Atmospheric Environment. Part A. General Topics最新文献

The reaction of nitrogen dioxide in air with water, and with a range of aqueous solutions, has been studied by measuring the loss of nitrogen dioxide from the gas-phase after bubbling through a fixed volume of solution. Concentrations of NO₂ between 10 and 40 ppbv (1 ppbv = 10⁻⁹ atm) were generated using a permeation tube. The characteristic mixing time of the reactor (60 s) was estimated by measuring the increase in conductivity of water as an air stream containing 1% CO₂ was passed through the reactor. All measurements were made at 10°C. Values for the second-order reaction rate constant (k₂) and the Henry's Law coefficient (H_NO2) were estimated from a least-squares fit to an equation which explicitly included the rate of mixing in the reactor. The second-order rate constant was defined from the equation $\text{-d[NO}{}_2\text{]}{}_{\mathrm{aq}}\text{dt}\text{=2·k}{}_2\text{·[NO}{}_2\text{]}{}^2{}_{\mathrm{aq}}$

There was no evidence of a parallel first-order reaction of NO₂ with water or solutes. The overall reaction rate coefficient for the second-order reaction with water (relative to the gas phase) at 10°C (k₂·H_NO2²) was 1.8 × 10⁴M s⁻¹ atm⁻², the best-fit values for k₂ and H_NO2 were (6.0±2.0) × 10⁶ M⁻¹ s⁻¹ and (5.5±0.6) × 10⁻² M atm⁻¹, respectively.

Synthetic sea water, made from NaCl alone, or including the other major ionic constituents, showed similar reaction rates to deionized water. A solution of sea sal salt gave an overall reaction rate of 7.4 × 10⁴ M s⁻¹ atm⁻², and a sample of coastal sea water gave an overall reaction rate of 15 × 10⁴ M s⁻¹ atm⁻², on the assumption of uniform concentration of NO₂(aq) in the test solution, which may not be valid. The apparent eight-fold increase in reaction rate for sea water relative to deionized water is, however, not sufficient to increase significantly the rate of removal of NO₂ from the atmosphere above the ocean such that atmospheric transport limits the process. Uptake of NO₂ is limited by aqueous-phase mixing in the sea surface, with overall deposition velocities unlikely to exceed 0.1 mms⁻¹.

A mechanistic model for calculating ammonia losses from stored slurry is developed. The model is tested against ammonia loss data determined with wind tunnels covering pilot slurry tanks. Wind speed within the tunnels was adjusted from 1.8 to 10 m s ⁻¹. There was agreement between the predicted and measured ammonia loss rates from uncovered slurry and slurry covered by surface crust or a 15 cm straw layer. A surface resistance parameter $\text{(r}{}_{\mathrm{<mtext>c</mtext>}}\text{)}$ is included in the transfer coefficient of the model. It is shown that surface resistance is of great importance if the slurry is covered by a surface crust or a 15 cm straw layer. Ammonia losses increased curvilinearly with wind speed approaching a maximum at about 6 m s⁻¹. The transport coefficient for ammoniacal nitrogen in the stored slurry was found to be about 10-times higher than the diffusion coefficient of ammonium in water. This is probably caused by convection.

Regional emission densities of anthropogenic non-methane volatile organic compounds (NMVOC) in Austria were calculated using statistical information on emission generation activities, emission factors from technical literature, and regional reference data.

Total anthropogenic NMVOC emissions in Austria were estimated to be 467,000 metric tons for the base year 1987. However, due to the high uncertainties of the available emission factors, the range could be as much as 316,000–754,000 t yr⁻¹. Anthropogenic NMVOC emissions consist of 32% paraffin, 8% olefin, 20% aromatic, 13% carbonyl, 6% photochemically “non-reactive”, and 20% other compounds.

The total emissions from each source group were regionally disaggregated based on settlement densities, traffic densities, and relevant regional source statistics. In total about 45,000 polygons were defined for an area of 84,000 km². While the theoretical average emission density for anthropogenic NMVOC in Austria would be around 5.6 t km⁻² yr⁻¹, the actual emission densities vary from 0 in unpopulated regions to 50–100 t km⁻² yr⁻¹ in urban areas and upto 700 t km⁻² yr⁻¹ along major highways. National average values for emission densities fail thus to reveal the scale of emission densities in populated areas.

The shrub-steppe area near Shaartuz, Tadzhik, S.S.R., is shown to be a net accumulator of dust despite being an occasional source of dust. For the accumulation of the dust to form the observed surface crust, a net deposition of about 290–490 g m⁻² yr⁻¹ of particles smaller than 20 μm is required, depending on the duration of the deposition period. The particles smaller than 20 μm are mixed with particles brought up from the sandy material below the surface crust by bioturbation and are incorporated into the surface crust. Measurements during the 16 and 20 September 1989 dust storms provided a total deposition of 41.1 g m⁻² of particles smaller than 20 μm. Because 10–30 dust storms are observed at Shaartuz, the measured average dust storm deposition would yield 206–617 g m⁻² yr⁻¹. This range of deposition is of the order of that needed to provide a mass balance for the observed crust formation. Cryptogams (including algae, lichen, and moss) and rainwater are the main agents of incorporation of the aeolian dust into a stable soil crust. The role that the vascular plants played at the Shaartuz site was to reduce the rate of soil movement to levels where the cryptogamic crusting was possible. the observed mechanisms of dust deposition followed by crust incorporation are possibly an important processes in loess formation in Central Asia.

An overview of the wet deposition of micropollutants (trace metals—Cd, Cr, Cu, Pb, Hg, Zn— and organic compounds—PAHs, PCBs, pesticides) to the North Sea and adjacent areas is presented. The results of (in)direct measurements of the wet flux are compared to modelling results. Attention is given to specific problems like revolatilization, sea-spray, contamination, gas-to-particle ratios in wet deposition of Hg and the organic substances. Also, the importance of wet deposition is weighted to that of dry deposition and non-atmospheric input routes to the North Sea. It is concluded that—especially for organic micropollutants—current knowledge is insufficient to yield an accurate and detailed image of the impact and importance of wet deposition to the North Sea.

Aerosol samples from dust storms were collected in Tadzhikistan (Soviet Central Asia) during September 1989, as a part of the joint U.S.S.R.-U.S. Dust Experiment. Physico-chemical characteristics of deposited dust were compared with those of soil-derived dust collected in other regions. Particle mass-size distributions appear to be characterized by a common log-normal mode between 1 and 10 μm. Chemical composition of the sampled material shows that the dust is particularly rich in calcium and silicon and poor in iron. Estimated mineral composition of dust indicates that this enrichment in Ca and Si for the Soviet Asian dust must be related to high contents of carbonate and quartz, respectively. Different Fe/Al also suggest a specific chemical composition for clay minerals in the Asian dust.

This paper compares published data on the complex refractive index of atmospheric dust aerosols, for different geographical regions, with data obtained for dust aerosol samples collected during the joint U.S.S.R.—U.S. experiment in Tadzhikistan, 1989. The disadvantages of methods used for estimation of the imaginary part, æ, of the refractive index are discussed. There is a considerable range of values of æ for dust aerosols, which is crucial for optical characteristic simulation. The existing discrepancy in æ can be due to uncertainties in methods used as well as due to the specific chemical composition of dust aerosols from various geographic locations.

This paper describes synoptic meteorological conditions during the U.S.S.R./U.S. dust experiment, September 1989. The 12 papers originating from the U.S.S.R./U.S. dust experiment are more fully described in Golitsyn and Gillette (1993, this issue). It is shown that dust episodes of this period may be categorized as dust haze transported to observational sites from a distant dust source and local dust produced by soil erosion. Two different types of dust storms (continuous and squall) are presented. Continuous storms occur when cold fronts of medium thickness (but greater than 1 km) intrude. Foothills which lie to the south in Afghanistan are believed to correspond to the area of dust generation for continuous storms, whereas the desert sand plateau in northern Afghanistan, to the west of the Kafirnigan River Valley, and local soil erosion are believed to correspond to the area of dust generation for squall storms. To aid in the description of synoptic meteorological conditions analyses of the televisual (t.v. = 0.5−0.7 μm) and infrared (i.r. = 8−12 μm) images from the Russian Meteor-2 satellite are presented.

Wetfall and bulkfall were collected on Mt Carmel, Israel, for three hydrological years, 1989–1992, using an acid precipitation sampler equipped with a moving cover. The analysis of 40 rain events indicated that in more than 65% of the events the pH was acid (<5–6) and in nearly 40% of the events strongly acid. Only in 12% of the events was the pH distinctly alkaline. Bulkfall collected on the same site had a higher pH, due to much higher Ca²⁺ and K⁺ concentrations, suggesting the effects of local aerosols emanating from calcareous soils. The relatively high Na⁺ and Cl⁻ levels and their Na⁺/Cl⁻ ratio of 0.866 indicated the marine origin of the major portion of dissolved salts. Alkaline wetfall, strongly enriched in K⁺, Cl⁻ and Na⁺, was associated with duststorms. X-ray and chemical analysis of the dryfall (dust) showed the presence of quartz, carbonates, clay minerals, feldspar, halite and gypsum. SO₄²⁻, responsible for the acidity of the wetfall, appears to be imported from Central or Eastern Europe, via the Mediterranean Sea, as suggested by back-trajectories of 26 rain events.

The purpose of this study was to determine the concentration of carbon monoxide (CO) in blood (COHb) and breath to demonstrate that breath hydrogen (H₂) can be a significant interferant. For this purpose, we measured blood COHb with CO-oximetry and breath CO with an electrochemical analyzer. In addition, the samples were analyzed by gas chromatography (GC). The concentration of CO in breath, collected with a Priestley tube after a 20 s breath hold, from healthy, nonsmoking adult males (n = 20) and females (n = 10) had a mean ± SD (range) of 2.6 ± 0.4 ppm (2.0–3.9), respectively, when measured by GC. However, these same samples when measured with an electrochemical (EC) analyzer showed elevated CO values of 4.7 ± 2.9 ppm (2.6–17.6). The concentration of H₂, a prominent trace gas in breath known to interfere with EC analyzers, correlated strongly with the observed EC analyzer response [EC (ppm CO) = 0.336 H₂ (ppm) + 1.93, r² = 0.98]. The EC analyzer was linear for H₂ concentrations up to 40 ppm, with a sensitivity of 0.035 V ppm⁻¹. The analyzer sensitivity to CO was 0.10 V ppm ⁻¹. Blood from this population showed COHb concentrations of 0.56 ± 0.11% (0.40–0.97), as measured by GC, but elevated values were found when measured by CO-oximeter (Ciba Corning Diagnostics Corp., Models 2500 and 270), 1.3 ± 0.2% (1.1–1.6) and 1.0 ± 0.3% (0.1–1.6), respectively. When breath CO was compared to blood COHb, only measurements by GC significantly correlated [COHb% = 0.241 CO(ppm) — 0.076, r² = 0.78]. We conclude that, relative to quantitative analysis by GC, (1) EC analyzers are susceptible to H₂ interference that cause falsely elevated CO measurements, and (2) CO-oximeters overestimate COHb concentrations in the range typical for healthy nonsmokers.