Atmospheric Environment (1967)最新文献

A one-dimensional cumulus cloud model is used to study the chemical transformations occurring during the formation, growth and dissipation of a cloud. A parabolic vertical velocity profile is introduced to create an updraft which entrains and detrains air laterally. The cloud forms in the upper half of the updraft structure where lateral detrainment occurs, all entrainment being from below the cloud base. As the updraft velocity increases in magnitude, the cloud grows and deepens. Downdraft is introduced into the fully developed cloud so that lateral entrainment into the parcel is from regions above cloud top. The cloud dissipates and eventually disappears as the downdraft penetrates and reaches the cloud base. Predicted liquid water contents and cloud structure are consistent with field observations.

Detailed gas- and aqueous-phase chemistries are included in the cloud model. First-order rate constants for the oxidation of S(IV) to S(VI) increase with increasing concentrations of H₂O₂ in the background and with increasing cloudwater content. The cloudwater pH depends primarily on the degree of oxidation of S(IV) to S(VI) by H₂O₂ which is the most important oxidant of S(IV) in the aqueous phase. HO₂, OH, Cl₂⁻ and the intermediate SO₄⁻ also make significant contributions to the oxidation, while for these runs, O₃contributes less than 2% to the overall oxidation. Cumulus clouds are shown to behave like large variable volume reactors with entrainment of background air from below-cloud regions and release of processed air from in-cloud regions. The first-order rate constant for the oxidation of S(IV) to S(VI) ranges from 1 % min⁻¹ to 33% min⁻¹, depending on cloud properties and trace species concentrations.

A field tracer study was conducted in a hilly area on the coast of California to provide data for evaluating air quality dispersion models. Dual tracers and meteorological measurements were taken both onshore and offshore in order to investigate the transport and dispersion of pollutant plumes released from offshore sources and carried to coastal complex terrain. This paper describes the study design and presents some preliminary conclusions from the data analysis.

Common analytical techniques for PAN determination were modified in order to obtain a sensitive and automatic analysis system. PAN was synthesized by nitration of peracetic acid in hexane, The PAN/hexane solution was purified by water extraction. The quantification was performed determining acetate or nitrite by ion chromatography following alkaline hydrolysis. The validity was checked by liquid i.r. speetroscopy. NMR studies revealed a singulet signal at 2.27 ppm. The precision and sensitivity of the gas Chromatographic analyses were improved by the use of wide bore capillary columns coated with Carbowax 400. The developed system enables automatic and continuous PAN measurements at a 10 min sampling sequence and with a detection limit of 50 ppt.

Regular ground level measurements of particulate sulphate in air taken at Bjørnøya (Bear Island) and Ny Ålesund (Svalbard) are studied. Annual cycles in mean values and variances are observed, both having maxima during winter/spring. The two time-series are transformed into approximately second order stationarity, and the high-pass residuals are used to identify positive and negative anomalies. Days with positive anomalies are frequent during winter/spring and early autumn, however, the autumn anomalies rarely represent pollution episodes. The meteorological analysis selects quasi-stationary, extratropical flow systems on the planetary scale, creating extended meridional exchange of air. Two indices are applied to the 500 hPa flow; a meridional index created by wave numbers 1, 2, 3 and 4, and a zonal index. The agreement between the values of the indices and Arctic ground level air pollution, on the annual as well as the episodic time scale, strongly suggests that the occurrence of quasi-stationary, atmospheric flow systems on the planetary scale is the major cause of long range transport of polluted air to the Arctic.

The isotopic composition of aerosol lead in the polar region potentially contains information on the origin of Arctic pollution which will complement that from meteorological and trace elemental composition studies. Weekly samples of atmospheric aerosols were collected at three locations in the Canadian Arctic from mid-1983 to mid-1984. They were analyzed for elemental composition and stable lead isotope ratios (Pb $\text{206}\text{207}$). High crustal enrichment factors confirmed that the majority of samples contained lead of anthropogenic origin. Pb $\text{206}\text{207}$ ratios were very uniform over time and between sites, suggesting a common origin of lead pollution in the Canadian Arctic. The mean isotope ratios at the Alert and Mould Bay stations were 1.160±0.010 and 1.161±0.006, respectively (samples from a third site at Igloolik were evidently contaminated by local sources). A small number of samples from Spitsbergen, taken during flow predominantly out of the northern U.S.S.R., were found to have a similar mean Pb $\text{206}\text{207}$ ratio of 1.154 ±0.006. From published lead isotope analyses of Soviet lead-bearing ores, we would expect a mean isotope ratio in industrial and vehicular emissions in the U.S.S.R. of around 1.158. Contributions to Arctic lead pollution from the U.S. and western Canadian sources can probably be ruled out, as they have significantly higher Pb $\text{206}\text{207}$ ratios. Similarly, emissions from northern Canadian and Kola Peninsula smelters can be disregarded, as they appear to have low isotope ratios. Eastern Canadian automotive lead aerosol contained only marginally lower Pb $\text{206}\text{207}$ratios than in the Arctic, but meteorological studies argue against this region being a major source area for Arctic pollution. Scant European data suggest that European Pb emissions generally have lower isotope ratios than the Arctic samples. However, more data in Eurasia are needed before apportionments of Arctic Pb between sources within the region can be made.

Detailed maps of the deposition of acidifying components in The Netherlands are presented. The deposition was estimated from measurements of concentrations in the atmosphere and precipitation. Lack of information on the concentration of ammonia and ammonium in air made it impossible to estimate dry deposition. Therefore, these were estimated by model calculations. The nationwide averaged deposition of total (potential) acid in 1980 was ca. 5800 mol H⁺ ha⁻¹ a⁻¹. The most important acidifying components are sulphur oxides, nitrogen oxides and ammonia and their reaction products. Sulphur compounds (SO_x) contributed about 49%, reduced nitrogen species (NH_x) 23% and oxidized nitrogen species (NO_ty) 28% to the total deposition. Wet deposition contributes 30% to the total deposition. The spatial distribution of the total deposition shows a gradient over The Netherlands with highest values in the south and lowest in the north.

In 1986 the total deposition was estimated to be ca. 4900 mol H⁺ ha⁻¹ a⁻¹ (40% SO_x, 32% NO_y and 28% NH_x. The decrease is mainly the result of the lower SO_x deposition. The relative contribution of inland emissions to the deposition in The Netherlands is about 41%. About 30% of the NH, deposition is due to foreign sources; for SO_x this is about 80% and for NO_y 65%. About 80% of Dutch emissions is deposited outside The Netherlands. The net export of SO_x decreased between 1980 and 1985 from 150 kt a⁻¹ to 35 kt a⁻¹, while the net export of NO_y (ca. 280 kt a⁻¹) and NH, (ca. 155 kt a⁻¹) has remained constant over the period 1980–1986.

The flux of fog droplets to a moor (elevation 330 m) in central England, measured by the fluxprofile technique, was usually less than 15 mg m⁻²s⁻¹. On average, turbulent deposition accounted for a third of this flux. The total flux depended on properties of the fog (droplet size and liquid water concentration) rather than parameters of eddy transfer (friction velocity or turbulent deposition velocity). The annual deposits of acidity, nitrogen (as nitrate) and sulphur were estimated to. be 7, 50 and 80 mg m⁻², respectively. Occult deposition of sulphur represented only 1.5% of the total (dry plus wet) deposition to the moor.

There is a need to be able to predict the compound-dependent volumes of gas that can be sampled with little breakthrough using porous polyurethane foam (PUF). Gas/solid sorption theory predicts that the specific retention volume per gram of sorbent at temperature T(K) (V_g.T., m³ g⁻¹) should correlate with the vapor pressure of the pure compound (p_T^o-, torr) at T. For compounds that are solids at the T of interest, the vapor pressure of the sub-cooled liquid (p_L^o,T) should be used. For polyether-type PUF that has a density of ~ 0.022 g cm⁻³, regressions of available data lead to the following correlation equations: (1) polycyclic aromatic hydrocarbons, log V_g,293 = −1.195 logp_L,293^o−1.884 (r² = 0.989); and (2) organochlorine compounds, log V_g,293= −1.059 logp_L,293^o−1.764 (r² = 0.950). These equations will be useful in predicting retention volumes for compounds whose behavior on PUF have not as yet been studied. If the entropy of desorption for a given compound from PUF is equal to the entropy of desorption from the pure form of the compound, then the'available data indicate that the difference between the enthalpy of desorption from PUF and the enthalpy of vaporization of the pure compound is about 6 kcal mol⁻¹ for both the PAHs and the organochlorine compounds.