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PubMed2001

[Study of the reproducibility and sensitivity of laser microspectral analysis in argon atmosphere at reduced pressure].

In argon atmosphere at reduced pressure, the spectral analysis reproducibility and sensitivity are experimentally studied with the laser microprobe emission spectral analysis(LMESA) system for the metal alloy standard samples. For the atomic spectral analysis line, the relative standard deviation(RSD) in argon atmosphere at reduced pressure is better than that in air atmosphere. For the ionic spectral analysis line, the RSD is almost the same in both cases. The RSD is strongly affected by the composition of the sample and the concentration of elements. The measured slope of calibration curves for the determination of Cu, Zn and Mg in an aluminum alloy in argon atmosphere is about 1.5-2 times of that in the air atmosphere, which indicates an obvious improvement of the sensitivity and is helpful to expand the dynamic range of the spectral analysis.

Alloys↗
PubMed2006

Reliable determination of oxygen and hydrogen isotope ratios in atmospheric water vapour adsorbed on 3A molecular sieve.

The isotope ratio of atmospheric water vapour is determined by wide-ranging feedback effects from the isotope ratio of water in biological water pools, soil surface horizons, open water bodies and precipitation. Accurate determination of atmospheric water vapour isotope ratios is important for a broad range of research areas from leaf-scale to global-scale isotope studies. In spite of the importance of stable isotopic measurements of atmospheric water vapour, there is a paucity of published data available, largely because of the requirement for liquid nitrogen or dry ice for quantitative trapping of water vapour. We report results from a non-cryogenic method for quantitatively trapping atmospheric water vapour using 3A molecular sieve, although water is removed from the column using standard cryogenic methods. The molecular sieve column was conditioned with water of a known isotope ratio to 'set' the background signature of the molecular sieve. Two separate prototypes were developed, one for large collection volumes (3 mL) and one for small collection volumes (90 microL). Atmospheric water vapour was adsorbed to the column by pulling air through the column for several days to reach the desired final volume. Water was recovered from the column by baking at 250 degrees C in a dry helium or nitrogen air stream and cryogenically trapped. For the large-volume apparatus, the recovered water differed from water that was simultaneously trapped by liquid nitrogen (the experimental control) by 2.6 per thousand with a standard deviation (SD) of 1.5 per thousand for delta(2)H and by 0.3 per thousand with a SD of 0.2 per thousand for delta(18)O. Water-vapour recovery was not satisfactory for the small volume apparatus.

Adsorption↗
PubMed2005

Fine root chemistry and decomposition in model communities of north-temperate tree species show little response to elevated atmospheric CO2 and varying soil resource availability.

Rising atmospheric [CO2] has the potential to alter soil carbon (C) cycling by increasing the content of recalcitrant constituents in plant litter, thereby decreasing rates of decomposition. Because fine root turnover constitutes a large fraction of annual NPP, changes in fine root decomposition are especially important. These responses will likely be affected by soil resource availability and the life history characteristics of the dominant tree species. We evaluated the effects of elevated atmospheric [CO2] and soil resource availability on the production and chemistry, mycorrhizal colonization, and decomposition of fine roots in an early- and late-successional tree species that are economically and ecologically important in north temperate forests. Open-top chambers were used to expose young trembling aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees to ambient (36 Pa) and elevated (56 Pa) atmospheric CO2. Soil resource availability was composed of two treatments that bracketed the range found in the Upper Lake States, USA. After 2.5 years of growth, sugar maple had greater fine root standing crop due to relatively greater allocation to fine roots (30% of total root biomass) relative to aspen (7% total root biomass). Relative to the low soil resources treatment, aspen fine root biomass increased 76% with increased soil resource availability, but only under elevated [CO2]. Sugar maple fine root biomass increased 26% with increased soil resource availability (relative to the low soil resources treatment), and showed little response to elevated [CO2]. Concentrations of N and soluble phenolics, and C/N ratio in roots were similar for the two species, but aspen had slightly higher lignin and lower condensed tannins contents compared to sugar maple. As predicted by source-sink models of carbon allocation, pooled constituents (C/N ratio, soluble phenolics) increased in response to increased relative carbon availability (elevated [CO2]/low soil resource availability), however, biosynthetically distinct compounds (lignin, starch, condensed tannins) did not always respond as predicted. We found that mycorrhizal colonization of fine roots was not strongly affected by atmospheric [CO2] or soil resource availability, as indicated by root ergosterol contents. Overall, absolute changes in root chemical composition in response to increases in C and soil resource availability were small and had no effect on soil fungal biomass or specific rates of fine root decomposition. We conclude that root contributions to soil carbon cycling will mainly be influenced by fine root production and turnover responses to rising atmospheric [CO2], rather than changes in substrate chemistry.

Atmosphere↗
PubMed2007

Interaction between atmospheric CO2 and glucosinolates in broccoli.

Total and individual glucosinolate contents of broccoli cv Marathon were assessed at ambient CO2 (430-480 ppm) and elevated atmospheric CO2 (685-820 ppm) to determine the ecological relationship between changing atmospheric CO2 concentrations and phytochemicals. Elevated atmospheric CO2 concentration had a differing effect on individual glucosinolates and glucosinolate groups. Total glucosinolate content increased at elevated atmospheric CO2 concentration as a result of a strong increase in both methylsulfinylalkyl glucosinolates glucoraphanin and glucoiberin. In contrast, indole glucosinolates simultaneously decreased, predominantly because of a reduction of glucobrassicin and 4-methoxy-glucobrassicin contents. We conclude that changes in N content and N/S ratios as well as alterations in photochemical processes at elevated atmospheric CO2 concentration can influence total and individual glucosinolates contents of Brassicaceae, as demonstrated in the greenhouse, for broccoli.

Atmosphere↗
PubMed2006

Land plants equilibrate O2 and CO2 concentrations in the atmosphere.

The role of land plants in establishing our present day atmosphere is analysed. Before the evolution of land plants, photosynthesis by marine and fresh water organisms was not intensive enough to deplete CO(2) from the atmosphere, the concentration of which was more than the order of magnitude higher than present. With the appearance of land plants, the exudation of organic acids by roots, following respiratory and photorespiratory metabolism, led to phosphate weathering from rocks thus increasing aquatic productivity. Weathering also replaced silicates by carbonates, thus decreasing the atmospheric CO(2) concentration. As a result of both intensive photosynthesis and weathering, CO(2 )was depleted from the atmosphere down to low values approaching the compensation point of land plants. During the same time period, the atmospheric O(2) concentration increased to maximum levels about 300 million years ago (Permo-Carboniferous boundary), establishing an O(2)/CO(2) ratio above 1000. At this point, land plant productivity and weathering strongly decreased, exerting negative feedback on aquatic productivity. Increased CO(2) concentrations were triggered by asteroid impacts and volcanic activity and in the Mesozoic era could be related to the gymnosperm flora with lower metabolic and weathering rates. A high O(2)/CO(2) ratio is metabolically linked to the formation of citrate and oxalate, the main factors causing weathering, and to the production of reactive oxygen species, which triggered mutations and stimulated the evolution of land plants. The development of angiosperms resulted in a decrease in CO(2) concentration during the Cenozoic era, which finally led to the glacial-interglacial oscillations in the Pleistocene epoch. Photorespiration, the rate of which is directly related to the O(2)/CO(2) ratio, due to the dual function of Rubisco, may be an important mechanism in maintaining the limits of O(2) and CO(2) concentrations by restricting land plant productivity and weathering.

Atmosphere↗
PubMed1983

The escape of molecular hydrogen and the synthesis of organic nitriles in planetary atmospheres.

What is the influence of hydrogen escape from the atmosphere of small planetary bodies on the synthesis of organic molecules in that atmosphere? To answer this question, laboratory experiments have been performed to study the evolution of different reducing model atmospheres submitted to electrical discharges, with and without the simulation of H2 escape. A study of mixtures of nitrogen and methane shows a very strong effect of H2 escape on the formation of organic nitriles, the only nitrogen containing organics detected in the gas phase. These are HCN, CH (triple bond) C-CN, (CN)2, CH2=CH-CN, CH3CN and CH3CH2CN. The yield of synthesis of most of these compounds is noticeably increased, up to several orders of magnitude, when hydrogen escape is simulated. The escape of H2 from the atmosphere of the primitive Earth may have played a crucial role in the formation of reactive organic molecules such as CH (triple bond) C-CN or (CN)2, which can be considered as important prebiotic precursors. These experimental results may also explain extant data concerning the nature and relative abundance of organics present in the atmosphere of Titan, a planetary satellite which may be an ideal model within our solar system for the study of organic cosmochemistry and exobiology.

Atmosphere↗
PubMed1984

Organic syntheses in gas phase and chemical evolution in planetary atmospheres.

Atmospheric chemistry may be one of the important pathways to the synthesis of organic compounds in a planetary periphery. Depending on the nature of the carbon source (CH4, CO or CO2), the main composition of the atmosphere, and the respective roles of the various energy sources, is it possible, and to what extent, to produce organics? What kind of gaseous mixture is the most favourable to prebiotic organic syntheses? How far can the results of laboratory works be extrapolated to the case of planetary atmospheres? These questions are discussed, on the basis of several available laboratory data, and by considering the main atmospheric composition of the planets of the solar system, and the list of organic compounds which have already been detected in their atmospheres.

Atmosphere↗
PubMed2005

Relation of atmospheric pressure changes and the occurrences of acute myocardial infarction and stroke.

Previous studies have demonstrated variation in vascular events with respect to season and time of day. Changes in barometric pressure display daily and seasonal variations and could modulate the occurrence of vascular events. The objective of this study was to determine whether a relation exists between changes in barometric pressure and occurrence of stroke or acute myocardial infarction (AMI). A retrospective analysis of hospital admissions for AMI and stroke from 1993 to 1996 in central Texas was related to changes in atmospheric pressure that were obtained from the National Climatic Data Center. Patients who had AMI (n = 1,327) or stroke (n = 839) were identified from a computerized hospital database. Mean atmospheric pressure, greatest change in pressure, and rate of change in pressure per 24-hour period were computed. One-, 2-, and 3-day and seasonal groupings of cardiovascular events were related to corresponding changes in barometric pressure. The fall and winter seasons had the highest variability in atmospheric pressure readings. There was a significant correlation (p = 0.0083) between a decrease in atmospheric pressure and the occurrence of AMI the day after a pressure decrease, especially during the fall and winter seasons. No relation between stroke and atmospheric pressure was demonstrated. In conclusion, we conclude that rapid decreases in barometric pressure are associated with the occurrence of AMI but not of stroke.

Atmospheric Pressure↗
PubMed2005

Atmospheric nitrogen inputs to the Delaware Inland Bays: the role of ammonia.

A previous assessment of nitrogen loading to the Delaware Inland Bays indicates that atmospheric deposition provides 15-25% of the total, annual N input to these estuaries. A large and increasing fraction of the atmospheric wet flux is NH(4)(+), which for most aquatic organisms represents the most readily assimilated form of this nutrient. Particularly noteworthy is a 60% increase in the precipitation NH(4)(+) concentration at Lewes, DE over the past 20 years, which parallels the increase in poultry production on the Delmarva Peninsula over this period (currently standing at nearly 585 million birds annually). To further examine the relationship between local NH(3) emissions and deposition, biweekly-integrated gaseous NH(3) concentrations were determined using Ogawa passive samplers deployed at 13 sampling sites throughout the Inland Bays watershed over a one-year period. Annual mean concentrations at the 13 sites ranged from <0.5 microg NH(3)m(-3) to >6 microg NH(3)m(-3), with a mean of 1.6+/-1.0 microg NH(3)m(-3). At most sites, highest NH(3) concentrations were evident during spring and summer, when fertilizer application and poultry house ventilation rates are greatest, and seasonally elevated temperatures induce increased rates of microbial activity and volatilization from soils and animal wastes. The observed north-to-south concentration gradient across the watershed is consistent with the spatial distribution of poultry houses, as revealed by a GIS analysis of aerial photographs. Based on the average measured NH(3) concentration and published NH(3) deposition rates to water surfaces (5-8 mm s(-1)), the direct atmospheric deposition of gaseous NH(3) to the Inland Bays is 3.0-4.8 kg ha(-1)yr(-1). This input, not accounted for in previous assessments of atmospheric loading to the Inland Bays, would effectively double the estimated direct dry deposition rate, and is on par with the NO(3)(-) and NH(4)(+) wet fluxes. A second component of this study examined spatial differences in NO(3)(-) and NH(4)(+) wet deposition within the Inland Bays watershed. In a pilot study, precipitation composition at the Lewes NADP-AIRMoN site (DE 02) was compared with that at a satellite site established at Riverdale on the Indian River Estuary, approximately 21 km southwest. While the volume-weighted mean precipitation NO(3)(-) concentrations did not differ significantly between sites, the NH(4)(+) concentration observed at Riverdale (26.3 micromoles L(-1)) was 73% greater than at Lewes (15.2 micromoles L(-1)). More recently, a NADP site was established at Trap Pond, DE (DE 99), which was intentionally located within the region of intense poultry production. A comparison of the initial two years (6/2001-5/2003) of precipitation chemistry data from Trap Pond with other nearby NADP-AIRMoN sites (Lewes and Smith Island) reveals fairly homogeneous NO(3)(-) wet deposition, but significant spatial differences ( approximately 60%) in the NH(4)(+) wet flux. Overall, these results suggest that local emissions and below-cloud scavenging provide a significant contribution to regional atmospheric N deposition.

Air Pollutants↗
PubMed2003

The potential of organic (electrospray- and atmospheric pressure chemical ionisation) mass spectrometric techniques coupled to liquid-phase separation for speciation analysis.

The use of mass spectrometry based on atmospheric pressure ionisation techniques (atmospheric pressure chemical ionisation, APCI, and electrospray ionisation, ESI) for speciation analysis is reviewed with emphasis on the literature published in and after 1999. This report accounts for the increasing interest that atmospheric pressure ionisation techniques, and in particular ESI, have found in the past years for qualitative and quantitative speciation analysis. In contrast to element-selective detectors, organic mass spectrometric techniques provide information on the intact metal species which can be used for the identification of unknown species (particularly with MS-MS detection) or the confirmation of the actual presence of species in a given sample. Due to the complexity of real samples, it is inevitable in all but the simplest cases to couple atmospheric pressure MS detection to a separation technique. Separation in the liquid phase (capillary electrophoresis or liquid chromatography in reversed phase, ion chromatographic or size-exclusion mode) is particularly suitable since the available techniques cover a very wide range of analyte polarities and molecular mass. Moreover, derivatisation can normally be avoided in liquid-phase separation. Particularly in complex environmental or biological samples, separation in one dimension is not sufficient for obtaining adequate resolution for all relevant species. In this case, multi-dimensional separation, based on orthogonal separation techniques, has proven successful. ESI-MS is also often used in parallel with inductively coupled plasma MS detection. This review is structured in two parts. In the first, the fundamentals of atmospheric pressure ionisation techniques are briefly reviewed. The second part of the review discusses recent applications including redox species, use of ESI-MS for structural elucidation of metal complexes, characterisation and quantification of small organometallic species with relevance to environment, health and food. Particular attention is given to the characterisation of biomolecules and metalloproteins (metallothioneins and phytochelatins) and to the investigation of the interaction of metals and biomolecules. Particularly in the latter field, ESI-MS is the ideal technique due to the softness of the ionisation process which allows to assume that the detected gas-phase ions are a true representation of the ions or ion-biomolecule complexes prevalent in solution. It is particularly this field, important to biochemistry, physiology and medical chemistry, where we can expect significant developments also in the future.

Atmospheric Pressure↗
PubMed2002

Uptake of atmospheric mercury by deionized water and aqueous solutions of inorganic salts at acidic, neutral and alkaline pH.

Mercury (Hg) is well known as a toxic environmental pollutant that is among the most highly bioconcentrated trace metals in the human food chain. The atmosphere is one of the most important media for the environmental cycling of mercury, since it not only receives mercury emitted from natural sources such as volcanoes and soil and water surfaces but also from anthropogenic sources such as fossil fuel combustion, mining and metal smelting. Although atmospheric mercury exists in different physical and chemical forms, as much as 90% can occur as elemental vapour Hg0, depending on the geographic location and time of year. Atmospheric mercury can be deposited to aquatic ecosystems through both wet (rain or snow) and dry (vapour adsorption and particulate deposition) processes. The purpose of the present study was to measure, under laboratory conditions, the rate of deposition of gaseous, elemental mercury (Hg0) to deionized water and to solutions of inorganic salt species of varying ionic strengths with a pH range of 2-12. In deionized water the highest deposition rates occurred at both low (pH 2) and high (pH 12). The addition of different species of salt of various concentrations for the most part had only slight effects on the absorption and retention of atmospheric Hg0. The low pH solutions of various salt concentrations and the high pH solutions of high salt concentrations tested in this study generally showed a greater tendency to absorb and retain atmospheric Hg0 than those at a pH closer to neutral.

Adsorption↗
PubMed2003

Marine sulfur cycling and the atmospheric aerosol over the springtime North Atlantic.

We investigated the distribution of phytoplankton species and the associated dimethyl sulfur species, dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) on a cruise into the spring bloom region of the northern North Atlantic (near 47 degrees N, 19 degrees W). The cruise was timed to characterize the relationship between plankton dynamics and sulfur species production during the spring plankton bloom period. At the same time, we measured the DMS concentrations in the atmospheric boundary layer and determined the abundance and composition of the atmospheric aerosol. The water column studies showed that the interplay of wind-driven mixing and stratification due to solar heating controlled the evolution of the plankton population, and consequently the abundance of particulate and dissolved DMSP and DMS. The sea-to-air transfer of DMS was modulated by strong variations in wind speed, and was found to be consistent with currently available transfer parameterizations. The atmospheric concentration of DMS was strongly dependent on the sea surface emission, the depth of the atmospheric boundary layer and the rate of photooxidation as inferred from UV irradiance. Sea-salt and anthropogenic sulfate were the most abundant components of the atmospheric aerosol. On two days, a strong dust episode was observed bringing mineral dust aerosol from the Sahara desert to our northerly study region. The background concentrations of marine biogenic sulfate aerosol were low, near 30-60 ppt. These values were consistent with the rate of sulfate production estimated from the abundance of DMS in the marine boundary layer.

Aerosols↗
PubMed2000

Biological control of blue mould on apple by a strain of Candida sake under several controlled atmosphere conditions.

The biocontrol potential of the yeast Candida sake (CPA-1) against Penicillium expansum decay of apples under several controlled atmosphere conditions was investigated. In a laboratory trial under different commercial cold storage conditions, increasing concentrations of C. sake improved decay control. A maximum reduction of decay was achieved at 3% O2-3% CO2 atmosphere. It amounted to a 97% lesion reduction after treatment with a suspension containing 2.4 x 10(6) CFU/ml of C. sake (CPA-1). In a semi-commercial trial at 1 degree C with wounded fruits, the reduction in decay diameter caused by C. sake exceeded 80% after 60 days at 21% O2 and 60% after 120 days of storage under controlled atmosphere conditions. For seven controlled atmosphere conditions studied, a significant influence by C. sake on the P. expansum decay was observed, and the lesion size was reduced more than 70% by C. sake at 10(7) CFU/ml. The populations of C. sake (CPA-1) on the apple surface followed the same pattern under all controlled atmosphere conditions studied. They decreased 4-10-fold during the first 2 weeks, followed by an increase to the initial level after 45 days, and thereafter the count remained constant for the period of 90 days examined. This indicated the capacity of C. sake (CPA-1) to colonize the surface of apples under various storage conditions. The ability to colonize was even higher in apple wounds.

Atmosphere↗
PubMed2001

Influence of modified atmospheric storage, lactic acid, and NaCl on survival of sublethally heat-injured Listeria monocytogenes.

The effect of package atmosphere on survival of uninjured and sublethally heat-injured Listeria monocytogenes, inoculated onto tryptose phosphate agar containing 0.85% lactic acid and 2% NaCl (TPALAS) was investigated. Inoculated TPALAS plates were packaged in air, 100% N2 (N2), 30% CO2-70% N2 (CO2-N2), and vacuum and stored at 4 and 20 degrees C for up to 31 days. Recovery of L. monocytogenes from TPALAS was influenced by the injury status (i.e., injured and uninjured) of the inoculum, storage atmosphere (air, N2, CO2-N2, and vacuum), storage temperature (4 and 20 degrees C), and recovery media [tryptose phosphate agar (TPA) and modified Oxford agar (MOX)] (P <0.05). Overall, storage at 4 degrees C supported greater survival than storage at 20 degrees C (P< 0.05). Uninjured L. monocytogenes stored at 4 degrees C was recovered on TPA better than sublethally heat-injured L. monocytogenes stored at 40 degrees C (P < 0.05). Recovery of sublethally heat-injured L. monocytogenes stored at 4 degrees C followed the order N2 > CO2-N2 > air > vacuum (P < 0.05), whereas recovery of uninjured L. monocyrogenes stored at 4 degrees C followed the order N2 > CO2-N2 > vacuum > air (P < 0.05). Air and vacuum atmospheres supported greater survival of uninjured and heat-injured L. monocytogenes than N2 and CO2-N2 atmospheres at 20 degrees C (P < 0.05). Recovery of sublethally heat-injured L. monocytogenes stored at 20 degrees C followed the order vacuum > air> CO2-N2 = N2 (P <0.05), whereas recovery of uninjured L. monocytogenes stored at 20 degrees C followed the order vacuum > air> CO2-N2 > N2 (P<0.05). Uninjured L. monocytogenes stored under N2 at 4 degrees C was recovered best, whereas sublethally heat-injured L. monocytogenes stored under N2 at 20 degrees C was recovered poorest (P < 0.05). Factors such as package atmosphere and storage temperature, involved in the production, storage, and distribution of fermented foods must be thoroughly evaluated when determining strategies for control and detection of L. monocytogenes in such products.

Air↗
PubMed2001

Estimation of the atmospheric corrosion on metal containers in industrial waste disposal.

Solid industrial waste are often stored in metal containers filled with concrete, and placed in well-aerated warehouses. Depending on meteorological conditions, atmospheric corrosion can induce severe material damages to the metal casing, and this damage has to be predicted to achieve safe storage. This work provides a first estimation of the corrosivity of the local atmosphere adjacent to the walls of the container through a realistic modeling of heat transfer phenomena which was developed for this purpose. Subsequent simulations of condensation/evaporation of the water vapor in the atmosphere were carried out. Atmospheric corrosion rates and material losses are easily deduced. For handling realistic data and comparison, two different meteorological contexts were chosen: (1) an oceanic and damp atmosphere and (2) a drier storage location. Some conclusions were also made for the storage configuration in order to reduce the extent of corrosion phenomena.

Atmosphere↗
PubMed1998

Do temperature and atmospheric pressure affect the incidence of serious odontogenic infection?

OBJECTIVE: The purpose of this study was to investigate the popular belief that the incidence of odontogenic cellulitis is weather-related. Two meteorologic parameters were examined: temperature and atmospheric pressure. STUDY DESIGN: To test the hypothesis being studied, a retrospective cohort study design was used. Medical reports of all patients with serious odontogenic cellulitis who were treated at the Salpêtrière University Hospital between January 1, 1995, and December 31, 1995, (a total of 301 cases) were evaluated in relation to the weather. Hypothesizing that the incidence of odontogenic cellulitis was constant over a period of 1 year, the authors calculated the probability of observed incidence for each month over a 12-month period. The mean number of cases of odontogenic cellulitis (+/- standard error of the mean) for days on which (1) the temperature was within the same 2 degrees -C (3.6 degrees -F) interval and (2) the atmospheric pressure was within the same 3-hPa (2.25-mmHg) interval was also calculated. RESULTS: When the monthly incidence of odontogenic cellulitis and either the average temperature or the average atmospheric pressure for each month were examined together, fluctuation in the former seemed to be independent of the latter. Similarly, when we calculated the mean number of cases of odontogenic cellulitis for several intervals of temperature and atmospheric pressure without taking the calendar into account, no direct relationship could be observed. CONCLUSION: The results of the study suggest that the occurrence of odontogenic cellulitis is not influenced by the weather, at least insofar as weather is measured by temperature and atmospheric pressure.

Adolescent↗
PubMed2002

Source reconciliation of atmospheric gas-phase and particle-phase pollutants during a severe photochemical smog episode.

A comprehensive organic compound-based receptor model is developed that can simultaneously apportion the source contributions to atmospheric gas-phase organic compounds, semivolatile organic compounds, fine particle organic compounds, and fine particle mass. The model is applied to ambient data collected at four sites in the south coast region of California during a severe summertime photochemical smog episode, where the model determines the direct primary contributions to atmospheric pollutants from 11 distinct air pollution source types. The 11 sources included in the model are gasoline-powered motor vehicle exhaust, diesel engine exhaust, whole gasoline vapors, gasoline headspace vapors, organic solvent vapors, whole diesel fuel, paved road dust, tire wear debris, meat cooking exhaust, natural gas leakage, and vegetative detritus. Gasoline engine exhaust plus whole gasoline vapors are the predominant sources of volatile organic gases, while gasoline and diesel engine exhaust plus diesel fuel vapors dominate the emissions of semivolatile organic compounds from these sources during the episode studied at all four air monitoring sites. The atmospheric fine particle organic compound mass was composed of noticeable contributions from gasoline-powered motor vehicle exhaust, diesel engine exhaust, meat cooking, and paved road dust with smaller but quantifiable contributions from vegetative detritus and tire wear debris. In addition, secondary organic aerosol, which is formed from the low-vapor pressure products of gas-phase chemical reactions, is found to be a major source of fine particle organic compound mass under the severe photochemical smog conditions studied here. The concentrations of secondary organic aerosol calculated in the present study are compared with previous fine particle source apportionment results for less intense photochemical smog conditions. It is shown that estimated secondary organic aerosol concentrations correlate fairly well with the concentrations of 1,2-benzenedicarboxylic acid in the atmospheric fine particle mass, indicating that aromatic diacids may be useful in the quantification of certain sources of secondary organic aerosol in the atmosphere.

Atmosphere↗
PubMed2004

Photolysis of chloral under atmospheric conditions.

The photolysis of chloral under atmospheric conditions was studied at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. The photodissociation rate coefficient, J(chloral), was measured directly under different sunlight conditions during April 1999. Values in the range of J(chloral) = (4.61-6.11) x 10(-5) s(-1) were obtained, yielding an average value of J(chloral)/J(NO2) = (6.15 +/- 0.62) x 10(-3). This corresponds to a photolysis lifetime of 4.5-6 h under conditions appropriate to the solar flux during summer months and confirms that atmospheric photolysis is the major degradation pathway for chloral. The overall quantum efficiency of photolysis under atmospheric conditions was determined to be 1.00 +/- 0.05. The atmospheric photolysis of chloral produced phosgene, CO, and Cl atoms with molar yields of 0.83 +/- 0.04, 1.01 +/- 0.05, and 1.18 +/- 0.06, respectively. The product yield data are consistent with a mechanism in which the primary photolysis channel produces a Cl atom and a CCl2CHO radical. The latter species is converted to the oxy radical OCCl2CHO,which decomposes by both C-C and C-Cl bond fission. A chemical mechanism for the photolysis of chloral by sunlight is proposed, and the atmospheric implications are discussed.

Air Pollutants↗