Transport Of Atmospheric Aerosols Research Articles

Regional model for formation, dynamics, and long-range transport of atmospheric aerosol

This paper is concerned with various aspects of regional transport modeling of atmospheric aerosols, or particulate matter (PM), including their physical and chemical transformations and presents a recently developed aerosol model. The model accounts for all of main aerosol processes, including aerosol emissions, formation, dynamics, atmospheric transport, and removal. The model includes primary and secondary aerosols of both anthropogenic and natural origin and allows calculating mass and number concentrations and size distribution of multicomponent aerosols. A flexible model structure makes it possible to change a description of aerosol size distribution, to include new aerosol components, to modify numerical schemes used in the model, and to include new schemes. The combination of model computational efficiency with satisfactory accuracy of results facilitates the use of the model for operational calculations of the current transboundary air pollution and pollution trends in Europe within EMEP (Co-operative Programme for Monitoring and Evaluation of the long-range transmission of air pollutants in Europe), as well as for estimation of future air pollution scenarios to support the strategy development for optimal emission regulations in Europe.

Transport of Atmospheric Aerosol by Gap Winds in the Columbia River Gorge

Abstract Typical diurnal wind patterns and their relationship to transport of atmospheric aerosol in the Columbia River gorge of Oregon and Washington are addressed in this paper. The measurement program included measurements of light scattering by particles (bsp) with nephelometers, and wind speed and direction, temperature, and relative humidity at seven locations in the gorge. Winds are shown to respond to along-gorge pressure gradients, and five common patterns were identified: strong, moderate, and light westerly (west to east), light easterly, and winter easterly. The strong westerly and winter easterly patterns were the most common summer and winter patterns, respectively, and represented strong gap flow. The light westerly and light easterly patterns occurred most frequently in spring and autumn transition periods. Winter easterly had the highest light scattering and indicated sources east of the gorge mainly responsible for haze. During summer, as westerly winds increased diurnally, a pulse of hazy air from the Portland, Oregon, metropolitan area is transported eastward into the gorge, arriving later with distance into the gorge. During light easterly flow impacts to haze from the city of The Dalles, Oregon, are noted as the wind shifts direction diurnally.

Soot in the arctic snowpack: a cause for perturbations in radiative transfer

Recent data collected in the Arctic have demonstrated the transport of atmospheric aerosol of anthropogenic origin into that region. Concern over the radiative effect of the highly-absorbing soot component of this aerosol has resulted in a variety of atmospheric sampling efforts aimed at assessing the climatic impact of this component. However, little attention has been given to the measurement of soot deposited on the Arctic snowpack and the resulting perturbation of snow albedo, snowmelt rates and radiative transfer. Here we report measurements of light-absorbing material in the Arctic snowpack for longitudes from 25 E to 160 W. The contributions to light absorption due to natural crustal and soot aerosol are identified by their wavelength dependence. Reductions in Arctic snow albedo of one to several percent appear probable for the soot/ice mass fractions obtained to date. Estimates of the impact of this reduced albedo on the Arctic radiation budget over a season are shown to approximately equal that of the Arctic haze itself. The absorption of shortwave radiation by the springtime snowpack is estimated to be 5–10% higher than that of soot-free snow for this data.

Turbulent transport of atmospheric aerosols and formation of large-scale structures

Turbulent transport of aerosols and droplets in a random velocity field with a finite correlation time is studied. We derived a mean-field equation and an equation for the second moment for a number density of aerosols. The finite correlation time of random velocity field results in the appearance of the high-order spatial derivatives in these equations. The finite correlation time and compressibility of the velocity field can cause a depletion of turbulent diffusion and a modification of an effective mean drift velocity. The coefficient of turbulent diffusion in the vertical direction can be depleted by 25 % due to the finite correlation time of a turbulent velocity field. The latter result is in compliance with the known anisotropy of the coefficient of turbulent diffusion in the atmosphere. The effective mean drift velocity is caused by a compressibility of particles velocity field and results in formation of large-scale inhomogeneities in spatial distribution of aerosols in the vicinity of the atmospheric temperature inversion. Results obtained by Saffman (1960) for the effect of molecular diffusivity in turbulent diffusion are generalized for the case of compressible and anisotropic random velocity field. A mechanism of formation of small-scale inhomogeneities in particles spatial distribution is also discussed. This mechanism is associated with an excitation of a small-scale instability of the second moment of number density of particles. The obtained results are important in the analysis of various atmospheric phenomena, e.g., atmospheric aerosols, droplets and smog formation.

In situ measurements of organics, meteoritic material, mercury, and other elements in aerosols at 5 to 19 kilometers

In situ measurements of the chemical composition of individual aerosol particles at altitudes between 5 and 19 kilometers reveal that upper tropospheric aerosols often contained more organic material than sulfate. Although stratospheric aerosols primarily consisted of sulfuric acid and water, many also contained meteoritic material. Just above the tropopause, small amounts of mercury were found in over half of the aerosol particles that were analyzed. Overall, there was tremendous variety in aerosol composition. One measure of this diversity is that at least 45 elements were detected in aerosol particles. These results have wide implications for the complexity of aerosol sources and chemistry. They also offer possibilities for understanding the transport of atmospheric aerosols.

Vertical profiles and horizontal transport of atmospheric aerosols and trace gases over central Ontario

The Canadian intensive measurement periods of the Eulerian Model Evaluation Field Study (EMEFS) were conducted in the summer of 1988 and the spring of 1990 in central Ontario, Canada. The project involved using instrumented research aircraft to measure vertical profiles of atmospheric aerosols and trace gases over special ground observing sites. Oxidant concentrations were often highest aloft. There were no strong diurnal variations in O3 and H2O2, suggesting that oxidant concentrations reported in this paper, as well as other species, seem to be most influenced by transport mechanisms rather than local chemical transformations. Aerosol and SO2 concentration vertical profiles tended to be similar to those of water vapor mixing ratio, showing a maximum near the surface, which points to a ground level source for these constituents. The inorganic aerosol was dominated by sulphate during the summer measurements, but particulate nitrate was important during the spring. The horizontal transport of these species was calculated for air with back trajectories from the north or south, showing transport to occur primarily from west to east for both cases, with components to the south or north, respectively. The sulphur is transported primarily as SO2 in the spring and about half as SO2 and half as SO4= in the summer. Air from the south is a source of particles, S, H2O, O3, H2O2 and NO2 to this region. Similarly, cloud water concentrations of sulphate and nitrate were higher with southerly trajectories, as were aircraft filter measurements of sulphate, nitrate, ammonium, and nitric acid.

Atmospheric transport of aerosols and trace gases over southern Africa

Atmospheric transport of airborne material over and out of a region has important consequences for global change. In this article, recent developments concerning the transport of air, aerosols and trace gases in the troposphere over southern Africa will be examined. Regional circulation patterns affecting horizontal advection of aerosols and trace gases and the thermo dynamic controls modifying their vertical transport are considered. From trajectory dispersion fields, preferred transport pathways over and out of southern Africa are determined, as too is the extent of recirculation taking place over the subcontinent. Estimates of the mass fluxes of aerosols are given and the consequences of increasing aerosol loading in the atmosphere are examined.

Transport of coagulating aerosol in the atmosphere

Transport of atmospheric aerosol by air masses is considered on the basis of a realistic model taking into account almost all factors influencing the particle size distribution: turbulent diffusion, energy-momentum thermo-hydrodynamic balance, the relief of the substrate surface, location of the sources of aerosols and the particle growth due to coagulation process. After formulating the set of basic equations the procedure of their numerical solution is described. The model is applied for reproducing the aerosol distribution over the town of Bratsk in the summer period. The results are compared with the concentration levels of submicron and highly disperse aerosols measured at several points over Bratsk during a two-week summer expedition in 1990. The model is shown to give reasonable information on the aerosol size spectra in the lower layer of the atmosphere at heights up to 500 m.

On the use of surface equivalent potential temperature in isolating the influence of local as opposed to transported sources on aerosol concentrations

An atmospheric aerosol transport hypothesis is presented. An analytical technique, based on an analysis of surface equivalent potential temperature, is used to isolate meteorological conditions that encourage an introduction of transported (advected) aerosols into the surface layer. The difference between the equivalent potential temperature at the surface and 700‐ mbars and the identification of periods of precipitation, are used to define the stability characterstics of the lower troposphere. It is suggested that these three meteorological parameters provide an excellent indication of the horizontal and vertical exchange occurring in the lower troposphere. These parameters, calculated for six upper air sounding stations in North America, are used to isolate those time periods when aerosol populations are most likely influenced by local as opposed to advected sources. Sources of particulate SO4, Al, Se, and crustal corrected V measured at sampling sites in New York State are evaluated with this technique.

Olfactory Navigation in Homing Pigeons: Are the Current Models Atmospherically Realistic?

True olfactory navigation necessitates that homing pigeons (Columba livia) employ an odor "map" when determining their position relative to the home loft. Two models exist currently to explain the nature of this olfactory map. The "mosaic" map model suggests that pigeons learn a patchwork of olfactory cues by direct experience with local odors and determine displacement from the home loft by recognizing these familiar odors upon release. The "gradient" map model postulates the existence of stable odor gradients that extend over distances of up to 1,000 km. Pigeons learn the home value of an olfactory gradient while growing up, and then determine their positions with respect to home by comparing this learned value with the gradient value detected at the point of release. I analyzed both the mosaic and gradient olfactory map models in light of new data on the long-range transport of atmospheric aerosols. These data, obtained in 1983 as part of the Cross-Appalachian Tracer Experiment (CAPTEX '83), cover the region of New York state where extensive experiments on pigeon homing have been conducted from the Cornell University pigeon loft during the past 18 yr. The CAPTEX '83 data provide the first opportunity to assess accurately the atmospheric plausibility of an odor-based navigation system for homing pigeons flown in the northeastern United States. I conclude that the observed patterns of long-range aerosol transport place important limits on the type of olfactory navigation system potentially utilized by homing pigeons. Moreover, a comparison of the CAPTEX '83 data with meterological information relevant to atmospheric conditions in other geographic locations suggests that regionally specific atmospheric patterns may dictate whether pigeons can reliably employ odors during navigation. This regional specificity is proposed as an explanation for the observed discrepancy between results obtained in olfactory navigation tests conducted in Italy and those performed in the northeastern United States.

Soot in the Arctic snowpack: a cause for perturbations in radiative transfer

Recent data collected in the Arctic have demonstrated the transport of atmospheric aerosol of anthropogenic origin into that region. Concern over the radiative effect of the highly-absorbing soot component of this aerosol has resulted in a variety of atmospheric sampling efforts aimed at assessing the climatic impact of this component. However, little attention has been given to the measurement of soot deposited on the Arctic snowpack and the resulting perturbation of snow albedo, snowmelt rates and radiative transfer. Here we report measurements of light-absorbing material in the Arctic snowpack for longitudes from 25 E to 160 W. The contributions to light absorption due to natural crustal and soot aerosol are identified by their wavelength dependence. Reductions in Arctic snow albedo of one to several percent appear probable for the soot/ice mass fractions obtained to date. Estimates of the impact of this reduced albedo on the Arctic radiation budget over a season are shown to approximately equal that of the Arctic haze itself. The absorption of shortwave radiation by the springtime snowpack is estimated to be 5–10 % higher than that of soot-free snow for this data.