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Over the past several years, a number of Gaussian plume–based computer codes have been produced. These codes describe transport, transformation, and deposition of air pollutants under a variety of atmospheric conditions. For a number of reasons, there is increasing interest in simulating wet-deposition processes in such codes, and several approaches have been applied to this end. Some of these approaches involve elaborate solubility and chemistry characterizations, but many of them resort to a diversity of approximate techniques. This paper presents a procedure that can be used as a practical guide to improve many of these formulations, especially for the case of pollutant gases. The approach takes the form of a set of analytical equations that correspond to five kinds of Gaussian plume formulations: standard bivariate-normal point-source plumes, line-source plumes, unrestricted instantaneous puffs, and point-source plumes and puffs that experience reflection from inversion layers aloft. These eq...

In this article, a research strategy for improving the estimates of the clear sky forcing is defined. The strategy encompasses five major, and necessarily coordinated, activities: surface-based observations of aerosol chemical and physical properties and their influence on the radiation field; aircraft-based observations of the same properties; process studies to refine model treatments; satellite observations of aerosol abundance and size distribution; and modeling studies to demonstrate consistency between the observations, to provide guidance for determination of the most important parameters, and to allow extension of the limited set of observations to the global scale. Such a strategy, if aggressively implemented, should allow these effects to be incorporated into climate models in the next several years. A similar strategy for defining the magnitude of the cloudy sky forcing should also be possible, but the less firm understanding of this forcing suggests that research of a more exploratory nature be carried out before undertaking a research strategy of the magnitude recommended for the clear sky forcing.

Receptacle regeneration in the adventive marine brown alga Sargassum muticum (Yendo) Fensholt (Fucales, Phaeophyta) is examined using light and electron microscopical (SEM, TEM) techniques and laboratory culture studies. After transverse bisection, receptacle regeneration occurred under a wide range of temperatures and at different daylengths but was inhibited under winter conditions (10°C, 8:16 h). Regeneration is a particularly rapid process with mature, zygote-bearing receptacles formed at the cut surface within 21 d at 20°C, 16: 8 h and 88 μmol photons m−2 s−1. Cytological and morphogenetic changes observed after wounding include: the breaking of intercellular plasmodesmatal connections; retraction of cytoplasm and deposition of new fibrillar material beneath the exposed degenerating cell walls, preventing cytoplasmic loss; the formation of a protective wound epidermis over the entire cortical wound surface by finite mitoses in the outermost cell layer; concurrent mitoses to a depth of at lea...

Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of shortwavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

In 1991, the Pacific Northwest Laboratory conducted a series of aircraft measurements to determine pollutant and radiative properties of the smoke plume from oil fires in Kuwait. This work was sponsored by the US Department emanating of Energy, in cooperation with several other agencies as part of an extensive effort coordinated by the World Meteorological Organization, to obtain a comprehensive data set to assess the characteristics of the plume and its environmental impact. This report describes field measurement activities and introduces the various data collected, but provides only limited analyses of these data. Results of further data analyses will be presented in subsequent open-literature publications.

In April 1990, forty-two scientists from eight countries attended a workshop at the Bermuda Biological Station for Research to compare field measurements with model estimates of the distribution and cycling of sulfur and nitrogen species in the North Atlantic Ocean's atmosphere. Data sets on horizontal and vertical distributions of sulfur and nitrogen species and their rates of deposition were available from ships' tracks and island stations. These data were compared with estimates produced by several climatological and event models for two case studies: (1) sulfate surface distributions and deposition and (2) nitrate surface distributions and deposition. Highlights of the conclusions of the case studies were that the measured concentrations and model results of nitrate and non-sea-salt sulfate depositions appeared to be in good agreement at some locations but in poor agreement for some months at other locations. The case studies illustrated the need for the measurement and modeling communities to interact not only to compare results but also to cooperate in improving the designs of the models and the field experiments.

This paper reports aircraft observations of the Kuwait oil fire plume conducted during the period July 31-August 17, 1991. During this study the plume was transported almost exclusively to the south of Kuwait over the Persian Gulf and the Arabian Peninsula. The plume base was generally found to be well above the surface, in some cases as high as 1–2 km; plume tops did not exceed 5 km. Aerosol mass (based on measured aerosol constituents) in the central section of the plume, ca. 150–200 km downwind of the source region, was found to be >500 μg/m3, with number densities in the size range (approximate) 0.2 < d < 3 μm (where d is diameter) as high as 30,000/cm3. The aerosol was composed of (in order of approximate contribution to mass) inorganic salts, elemental carbon, and organic carbon. Sodium chloride constituted a surprisingly large component of the soluble inorganic mass. The aerosol particles appeared to function as good cloud condensation nuclei, with a large fraction of accumulation mode particles (by number) activated at a supersaturation of 0.6%. Under conditions in which the plume was relatively compact, transmittance of solar radiation to the surface was only 10–20%. Plume albedo was observed to be as low as 2–3% close to the source region, consistent with the high elemental-carbon concentrations present in the plume. Trace gas concentrations were consistent with fuel composition and with current knowledge of atmospheric chemical processes. Sulfur dioxide concentrations close to the source region were found to be as high as 300–400 ppb. The emissions factor for S (expressed as a percentage) was estimated to be 1.8%, which is consistent with estimates of a fuel sulfur content of 2–2.5%. SO2 was found to be only slowly oxidized (

Three demands for wet-deposition data and dry-deposition data are particularly important at the present time: 1) the analysis of long-term trends to evaluate the consequences of emission changes, 2) the measurement of deposition loadings to determine impacts to receptors, and 3) model development and the analysis of atmospheric source-receptor phenomena. The diversity of these demands has led to deployment of a variety of networks to satisfy different measurement requirements. Consideration of this diversity of network goals has led to a distinction between research-oriented networks and routine measurement networks. Research-oriented networks generally contain a comparatively small number of stations, and make relatively intensive measurements with fine time resolution, to focus on relevant processes. These networks use relatively advanced measurement techniques and require much-greater scientific attention than routine measurement networks. Routine networks usually have a greater number of simp...

A comparison is made of the roles played by thermophoresis, Brownian diffusion and diffusiophoresis in the precipitation scavenging of aerosol particles. It is shown, for a certain range of particles sizes, that thermophoresis dominates provided that the latent heat associated with the phase transition of water is transferred through the air, to or from the precipitation element by conduction. A plot of the resulting washout coefficient shows that thermophoresis enhances the below-cloud rain scavenging of aerosol particles whose radii are between 0.01 and 1.0μ. The solution is presented for the appropriate convective diffusion equation which describes thermophoretic effects on the in-cloud scavenging problem.

The general belief that significant fractions of atmospheric sulfur are donated naturally from the earth's surface in the form of hydrogen sulfide and/or its organic homologs implies that atmospheric breakdown of these materials must be a rather fast process. It has been expected that oxidation of these materials by atmospheric ozone should contribute significantly in accomplishing this breakdown; and experimental measurements have been published which do, indeed, indicate rapid ozone oxidation rates, corresponding to lifetimes of the order of hours under typical tropospheric conditions. This paper discusses some later experimental measurements on H 2 S ozone reaction rates which disagree with former determinations, predicting typical H 2 S lifetimes of the order of months—much too long for this reaction to be a significant mechanism of atmospheric removal. The results also indicate the H 2 S ozone reaction should be expected to proceed homogeneously in the atmosphere, with catalytic effects being of little or no importance. The reaction proceeds thermally; light in the visible region does not affect its rate appreciably. These measurements indicate that some mechanism(s) other than ozonation must be responsible for atmospheric breakdown of reduced sulfur compounds. Final portions of the paper examine some possibilities for these mechanisms. DOI: 10.1111/j.2153-3490.1974.tb01978.x

This chapter examines the physical basis for precipitation scavenging, and provides an intermediate-level primer for scavenging calculations. The discussion is presented in the context of spatial and temporal variability of precipitation chemistry. It begins with a qualitative overview of behavior observed on precipitation-chemistry networks, and then provides a physically based rationale for these observations.

METROMEX observations relating to urban weather modification are summarized and examined against background knowledge and theory.

Mass-transfer effects and surface reactions may severely obscure the observation of homogeneous chemical reaction rates from experimental reactor data. Such problems are particularly pertinent to studies in the atmospheric sciences, owing to the tendency for increased surface-reaction interference at the low concentrations usually of interest. Criteria are presented for ideal behavior in three basic types of experimental reactors. Under conditions satisfying these criteria the effects of competing surface reactions can be accounted for quantitatively, allowing the true homogeneous effect to be observed. Data from tubular reactors can be analyzed accurately even under some nonideal conditions. The available solutions to tubular reactor models useful for this purpose were compiled and tabulated. (auth)

Observations are presented of the mean annual concentration and deposition of H + , SO 4 NO - 4 and NH + ions in precipitation in North America during 1980, the first year that a reasonably compatible merger of US and Canadian federal network data was possible. The maximum concentration and wet deposition of H + , SO = 4 and NO - 3 occurred in-and south of-the great lakes region near maximum anthropogenic emissions of sulphur and nitrogen oxides. The NH + 4 maximum, however, was located in the north central US where American livestock feedlots are concentrated. Peak H* concentrations were 60-80 μmole l -1 . In the region of maximum emissions, 1980 observations of H + , SO = 4 and NO - 3 wet deposition are within 25% of the 5-year mean for 1977-1981. The respective fraction of anthropogenic sulphur and nitrogen oxides released in eastern North America that are wet deposited in the same area is 24 ± 6 and 25 ± 6%. On a smaller scale, in the high sulphur and nitrogen oxide emissions area of the northeastern US. the deposition was 13 and 18% of emissions, respectively. Trends in emissions as well as in SO = 4 and NO - 3 concentrations in precipitation support the conclusion that a real increase in acidity of precipitation of 30-37 μmol l -1 has occurred in the southeastern US since 1955/56 DOI: 10.1111/j.1600-0889.1984.tb00253.x