Atmospheric Environment. Part A. General Topics最新文献

High volume filter samples were collected at Poker Flats in central Alaska, between 1984 and 1987, and analysed for a comprehensive suite of elements. In this report we focus on the results for the halogen elements Br, Cl and I, and their correlations with other selected elements (Al, As, Na, Se, and V). Seasonal cycles were observed for the halogens, including a pronounced spring peak in Br and a weak fall peak, pronounced spring and fall peaks in I, and increased winter/spring Cl. A significant correlation between Br and Se was shown to be partly due to common transport pathways, and possibly some common sources. Iodine showed enrichments of three orders of magnitude over sea water composition. Correlations to marine elements suggested a marine biogenic source. Chlorine evidently originated from sea salt aerosols, but showed evidence of substantial volatilization, correlated to the degree of pollution of the air mass.

Controlled exposure of ice to a reactive gas, SO₂, demonstrated the importance of the chemical composition of the ice surface on the accumulation of acidity in snow. In a series of bench-scale continuous-flow column experiments run at four temperatures (−1, −8, −30 and −60°C), SO₂ was shown to dissolve and to react with other species in the ice-air interfacial region at temperatures approaching the melting point of ice. Experiments consisted of passing air containing SO₂ through glass columns packed with 100-μm ice spheres of varying bulk composition (0–5 μM H₂O₂, and 0–1 mM NaCl), and analysing SO₂ in the air and SO₄²⁻ in the ice. At all temperatures (−60 to −1°C), increased retention volumes were found for increasing ionic strength and oxidant concentration. At the coldest temperatures and with no NaCl, increased retention volumes for −60 vs −30°C are consistent with SO₂ uptake by physical adsorption. At warmer temperatures, −8 and −1°C, the observed tailing in the sorption curves indicated that other processes besides physical adsorption were occurring. The desorption curves showed a rapid decrease for the warmer temperatures, indicating the sorbed SO₂ is irreversibly oxidized to SO₄²⁻. Results indicate that aqueous-phase reactions can occur below −8°C (i.e. −30 and −60°C). Results for different salt concentrations show that increasing ionic strength facilitates SO₂ oxidation at colder temperatures, which is consistent with freezing point depression. One environmental implication is that snowpacks in areas with background SO₂, can accumulate acidity during the winter months. As acidity accumulates, the solubility of SO₂ will decrease causing a concomitant decrease in the air-to-surface flux of SO₂. Modeling dry deposition of gases to snow surfaces should incorporate the changing composition of the ice surface.

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.

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.

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.

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.

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.

A dust aerosol optical model is proposed as a result of analysis of the data obtained during the U.S.S.R.-U.S. experiment in Tadzhikistan, 1989. The model consists of spectral dependencies of the single scattering albedo, ω, the asymmetry parameter of the scattering phase function, g, and of possible values of the aerosol optical thickness, τ, for background conditions and for dust storms. This model and available published optical models of dust aerosols were used to perform simulations of radiative forcing in the dusty atmosphere. Results obtained are compared with corresponding results for Saharan aerosol. It is shown that atmospheric dust strongly decreases the total radiative balance of the underlying surface and at the same time induces general warming of the underlying surface-atmosphere system due to a decrease in the system albedo over the arid zones. The calculated heating/cooling rates in the atmosphere are analysed together with data from aerological soundings and radiation measurements.

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.