Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Atmospheric Environment (v.40, #11)
Seasonal and interannual variability in absorbing aerosols over India derived from TOMS: Relationship to regional meteorology and emissions by Gazala Habib; Chandra Venkataraman; Isabelle Chiapello; S. Ramachandran; Olivier Boucher; M. Shekar Reddy (pp. 1909-1921).
The objective of this study is an analysis of the spatial, seasonal and interannual variability of regional-scale aerosol load over India, detected by TOMS during 1981–2000, with an evaluation of potential contributing factors, including estimated anthropogenic aerosol emission trends and regional meteorology (rainfall and circulation patterns). Spatial distributions in TOMS Ai were related to the emission densities of anthropogenic absorbing aerosols in April–May, but varied seasonally and were modified significantly by higher atmospheric dispersion in January–March and rainfall in June–September, both of which lead to low TOMS Ai, even in regions of high aerosol emissions. Dust emissions explain the high TOMS Ai over northwest region during April–May and June–September when rainfall is scanty and significant air-mass decent occurs in this region. The magnitude of TOMS Ai correlated with the anthropogenic absorbing aerosol (black carbon and inorganic matter) emission flux in five selected regions, dominated by biomass/biofuel burning and fossil fuel combustion, but not in a region with significant mineral dust emissions. The seasonal cycle in TOMS Ai was related to the seasonal variability in dust, biomass burning emissions and rainfall. Interannual variability in TOMS Ai was linked to that in forest burning emissions in the northeast, as evidenced by a correlation with ATSR fire-counts, both significantly enhanced in 1999. Trends in anthropogenic emissions during 1981–2000 potentially contribute to increases in the aerosol load detected by TOMS. This would need further investigation using analysis incorporating both trends in anthropogenic emissions and the interannual variability in natural sources of aerosols.
Keywords: Aerosols; Long-term trends; Satellite remote sensing; Emission inventory; Rainfall; Regional circulation
Optical properties of urban aerosols in the region Bratislava–Vienna I. Methods and tests by M. Kocifaj; H. Horvath; Jovanovic O. Jovanović; M. Gangl (pp. 1922-1934).
Aerosol optical data obtained by means of ground-based methods are applied to determine microphysical properties of aerosols in the atmosphere of Vienna-city. The measured aerosol extinction coefficientσA serves as a source of information on the ambient aerosols. A large database of extinction efficiency factors for a set of irregularly shaped as well as the spherical particles of various sizes is pre-calculated and employed in the inversion procedure. The assumed particle models differ in chemical composition and are representative for most typical aerosol systems in the urban atmospheres. All database records are taken into a regularization scheme to solve the inverse problem for aerosol size distribution using measured extinction data. In addition, subsidiary data on spectral sky radiance are successfully incorporated into the mathematical model to retrieve the information on aerosol effective refractive index in the visible.As for Vienna, the aerosol extinction is a decreasing function of wavelength in visible spectrum—it indicates the predominance of sub-micrometer-sized particles in the atmosphere. The surface distribution function s( r)=d S/d r of aerosol particles customarily peaks at radii r≈0.2–0.3μm, while the volume distribution function v( r)=d V/d r∼ rs( r) has a mode at radii about 0.3–0.4μm. Analysing size distributions d V/dlog( r) for irregularly shaped particles it is shown that the daily profile of this function is smoothly evolving and almost typically accounts for a first mode at radii between 0.8 and 0.9μm.
Keywords: Aerosol size distribution; Aerosol extinction coefficient; Non-spherical particles
Optical properties of urban aerosols in the region Bratislava–Vienna—II: Comparisons and results by M. Kocifaj; H. Horvath; Hrvol J. Hrvoľ (pp. 1935-1948).
The optical and microphysical properties of aerosols in highly urbanized region Bratislava–Vienna were determined by means of ground-based optical methods during campaign in August and September 2004. Although both cities are close to each other forming a common metropolitan region, the features of their aerosol systems are distinct. While urban and suburban zones around Vienna have mostly a clean air without major influences of emissions from industry, Bratislava itself need to be classified as polluted area—the optical data collected in the measuring site are influenced mainly by Technické Sklo factory (NW positioned), Matador (SSE), Istrochem (ENE) and Slovnaft (ESE). In contrary to an observed smooth evolution of the aerosol system in Vienna, the aerosol environment is quite unstable in Bratislava and usually follows the day changes of the wind directions (as they correspond to the position of individual sources of pollution). The particle sizes in Bratislava are predominately larger compared to Vienna. A subsidiary mode within surface size distribution frequently occurs at radius about 0.7μm in Bratislava but not in Vienna. The size distribution of airborne particles in Vienna is more dependent on relative humidity than in Bratislava. It suggests the particles in Bratislava are larger whenever, or non-deliquescent to a great extent.The spectral attenuation of solar radiation by aerosol particles shows a typical mode atλ≈0.4μm in Bratislava, which is not observed in the spectral aerosol extinction coefficient in Vienna. In Bratislava, the average aerosol optical thickness grows from morning hours to the evening, while an opposite effect can be observed in Vienna in the same time.
Keywords: Aerosol size distribution; Optical thickness; Urban particles
Observation of coinciding arctic boundary layer ozone depletion and snow surface emissions of nitrous acid by Antonio Amoroso; Harry J. Beine; Roberto Sparapani; Marianna Nardino; Ivo Allegrini (pp. 1949-1956).
Measurements of snow surface—atmosphere exchange fluxes of nitrous acid at Ny-Ålesund, Svalbard during springtime confirmed earlier findings that no significant emissions occurred from alkaline snow surfaces at this marine high Arctic location. On 29 April 2004 air arriving from the North Pole brought both ozone depleted air and significant snowfall. On that day we observed HONO emission fluxes of up to 40nmolm−2h−1. These emissions were made possible by the combination of two independent phenomena. The acidic snow allowed the transport of NO3− ions to photochemically reactive areas and the release of produced HONO from the snow interstitial air; while the absence of ozone likely increased the HONO/NO fraction over that of NO2 in the snow interstitial air.
Keywords: HONO; Nitrous acid; Atmospheric chemistry; Snow surface chemistry; Ozone depletion; Arctic
Comparative effects of MTBE and ethanol additions into gasoline on exhaust emissions by C.-L. Chong-Lin Song; W.-M. Wen-Mei Zhang; Y.-Q. Yi-Qiang Pei; G.-L. Guo-Liang Fan; G.-P. Guan-Peng Xu (pp. 1957-1970).
The effects of the additives of ethanol (EA) and methyl tert-butyl ether (MTBE) in various blend ratios into the gasoline fuel on the exhaust emissions and the catalytic conversion efficiencies were investigated in an EFI gasoline engine. The regulated exhaust emissions (CO, THC and NO X) and the unregulated exhaust emissions (benzene, formaldehyde, acetaldehyde, unburned EA and MTBE) before and after the three-way catalytic converter were measured.The experimental results showed that EA brought about generally lower regulated engine-out emissions than MTBE did. But, the comparison of the unregulated engine-out emissions between both additives was different. Concretely, the effect of EA on benzene emission was worse than that of MTBE on the whole, which was a contrast with formaldehyde emission. The difference in the acetaldehyde comparison depended much on the engine operating conditions, especially the engine speed. Both EA and MTBE were identified in the engine exhaust gases only when they were added to the fuel, and their volume fraction increased with blend ratios. The catalytic conversion efficiencies of the regulated emissions for the EA blends were in general lower than those for MTBE blends, especially at the low and high engine speeds. There was little difference in the catalytic conversion efficiencies for both benzene and formaldehyde, while distinct difference for acetaldehyde.
Keywords: EFI gasoline engine; MTBE; Ethanol; Regulated emission; Unregulated emission; Catalytic conversion efficiency
Winter measurements of children's personal exposure and ambient fine particle mass, sulphate and light absorbing components in a northern community by Melanie Noullett; Peter L. Jackson; Michael Brauer (pp. 1971-1990).
The relationship between ambient fine particle (PM2.5) concentration and children's personal exposure was investigated in Prince George, British Columbia. Repeated personal exposure measures (10 per subject) of 15 children and ambient concentrations at their neighbourhood schools were collected for a 6-week winter period in 2001. PM2.5 mass, sulphate (SO42−) and light absorbing carbon (ABS) were determined for all samples and the relationship between ambient concentration and personal exposure was investigated. Overall, lower particle exposures and a lower personal–ambient regression slope were found for Prince George children compared to results from other longitudinal studies of children. This suggests that in this setting indoor environments may have less influence from ambient sources and greater influence from non-ambient sources. Comparison of personal exposures and ambient concentrations for each individual indicated higher Spearman correlations for SO42− (median=0.95) and ABS (median=0.73) compared to total PM2.5 mass (median=0.55). A large degree of individual variability in the personal–ambient correlation was found for PM2.5 mass, while SO42− showed very consistent results, supporting its use as an indicator of exposure to particulate matter of ambient origin. ABS was slightly more variable than SO42− due to the influence of non-ambient or very local sources in a low number of samples. The impact of local meteorology was also investigated and inversion conditions were connected to all high ambient levels (>30μgm−3). In addition, associations were found between inversion strength and personal exposure. This finding suggests that reduction of ambient concentrations during stagnant periods would result in lower personal exposure levels. This study highlights the importance of both ambient and non-ambient sources, supports the use of both SO42− and ABS as tracers of background ambient particle exposure and demonstrates the significant effect of winter meteorology on both outdoor levels and personal exposure in a valley community.
Keywords: Air pollution; Personal monitoring; PM; 2.5; Spatial distribution; Winter meteorology; Absorption coefficient/reflectance; Sulphate (SO; 4; 2−; )
Validation of an efficient non-negative matrix factorization method and its preliminary application in Central California by Jinyou Liang; David Fairley (pp. 1991-2001).
Positive matrix factorization (PMF) techniques have been applied in many environmental studies. The commercial version of the PMF method has a relatively moderate practical limit for the size of the input data matrix, since the computer memory and time needed for the commercial method increases quadratically with the number of elements of solution matrices. To extend the applications of the PMF techniques to large datasets, we exercised alternative methods that demand less computer memory and time. One such method, called non-negative matrix factorization (NMF) here, is extremely memory efficient, compared with the commercial PMF method. Both NMF and PMF methods are sensitive to the initialization of solution matrices, and the use of random numbers in the initialization usually starts with a large prediction error, and requires a number of model runs with different random seeds. A novel, chemical mass balance method (ROC) is introduced here to provide a reasonable initialization for the NMF method for large data sets. Both NMF and ROC methods were validated with an ideal Cross example and the benchmark example of the commercial PMF method. The NMF-ROC method was further evaluated, in terms of computer time and the prediction error, in the preliminary application to a data set that contains particle-phase polar organic compounds analyzed for a number of samples collected in Central California during the California Regional PM10/PM2.5 air quality study (CRPAQS, 1999–2001). The NMF-ROC method was demonstrated to perform better than the NMF, PMF and PMF-ROC methods in the CRPAQS data set. This performance enhancement is expected to be magnified for larger data sets.
Keywords: Chemical mass balance; Inverse cluster analysis; PM; CRPAQS
The investigation of emission characteristics and carbon deposition over motorcycle monolith catalytic converter using different fuels by L.-W. Li-Wei Jia; W.-L. Wen-Long Zhou; M.-Q. Mei-Qing Shen; Jun Wang; M.-Q. Man-Qun Lin (pp. 2002-2010).
The effects of MTBE-blended gasoline and 10% (v/v) ethanol–gasoline blended fuel (E10) on HC, CO and NO x conversions over catalytic converters were investigated. Two 4-stroke motorcycle engines outfitted with typical three-way catalytic converters were used and regulated emissions were measured according to ECE-40 test cycle. The results show that the influence of E10 on the catalytic conversion is less significant at grinding stages, compared with that of MTBE-blended gasoline, the catalytic conversion, however, decreases remarkably for E10 at the point of 10000km. The carbon deposition information in the direction of the radius of two used monolith exhaust catalytic converters was studied by SEM, EPMA, XPS, TG–DTA and FTIR after a 10000km test program. The results indicate that carbon deposition occurs first at the center of a converter, gradually extending to its edge. The carbonaceous species are in the form of C xH y if the vehicle is fueled with MTBE-blended gasoline, whereas the carbonaceous species are C xH yO for E10. The majority of the carbonaceous species are deposited on the precious metal (PM) sites. Further, aromatic rings, alkyl groups and their partial oxidation products are found in the carbonaceous deposit.
Keywords: Carbon deposition; Motorcycle exhaust control catalyst; Blended ethanol fuel; Emissions
Tropospheric degradation of 2-hydroxy-2-methylpropanal, a photo-oxidation product of 2-methyl-3-buten-2-ol: Kinetic and mechanistic study of its photolysis and its reaction with OH radicals by Nathalie Carrasco; J.-F. Jean-François Doussin; B. Bénédicte Picquet-Varrault; Patrick Carlier (pp. 2011-2019).
This article presents the first study of the chemical reactivity of a photo-oxidation product of the 2-methyl-3-buten-2-ol (MBO) in the troposphere, the 2-hydroxy-2-methylpropanal (HMPr). Experiments were performed under controlled conditions for pressure (atmospheric pressure) and temperature (296±2K) in the LISA indoor simulation chamber and in the EUPHORE outdoor simulation chamber to understand the transformations of HMPr in the atmosphere, using FTIR spectrometry. Reaction with OH radicals was studied in the presence and in the absence of NO x. All the kinetic studies were carried out by relative rate study using isoprene and/or n-butylether as the reference compound. The rate constants found for these reactions were J=(1.01±0.39)×10−5s−1 and kHMPr+OH=(1.52±0.36)×10−11molecule−1cm3s−1. For the reaction with OH radicals, an important production of acetone was observed, with a yield of Racetone=1.06±0.06.
Keywords: Biogenic compound; 2-Hydroxy-2-methylpropanal; 2-Methyl-3-buten-2-ol; OH radicals; Photo-oxidation; Troposphere
Polychlorinated naphthalenes in the gas-phase of the Venice Lagoon atmosphere by L. Manodori; A. Gambaro; R. Zangrando; C. Turetta; P. Cescon (pp. 2020-2029).
The gas-phase concentrations of polychlorinated naphthalenes (PCNs) (16 congeners) were investigated over 1 year at two sites in the Venice Lagoon (‘marine’ and ‘industrial’) and at a mainland station (‘rural’). ΣPCN concentrations were mainly composed of lighter congeners and ranged from 191 to 3415fgm−3 with values comparable with those of ‘background’ air. The lowest ΣPCN concentration was detected at the ‘marine’ site while no significant differences were found between the ‘industrial’ and ‘rural’ stations. The presence of combustion marker congeners in most samples suggests that this is the main source of PCN at all sites.The variation of ΣPCN concentrations over the year showed that the highest values occurred from autumn to early spring months at the ‘industrial’ and ‘marine’ sites, while at the ‘rural’ station the values were quite homogeneous, with some peaks in summer. The temperature–PCN relationship was statistically significant only at the ‘marine’ station, but with a weak correlation. The linear regression between PCN, PAH and PCB, and the seasonal evolution of their ratios was investigated to gain a better understanding of the potential sources of PCNs. At the ‘marine’ site, it may be supposed that combustion processes constitute PCN sources, with a substantial sea influence. At the ‘rural’ site, continuous PCN sources from distant points of emission are hypothesized while the ‘industrial’ site may be supposed to feature an unidentifiable continuous source as well as other seasonal sources.
Keywords: HRGC-HRMS; Venice Lagoon; PCN; Air pollution; Persistent organic pollutants
Formation and growth of sulfuric acid–water cluster ions: Experiments, modelling, and implications for ion-induced aerosol formation by A. Sorokin; F. Arnold; D. Wiedner (pp. 2030-2045).
The formation, growth, and composition of mixed cluster ions HSO4−A aW w and H+A aW w (A=H2SO4, W=H2O) with a up to 6 were investigated in the laboratory using a flow reactor-mass spectrometer apparatus. In the flow reactor the buffer gas (N2) pressure and temperature were kept constant at 80hPa and 295K, respectively, while the partial pressures of the trace gases H2SO4 and H2O and thereby also the relative humidity were varied. It was found that for small a (<5) positive ions are markedly enriched in H2O and negative ions are enriched in H2SO4 molecules. For larger a the composition of positive and negative ions becomes similar and approaches the modelled composition of a liquid A aW w droplet (respectively, fora>8 anda>15). When increasing the partial pressure of gaseous H2SO4 in the flow reactor both positive and negative ions grow via A uptake. This growth is more pronounced for negative ions where it becomes very efficient fora>8 reflecting A attachment to become faster than A detachment. We also have made model calculations indicating that fora>10 negative ion growth via A attachment occurs on nearly every collision of an A-molecule with an ion.
Keywords: Cluster ions; Ion-induced nucleation; Aerosol formation
Long-term trends of benzo(a)pyrene concentration on the eastern coast of the Baltic Sea by Audrone R. Milukaite (pp. 2046-2057).
Concentration of benzo(a)pyrene (B(a)P) was investigated in atmospheric air at Preila background station located on the eastern coast of the Baltic Sea in 1980–2002. A significant difference in daily concentration of benzo(a)pyrene, reaching more than two orders of magnitude, was determined during the period of investigation. The variability of benzo(a)pyrene daily concentration was considered. The main part of extreme benzo(a)pyrene daily concentration of over 5ngm−3 was related to the air masses coming to the background site from W-SW to N-NW over the period of 1980–1994. Owing to the variability of benzo(a)pyrene daily concentration, the monthly concentration of benzo(a)pyrene in atmospheric air of the background site varied from 0.18 to 3.30ngm−3 in cold season and from 0.02 to 1.72ngm−3 in warm season. A slowly decreasing trend of benzo(a)pyrene monthly concentration was determined in both seasons during the whole period of investigation. Comparison of B(a)P monthly concentration determined at Preila background station with that in other countries since 1994 (according to the EMEP program) has shown that monthly concentration of benzo(a)pyrene is nearly of the same level in the Czech Republic and it is by one order of magnitude higher than at Scandinavian background stations. The course of carcinogen concentration at Preila background station is similar to that of Swedish stations with tendency to decrease from 1999.
Keywords: Benzo(a)pyrene; Concentration; Atmospheric air; Pollution sources
Source apportionment of atmospheric urban aerosol based on weekdays/weekend variability: evaluation of road re-suspended dust contribution by S.M. Almeida; C.A. Pio; M.C. Freitas; M.A. Reis; M.A. Trancoso (pp. 2058-2067).
During 1 year, twice per week (one working day and one sunday), 24-h averaged, separated fine and coarse atmospheric aerosol were measured, for total mass and chemical composition, in a suburban site on the outskirts of Lisbon. The relative concentration variability between working days and sundays allowed a better insight into the sources of atmospheric particulate matter. Receptor modelling based on Principal Component Analysis and Multilinear Regression applied to sunday and working day samples revealed marked differences during weekdays, in autumn/winter period. Based on the characteristics of the Principal Components it was possible to conclude that during autumn/winter, a predominant fraction of coarse and fine soil dust provides from anthropogenic activities, being presumably associated with road dust re-suspension by road traffic.
Keywords: PM; 2.5; PM; 2.5−10; Weekday variability; Receptor modelling; Road traffic
Statistical models for the prediction of respirable suspended particulate matter in urban cities by P. Goyal; Andy T. Chan; Neeru Jaiswal (pp. 2068-2077).
Particulate matters (PM) constitute a major concern for air quality of metropolitan cities. In this paper, the problem of air quality forecasting of respirable suspended particulate matter (RSPM) based on some meteorological factors has been discussed. The present work deals with the application of three statistical models to forecast daily averaged concentration of RSPM in urban Delhi and Hong Kong. Model 1 is based on multiple linear regression of meteorological parameters, model 2 is based on Box-Jenkins time series auto regressive integrated moving average (ARIMA) model and model 3 is a combination of the two. A detailed analysis of results of above models shows that the combination of ARIMA and multiple regression (model 3) gives better results in comparison to the other two models with respect to observed data. Thus the model 3 has been used, in the present study, to forecast the air quality of Delhi and Hong Kong with respect to RSPM. It has been concluded that the same model may be used as a practical prognostic model for prediction of RSPM in urban cities.
Keywords: RSPM; ARIMA model; Regression; Air quality; Concentration