Showing papers by "Michael H. Bergin published in 2007"
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Villanova University1, Natural Environment Research Council2, University of New Hampshire3, Paul Scherrer Institute4, University of California, Davis5, Georgia Institute of Technology6, Environment Canada7, California Institute of Technology8, University of Cambridge9, Langley Research Center10, Joseph Fourier University11, University of California, Merced12, Harvard University13, University of Leeds14, Institute of Arctic and Alpine Research15, Michigan Technological University16, Alfred Wegener Institute for Polar and Marine Research17, Masaryk University18, University of Houston19, York University20, Max Planck Society21, Purdue University22, University of Alaska Fairbanks23, University College Cork24, Peking University25
TL;DR: In this paper, the authors consider the nature of snow at a fundamental, physical level; photochemical processes within snow and the caveats needed for comparison to atmospheric photochemistry; our current understanding of nitrogen, oxidant, halogen and organic photochemistry within snow; the current limitations faced by the field and implications for the future.
Abstract: It has been shown that sunlit snow and ice plays an important role in processing atmospheric species. Photochemical production of a variety of chemicals has recently been reported to occur in snow/ice and the release of these photochemically generated species may significantly impact the chemistry of the overlying atmosphere. Nitrogen oxide and oxidant precursor fluxes have been measured in a number of snow covered environments, where in some cases the emissions significantly impact the overlying boundary layer. For example, photochemical ozone production (such as that occurring in polluted mid-latitudes) of 3–4 ppbv/day has been observed at South Pole, due to high OH and NO levels present in a relatively shallow boundary layer. Field and laboratory experiments have determined that the origin of the observed NOx flux is the photochemistry of nitrate within the snowpack, however some details of the mechanism have not yet been elucidated. A variety of low molecular weight organic compounds have been shown to be emitted from sunlit snowpacks, the source of which has been proposed to be either direct or indirect photo-oxidation of natural organic materials present in the snow. Although myriad studies have observed active processing of species within irradiated snowpacks, the fundamental chemistry occurring remains poorly understood. Here we consider the nature of snow at a fundamental, physical level; photochemical processes within snow and the caveats needed for comparison to atmospheric photochemistry; our current understanding of nitrogen, oxidant, halogen and organic photochemistry within snow; the current limitations faced by the field and implications for the future.
547 citations
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TL;DR: In this paper, a parallel ∼50-day time series of water-soluble organic carbon (WSOC), water-insoluble organic compounds (WIOC), and elemental carbon (EC) were quantified at time increments of 4-24 h in the surface snow.
Abstract: [1] Carbonaceous particulate matter is ubiquitous in the lower atmosphere, produced by natural and anthropogenic sources and transported to distant regions, including the pristine and climate-sensitive Greenland Ice Sheet. During the summer of 2006, ambient particulate carbonaceous compounds were characterized on the Greenland Ice Sheet, including the measurement of particulate organic (OC) and elemental (EC) carbon, particulate water-soluble organic carbon (WSOC), particulate absorption coefficient (σap), and particle size-resolved number concentration (PM0.1–1.0). Additionally, parallel ∼50-day time series of water-soluble organic carbon (WSOC), water-insoluble organic carbon (WIOC), and elemental carbon (EC) were quantified at time increments of 4–24 h in the surface snow. Measurement of atmospheric particulate carbon found WSOC (average of 52 ng m−3) to constitute a major fraction of particulate OC (average of 56 ng m−3), suggesting that atmospheric organic compounds reaching the Greenland Ice Sheet in summer are highly oxidized. Atmospheric EC (average of 7 ng m−3) was well-correlated with σap (r = 0.95) and the calculated mass-absorption cross-section (average of 24 m2 g−1) appears to be similar to that measured using identical techniques in an urban environment in the United States. Comparing surface snow to atmospheric particulate matter concentrations, it appears the snow has a much higher OC (WSOC+WIOC) to EC ratio (205:1) than air (10:1), suggesting that snow is additionally influenced by water-soluble gas-phase compounds. Finally, the higher-frequency (every 4–6 h) sampling of snow-phase WSOC revealed significant loss (40–54%) of related organic compounds in surface snow within 8 h of wet deposition.
70 citations
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TL;DR: Water-soluble organic carbon, water-insoluble particulate organic carbon (WIOC), and particulate elemental carbon (EC) were measured simultaneously for the first time on the Greenland Ice Sheet in surface snow and in a 3-meter snow pit.
Abstract: [1] Water-soluble organic carbon (WSOC), water-insoluble particulate organic carbon (WIOC), and particulate elemental carbon (EC) were measured simultaneously for the first time on the Greenland Ice Sheet in surface snow and in a 3-meter snow pit. Snow pit concentrations reveal that, on average, WSOC makes up the majority (89%) of carbonaceous species, followed by WIOC (10%) and EC (1%). The enhancement of OC relative to EC (ratio 99:1) in Greenland snow suggests that, along with atmospheric particulate matter, gaseous organics contribute to snow-phase OC. Comparison of summer surface snow concentrations in 2006 with past summer snow pit layers (2002–2005) found a significant depletion in WSOC (20–82%) and WIOC (46–65%) relative to EC for 3 of the 4 years. The apparent substantial loss of WSOC and WIOC in aged snow suggests that post-depositional processes, such as photochemical reactions, need to be considered in linking ice core records of organics to atmospheric concentrations.
64 citations
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TL;DR: Li et al. as discussed by the authors provided new source information through ground measurements and statistical analysis of 24 elements associated with particulate matter collected on filters at seven sites throughout the Pearl River Delta, with three sites located in Hong Kong and four sites in Guangdong.
47 citations
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TL;DR: The immobilized enzyme reactors (IMERs) were integrated with an impinger-based aerosol sampling system for collection of chemical contaminants in air and proved suitable for detection of a range of organophosphates including paraoxon, demeton-S and malathion.
29 citations
01 May 2007
TL;DR: In this article, an enzyme-based monitoring system provides the basis for continuous sampling of organophosphate contamination in air, where the enzymes butyrylcholinesterase (BuChE) and OPH are stabilized by encapsulation in biomimetic silica nanoparticles, entrained within a packed bed column.
Abstract: : An enzyme-based monitoring system provides the basis for continuous sampling of organophosphate contamination in air. The enzymes butyrylcholinesterase (BuChE) and organophosphate hydrolase (OPH) are stabilized by encapsulation in biomimetic silica nanoparticles, entrained within a packed bed column. The resulting immobilized enzyme reactors (IMERs) were integrated with an impinger-based aerosol sampling system for collection of chemical contaminants in air. The sampling system was operated continuously and organophosphate detection was performed in real-time by single wavelength analysis of enzyme hydrolysis products. The resulting sensor system detects organophosphates based on either enzyme inhibition (of BuChE) or substrate hydrolysis (by OPH). The detection limits of the IMERs for specific organophosphates are presented and discussed. The system proved suitable for detection of a range of organophosphates including paraoxon, demeton-S and malathion.
26 citations
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TL;DR: In this article, the size-resolved number concentration of water-insoluble aerosols (WIA) from 0.25 to 2.0μm was measured in real-time in the urban center of Atlanta, GA.
7 citations