Atmospheric Environment (v.40, #29)

Nanostructure of atmospheric soot particles by Viktória Kovács Kis; Mihály Pósfai; János L. Lábár (5533-5542).
We studied the structure of atmospheric soot using electron-diffraction-based pair distribution function (PDF) analysis, and compared it with other carbon structures. Two reference materials were used: hydrogen-free amorphous carbon and a kerogen sample with a H/C ratio of 0.61. First-neighbour atomic distances in atmospheric soot are as small as 0.134 nm, much shorter than in graphite (0.142 nm) or in amorphous carbon (0.141–143 nm), but larger than the typical value (0.131–0.132 nm) for kerogen. These results suggest that a high molar ratio of hydrogen is present in soot in small-sized aromatic clusters. Such aromatic components can strongly influence the optical properties of soot particles. We found that the quantitative electron diffraction method is an independent and efficient alternative to the commonly used spectroscopic methods for the analysis of the atomic structure of individual soot particles.
Keywords: Soot; Nanostructure; Electron diffraction; Aromatic structures;

Launceston is one of the Australian cities most affected by particle pollution due to the use of woodheaters in the winter months, with frequent exceedences of the national standard, the National Environment Protection Measure for Ambient Air Quality (or Air NEPM in short), of 50 micrograms per cubic metre for daily PM10 (particulate matter with an aerodynamic diameter of 10 μm or less). The main objective of the present study was to determine the woodheater carrying capacity for Launceston—the number of woodheaters that can operate in the city without exceeding the Air NEPM. For this purpose, a prognostic meteorological and air pollution model called TAPM is used, coupled to a gridded woodheater PM10 emissions inventory. The latter was derived using information on dwelling density, the percentage of dwellings with woodheaters, woodheater emission rates and their diurnal and seasonal variations, and the proportions of compliant/non-compliant woodheaters and open fireplaces. The model simulations are performed for the year 1998, and the concentrations are scaled for previous and subsequent years using trends in woodheater numbers and types. The modelled number of exceedences of the Air NEPM for the period 1997–2004 is in good agreement with the observations. The modelling indicates that the PM10 Air NEPM would be met in Launceston when the total number of woodheaters is 20% of the total number of dwellings, of which 76%, 18%, 6% would be compliant woodheaters, non-compliant woodheaters and open fireplaces, respectively. With the present trends in the regional woodheater profile, this should occur in the year 2007.
Keywords: TAPM; Woodsmoke; Woodheaters; Emission inventory; Air pollution modelling; Particulate matter; Carrying capacity;

Polybrominated diphenyl ethers (PBDEs) over the open Indian Ocean by Oliver Wurl; John Robert Potter; Caroline Durville; Jeffrey Philip Obbard (5558-5565).
Atmospheric concentrations of polybrominated diphenyl ethers (PBDEs), a group of industrial chemicals widely used as flame retardants were measured over the Indian Ocean and represent the first comprehensive data of atmospheric contaminations of PBDEs over the open ocean. Air back trajectory analysis shows that PBDEs have great potential for long-range atmospheric transport to remote regions of the world. In this report, we show that PBDE concentrations (mean 2.5 pg m−3) over the open Indian Ocean are in a similar range to those reported for remote land-based locations in the more industrialized northern hemisphere. Concentrations along the coastline of Java, Indonesia, were as high as 15 pg m−3. Overall, data suggests that PBDEs are now ubiquitous in their global atmospheric distribution.
Keywords: Flame retardants; Polybrominated diphenyl ethers; Indian Ocean; Atmosphere; Air pollution;

Rate constants for the reaction of OH radicals with n-propyl vinyl ether (PVE, CH3CH2CH2OCH=CH2), n-butyl vinyl ether (BVE, CH3CH2CH2CH2OCH=CH2), iso-butyl vinyl ether (IBVE, (CH3)2CHCH2OCH=CH2) and tert-butyl vinyl ether (TBVE, (CH3)3COCH=CH2), have been measured in the temperature and pressure ranges 232–373 K and 30–300 Torr using the pulsed laser photolysis-laser-induced fluorescence method, and at 298 K and 760 Torr using the relative method. The obtained results are k 1=(9.3±0.6)×10−12 exp[(708±20)/T], k 2=(1.5±0.2)×10−11 exp[(572±42)/T], k 3=(1.6±0.1)×10−11 exp[(567±20)/T], k 4=(1.7±0.2)×10−11 exp[(549±25)/T] cm3  molecule−1  s−1. The values at 298 K are k 1=(1.0±0.1)×10−10, k 2=(1.0±0.1)×10−10, k 3=(1.1±0.1)×10−10, k 4=(1.1±0.1)×10−10  cm3  molecule−1  s−1. The deduced tropospheric lifetimes of these ethers for reaction with OH are of the order of 1 h and they are comparable to those for reaction with ozone.
Keywords: Vinyl ethers; OH radicals; Kinetics; Troposphere;

An aircraft exerts a downward force on the air, so aircraft exhausts tend to descend toward the ground within the aircraft's wake. The wake of an aeroplane descends in an essentially inviscid and thus long-lived manner, through the action of a pair of trailing counterrotating vortices on one another. The vortices derive from the circulation about the wings yielding the lift. Exhaust pollutants may thus be conveyed to the ground close to airports, far more effectively than through ambient atmospheric dispersion alone, as has hitherto been assumed occurs within air-quality models. The presence of the vortices in the vicinity of airports is well-established, as it is the need to wait for their decay or movement out of the flight corridor—for the safety of the following aircraft—that caps departure and arrival rates at busy periods. The dynamics of the transport are elucidated, so that the impact of the transport on pollutant concentrations at ground level in an airport environs may be established.

This study was set out to characterize particulate emissions from diesel engines fuelled by (i) mineral diesel and (ii) B20 (a blend of 20% biodiesel with diesel); in terms of metals and benzene soluble organic fraction (BSOF), which is an indicator of toxicity and carcinogenicity.A medium duty, transport diesel engine (Mahindra MDI 3000) was operated at idling, 25%, 50%, 75% and rated load at maximum torque speed (1800 rpm) and samples of particulate were collected using a partial flow dilution tunnel for both fuels. Collected particulate samples were analyzed for their metal contents. In addition, metal contents in mineral diesel, biodiesel and lubricating oil were also measured to examine and correlate their (metals present in fuel) impact on particulate characteristics. Results indicated comparatively lower emission of particulate from B20-fuelled engine than diesel engine exhaust. Metals like Cd, Pb, Na, and Ni in particulate of B20 exhaust were lower than those in the exhaust of mineral diesel. However, emissions of Fe, Cr, Ni Zn, and Mg were higher in B20 exhaust. This reduction in particulate and metals in B20 exhaust was attributed to near absence of aromatic compounds, sulphur and relatively low levels of metals in biodiesel. However, benzene soluble organic fraction (BSOF) was found higher in B20 exhaust particulate compared to diesel exhaust particulate.
Keywords: Particulate; Biodiesel; Metals; Benzene soluble organic fraction; Toxicology;

Measurements and modelling of marine salt transportation and deposition in a tropical region in Brazil by G.R. Meira; M.C. Andrade; I.J. Padaratz; M.C. Alonso; J.C. Borba (5596-5607).
This work presents results of marine salt deposition in a marine atmosphere zone in a tropical region in the northeast of Brazil. A general model that represents marine aerosol behaviour in coastal regions is applied. Results show that marine salt deposition data are strongly influenced by wind speeds above the critical value of 3.0 m/s. The effect of the distance from the sea on marine salt data is also observed. This effect is better represented when changes in marine aerosol composition, while being transported inland, are taken into account. Deposition parameters obtained from the model application at a Brazilian site show good agreement with data from other countries. Parametric equations to represent the behaviour of each model parameter are proposed for the studied region and form a specific model that is more accurate than the simple empirical relations previously used.
Keywords: Chloride; Marine aerosol; Marine atmosphere zone; Sea-salt model; Tropical region;

The tapered element oscillating microbalance (TEOM) is used to measure ambient particulate matter concentrations worldwide. The instrument is configured with a correction factor required by the US Environmental Protection Agency (EPA) to account for the difference between the TEOM and the gravimetric method. However, numerous studies have shown that this factor does not fully account for these differences, consequently, the European Commission (EC) insists on an independent assessment of the differences. The US EPA correction was found to contribute between 3 and 5 μg m−3 to the daily mean PM10 and PM2.5 concentrations at Marylebone Road, London, between 1 January 2001 and 31 December 2004. The TEOM is also configured to express measurements to a standard temperature (25 °C) and a standard pressure (1 atm). This differs from the US EPA requirement of ambient reporting conditions for both PM10 and PM2.5. It also differs from the European position, which also requires reporting at ambient conditions. When compared to ambient reporting conditions, the TEOM standard temperature and pressure correction was found to contribute between −1 and 7 μg m−3 to the daily mean PM10 and PM2.5 concentrations, and 2 μg m−3 to the annual mean concentrations. The standard temperature and pressure correction was also demonstrated to vary the annual mean concentration measured using the TEOM by 2–8% between European capital cities, with higher values in colder northern cities. The standard temperature and pressure correction to individual daily mean concentrations was shown to be up to 20%. It is recommended that the US EPA correction factor is removed from TEOM measurements and that all measurements are reported at ambient temperature and pressure.
Keywords: TEOM; Gravimetric; PM10; PM2.5; Temperature; Pressure;

Atmospheric CH4 along the Trans-Siberian railroad (TROICA) and river Ob: Source identification using stable isotope analysis by O.A. Tarasova; C.A.M. Brenninkmeijer; S.S. Assonov; N.F. Elansky; T. Röckmann; M. Brass (5617-5628).
The concentration and stable isotope (13C, D) signatures of methane (CH4) were determined in air samples collected in Russia, summer of 1999 plus 2001 and spring 2004, using the Trans-Siberian railway (TROICA project) and a boat as atmospheric measurement platforms. CH4 concentrations over wetlands in Western Siberia, especially in the Middle Ob area, are significantly enhanced relative to the background mixing ratios. The source isotopic signature of the samples collected in Western Siberia is δ 13Csource=−62.9±0.7‰ (n=5) and δDsource=−369±11‰ (n=5) in June–July 1999, confirming that biogenic CH4 from wetlands dominated the substantial CH4 excess along the Siberian transect and on the Ob river. Source estimates (δ 13Csource) are in the range between −54.1±2.8‰ and −67.4±1.6‰ for different regions in June–July 2001. It the spring expedition the individual source signatures are more uncertain as deviations of CH4 concentration from a background are rather small. The strongest deviations of the isotopic composition from the mean expedition values occur in vicinity of Perm (1999, 2001) and Novosibirsk (2004), where the isotopic signature of natural gas in atmospheric CH4 is evident.
Keywords: Atmospheric methane; Stable isotopes of methane; Natural gas; Russian wetlands; Trans-Siberian railroad;

A gas chromatograph iontrap mass spectrometer (GC-ITMS) was used to analyze the gas-and particle-phase products of α-pinene ozone oxidation in the presence of three different inorganic seed aerosols: sodium chloride, ammonium sulfate only, and ammonium sulfate with sulfuric acid. Products of α-pinene ozone oxidation common to the literature showed little difference in gas or particle-phase concentrations between seed types within the precision of the measurements even though significantly different aerosol yields were found between seed types. Small amounts of ring-opening products of four-membered cyclic oxygenates and markers of aldol condensation products were tentatively identified in the particle-phase for all seed types. These tentatively identified products are thought to be the result of acid-catalyzed heterogeneous reactions in the particle-phase or during sampling processes or analysis. The mechanisms for their formation are also proposed in this study.
Keywords: SOA; Mass spectrometry; Ion trap; Aldol condensation; Cycloreversion; Oligomers;

Recent progress in CFD modelling of wind field and pollutant transport in street canyons by Xian-Xiang Li; Chun-Ho Liu; Dennis Y.C. Leung; K.M. Lam (5640-5658).
With rapid development in computer hardware and numerical algorithms, computational fluid dynamics (CFD) techniques are widely utilized to study the wind field and pollutant transport in urban street canyons. The recent advancements and achievements in street-canyon pollution research using mathematical modelling approaches are reviewed in this paper. The standard, renormalized-group (RNG), and realizable k – ε turbulence closure schemes are the most commonly used Reynolds-averaged Navier–Stokes (RANS) models in street-canyon flow research, including the studies on the effects of street-canyon aspect ratio, building configuration, ambient wind direction, inflow turbulence intensities, vehicle-induced turbulence, and thermal stratifications. Another approach to turbulence simulation inside street canyons is large-eddy simulation (LES) which can handle a broad range of turbulent motions in a transient manner. These two approaches have their merits and the choice between them will be a compromise between accuracy and cost. Several guidelines on this choice as well as some comments on the 2D and 3D CFD simulations are given.The outputs from wind field models can be used with pollutant transport models to calculate the pollutant distribution inside street canyons. The most commonly employed pollutant transport models include Lagrangian, Eulerian, and Lagrangian/Eulerian hybrid models. The advantages and shortcomings of these models are summarized. Several other modelling concerns, such as chemically reactive pollutant dispersion and boundary conditions treatment, are also discussed.
Keywords: k – ɛ turbulence model; Large-eddy simulation (LES); Lagrangian particle dispersion model (LPDM); Eulerian dispersion model; Photochemical reactions; Thermal effects;

We present a three-dimensional solution of the steady-state advection-diffusion equation considering a vertically inhomogeneous planetary boundary layer (PBL). We reach this goal applying the generalized integral transform technique (GITT), a hybrid method that had solved a wide class of direct and inverse problems mainly in the area of heat transfer and fluid mechanics. The transformed problem is solved by the advection-diffusion multilayer model (ADMM) method, a semi-analytical solution based on a discretization of the PBL in sub-layers where the advection-diffusion equation is solved by the Laplace transform technique. Numerical simulations are presented and the performances of the solution are compared against field experiments data.
Keywords: Mathematical modeling; Semi-analytical solution; Advection-diffusion equation; Air pollution modeling; Planetary boundary layer;

Urban-scale variability of ambient particulate matter attributes by M.T. Freiman; N. Hirshel; D.M. Broday (5670-5684).
Real-time sampling of ambient particulate matter (PM) in the size range 0.23–10 μm and of carbonaceous matter concentrations has been carried out in a carefully designed field campaign in proximate paired neighborhoods in Haifa, Israel. The paired sites are characterized by a similar population density and neighborhood-wise socioeconomic (deprivation) index but show distinct canopy coverage. The data indicate clear sub-urban (neighborhood) scale variations in any measured PM attribute, such as concentrations, size distribution, and carbonaceous matter content. Mean ambient PM levels were comparatively higher than in other urban studies whereas carbonaceous airborne PM concentrations were lower. On top of the diurnal and seasonal variability and in spite of the significant regional effect of the semi-arid climate, local emissions and removal processes affect the PM concentrations to which people residing in urbanized regions are exposed. Analysis of possible mechanisms that could affect the observed spatial sub-urban PM differences, including local meteorology and emissions, reveal that sub-urban variability of removal processes has a major influence on ambient PM levels. Observations suggest that on top of the regional air masses which affect the city air quality and emissions from local sources, a normally unnoticed removal process, showing urban scale variability, is interception by trees and dense vegetation. In particular, the observed sub-urban variability in ambient PM concentrations is attributed, in part, to local variation of removal processes, among them the neighborhood-wise deposition on available surfaces, including canopy.
Keywords: Urban air quality; Particulate matter; Concentration variability; Neighborhood-scale; Trees and vegetation;

Time–activity relationships to VOC personal exposure factors by Rufus D. Edwards; Christian Schweizer; Vito Llacqua; Hak Kan Lai; Matti Jantunen; Lucy Bayer-Oglesby; Nino Künzli (5685-5700).
Social and demographic factors have been found to play a significant role in differences between time–activity patterns of population subgroups. Since time–activity patterns largely influence personal exposure to compounds as individuals move across microenvironments, exposure subgroups within the population may be defined by factors that influence daily activity patterns. Socio-demographic and environmental factors that define time–activity subgroups also define quantifiable differences in VOC personal exposures to different sources and individual compounds in the Expolis study.Significant differences in exposures to traffic-related compounds ethylbenzene, m- and p-xylene and o-xylene were observed in relation to gender, number of children and living alone. Categorization of exposures further indicated time exposed to traffic at work and time in a car as important determinants. Increased exposures to decane, nonane and undecane were observed for males, housewives and self-employed. Categorization of exposures indicated exposure subgroups related to workshop use and living downtown. Higher exposures to 3-carene and α-pinene commonly found in household cleaning products and fragrances were associated with more children, while exposures to traffic compounds ethylbenzene, m- and p-xylene and o-xylene were reduced with more children. Considerable unexplained variation remained in categorization of exposures associated with home product use and fragrances, due to individual behavior and product choice. More targeted data collection methods in VOC exposure studies for these sources should be used. Living alone was associated with decreased exposures to 2-methyl-1-propanol and 1-butanol, and traffic-related compounds.Identification of these subgroups may help to reduce the large amount of unexplained variation in VOC exposure studies. Further they may help in assessing impacts of urban planning that result in changes in behavior of individuals, resulting in shifts in the patterns of exposure experienced by the population.
Keywords: Volatile organic compounds; Determinants of exposure; Time–activity patterns; Socio-demographic factors; Population subgroups.;

Determination of carbonyl compounds in air and cancer risk assessment in an academic institute in Fortaleza, Brazil by Rivelino M. Cavalcante; Clayton S. Campelo; Marcelo J. Barbosa; Edilberto R. Silveira; Tecia V. Carvalho; Ronaldo F. Nascimento (5701-5711).
Carbonyl compounds (CCs) were measured in outdoor and indoor air of libraries, classrooms, laboratories, and offices at the Universidade Federal do Ceará, Fortaleza, Brazil, from 5 November to 20 December 2004. Indoor air was sampled during normal activities of personnel and students. The results showed that acetone was the most abundant carbonyl compound in outdoor and indoor air, with an average concentration of 52.48 μg m−3, followed by formaldehyde (12.42 μg m−3), acetaldehyde (2.90 μg m−3), benzaldehyde (2.35 μg m−3), butyraldehyde (2.31 μg m−3), and acrolein (2.02 μg m−3). Acetone was the main compounds in research laboratories and offices, whereas formaldehyde was predominantly present in the libraries, student laboratories, and classrooms. The indoor/outdoor (I/O) ratio indicated that levels of CCs in indoor air are more elevated than in outdoor air. Ratios were 11.20 for acetone in research laboratories, 8.48 for acetaldehyde in offices, and 8.37 for formaldehyde in student laboratories. The cancer risk for professionals was 5–30-fold higher than that for students, while the risk was even higher in some libraries and offices when compared to particular laboratories. For women, the estimated cancer risk is 4% higher than that calculated for men.
Keywords: Carbonyl compounds; Formaldehyde; Cancer risk assessment; Academic environment; Indoor air quality;

Deposition and emissions of reactive nitrogen over European forests: A modelling study by D. Simpson; K. Butterbach-Bahl; H. Fagerli; M. Kesik; U. Skiba; S. Tang (5712-5726).
The EMEP MSC-W Eulerian chemical transport model is used to investigate a number of features concerning the concentrations and depositions of reactive nitrogen species over Europe, with a focus on forest ecosystems and soil emissions. We illustrate the relative contributions of oxidised versus reduced nitrogen, and of dry versus wet deposition, to nitrogen inputs to forests. A comparison with measurements, including data for the NOFRETETE sites, showed that the EMEP model performs generally well for N-compounds, although with some problems for NH 3 which is difficult to model with a large-scale model.The model was modified to make use of a new forest-soil–NO inventory (with daily resolution) from the NOFRETETE project and used to calculate the potential effects of these emissions on N-deposition to forests, and on the ozone-indicator AOT40. The contribution of soil–NO to these environmental measures was found to be generally small, but significant in some areas, with changes ranging between 0–20% in Central Europe and even greater in Scandinavia. Given the large uncertainties in soil–NO emission estimates, it is clear that this source is potentially comparable in its importance to many combustion sources in parts of Europe, and deserves more attention.
Keywords: Nitrogen oxides; Deposition; Soil emissions; Modelling; EMEP;

Prediction of the production of nitrogen oxide ( NO x ) in turbojet engines by Louis Tsague; Joseph Tsogo; Thomas Tamo Tatietse (5727-5733).
Gaseous nitrogen oxides ( NO + NO 2 = NO x ) are known as atmospheric trace constituent. These gases remain a big concern despite the advances in low NO x emission technology because they play a critical role in regulating the oxidization capacity of the atmosphere according to . Aircraft emissions of nitrogen oxides ( NO x ) are regulated by the International Civil Aviation Organization. The prediction of NO x emission in turbojet engines by combining combustion operational data produced information showing correlation between the analytical and empirical results. There is close similarity between the calculated emission index and experimental data. The correlation shows improved accuracy when the 2124 experimental data from 11 gas turbine engines are evaluated than a previous semi empirical correlation approach proposed by Pearce et al. [1993. The prediction of thermal NO x in gas turbine exhausts. Eleventh International Symposium on Air Breathing Engines, Tokyo, 1993, pp. 6–9]. The new method we propose predict the production of NO x with far more improved accuracy than previous methods. Since a turbojet engine works in an atmosphere where temperature, pressure and humidity change frequently, a correction factor is developed with standard atmospheric laws and some correlations taken from scientific literature [Swartwelder, M., 2000. Aerospace engineering 410 Term Project performance analysis, November 17, 2000, pp. 2–5; Reed, J.A. Java Gas Turbine Simulator Documentation. pp. 4–5]. The new correction factor is validated with experimental observations from 19 turbojet engines cruising at altitudes of 9 and 13 km given in the ICAO repertory [Middleton, D., 1992. Appendix K (FAA/SETA). Section 1: Boeing Method Two Indices, 1992, pp. 2–3]. This correction factor will enable the prediction of cruise NO x emissions of turbojet engines at cruising speeds. The ICAO database can now be completed using the approach we propose to complete the whole mission flight NO x emissions.
Keywords: Nitrogen oxides ( NO x ) emission; Turbojet engines; Semi-empirical correlation; Cruise emission prediction; Correction factor;

Filters impregnated with XAD-4™ resin were used in a small series of high-volume air samples to compare their collection of gas-phase semivolatile toxic substances (organochlorine pesticides, OCs, and polycyclic aromatic hydrocarbons, PAHs) with that achieved by polyurethane foam (PUF). The advantages of the use of such sorbent-impregnated filters (SIFs) include a reduction in size which leads to numerous benefits. The latter include simplified sample handling, shipping and storage, and the potential for a decrease in solvent requirements for pre-cleaning and extraction. Furthermore, such SIFs could be used to measure combined particle/gas concentrations of target compounds.Gas concentrations derived from the SIFs in a filter-SIF–SIF–PUF configuration agreed well with values derived from the PUF plugs in a comparison filter-PUF configuration. The collection efficiency of a single SIF was ∼80% on average. As such, these SIFs are viewed as a promising alternative to PUF and further, more extensive study of their performance characteristics appears to be warranted.
Keywords: High-volume sampling; XAD resin; Polyurethane foam; Semivolatile organic compounds;

New Directions: Watching over tropospheric hydroxyl (OH) by J. Lelieveld; C.A.M. Brenninkmeijer; P. Joeckel; I.S.A. Isaksen; M.C. Krol; J.E Mak; E. Dlugokencky; S.A. Montzka; P.C. Novelli; W. Peters; P.P. Tans (5741-5743).