed two dominant modes near 0.1 and 0.8 μm. A method of retrieving the angular dependence of scattered radiation is presented and suggests the presence of thin cirrus.

Concentrations of cosmogenic ⁷Be and the radon daughter ²¹⁰Pb were determined in surface-level aerosols and fresh and aging snow throughout DGASP. The distinct sources, yet common association with submicron aerosols, of these atmospheric radionuclides makes them valuable tracers of the transport, depositional and post-depositional processes leading to incorporation of submicron aerosols (and associated species) into the Greenland Ice Sheet.

The aerosol concentrations of atmospheric radionuclides tended to covary on the 1–7 day time scale of individual samples (r = 0.57, n = 114, p = 0.001) and were also highly correlated when averaged by month (r = 0.80, p = 0.002). The year-long time series of both ⁷Be and ²¹⁰Pb showed concentration peaks in spring (April) and fall (September–October) and minima in summer (July) and winter (November–February). This finding is in stark contrast to results from other arctic sites, where both radionuclides, but particularly ²¹⁰Pb, show pronounced concentration peaks in the winter. This indicates that the air masses over the Greenland Ice Sheet may be distinct from the air in the polar basin, or boundary layer processes strongly bias surface-level aerosol characteristics over the ice sheet, or, likely, some combination of these factors are operating.

The concentrations of ⁷Be and ²¹⁰Pb in fresh snow at Dye 3 show wide variability between snow fall events. The lack of any obvious correlation between concentrations in aerosol and fresh snow support the contention that surface-level air at this site is often not reflecting air aloft. Aging snow studies did not reveal consistent trends in concentration, suggesting important heterogeneity in the initial concentrations of ⁷Be and ²¹⁰Pb in surface snow over small spatial scales. Poor agreement between the ²¹⁰Pb profile in a 2 m snowpit sampled at the end of the project and the observed deposition of ²¹⁰Pb through the year indicate the potential importance of post-depositional processes in modifying the atmospheric “signals” preserved in the snowpack.

During the third Arctic Gas and Aerosol Sampling Program (March 1989), aircraft measurements of atmospheric gases and aerosols were performed in the European Arctic for the purpose of investigating the phenomenon of boundary layer O₃ destruction. Eight high-volume aerosol filter samples were collected in tropospheric air over the pack ice. In these sampling periods, continuous O₃ measurements were made and trace gases were collected in flasks. For all samples, total elemental bromine collected on the filters in excess of the estimated sea salt component (XSFBr) was found to anticorrelate stronly (r = −0.90) with the mean ozone concentration observed during the sampling period. These findings are similar to earlier observations at Alert and Barrow.

Air samples collected during these periods were analysed for Br-containing gases and hydrocarbons. None of these compounds were well correlated with either O₃ or XSFBr concentration over the course of the experiment. This is probably because variable conditions of local meteorology, atmospheric structure and geographic location influenced the degree to which O₃ was depleted, by affecting the size of the reaction reservoir and the source(s) of the reactants. Samples collected in the surface (∼ 50 m deep) isothermal or slightly stable layer (SSL) over pack ice and with light winds from the direction of the central Arctic showed the highest O₃ depletions. When winds were from the direction of open water, significantly higher O₃ and lower XSFBr values were observed. When the SSL was not present, samples collected below the strong inversion showed less O₃ destruction and lower XSFBr concentrations than similar low altitude samples collected within the SSL. This is consistent with the notion of a larger reservoir volume available for reaction. Gas and aerosol chemistry results were compared for two samples collected close spatially and temporally over ice north of Spitsbergen. Our data indicate that (1) CHBr₃ may be the key organobromine species supplying Br atoms and BrO radicals in a heterogeneous photochemical reaction cycle causing the photolytic destruction of O₃ in the springtime Arctic surface layers, and (2) ambient hydrocarbons (especially C₂H₂) are depleted during O₃ destruction, and may be important in the overall reaction mechanism. This catalytic O₃ depletion process was observed to occur to an extent causing near-total O₃ destruction in the SSL over a 1–2 d period. Thus, relatively rapid photochemical reactions between atmospheric Br, hydrocarbons and aerosols are suggested as driving the photolytic O₃ destruction process.

DGASP was designed as an international effort to study the processes influencing chemical species that eventually reach the deep ice in the south of Greenland. These processes include long-range atmospheric transport, wet and dry deposition to the snow surface, and changes during aging of the snow. The program took place during August 1988–July 1989. Experimental work included sampling of aerosols and gases, collection of fresh and older surface snow, and sampling of snowpits. The various samples were analysed for chemical species that are tracers of specific sources categories. Results of the program show that the southern Greenland Ice Sheet experiences very different airborne concentration patterns than sea-level arctic sites. Concentrations of SO₄²⁻, trace metals, and other species are episodic and peak in April, unlike the consistently high concentrations during January–April seen at lower elevations. Source regions influencing Dye 3 are variable, and include North America, western Europe, and the Arctic Basin. The last region is particularly important, as it may contain relatively high concentrations of chemical constituents from eastern Europe and western Asia that eventually reach Dye 3. The seasonal variations in airborne concentrations are generally also reflected in fresh snow. Similarly, these patterns are seen in snowpits, although some modifications to the glacial record are apparent. Other information on the extent of riming, aerosol/gas partitioning, and aerosol size distributions demonstrate the complexity of air-snow transfer processes, and illustrate the need for further research.

Non-sea salt sulfate aerosol (NSS) is an important factor for the Earth's albedo because it backscatters solar radiation and is the major cloud condensation nucleus over oceans. At Vostok, Antarctica, NSS concentration shows an increase in glacial period ice of 20–46% that cannot be attributed to changes in accumulation rate. The additional NSS may be due to enhanced dry deposition of NSS by topographic windpumping during the windy glacial periods. We model the volume flux of air into snow due to barometric pressure changes and air flow over surface microrelief. The Gormley-Kennedy equation approximately describes how aerosols advected into the snow pack are removed from the air by diffusion to the snow matrix. Barometric pressure and wind speed data from several polar sites have been used to quantify the vertical volume flux of air and mass flux of NSS. Model results indicate that air flow over small sastrugi, wind carved snow dunes commonly found on ice caps, is the dominant dry deposition mechanism for NSS. Paleo wind speed and surface roughness can significantly influence the aerosol record in ice cores.

Aerosol samples collected at Barrow, Alaska, during February and March 1990 were found to have uniform stable lead isotope compositions. The mean ²⁰⁸Pb/²⁰⁷Pb ratio was 2.423±0.009 and the mean ²⁰⁶Pb/²⁰⁷Pb ratio was 1.161±0.014. The latter ratio is essentially the same as that obtained from an earlier study of aerosols at two Canadian stations in the High Arctic and is typical of, but not unique to, Eurasian sources of atmospheric lead. Further discriminating power was available in this study through the inclusion of ²⁰⁸Pb/²⁰⁷Pb ratios, which provided additional evidence that the former Soviet Union and eastern Europe are major contributors to atmospheric particulate lead in the Alaskan Arctic, accounting for around two-thirds of the particulate lead measured at Barrow. The remaining third of the lead is attributed to west European sources. There was no evidence for a substantial North American component, other than local contamination.