John W. Winchester

Seasonal surface ozone and filterable bromine relationship in the high Arctic

Ozone and filterable bromine measurements in the high Arctic during the spring return of solar radiation suggest a rapid concurrent destruction of O3 and conversion of gaseous to particulate Br. Multiyear observations show that this pattern is an annual feature of O3 measured near the surface at Barrow, Alaska, and other Arctic locations. Aircraft measurements show low O3 amounts and high filterable Br concentrations beneath the surface temperature inversion over ice throughout the Arctic in the spring. A wintertime build-up of the gaseous organic compound bromoform and a rapid depletion of bromoform in the spring may be a link between the episodic O3 depletion events and the accompanying rise in filterable Br.

PIXE analysis of aerosol samples collected over the atlantic ocean from a sailboat

Abstract Size-fractionated aerosol samples, collected over the Atlantic Ocean, were analyzed for up to 20 elements by PIXE. Using a sailboat as sampling platform, duplicate samples were taken for two-day periods by means of battery operated 6-stage cascade impactors, positioned about 8 m above the sea surface. In the PIXE analysis of the fine particle stages (stages 3 to 5) a 5 times smaller beam size was used than for stages 1 and 2. This led to significant improvement in the detection limits for the former stages. The results from the duplicate impactor samples were normally in good agreement, indicating that the combined uncertainty of sampling and PIXE analysis was of the order of 20%. The precision of the PIXE analysis alone was investigated by rebombarding some samples six months after the first analysis. The trends with time of the fine particle sulfur and the coarse particle iron concentrations are discussed in some detail.

Acidity in air and water in a case of warm frontal precipitation

Abstract The acidity of dry air south of a warm front was measured before it ascended producing a large area of warm frontal precipitation. Comparison of the chemical compositions of the dry air and precipitation at cloud base suggest a significant production of both sulfuric and nitric acids in the cloud. Below-cloud processes did not appear to significantly affect the concentration of acids in rain at ground level. Rates of nitric acid and sulfuric acid production in the cloud are estimated.

Fine and coarse aerosol composition from a rural area in north China

Abstract The elemental composition of duplicate aerosol samples from north China, collected in particle size fractions by eight-stage cascade impactors on the Great Wall, near Beijing, is reported for 21 elements measured by particle induced X-ray emission analysis. Meteorological conditions during sampling on 1 April 1980 indicated that relatively clean northerly air from Mongolia and Siberia was sampled. Coarse terrestrial dust and additional fine aerosol components mainly of 0.5–1 μm aerodynamic diameter could be distinguished. Relative elemental abundances in the coarse mode resembled earth crust composition. Those in the fine mode resembled the South Pole aerosol, and fine mode elemental concentrations were low enough to suggest approximately background levels of several trace metals.

Fine and coarse aerosol composition in an urban setting: A case study in Beijing, China

Abstract Components of the near-ground urban aerosol in Beijing, China, which are derived from natural and pollution sources, have been identified by means of PIXE analysis of particle size fractionated samples and relationships among the concentrations of 18 elements. Samples were collected in city center and outlying suburban and rural locations on five days in July and December 1980. The panicle size distributions of most elements were bimodal, with a gradual progression from mainly coarse mode Ca, Ti and Al to mainly fine mode S, As, and Br. Pb, Zn and Cu occurred mainly in fine particles and were apparently pollutants derived from the combustion of coal and other fuels, but not gasoline. Fine particle Cr, Mn and Fe concentrations were especially high on one July day and may have derived from a pulse of industrial air pollution. Si concentrations were singularly high in ultra-fine particles as if from the condensation of high temperature vapors from coal combustion. Coarse particles in the city center were apparently from local surface dust raised by vehicle traffic, and they were enriched in Pb, Zn and Cu compared to a rural location, suggesting a significant degree of city soil contamination by fine pollution aerosol fallout over time.

A standard crustal aerosol as a reference for elemental enrichment factors

Abstract Elemental composition measurements of > 4μ m aerodynamic diameter aerosol particles have been made with cascade impactors at remote continental locations in Argentina, Bolivia, and Brazil during the winter 1976 and summer 1977 seasons. The aerosol samples have been analyzed by proton induced X-ray emission (PIXE) for the crustal elements Al, Si, K, Ca, Ti, and Fe. Experimental results show that a high degree of homogeneity is exhibited by the crustal elements in the remote continental aerosol. Although the crustal element concentrations in air vary by two orders of magnitude, the data suggest that a standard crustal aerosol (SCA) having the following geometric means of ratios to Fe can be used as the reference material in aerosol enrichment factor calculations: Ti = 0.10(1.2) ; Al = 2.0(1.4) ; Si = 4.5(1.5) ; Ca = 0.41 (1.9) ; K = 0.20 (2.0) , where the numbers in parentheses are standard deviations over 8 locations weighted equally. The elements Al, Si, Ti, and Fe, which show constancy in relative proportions to a factor of 1.5 or better, are shown to be suitable reference elements in the enrichment factor calculations. The SCA is used to examine enrichments from different continental locations. SCA enrichment factor calculations for the South American cities of La Paz, Bolivia, Buenos Aires, Argentina, and Brasilia and Sao Paulo, Brazil show that the proportions of crustal elements in these cities are similar to those found in remote continental locations, although concentration variations of at least two orders of magnitude are present. The inclusion of additional elements in the SCA obtained by other analytical techniques is suggested.

Background aerosol composition on chacaltaya mountain, Bolivia

Abstract The elemental composition of aerosol particles collected at 5220 meters altitude from Chacaltaya Mountain, Bolivia, in the eastern cordillera of the altiplano, has been determined by X-ray, neutron activation and atomic absorption techniques. Concentrations are comparable to previously reported continental nonurban levels. The elemental composition is similar to that measured at other remote locations in the Northern Hemisphere and Antarctica. The site has potential value for baseline measurements of the continental atmosphere in the Southern Hemisphere.

Water soluble organic constituents in Arctic aerosols and snow pack

Eight water-soluble organic anions were measured in 70 aerosol samples and 10 snow samples at Barrow, Alaska in March–April, 1989. The ranking of the ions in aerosols according to total (coarse+fine aerosol) median concentrations was acetate (44 ng m−3), oxalate (27), benzoate (23), formate (22), propionate (6), methanesulfonate (5), lactate (4), and pyruvate (4). When added up, the median organic anion mass was 156 ng m−3. The organic anions/nssSO4= mass ratio had a median of 0.18 and 0.07 in the coarse (>1 μm) and fine ( 0.5, substantially higher than in aerosols.

Electron microscopy of acidic aerosols collected over the northeastern United States

Abstract As part of the acid precipitation experiment (APEX) conducted in the northeastern U.S. by the National Center for Atmospheric Research and cooperating universities, aerosols were collected from an aircraft in different seasons, locations and meteorological conditions. Particles were impacted on electron microscope grids for morphological analysis and thin-film chemical tests for sulfate and nitrate. Under most conditions the accumulation mode aerosols ( c . 0.1–1.0 μm diameter) collected in the boundary layer were composed of sulfate particles of uniform composition (i.e. an internally mixed aerosol), indicating that individual particle composition could be inferred from bulk measurements. Externally mixed aerosols (i.e. assemblages of different kinds of particles) were found to exist near certain sources (e.g. power plants), in urban plumes, and near fair weather cumulus clouds. Direct evidence of rapid oxidation of SO 2 to H 2 SO 4 in cloud droplets was obtained in samples collected near clouds in northern New York and central Illinois, and this represents a potentially major pathway for SO 2 oxidation in the lower troposphere.

Tree-ring analysis by pixe for a historical record of soil chemistry response to acidic air pollution

Tree cores have been analyzed intact in 1 mm steps, corresponding to time intervals in the rings as short as half a growing season, providing a chronological record of 16 elemental concentrations extending over thirty years back to 1950. Samples were collected in a forested region of western Canada in sandy soil which was impacted by acid-forming gases released by a sulfur recovery sour natural gas plant. Tree core samples of the hybrid lodgepole-Jack pine (Pinns contorta Loud. × Pinus banksiana Lamb.) were taken in five ecologically similar locations between 1.2 and 9.6 km from the gas plant stacks. Concentrations of some elements showed patterns suggesting that the annual rings preserved a record of changing soil chemistry in response both to natural environmental conditions and to deposition from sulfur gas emissions, commencing after plant start-up in 1959 and modified by subsequent modifications in plant operating procedures. These patterns were most pronounced nearest the gas plant. Certain other elements did not exhibit these patterns, probably reflecting greater importance of biological than of soil chemical properties. The high time resolution of tree-ring analysis, which can be achieved by PIXE, demonstrates that the rings preserve a historical record of elemental composition which may reflect changes in soil chemistry during plant growth as it may be affected by both natural ecological processes and acidic deposition from the atmosphere.