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PubMed2003

The influence of atmospheric pressure on landfill methane emissions.

Landfills are the largest source of anthropogenic methane (CH4) emissions to the atmosphere in the United States. However, few measurements of whole landfill CH4 emissions have been reported. Here, we present the results of a multi-season study of whole landfill CH4 emissions using atmospheric tracer methods at the Nashua, New Hampshire Municipal landfill in the northeastern United States. The measurement data include 12 individual emission tests, each test consisting of 5-8 plume measurements. Measured emissions were negatively correlated with surface atmospheric pressure and ranged from 7.3 to 26.5 m3 CH4 min(-1). A simple regression model of our results was used to calculate an annual emission rate of 8.4 x 10(6) m3 CH4 year(-1). These data, along with CH4 oxidation estimates based on emitted landfill gas isotopic characteristics and gas collection data, were used to estimate annual CH4 generation at this landfill. A reported gas collection rate of 7.1 x 10(6) m3 CH4 year(-1) and an estimated annual rate of CH4 oxidation by cover soils of 1.2 x 10(6) m3 CH4 year(-1) resulted in a calculated annual CH4 generation rate of 16.7 x 10(6) m3 CH4 year(-1). These results underscore the necessity of understanding a landfill's dynamic environment before assessing long-term emissions potential.

Atmospheric Pressure↗
PubMed1999

A summary of the atmospheric surveys published in the United States allergy literature, 1966-1996.

OBJECTIVE: In this investigation we sought to summarize the atmospheric surveys that were published in two United States allergy journals (and subsequent series) during a 31-year period beginning in 1966. DATA SOURCES: All original articles published in the Annals of Allergy (and its subsequent series) and the Journal of Allergy (and its subsequent series) were cataloged in a computer database beginning with the first issues of 1966. Publications were classified in a manner reflecting their aerobiologic content. STUDY SELECTION: From this database of articles (n = 7,403), atmospheric surveys for pollen, spores, and other aeroflora were identified and summarized according to standard criteria. For each study we documented the sampling instruments used, the height of these instruments off of the ground, the study period, and the sampling schedule. RESULTS: Sixty-one atmospheric surveys were summarized: 30 from locations in the United States and 31 from outside of the country. Various volumetric and nonvolumetric samplers were used; the height of instruments above the ground and the sampling protocols varied widely. CONCLUSIONS: This investigation can serve as a companion to earlier compilations. These data should prove more useful than information available via electronic and paper indexes.

Air Microbiology↗
PubMed1999

Radiation dose rates in Space Shuttle as a function of atmospheric density.

Current models of the inner trapped belt describe the radiation environment at times of solar minimum and solar maximum, respectively. These two models were constructed using data acquired prior to 1970 during a small solar cycle, and no valid model for the past two high solar cycles exists. There is a clear need to accurately predict the radiation exposure of astronauts at all times between the solar minimum and solar maximum, not only on the short duration Space Shuttle flights, but on the longer term stay onboard the Mir orbital station and the planned International Space Station (ISS). An analysis of the trapped absorbed dose rate, D, at six fixed locations in the habitable volume of the Shuttle shows a power law relationship, D=A rho-n, where rho is the atmospheric density, rho. The index, n, is weakly dependent on the shielding, decreasing as the average shielding increases. A better representation is provided by D=A tan-1 [(Xi-Xi c)/(Xi c-Xi m)], where Xi=ln(rho), and A, Xi c, and Xi m are constants. Xi c is related to the atmospheric density near the altitude of atmospheric cutoff. These relationships hold over nearly four decades of density variation and throughout the solar cycle. This then provides a method of calculating absorbed dose rate at anytime in the solar cycle. These empirically derived relations were used to predict the dose rates for eleven Space Shuttle flights carried out since January 1997. The predictions are in excellent agreement with measured values. This method reduces the uncertainties of a factor of about 2 for the AP-8 MIN/MAX models to less than 30%.

Altitude↗
PubMed1993

Detection of liquid injection using an atmospheric pressure ionization radiofrequency plasma source.

An atmospheric pressure rf plasma source which operates in a variety of different buffer gases has been developed as an ionization method for organic samples introduced by liquid injection into atmospheric pressure ionization mass spectrometry (API/MS). The rf source can operate in He at < 1 W of load power at 165 kHz. It can also be sustained in Ar, N2, air, and CO2 at a load power of < 15 W. In most cases studied, the protonated molecule, MH+, is observed with little or no fragmentation even under the relatively high current conditions of the discharge. However, using increasingly higher acceleration voltages between the skimmers in the differentially pumped region between atmospheric pressure and high vacuum, one can induce fragmentation via collision-induced dissociation. This can be assisted in these experiments via the use of a heavy buffer gas. The detection limits achieved for rf/API plasma detection are typically in the low femtomole region for small organic molecules including neurotransmitters, PTH-amino acids, steroids, drugs, pesticides, and explosives. The detection can be performed with quantitation over at least 4 orders of magnitude.

Air Ionization↗
PubMed2000

Radical-water complexes in Earth's atmosphere.

In the atmosphere, many chemical processes are controlled by open-shell radical species. While these species are present in relatively small number densities, they initiate many of the cycles that control the chemistry of the atmosphere. The purpose of this Account is to examine recent studies of radical-water complexes that are composed of atmospherically important species. We hope this Account will provide a report on the status of this topical field, while encouraging new research directions.

Atmosphere↗
PubMed2002

Mass spectrometric contributions to problems related to the chemistry of atmospheres.

Recent mass spectrometric studies of species and processes relevant to the chemistry of atmospheres are reported. New species have been detected, including HO(3); a stratospheric reservoir of OH radicals; the [H(2)O(+)O(2)(-)] charge transfer complex, central to the atmospheric photonucleation theory; and the OSOSO oxide and its cation, likely present in the Io's atmosphere. As to ionic processes, a new route to tropospheric N(2)O in air ionized by lightning and coronas is reported, as well as the complex chemistry promoted by ionization of ozone/freon and ozone/carbonyl sulfide mixtures and the formation of O(5)(+), relevant to the problem of (18)O excess in stratospheric ozone.

Air Ionization↗
PubMed2002

Kinetic and mechanistic study of the atmospheric oxidation by OH radicals of allyl acetate.

Acetates are emitted into the atmosphere by several anthropic and natural sources. To better evaluate the environmental impact of these compounds, OH-induced oxidation kinetic and mechanism of allyl acetate (CH3C(O)OCH2-CH=CH2) have been investigated at room temperature and atmospheric pressure using three environmental chambers: an indoor Teflon-film bag (LISA, Créteil), an indoor Pyrex photoreactor (LISA, Créteil), and the outdoor Smog chamber EUPHORE (Valencia). Rate constant of the reaction of allyl acetate with OH radicals was determined by relative rate technique in the indoor Teflon-film bag. It is (30.6 +/- 3.1) x 10(-12) cm3 molecule-1 s-1. Mechanistic experiments were performed in the indoor photoreactor and in the outdoor Smog chamber EUPHORE. The main oxidation products observed by FTIR in both chambers were acetoxyacetaldehyde and formaldehyde. From these data, a mechanism was developed to describe the OH-induced oxidation of this acetate in the presence of NOx. Finally, atmospheric impact of allyl acetate emissions was evaluated using kinetic and mechanistic results.

Acetates↗
PubMed2003

Atmospheric pressure mass spectrometry: a new analytical chemical characterization method for dissolved organic matter in rainwater.

The complex mixture of organic compounds in the atmosphere influences climate, air quality, and ecosystem processes. Atmospheric pressure electrospray ionization mass spectrometry (APESI-MS) was evaluated as a potential tool for direct measurement of the total suite of individual dissolved organic matter (DOM) compounds in rainwater. The APESI-MS response was linear to all DOM compounds of atmospheric significance examined as standard solutions. Urban precipitation samples from New Brunswick, NJ (USA) were analyzed by APESI-MS over the mass-to-charge (m/z) range 50-3,000. Over 95% of the m/z ions detected were in the low m/z range (50-500). Over 300 unique m/z ions were detected across the 11 rainwater samples indicating the complexity of the mixture of DOM in rainwater. Forty percent of the organic bases (positive mode detection) and 22% of the organic acids (negative mode) occurred in at least 6 of the 11 rainwater samples. Ions corresponding to the m/z of carboxylic acids standards (nonanedioic acid; 1,4-butanedicarboxylic acid; pentanedioic acid; hydroxybutanedioic acid; and butanedioic acid) and to reduced N standards (allylurea; caffeine; imidazole; and N-2-propenylurea) occurred in at least one of the 11 rainwater samples. Total dissolved organic carbon (DOC) estimated from the APESI-MS analysis and measured by standard DOC methods were not statistically different.

Air Pollutants↗
PubMed2003

Atmospheric deposition of V, Cr, and Ni since the late glacial: effects of climatic cycles, human impacts, and comparison with crustal abundances.

Vanadium, Cr, and Ni accumulating in a Swiss peat bog since 12 370 14C yr B.P. have been measured using inductively coupled plasma-mass spectrometry (ICP-MS) after acid dissolution in a microwave autoclave. Strict quality control schemes were applied to guarantee the accuracy of the applied analytical methodology. The concentration gradients in the peat column and comparison with Pb indicate that V, Cr, and Ni are effectively immobile in the ombrotrophic section of the peat profile but that Ni is added to the minerotrophic peat layers by chemical weathering of the underlying sediments. The lowest metal concentrations were found during the Holocene climate optimum (5320-8230 14C yr B.P.) when "natural background" values averaged 0.55 +/- 0.13 microg g(-1) V, 0.76 +/- 0.17 microg g(-1) Cr, and 0.46 +/- 0.09 microg g(-1) Ni (n = 18); given the average bulk density (0.05 g/cm3) and accumulation rate (0.05 cm/ yr) of peat in this zone, the corresponding atmospheric fluxes are approximately 14, 19, and 12 microg m(-2) yr(-1) for V, Cr, and Ni, respectively. The highest concentrations of V, Cr, and Ni were found during the Younger Dryas cold climate event (centered at 10 590 14C yr B.P.) when background values were exceeded by about 40 times. Elevated concentrations and accumulation rates were also found at 8230 and 5320 14C yr B.P., which are consistent with the elevated dust fluxes recorded by Greenland ice cores. By far the greatest contribution of the three elements to the peat inventory is atmospheric soil dust, and the metal fluxes vary not only with climate change but also land-use history (especially the beginning of forest clearing for agriculture ca. 6 millennia ago). The V/Sc, Cr/Sc, and Ni/ Sc ratios were remarkably similar to their corresponding ratios in the earth's crust until the onset of the Industrial Revolution (240 14C yr B.P.), which largely validates the use of crustal concentrations for calculating enrichment factors (EF) for these elements. In modern samples, the EFs of V, Cr, and Ni reach maximum values between 2.4 and 4.1, relative to background; anthropogenic emissions are a more likely explanation of the elevated EFs than either plant uptake or chemical diagenesis. This study demonstrates the usefulness of peat bogs as archives of atmospheric metal deposition and underpins the potential of peat cores to help distinguish between lithogenic and anthropogenic metal sources.

Air Pollutants↗
PubMed2004

Characterization of atmospheric ammonia emissions from a commercial chicken house on the Delmarva Peninsula.

A three-dimensional sampling grid using passive collectors was used to characterize the downwind gas-phase ammonia plumes originating from a commercial chicken house on the Delmarva Peninsula in the Chesapeake Bay watershed. Inverse Gaussian plume modeling was used to determine the source strength of the chicken house and the corresponding chicken emission factors. A total of seven field deployments were performed during two different flocks with a sampling duration ranging from 6 to 12.6 h. The deployments occurred during weeks 3, 4, and 5 of the 6-week chicken grow-out period in the months of May-July 2002. The ammonia emission factors ranged from 0.27 to 2.17 g of NH3-N bird(-1) day(-1) with a mean of 1.18 g of NH3-N bird(-1) day(-1). Weighted emissions factors that accounted for the nonlinear increase in ammonia emissions over the 6-week grow-out period were also calculated and ranged from 0.14 to 1.65 g of NH3-N bird(-1) day(-1) with a mean of 0.74 g of NH3-N bird(-1) day(-1). These weighted emission values would correspond to an annual release of approximately 18 x 10(6) kg of NH3-N to the atmosphere from broiler production on the Delmarva Peninsula. This assumes that the emission factors in this study are representative for the entire year with varying meteorological conditions and are representative of all chicken husbandry practices. The Delmarva Peninsula could represent a significant source of nutrient nitrogen to the Chesapeake Bay and Delaware Bay watersheds through atmospheric deposition when considering the size of this annual release rate, the relative short atmospheric lifetime of ammonia due to deposition, and the proximity of the Delmarva Peninsula to the Chesapeake and Delaware Bays.

Agriculture↗
PubMed2004

Modeling of TCE diffusion to the atmosphere and distribution in plant stems.

Fate of chlorinated solvents in phytoremediation has been delineated by many discoveries made in recent years. Plant uptake, metabolism, rhizosphere degradation, accumulation, and volatilization were shown to occur to differing degrees for many organic contaminants including chlorinated solvents. Among these mechanistic findings, recent research confirmed that volatile organic compounds (VOCs) volatilize from stems and that the resulting diffusive flux to the atmosphere is related to exposure concentration and to height up the stem. A comprehensive model was developed based upon all identified fate and transport mechanisms for VOCs, including translocation in the xylem flow and diffusion. The dispersion and diffusion in the radial direction were considered as one process (effective diffusion) as the two could not be investigated individually. The mechanism-based model mathematically indicates an exponential decrease of concentrations with height. While an analytic solution for the comprehensive model was not attained, it can serve as a starting point for other modeling efforts. The comprehensive model was simplified in this work for practical application to experimentally obtained data on trichloroethylene (TCE) fate. Model output correlated well with experimental results, and effective diffusivities for TCE in plant tissues were obtained through the model calibrations. The simplified model approximated TCE concentrations in the transpiration stream as well as TCE volatilization to the atmosphere. Xylem transport, including advection, dispersion, and diffusion through cell walls with subsequent volatilization to the atmosphere, is a major fate for VOCs in phytoremediation.

Atmosphere↗
PubMed2005

Milwaukee, WI, as a source of atmospheric PCBs to Lake Michigan.

A field study of atmospheric PCBs in Milwaukee, WI, U.S.A. was conducted on the shore of Lake Michigan. We believe this is the first report of atmospheric PCBs in Milwaukee, although PCBs are well-known to contaminate the sediments of the Milwaukee River and Outer Harbor. Concentrations of PCBs collected during the June 2001 study are similar to concentrations in other urban-industrial areas and higher than PCBs in background air. The average sigmaPCB (sum of 88 congener groups) gas-phase concentration in Milwaukee was 1.9 ng m(-3)+/-standard deviation 0.78 ng m(-3). The average and standard deviation for the particulate-associated PCBs are 0.05+/-0.02 ng m(-3). Particulate-phase PCBs account for less than 5% of the total atmospheric concentration. PCBs in Milwaukee air are a source of PCBs to Lake Michigan. Calculated net gas exchange fluxes predicted forthe Milwaukee sampling period ranged from -60 to -400 ng m(-2) d(-1), where net deposition is indicated by the negative sign. Calculated particle-associated PCB deposition ranged from 80 to 500 ng m(-2) d(-1). Most of the particle-phase deposition flux is a result of coarse particle deposition and decreases rapidly with distance from shore. Under typical meteorological conditions, particle-associated PCBs depositional flux to the lake surface decreases by 90% within 40 km. For net gas-exchange, the flux reaches zero at about the same distance. At greater distances, particle-phase PCB deposition is negligible, and PCBs are volatilizing at a higher rate than they are being deposited. We calculated that Milwaukee air contributes about 120 kg of PCBs to Lake Michigan each year. This is about 10 times larger than the discharge of PCBs from the Milwaukee River.

Air Movements↗
PubMed2004

Degradation of fluorotelomer alcohols: a likely atmospheric source of perfluorinated carboxylic acids.

Human and animal tissues collected in urban and remote global locations contain persistent and bioaccumulative perfluorinated carboxylic acids (PFCAs). The source of PFCAs was previously unknown. Here we present smog chamber studies that indicate fluorotelomer alcohols (FTOHs) can degrade in the atmosphere to yield a homologous series of PFCAs. Atmospheric degradation of FTOHs is likely to contribute to the widespread dissemination of PFCAs. After their bioaccumulation potential is accounted for, the pattern of PFCAs yielded from FTOHs could account for the distinct contamination profile of PFCAs observed in arctic animals. Furthermore, polar bear liver was shown to contain predominately linear isomers (>99%) of perfluorononanoic acid (PFNA), while both branched and linear isomers were observed for perfluorooctanoic acid, strongly suggesting a sole input of PFNA from "telomer"-based products. The significance of the gas-phase peroxy radical cross reactions that produce PFCAs has not been recognized previously. Such reactions are expected to occur during the atmospheric degradation of all polyfluorinated materials, necessitating a reexamination of the environmental fate and impact of this important class of industrial chemicals.

Air Pollutants↗
PubMed2005

Seasonal and spatial relationship of chemistry and toxicity in atmospheric particulate matter using aquatic bioassays.

In light of current interest in better understanding the environmental impact of atmospheric particulate matter (PM), a new strategy has been employed to screen the relative toxicities of ambient and source aerosols. Short-term and acute aquatic bioassays using Ceriodaphnia dubia and a green alga (Selenastrum capricornutum) as test organisms have been in use for many years in the regulation of wastewater effluents. These tests have been employed in the present study to compare the toxicity of water extracts of atmospheric particulate matter and dichloromethane (DCM) extracts that have been transferred to dimethyl sulfoxide and diluted in water. Atmospheric PM was collected at four sites located near the south shore of Lake Michigan and one site in Michigan's Upper Peninsula at discrete events during three seasons. Parallel chemical analyses of the two extracts directly assessed the relation between the chemical composition and the toxicity of the extract. Inductively coupled plasma analysis of the metals in the water extract and gas chromatography-mass spectroscopy of the organics in the DCM extract showed a relationship between high toxicity and high water-soluble copper concentration and high secondary organic aerosol tracers in the extracted aerosol. Although previous fractionation studies have not looked at water-soluble copper, significant toxicity has been measured in the semipolar and polar organic fractions of ambient aerosols and diesel exhaust particles, which are the fractions in which secondary organic aerosol components would be expected. For the water extracts, the summer samples were consistently more toxic than the autumn or spring samples. There was not a seasonal pattern for the toxicity of the DCM extracts; however, spatial differences were apparent. The toxicity end points of select samples from one site qualitatively correlate with the high polycyclic aromatic hydrocarbon concentrations. Additionally, high toxicity in the July DCM extracts from another site may be tied to the presence of the insecticide carbaril. The seasonal and spatial variations captured in the toxicity results in this study tend to qualitatively correlate with trace organic components and metals and not bulk particulate matter composition.

Air Pollutants↗
PubMed2005

Brominated flame retardants in the atmosphere of the East-Central United States.

Air samples were collected at five sites (urban, semiurban, agricultural, and remote) from Lake Michigan through the U. S. Midwest to the Gulf of Mexico every 12 days during 2002-2003 using high-volume samplers so that we could study the spatial trends of brominated flame retardants (polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDs), and 1,2-bis(2,4,6-tribromophenoxy)-ethane (TBE)). The mean sigmaPBDE atmospheric concentration was 100 +/- 35 pg/m3 at the Chicago site, which was 3-6 times higher than that at the other sites. The sigmaPBDE atmospheric concentrations at the Chicago site were significantly higher than previous measurements made in 1997-1999. Unlike these former measurements, BDE-209 is now relatively abundant. Lower BDEs (tri- through hex-BDEs) were detected in both the particle and the gas phases, and the partitioning of these compounds between phases was highly dependent on atmospheric temperature. Higher BDEs (hepta- through deca-BDEs) were mostly detected in the particle phase. On the basis of the congener distributions in the samples, the concentrations were divided into three groups: penta-BDEs, octa-BDEs, and deca-BDEs. Penta-BDEs were the most concentrated at the Chicago site and the least concentrated at the Louisiana site; octa-BDE concentrations were low at all of the sites; deca-BDEs were the most concentrated at the Chicago site and notably high atthe Arkansas site. High concentrations of deca-BDEs, HBCDs, and TBE at the Arkansas site suggest that manufacturing areas in southern Arkansas could be the source regions. Backward trajectories for air masses with high concentrations of deca-BDEs coming to the Arkansas site suggestthat deca-BDEs bound to particles can move long distances from source regions to nonsource regions.

Air Movements↗
PubMed2005

Aqueous atmospheric chemistry: formation of 2,4-dinitrophenol upon nitration of 2-nitrophenol and 4-nitrophenol in solution.

Field studies have shown that the powerful phytotoxic agent 2,4-dinitrophenol is very likely to form in the atmospheric aqueous phase upon nitration of 2-nitrophenol or 4-nitrophenol. However, until now, the nitration pathway and the relative importance of the two mononitrophenols as sources of 2,4-dinitrophenol were not known. The present study shows that 2,4-dinitrophenol formation from mononitrophenols can take place upon photolysis and photooxidation of nitrite/nitrous acid (NO2-/HONO) and that nitrogen dioxide plays a key role in the process. A possible pathway might be the reaction between light-excited mononitrophenols (both 2- and 4-isomers) and nitrogen dioxide, in the presence of oxygen. As an alternative, nitration might involve *NO3 + *NO2. Possible sources of nitrogen dioxide in the atmospheric aqueous phase are dissolution from the gas phase and oxidation of NO2-. In the latter case, however, it is necessary that NO2- oxidation is faster than the oxidation of mononitrophenols. This would happen, for instance, in the presence of hematite under irradiation. Radiation absorption and scattering by hematite would also inhibit the direct photolysis of nitrophenols. The formation rate and the yield of 2,4-dinitrophenol are slightly higher when starting from 2-nitrophenol than those from 4-nitrophenol, but they are compensated by the higher concentration of 4-nitrophenol in the atmospheric aqueous phase.

2,4-Dinitrophenol↗
PubMed2006

Formation of C7F15COOH (PFOA) and other perfluorocarboxylic acids during the atmospheric oxidation of 8:2 fluorotelomer alcohol.

Calculations using a three-dimensional global atmospheric chemistry model (IMPACT) indicate that n-C8F17CH2CH2OH (widely used in industrial and consumer products) degrades in the atmosphere to give perfluorooctanoic acid (PFOA) and other perfluorocarboxylic acids (PFCAs). PFOA is persistent, bioaccumulative, and potentially toxic. Molar yields of PFOA depend on location and season, are in the range of 1-10%, and are of the correct order of magnitude to explain the observed levels in Arctic fauna. Fluorotelomer alcohols such as n-C8F17CH2CH2OH appear to be a significant global source of persistent bioaccumulative perfluorocarboxylic acid pollution. This is the first modeling study of the atmospheric chemistry of a fluorotelomer alcohol.

Alcohols↗
PubMed2006

Use of Br and Se in peat to reconstruct the natural and anthropogenic fluxes of atmospheric Hg: A 10000-year record from Caribou Bog, Maine.

Using Br and Se as reference elements, the natural and anthropogenic fluxes of atmospheric Hg were reconstructed for the past 10,000 years using peat cores from Caribou Bog, ME. In the ombrotrophic peat layers, the average background Hg accumulation rate (AR) was 1.7 +/- 1.3 microg m(-2) year(-1) which is comparable with the natural rate of atmospheric Hg accumulation reported in other retrospective studies. The average Hg AR determined using all peat samples dating from preindustrial times, including minerotrophic peat, was slightly greater (3.1 +/- 2.3 microg m(-2) year(-1)) which may reflect differences in canopy interception due to the changes in plant communities, aquatic inputs, or possibly climatic factors. The maximum Hg AR (32 microg m(-2) year(-1)) occurred ca. 1961 A.D. In samples predating the settlement by Europeans, there is a linear correlation between the AR of Hg and those of Br and Se; this relationship allows both Br and Se to be used to calculate the natural AR of Hg (Hgnat). The difference between Hg AR and Hg(nat) is the Hg AR in excess of background (Hg(ex)). Because Hg(ex) was positive only after ca. 1840 A.D., it is assumed to represent the anthropogenic Hg component. By the late 19th century, Hg(ex) deposition was equal to the natural flux. At the peak in Hg deposition in 1961 A.D., Hgex made up >90% of total atmospheric Hg deposition. The AR in the uppermost peat decreased to 25% of peak values by 2000 A.D.

Air Pollutants↗