Kenneth A. Rahn

Elemental Tracers of Distant Regional Pollution Aerosols

A seven-element tracer system shows that regional pollution aerosols of both North America and Europe have characteristic signatures that can be followed into remote areas up to several thousand kilometers downwind. In aerosols of mixed origin, regional contributions to the tracer elements can be resolved by least-squares procedures. After transport of several hundred kilometers, secondary sulfate can also be apportioned satisfactorily. Regional elemental tracers thus offer a way to determine the sources of pollution aerosol in important areas such as the northeastern United States, Scandinavia, and the Arctic.

ON THE ORIGIN AND TRANSPORT OF THE WINTER ARCTIC AEROSOL

Results of a systematic study of the winter aerosol at Barrow, Alaska, are presented which show that the atmosphere of arctic Alaska contains an abundance of pollution-derived aerosol, particularly during the winter half-year, and that Europe, rather than the U.S., appears to be primarily responsible for the winter arctic aerosol. It is found that the aerosol is an order of magnitude more concentrated in winter than in summer throughout most of the troposphere, is gray in winter but colorless in summer, is much more enriched in pollution-derived constituents (such as V, Mu, and SO/sub 4/) in winter than in summer, and appears to be highly secondary in nature. A simple transport model is described, and it is demonstrated that the actual concentrations of V, SO/sub 4/, and Pb-210 at Barrow are quantitatively consistent with polluted European air masses as the source, followed by transport over the European USSR and then to the north.

Relative importances of North America and Eurasia as sources of arctic aerosol

Abstract During winter, the Arctic atmosphere is filled with high concentrations of aerosol which is largely pollution-derived. This article reviews a series of meteorological, meteorological-chemical, observational and compositional arguments in an attempt to determine which, if any, of the two most likely sources of Arctic aerosol, eastern North America and Eurasia, dominates. The majority, but not all, of the presently available evidence indicates that Eurasia is the more important source.

Trace-element concentrations in erodible soils

Abstract Concentrations of 40 elements in 11 desert soils from Africa and North America have been determined as a function of particle size by neutron activation. Concentrations generally increase with decreasing particle size down to radius 10–20 μm, below which they remain nearly constant. This increase is greatest in highly weathered and wind-eroded soils and is negligible in cultivated soils. In the plateau region below 10–20 μm, most elements were within a factor of 2–3 of crustal rock proportions, suggesting that bulk crustal rock is an acceptable reference material for calculating aerosol-crust enrichment factors. The coincidence of the plateau region with the aerosol size range implies that the composition of mineral aerosol should not change markedly during long-range transport; this is borne out by observation. Elements associated with highly resistive minerals such as zircon and rutile can sometimes become unusually enriched in the radius range 10–30 μm.

Tropospheric Halogen Gases: Inorganic and Organic Components

Inorganic and organic components of the gaseous tropospheric halogens chlorine, bromine, and iodine have been simultaneously measured. At four diverse remote locations the organic component contained the bulk of the halogen mass, varied less than the inorganic component, and was comparable in concentration to the independently measured halocarbon component.

Compositional differences between Arctic aerosol and snow

UNIQUE information on trace elements in polar atmospheres is available through records of deposition in snow and ice. Proper interpretation of these data requires a knowledge of the nontrivial chemical relationship between the deposition and its parent aerosol. Because several complex processes determine the trace-element content of precipitation, polar ice and snow cannot be considered a priori to have the same composition as polar aerosol1. In most of the current literature, such an assumption is usually made. Within the past year or so, the first tests of the long-term relationship between aerosol and deposition have been (inadvertently) produced for the Antarctic and the Arctic. The results are different for each region, and illustrate the great caution that must be exercised in this entire field. At the South Pole, snow from 1973–742 compares very well with aerosol from 1974–753—both media give the same impression of the environment2,4. In the Arctic, on the other hand, opposite conclusions about the atmosphere have been drawn from snow and aerosol, and this problem is discussed here.

Sources and source variations for aerosol at Mace Head, Ireland

Abstract The sources and source variations for aerosol at Mace Head, Ireland, were studied by applying positive matrix factorization (PMF), a variant of factor analysis, to a 5-yr data set for bulk aerosol. Signals for the following six sources were evident year round: (1) mineral dust, (2) sea salt, (3) general pollution, (4) a secondary SO 4 2− –Se signal that is composed of both natural (marine) and pollution (coal) components, (5) ferrous industries, (6) and a second marine (possibly biogenic) source. Analyses of seasonally stratified data suggested additional sources for iodine and oil emissions but these were present only in certain seasons, respectively. The marine signal is particularly strong in winter. The main pollution transport from Europe to Mace Head occurs in May, but the influence of continental European emissions is evident throughout the year. Mineral aerosol evidently follows a transport pathway similar to that of pollution aerosol, i.e., recirculation via the westerlies brings pollutants mixed with dust to the site from nearby land, i.e., Ireland, the United Kingdom, and the Belgium, Netherlands, and Luxemburg (Benelux) region, with some inputs from Scandinavia, Western Europe, Eastern Europe, and even the Mediterranean region. Compared with Bermuda, aerosol at Mace Head has stronger marine sources (especially marine-derived secondary SO 4 2− and Se) but weaker crustal and oil signals. Transport across the North Atlantic, especially in winter, cannot be ruled out.

Semiannual cycles of pollution at Bermuda

To identify the sources and determine the transport pathways for aerosol during the Atmosphere/Ocean Chemistry Experiment (AEROCE), we examined the temporal variations of trace elements in daily aerosol samples collected at Bermuda from 1988 to 1994. Crustal (e.g., Al) and marine (e.g., Na) elements showed annual cycles with summer and winter maxima, respectively. In contrast, pollution-derived elements (e.g., Sb) showed unusual semiannual cycles with strong spring maxima and weaker fall maxima, which to the best of our knowledge, have not been previously documented. The seasonality in trace element concentrations was mainly transport-driven: The spring maxima of pollutants were caused by rapid westerly transport from North America, and the fall maxima were caused by North American air slowly transported to Bermuda by large high-pressure systems that stagnated over the lower mid-Atlantic states. Low concentrations of pollution elements in winter resulted from the southwestward extension of the Bermuda-Azores high-pressure system that brought marine air to Bermuda from the east or northeast while hindering transport from North America and Africa. The summer minima in pollutants were associated with air transported from the eastern Atlantic and Africa. The variations of the trace gases O3 and CO and two naturally occurring radionuclides, 210Pb and 7Be, showed semiannual cycles similar to those of the pollution-derived trace elements.

Atmospheric, riverine and oceanic sources of seven trace constituents to the arctic ocean☆

Abstract The Arctic atmosphere contains surprisingly high concentrations of aerosol during the winter half-year, to the point that deposition to the Arctic Ocean becomes of interest. For lack of better information, we assume that wet deposition dominates dry deposition in the Arctic to the same degree as in midlatitudes. If so, most of the Arctic deposition should take place in winter, when anthropogenic contributions to the Arctic aerosol are the greatest. Thus, anthropogenic influences should be seen in Arctic deposition, but to a lesser extent than in the Arctic aerosol. Estimates of atmospheric deposition and riverine transport of seven trace species (A1, V, Mn, Cd, Pb, SO 4 2− , NO 3 − ) to the Arctic Ocean suggest that riverine sources deposit more material than atmospheric sources, that riverine fluxes are often comparable to oceanic fluxes, and that atmospheric fluxes are usually much less than riverine or oceanic fluxes. Under certain circumstances, riverine Al, Mn, Cd and NO 3 − may significantly affect the oceanic concentrations. Atmospheric and riverine sources of SO 4 2− and V are both unimportant. Pb was the only element considered here whose atmospheric flux equals or exceeds the riverine and oceanic fluxes into and out of the Arctic basin; the atmosphere should thus have a major effect on Pb concentration in the Arctic Ocean.

A study of winter variability in carbon dioxide and Arctic haze aerosols at Barrow, Alaska

Abstract Relationships among atmospheric CO2 concentration, excess sulfate and vanadium, and meteorological analyses for one winter at Barrow, Alaska were investigated. The results provided a basis for understanding the causes of short term CO2 variability. The study indicated that peaks in CO2 concentration were related to direct atmospheric transport of industrial pollutants from Eurasia. Evidence that background Arctic concentrations contained a pollution component was also found. Lowest CO2 concentrations occurred with intrusions of Pacific air above the surface-based polluted Arctic air mass.