摘要:

During the first cruise operated by the United States of America and the People's Republic of China cooperative program, from December 12, 1985, to February 21, 1986, aerosol samples were collected with a KA‐200 Anderson cascade impactor and a KB‐120 sampler. Neutron activation analysis was used to determine the elemental composition of the aerosols. Maximum mass concentrations of sea‐salt elements (Na, Cl, and Br) were found in the size range 3.3–4.7 μm. The “bulk” enrichment factor for Cl in aerosols, relative to Na in seawater, was close to unity, but a very pronounced depletion was found for Br. The enrichment factor for Cl in different size ranges decreased with increasing particle size and for Br had a U‐shaped curve. The size distributions for Fe, Al, and Sc over the remote ocean and over the ocean area close to the Asian continent were quite different. Aerosols over the western Pacific showed significant enrichment of Sb and Se, relative to Fe. Some characteristics of marine aerosols are discussed as they relate to long‐range transport of crustal elements and pollution elements from the Asian continent to the

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01779

年代:1990

数据来源: WILEY

摘要:

Biomarker source information provided by long‐chain alkenone (LCA) distribution patterns was used to assess the transport pathways of marine aerosols. The C37–C39LCA were found in significant amounts in aerosols collected in New Zealand. Their occurrence in the atmosphere stems from their introduction by bubble‐bursting processes during wave breaking. The surface water temperatures calculated from the U37kratios suggested a local origin and short atmospheric residence times of the LCA. They were not detected in aerosol samples collected on American Samoa due to the absence of the source organisms in surface waters. The distribution of LCA was also investigated in size‐fractionated aerosols over a range of3.0 μm), suggesting a direct injection of algal cells and/or their fragments into the a

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01789

年代:1990

数据来源: WILEY

摘要:

Three coarse and five fine aerosol components of different elemental compositions were identified at Barrow, Alaska, from March 17 to April 21, 1986, resolved by absolute principal component analyses of element concentrations in 280 sequential coarse and fine size fraction time step samples. In the coarse (>2.5 μm), two components C‐1 and C‐2 had abundant Si, S, Cl, K, and Ca, but no Al, and together contained 85% of coarse S. Their compositions resembled expected products of carbonaceous fuel combustion, with Si being volatilized by carbon reduction and other metals volatilized perhaps as chloride salts. C‐1, with high trace metal contents, might be from nonferrous smelting, whereas C‐2, with high Fe, might be associated with conventional coal combustion. Both appeared semi‐aged with respect to acidic gas uptake because the S chemical equivalents were less than those of metals contributing to alkalinity. When combined with Cl, S was close to the metal equivalents, indicating complete acid‐base titration. A strong concentration rise of C‐1 and C‐2 occurred from March 25 to April 2 during a haze event, although C‐1 was also present at other times. Air trajectories showed that air masses arrived at Barrow during the haze event from eastern or northern Europe. The third component C‐3 was a dust aerosol rich in Al that contained high S but low Cl, suggesting saturation with H2SO4and therefore aged and regional aerosols perhaps typical of the late winter Arctic. No major change in its concentration was observed to correspond to synoptic events. In the fine (<2.5 μm), five components represent a sea‐salt aerosol, an S‐rich aerosol with some Si, K, Ca, and Fe, a trace metal aerosol, an Al‐rich dust, and a marine product with Br, S, and Cl. The sea‐salt was found only in three plumes when synoptic meteorology and air trajectories suggested origins in the North Pacific. The S‐rich aerosol, accounting for 73% of S and 40% of Si, was enhanced during the haze event by 75%, and existed over the entire period at rather high levels and might be due to SO2oxidation and condensation on fine Si‐rich particles. The trace metal aerosol was always present and could have been generated from nonferrous smelters at lower latitudes. The Al‐rich dust particles contained 7% of S and were similar to component C‐3. The marine aerosol contained 74% of Br, 69% of Cl, and 20% of S, and could be from oxidation of marine biogenic Br and S gases. All but the sea‐salt were present at Barrow throughout the period, with no clear relation to air trajectories or synoptic meteorology. The results show that certain winter meteorological conditions favor pollutant transport from lower latitudes to the Arctic. But while haze is related to industrial pollutants, other nonpollution products are present in the winter Arctic and may be important constituents of haze. They also show that by careful data reduction and meteorological analysis, the sources and transport pa

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01797

年代:1990

数据来源: WILEY

摘要:

Samples of snow collected near the south pole during January and February 1986 were analyzed for the presence of light‐absorbing particles by passing the melted snow through a nuclepore filter. Transmission of light through the filter showed that snow far from the station contains the equivalent of 0.1–0.3 ng of carbon per gram of snow (ng/g). Samples of ambient air were filtered and found to contain about 1–2 ng of carbon per kilogram of air, giving a scavenging ratio of about 150. The snow downwind of the station exhibited a well‐defined plume of soot due to the burning of diesel fuel, but even in the center of the plume 1 km downwind, the soot concentration was only 3 ng/g, too small to affect snow albedo significantly. Measurements of snow albedo near large inland stations are therefore probably representative of their surrounding

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01811

年代:1990

数据来源: WILEY

摘要:

Measurements of the concentrations of NO and NO2were made in the rural troposphere during a year's period in 1980–1981, during the summers of 1983, 1984, and 1987, and during the fall of 1984. The field site was located near Niwot Ridge, Colorado, at an elevation of 3 km. NO was measured with a chemiluminescence instrument, and NO2was photolyzed to NO and measured by the same instrument. The performance of this instrument is discussed in detail. Aspects of the NOx(sum of NO and NO2) concentrations discussed include the overall distribution, the seasonal and diurnal cycles, the interannual variations, and the correlation with meteorological parameters. The meteorological dependence of [NOx] elucidates the mechanisms that transport NOxto the site. Even though the Denver urban area lies downwind from the site with respect to the prevailing winds, it is NOxfrom that area that predominates and is responsible for the enhanced acidic deposition and elevated ozone levels at the site. The valley‐mountain flow that is primarily responsible for this transport also may be an important mechanism for transporting anthropogenic pollution from the planetary boundary layer to the free troposphere. The major photochemical loss processes of NOxare reaction of NO2with hydroxyl radicals to form HNO3and the formation of PAN (peroxyacetyl nitrate) and perhaps other organic nitrates in the summer and reaction of NO2with O3to form NO3, N2O5, and further oxidized species in the win

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01817

年代:1990

数据来源: WILEY

摘要:

We examine the sensitivity of ozone concentrations in rural areas of the United States to emissions of NOxand hydrocarbons using a regional photochemical model. Ozone production in rural areas appears to be limited by the availability of NOx. Rural ozone is strongly dependent on emission rates for NOxbut is almost independent of hydrocarbons. This relationship is quite different from that in urban air, where ozone levels depend on both NOxand hydrocarbons. The predicted relationship between ozone and nitrogen oxides appears to be consistent with observations in rural air. For the low NOxregime (<2 ppb) in rural areas, increases in NOxlead to increases in OH and to corresponding increases in the oxidation rate of hydrocarbons and in levels of ozone. Ozone concentrations in urban plumes appear to be related to regional scale production in addition to production within the plume.

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01837

年代:1990

数据来源: WILEY

摘要:

Enhanced emissions of methane (CH4) and nitric oxide (NO) were measured following three controlled burns in a Florida wetlands in 1987 and 1988. Wetlands are the major global source of methane resulting from metabolic activity of methanogenic bacteria. Methanogens require carbon dioxide, acetate, or formate for their growth and the metabolic production of methane. All three water‐soluble compounds are produced in large concentrations during biomass burning. Postfire methane emissions exceeded 0.15 g CH4m−2d−1. Nitric oxide is produced by nitrifying bacteria using ammonium as the substrate. Ammonium is also produced in large concentrations during biomass burning. Preburn and postburn measurements of soil nutrients indicate significant postburn increases in soil ammonium, from 8.35 to 13.49 parts per million (ppm) in the upper 5 cm of theJuncusmarsh and from 8.83 to 23.75 ppm in the upper 5 cm of theSpartinamarsh. Soil nitrate concentrations were found to decrease in both marshes after the fire. These measurements indicate that the combustion products of biomass burning exert an important “fertilizing” effect on the biosphere and on the biogenic production of environmentally significant atmospheric gases. These findings are particularly important since global biomass burning appears to be far more widespread and extensive than previously

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01853

年代:1990

数据来源: WILEY

摘要:

Measurements of biomass burn‐produced trace gases are presented that were obtained using a helicopter at low altitudes above burning Florida wetlands on November 9, 1987, and from both helicopter and light‐aircraft samplings on November 7, 1988. Carbon dioxide (CO2) normalized emission ratios (ΔX/ΔCO2;V/V; whereXis trace gas) for carbon monoxide (CO), hydrogen (H2), methane (CH4), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N2O) were obtained over burning graminoid wetlands consisting primarily ofSpartina bakeriandJuncus roemerianus. Some interspersed scrub oak (Quercus spp) and saw palmetto (Screnoa repens) were also burned. No significant differences were observed in the emission ratios determined for these gases from samples collected over flaming, mixed, and smoldering phases of combustion during the 1987 fire. Combustion‐categorized differences in emission ratios were small for the 1988 fire. Combustion efficiency was relatively good (low emission ratios for reduced gases) for both fires. We believe that the consistently low emission ratios were a unique result of graminoid wetlands fires, in which the grasses and rushes (both small‐size fuels) burned rapidly down to standing water and were quickly extinguished. Consequently, the efficiency of the combustion was good and the amount and duration of smoldering combustion was greatly d

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01865

年代:1990

数据来源: WILEY

摘要:

The first measurements of methacrolein (MACR) and methyl vinyl ketone (MVK) in the atmosphere are reported. The compounds both show a strong seasonal variation, with a maximum in the summer. The concentrations of MACR and MVK are highly correlated with each other and with the concentration of isoprene, in accord with the expectation that they are the major initial products of isoprene oxidation. However, the observed MACR/MVK ratio does not agree with the model predictions over the range of conditions normally observed in the nonurban continental boudary layer. We suggest that this indicates a major gap in our understanding of the photochemistry of hydrocarbons in the nonurban troposphere.

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01871

年代:1990

数据来源: WILEY

摘要:

Using the general circulation model of the Etablissement d'Etudes et de Recherches Météorologiques, a comprehensive simulation is made of the springtime Antarctic ozone depletion. Ozone is treated as an interactive variable calculated by means of a continuity equation which takes account of advection and photochemical production and loss. The ozone concentration is also used to compute the heating and cooling rates due to the absorption of solar ultraviolet radiation, and the infrared emission in the stratosphere. The daytime ozone decrease due to the “perturbed” chlorine chemistry found at high southern latitudes is introduced as an extra loss in the ozone continuity equation, with a rate dependent on altitude and temperature and adjusted to fit the ozone losses observed in September 1987 over several stations in Antarctica. Results of the perturbed simulation show a very good agreement with the ozone measurements made during spring 1987. The ozone decrease starts in late August inside the south polar vortex and reaches a minimum of 150 Dobson units in mid‐October. The relative ozone depletion between the “ozone hole” and the unperturbed calculations also agrees well with satellite observations. In October, after the high‐latitude sunrise, the temperatures inside the vortex at 50 hPa are 6–8 K colder in the ozone hole experiment than in the unperturbed experiment, and the final warming in November is delayed by about 2 weeks. This simulation also shows the development of a high‐latitude anomalous circulation, with a warming of the upper stratosphere resulting mainly from dynamical heating. All these features have been observed in spring 1987. In addition, a substantial ozone decrease is found at mid‐latitudes in a thin stratospheric layer located between the 390 and the 470 K θ surfaces. It is attributed to the cooperative effects of chemical depletion at the edge of the vortex in situations where an upward meridional flow is forced by vertically propagating tropospheric motions (the “chemical eddies”), and of the irreversible air mixing between the outer boundary of the vortex and the mid‐latitudes. Above the 470 K θ surface the air within the vortex is more contained, and the vision of the vortex acting as a chemical containment vessel holds; but below that level the vessel is apparently leaking! A significant residual ozone decrease is found at the end of the model integration, 7 months after the final warming and the vortex breakdown. If there is a significant residual ozone decrease in the atmosphere, the ozone trends predicted by photochemical models which do not take into account the high‐latitude perturbed chemistry are clearly inadequate. The ozone decrease anticipated for the next decades could be worse than expected. Finally, it is concluded that further model simulations at higher horizontal resolution, possibly with a better representation of the heterogeneous chemistry, will be needed to evaluate with more confidence the magnitude of the mid‐latitudinal ozone depletion indu

ISSN:0148-0227    

DOI:10.1029/JD095iD02p01883

年代:1990

数据来源: WILEY