Atmospheric Environment. Part A. General Topics最新文献

At a high altitude site at Summit, Greenland, aerosol sulfur, chlorine, and potassium were found to occur mainly during sporadic high concentration episodes, lasting less than 24 h, over a much lowwer background level. Particle size resolved time sequence sampling was performed by automated two-stage streaker and high sensitivity elemental analysis by proton induced X-ray emission, PIXE, with a detection limit of 9 ng m⁻³. In a series of 165 4-h samples during one summer month in 1989, peak concentrations in the fine <2 μm diameter fraction were sometimes coincident and sometimes not, indicating different degrees of association of those elements in air masses passing over the site. Most of the S, Cl, and K was measured during the short high concentration episodes. This finding could not have been made by using a long time average sampling strategy.

Recent observations have highlighted ozone destruction in the lower Arctic atmosphere during spring, as the Sun rises. The ozone destruction occurs in the surface radiation inversion layer and has been linked to the presence of bromine. The purely gas-phase mechanisms that have been previously proposed are inadequate to explain the observations of rapid destruction of boundary layer ozone. In view of the widespread occurrence of lower tropospheric ice crystals in the Arctic, heterogeneous chemical reactions occurring on the surfaces of ice crystals are proposed here as a mechanism to explain the rapid ozone destruction. Heterogeneous reactions have the potential to modulate the ozone destruction both through the production of BrO_x and also by depleting the atmosphere of NO_x. Using data obtained from the University of Washington research aircraft, observational evidence is presented for the coincidence of ozone destruction and the presence of ice crystals in the Arctic troposphere. The ozone destruction is hypothesized to be modulated by the availability of sufficient sunlight and Br_x. The proposed mechanism has the advantage of potentially explaining the oberved rate of ozone destruction in the lower Arctic troposphere, while at the same time being consistent with the dynamics and thermodynamics of the Arctic troposphere.

Chemical constituent concentrations in air and snow from the Dye 3 Gas and Aerosol Sampling Program show distinct seasonal patterns. These patterns are different from those observed at sea-level sites throughout the Arctic. Airborne SO₄²⁻ and several trace metals ofcrustal and anthropogenic origin show strong peaks in the spring, mostly in April. Some species also have secondary maxima in the fall. The spring peaks are attributed to transport over the Pole from Eurasian sources, as well as transport from eastern North America and western Europe. The fall peaks are attributed primarily to transport from North America, and less frequent transport from Europe. Airborne ⁷Be and ²¹⁰Pb show strong peaks in both spring and fall, suggesting that vertical atmospheric mixing is favored during these two seasons. Several other airborne constituents peak at other times. For example, Na peaks in winter due to transport of seaspray from storms in ice-free oceanic areas, while MSA peaks in summer due to biogenic production in the oceans nearby. Many trace gases such as freons and other chlorine-containing species show roughly uniform concentrations throughout the year. CO and CH₄ show weak peaks in February–March. Concentrations of chemical constituents in fresh snow at Dye 3 also show distinct seasonal patterns. SO₄²⁻ and several trace metals show springtime maxima, consistent with the aerosol data. Na shows a winter maximum and MSA shows a summer maximum in the snow, also consistent with the aerosols. ⁷Be and ²¹⁰Pb in the snow do not show any strong variation with season. Similarly, soot and total carbon in snow do not show strong variation. When used with dry deposition models, these air and snow concentration data suggest that dry deposition of submicron aerosol species has relatively minor influence on constituent levels in the snowpack at Dye 3 compared to wet deposition inputs (including scavenging by fog); crustal aerosol, on the other hand, may have a more significant input by dry deposition. Overall, the results suggest that gross seasonal patterns of some aerosol species are constistent in the air and in fresh snow, although individual episodes in the air are not always reflected in the snow. The differences in data reported here compared with data sets for sea-level arctic sites demonstrate the need for sampling programs on the Ice Sheet in order to properly interpret Greenland glacial record data.

In the spring of 1989, airborne observations were made of C₂−C₄ hydrocarbons, ozone, and aerosols in the tropospheric boundary layer over a 96,000 km² area in the vicinity of Alert, NWT, Canada (82.5° N, 61.5° W). Samples were collected in stainless steel canisters and on filters. Aerial ozone measurements, particle counting measurements, and meteorological observations were also made.

Analysis of the canister and filter samples has provided data on C₂−C₄ hydrocarbons and ionic species (Cl⁻, Br⁻, NO₃⁻, SO₄²⁻, Na⁺, K⁺, and NH₄⁺). These data, together with observations of ozone, have provided further insight into the near-ground level ozone depletion during the Arctic spring. A positive correlation between the concentrations of ozone, ethane, propane, i-butane, n-butane, and acetylene was observed. In addition, there is an indication of a negative correlation between ozone concentrations and filterable bromine. An analysis of the relationship between the concentrations of ozone and hydrocarbons has provided evidence that chlorine atoms may be responsible for the observed depletion of hydrocarbons, but not ozone. The latter is more readily explained by reaction with bromine atoms.

Elemental composition of Arctic aerosols is being studied on the Greenland Icecap and in northeast Greenland to determine the level, composition, seasonal variation and origin of the aerosols, of which little is known in the remote and elevated central region. In particular, the degree of penetration of arctic haze aerosols is of interest since this may cause perturbations of climatic parameters.

Arctic haze aerosols have previously been found at four coastal sites notably in north Greenland. Receptor modelling of the aerosol by factor analysis revealed three to fivecomponents of remote origin from both natural and anthropogenic sources. In north Greenland the anthropogenic components exhibited large annual cycles with pronounced maxima in winter caused by long-range atmospheric transport from midlatitude areas. These measurements have been resumed as a reference to the Icecap Experiment.

On the Icecap, aerosol samples are being collected in two size ranges on a continuous basis concurrent with the Greenland Icecore Programme 1989–1993 at Summit, 3200 m a.s.l. The sampling equipment is designed for collection of weekly samples especially suited for PIXE analysis, retrieval once a year, automatic operation under extremely cold conditions and very low energy consumption. Preliminary results from samples covering for the first time also the winter season on the central Icecap are discussed in relation to arctic haze occurrences at sea level.

Airborne concentrations and size distributions of 15 elements over the Greenland Ice Sheet have been measured during a one-month period in March 1989. The concentrations are relatively uniform, varying by less than a factor of three for virtually all of the elements. Notable exceptions are Na and Cl which vary by more than an order of magnitude; these differences can probably be accounted for by the link with transport from the oceans surrounding Greenland, although a significant fraction of the Na is of crustal origin in some samples.

The size distributions show strong peaks in the accumulation mode (0.4–1.0 μm) or the coarse particle mode (1.0–2.5 μm); some species show bimodal distributions with the presence of both modes. The aerosol chemistry and size distribution data are consistent with back trajectories and local weather conditions. For example, relatively high concentrations of Pb, Zn, Ni, Fe, and Mn in the accumulation mode during one of the runs are associated with trajectories from industrial regions of the Soviet Arctic. The elements Si, Al, Fe, K, Ca, Mn, and Ti in the coarse mode are believed to be dominated by crustal sources. However, some runs show the presence of an accumulation mode for most of these elements (with the exception of Al), suggestive of combustion sources. Overall, the results show that use of an impactor with several submicron size cuts combined with a suitable data inversion program can provide insights into the sources and transport of aerosols at remote locations such as the Greenland Ice Sheet.

Airborne aerosol samples were collected during the third experiment of the Arctic Gas and Aerosol Sampling Program (AGASP-III), and the individual particles were analysed with electron microscopes and an X-ray energy spectrometer. The temporal and spatial variations of arctic aerosol physiochemical characteristics were studied relevant to the source, transport and transformation. Air trajectories arriving at the sampling sites generally provided useful information to interpret the aerosol chemistry. When the air masses passed over northern Russia, most of the aerosols were crustal dust, and approximately one-half of them were coated with sulfate. When the air masses were from northwestern Europe, solid particles, coated with sulfuric acid droplets and sulfate particles were the majority. These were probably formed by heterogeneous nucleation of H₂SO₄ followed by partial or complete neutralization. Oven open water, numerous large drops containing solid particles and cubic NaCl crystals were observed. However, over the frozen ocean, the drops and seasalt crystals were diminished. Instead, small sulfuric acid droplets, which were probably formed by homogeneous nucleation, were the principal aerosol species. At high altitudes (>5 km), pure sulfuric acid droplets and sulfuric acid drops with foreign nuclei were the dominant aerosols; however, alumina particles occasionally appeared in large quantities. Sulfate aerosols were omnipresent in the arctic stratosphere, troposphere and planetary boundary layer, whereas few nitrate-containing particles were found and then only in the boundary layer.

The aerosol dust optical thickness during a dust experiment in Tadzhikistan is derived from satellite measurements of reflected sunlight. The method estimates the surface reflectance on days with low optical thickness for the same ground area where dust occurs. In order to avoid changes in the surface bidirectional reflectance between the dusty and clear days, nearly identical geometry between the solar and view directions is obtained eight days before a dust storm. Lookup tables are utilized to obtain the surface reflectance on the clear day, and another set of lookup are tables is used to assign an optical depth to the dust. The optical depth lookup tables utilize Mie scattering for a representative size distribution and index of refraction for the dust aerosol. The observed similarity of size distributions and indices of refraction for dust aerosols at many locations over the earth justify this method. A map of the dust optical thickness is given.

Bulk filtration and sedimentation samples of soil-derived aerosol were collected during dust storms in Tadzhikistan (Soviet Central Asia) during September 1989. This study describes results about morphological, chemical and mineral characteristics of dust. The data obtained may be useful in determining the origion of the dust deposited over the sampling sites. It is suggested that the source region of the dust differs from the sampling sites and that the soil of this source area is rich in quartz and calcium carbonate.

Estimates were made of the amounts of volatile organic compounds (VOCs) released into the atmosphere as a result of the industrial manufacture and processing of food and drink in the European Community. The estimates were based on a review of literature sources, industrial and government contacts and recent measurements. Data were found on seven food manufacturing sectors (baking, vegetable oil extraction, solid fat processing, animal rendering, fish meal processing, coffee production and sugar beet processing) and three drink manufacturing sectors (brewing, spirit production and wine making). The principle of a data quality label is advocated to illustrate the authors' confidence in the data, and to highlight areas for further research.

Emissions of ethanol from bread baking and spirit maturation were found to be the principle sources. However, significant losses of hexane and large quantities of an ill-defined mixture of partially oxidized hydrocarbons were noted principally from seed oil extraction and the drying of plant material, respectively. This latter mixture included low molecular weight aldehydes, carboxylic acids, ketones, amines and esters. However, the precise composition of many emissions were found to be poorly understood.

The total emission from the food and drink industry in the EC was calculated as 260 kt yr⁻¹. However, many processes within the target industry were found to be completely uncharacterized and therefore not included in the overall estimate (e.g. soft drink manufacture, production of animal food, flavourings, vinegar, tea, crisps and other fried snacks). Moreover, the use of data quality labels illustrated the fact that many of our estimates were based on limited data. Hence, further emissions monitoring is recommended from identified sources (e.g. processing of sugar beet, solid fat and fish meal) and from uncharacterized sources.