Atmospheric Environment (v.41, #37)

The aim of this study was to review and summarise the levels of particulate air pollution, its elemental composition, its determinants, and its potential health effects in metro systems. A number of studies have been conducted to assess the levels of particulate matter and its chemical composition in metro systems. The monitoring equipment used varied and may have led to different reporting and makes it more difficult to compare results between metro systems. Some of the highest average levels of particulate matter were measured in the London metro system. Whereas some studies have reported higher levels of particulate matter in the metro system (e.g. London, Helsinki, Stockholm) compared to other modes of transport (London) and street canyons (Stockholm and Helsinki), other studies reported lower levels in the metro system (e.g. Hong Kong, Guangzhou, and Mexico City). The differences may be due to different material of the wheel, ventilation levels and breaking systems but there is no good evidence to what extent the differences may be explained by this, except perhaps for some elements (e.g. Fe, Mn). The dust in the metro system was shown to be more toxic than ambient airborne particulates, and its toxicity was compared with welding dust. The higher toxicity may be due to the higher iron content. Although the current levels of particulate matter and toxic matter are unlikely to lead to any significant excess health effects in commuters, they should be reduced where possible. It will be difficult to introduce measures to reduce the levels in older metro systems, e.g. by introducing air conditioning in London, but certainly they should be part of any new designs of metro systems.
Keywords: Metro; Underground; Subway; Air pollution; Health effects; Personal exposure; Microenvironment;

Estimation of particle resuspension source strength on a major London Road by Alistair J. Thorpe; Roy M. Harrison; Paul G. Boulter; Ian S. McCrae (8007-8020).
Non-exhaust particles from road traffic arise from both abrasion sources and the resuspension of particles from the road surface. This paper reports a new combination of existing methods for indirect estimation of resuspension emission factors for Marylebone Road, London, a busy multi-lane highway in a street canyon. The method involves firstly estimating the total source strength of coarse particles (PM2.5–10) arising from the road by calculating the roadside incremental concentration of coarse particles above the urban background. This is converted to a source strength by its ratio to NO x whose source strength is estimated from the knowledge of the traffic mix and mean speed. This coarse particle source strength is assumed to represent the sum of resuspension emissions and the coarse particle component of abrasion emissions. Using information on the traffic mix and speed, the abrasion emissions have been calculated from the EMEP/CORINAIR emissions factor database, the result subtracted from the total coarse particle emissions in order to yield resuspension emissions, and combined with traffic count data to derive fleet-average emission factors. Using the fact that the traffic mix differs substantially between weekdays and weekends, separate average emission factors for light- and heavy-duty vehicles have been estimated. In addition to traffic mix, the influence of wind speed and the time elapsed since the last rainfall upon resuspension have been estimated. Wind speed was found to have by far the larger influence, although this was still secondary to the number of heavy-duty vehicles. Uncertainties arising from the choice of urban background site and poor data quality are discussed.
Keywords: PM10; Coarse fraction; Resuspension; Non-exhaust particles; Particulate matter;

The morphology of size-classified ambient particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) was studied in samples collected at the USEPA supersite located in Baltimore, MD. Size classification was accomplished through the use of a low pressure impactor to produce samples with cut-off diameters of 0.10, 0.15, 0.55, and 2.0 μm. Sampling was conducted in two campaigns during the fall of 2002, with separate sampling occurring during early morning, mid-day, late afternoon, and evening periods. Particles with cut-off diameters of 2 μm were generally round in shape, with a border fractal dimension close to 1 based on the analysis of transmission electron microscope (TEM) images of collected samples. Particles with a cut-off diameter of 0.15 μm had on average higher fractal dimensions than the other size classes considered, regardless of time of day associated with the sample. As expected, the time of the day influenced the shape of particle populations sampled. Particles collected during early morning were found to have higher fractal dimension than those collected at other sampling times. At night, particles presented mostly round shapes. This difference was particularly pronounced in particles with cut-off diameters of 0.15 μm.
Keywords: Fractal dimension; PM2.5; Air pollution; Shape; TEM;

Various water management regimes, such as continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding-moist intermittent irrigation, but without water logging (F-D-F-M), are currently practiced in paddy rice production in mainland China. These water regimes have incurred a sensitive change in direct N2O emission from rice paddy fields. We compiled and statistically analyzed field data on N2O emission from paddy fields during the rice growing season (71 measurements from 17 field studies) that were published in peer-reviewed Chinese and English journals. Seasonal total N2O was, on average, equivalent to 0.02% of the nitrogen applied in the continuous flooding rice paddies. Under the water regime of F-D-F or the F-D-F-M, seasonal N2O emissions increased with N fertilizer applied in rice paddies. An ordinary least square (OLS) linear regression model produced the emission factor (EF) of nitrogen for N2O averaged 0.42%, but background N2O emission was not pronounced under the water regime of F-D-F. Under the F-D-F-M water regime, N2O EF and background emission were estimated to be 0.73% and 0.79 kg N2O-N ha−1, respectively, during the paddy rice growing season. Based on results of the present study and national rice production data, subsequently, direct N2O emissions during the rice growing season amounted to 29.0 Gg N2O-N with the uncertainty of 30.1%, which accounted for 7–11% of the reported estimates of annual total emission from croplands in mainland China. The results of this study suggest that paddy rice relative to upland crop production could have contributed to mitigating N2O emissions from agriculture in mainland China.
Keywords: Background emission; Emission factor; Nitrous oxide; Regression model;

Enhanced gamma (Δγ) ray dose rates due to 222Rn progeny wet deposited on the ground surface measured at six monitoring sites in Japan were statistically analyzed to investigate their temporal and spatial variations. Variations of Δγ ray dose rates indicated significant regional differences between the sites on the Sea of Japan coast and those located inland and on the Pacific coast in Japan. At the sites located on the Sea of Japan coast, significant seasonal variation was evident, with higher dose rates in autumn and winter, and lower dose rates in summer. In contrast, however, no significant seasonal variation was observed at the inland and Pacific coast sites in Japan. The variation of Δγ ray dose rates was characterized by three major factors: climatologically changed air masses arriving in Japan, variation of 222Rn and its progeny concentrations in the air column, and the regional characteristics of precipitation. It is evident that the contribution from local 222Rn to Δγ ray dose rates was smaller than those from continental 222Rn. Meso-scale atmospheric disturbance, however, was suggested as an important process for extremely high Δγ ray dose rates, possibly by the accumulation of additional local 222Rn with stronger convergence. It is therefore possible that the variation of Δγ ray dose rates reflects the chemical climatology of 222Rn and its progeny.
Keywords: Gamma ray dose rates; 222Rn and its progeny; Precipitation; Long-range transport of air masses; Meso-scale disturbance;

Chemical composition and complex refractive index of Saharan Mineral Dust at Izaña, Tenerife (Spain) derived by electron microscopy by Konrad Kandler; Nathalie Benker; Ulrich Bundke; Emilio Cuevas; Martin Ebert; Peter Knippertz; Sergio Rodríguez; Lothar Schütz; Stephan Weinbruch (8058-8074).
Samples from two strong homogeneous dust plumes from the Saharan desert reaching Izaña (Tenerife, Spain) in July and August 2005 were taken with a miniature impactor system and filter samplers. Size, aspect ratio and chemical composition of more than 22,000 individual particles were studied by scanning electron microscopy. The mineralogical phase composition of about 200 particles was investigated by transmission electron microscopy. In addition, the aerosol size distribution was measured with an optical particle spectrometer. In all samples, the aerosol was dominated by mineral dust with an average composition (by volume) of 64% silicates, 6% quartz, 5% calcium-rich particles, 14% sulfates, 1% hematite, 1% soot and 9% other carbonaceous material. Sulfate was found predominantly as coating on other particles with an average thickness of approximately 60 nm. The aerosol calcium content is correlated with the calcite concentrations of soils in the source region, highest values were observed for northern and central Algeria and Morocco. The average aspect ratio of the particles was 1.64. The distributions of the aspect ratios are parameterized by log-normal functions for modeling purpose. Single-scattering albedo (0.95) and asymmetry factor (0.74–0.81) was measured by polar aerosol photometry on filter samples using a light source resembling the solar spectrum. The apparent soot content of the sample (1 vol%) was determined by the same technique. From the mineralogical data, an average complex refractive index of 1.59–9×10−3i for visible light was derived. The imaginary part of the complex refractive index decreases with increasing particle size from −2.5×10−2i to <−10−3i, reflecting the decreasing hematite and soot contents. The imaginary part derived from optical measurements was −7×10−3i.
Keywords: Mineral dust; Electron microscopy; Chemical composition; Aspect ratio; Complex refractive index; Mixing state; Coatings;

Impacts of Russian biomass burning on UK air quality by Claire Witham; Alistair Manning (8075-8090).
Unusually high levels of PM10 were observed in the UK in May 2006 and September 2002. This paper investigates the possible contribution of long-range transport of smoke from widespread agricultural burning and forest fires in western Russia to these air pollution episodes. The Lagrangian dispersion model NAME is run in both forwards and backwards modes to determine the transport and sources of the polluted air masses for the two incidents. Comparison of the model results to satellite data and ground observations from across Europe demonstrates good agreement for both the timing and magnitude of the episodes and suggests that fires in western Russia were the primary cause of both incidents. Secondary contributions to the 2006 episode may have come from European anthropogenic pollution and pollen released in northern Europe. The occurrence and timing of both pollution episodes were strongly controlled by the meteorological situation at the time. Scaling of model results to observations suggests that 0.5–0.7 Mtonnes of biomass per day could have been burnt during periods when winds reaching the UK were from the east. The newly reported 2006 episode means that Russian fires have affected UK air quality at least twice since 2000 and it is suggested that, without changes in current practice, such events are likely to occur again in the future with implications for UK and European air quality.
Keywords: Smoke; Atmospheric dispersion modelling; Forest fires; Long-range transport; Pollution;

Turbulent Schmidt numbers for CFD analysis with various types of flowfield by Yoshihide Tominaga; Ted Stathopoulos (8091-8099).
The application of CFD (computational fluid dynamics) using RANS (Reynolds-averaged Navier–Stokes equations) model to turbulent flows with mass transfer generally estimates the turbulent scalar flux assuming the gradient diffusion hypothesis, which requires definition of the turbulent Schmidt number, Sc t However, no universal value of Sc t has been established and empirical values have been used in different studies. In this paper, previous research related to the application of optimum values of Sc t for engineering flowfields relevant to atmospheric dispersion is reviewed. The optimum values for Sc t are widely distributed in the range of 0.2–1.3 and the specific value selected has a significant effect on the prediction results. On the basis of the present study results and since the optimum values of Sc t largely depend on the local flow characteristics, it is recommended that Sc t should be determined by considering the dominant flow structure in each case.
Keywords: Turbulent Schmidt number; CFD; Dispersion; RANS (Reynolds averaged Navier–Stokes equations) model; Optimum values;

Comparison of structural features of water-soluble organic matter from atmospheric aerosols with those of aquatic humic substances by Regina M.B.O. Duarte; Eduarda B.H. Santos; Casimiro A. Pio; Armando C. Duarte (8100-8113).
Elemental analysis, Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR) and solid-state cross polarization with magic angle spinning-13C-nuclear magnetic resonance (CPMAS 13C NMR) spectroscopies were used to compare the chemical features of water-soluble organic compounds (WSOC) from atmospheric aerosols with those of aquatic humic and fulvic acids. The influence of different meteorological conditions on the structural composition of aerosol WSOC was also evaluated. Prior to the structural characterisation, the WSOC samples were separated into hydrophobic acids and hydrophilic acids fractions by using a XAD-8/XAD-4 isolation procedure. Results showed that WSOC hydrophobic acids are mostly aliphatic (40–62% of total NMR peak area), followed by oxygenated alkyls (15–21%) and carboxylic acid (5.4–13.4%) functional groups. Moreover, the aromatic content of aerosol WSOC samples collected between autumn and winter seasons is higher (∼18–19%) than that of samples collected during warmer periods (∼6–10%). The presence of aromatic signals typical of lignin-derived structures in samples collected during low-temperature conditions highlights the major contribution of wood burning processes in domestic fireplaces into the bulk chemical properties of WSOC from aerosols. According to our investigations, aerosol WSOC hydrophobic acids and aquatic fulvic and humic acids hold similar carbon functional groups; however, they differ in terms of the relative carbon distribution. Elemental analysis indicates that H and N contents of WSOC hydrophobic acids samples surpass those of aquatic fulvic and humic acids. In general, the obtained results suggest that WSOC hydrophobic acids have a higher aliphatic character and a lower degree of oxidation than those of standard fulvic and humic acids. The study here reported suggests that aquatic fulvic and humic acids may not be good models for WSOC from airborne particulate matter.
Keywords: Atmospheric aerosols; Water-soluble organic compounds; Humic substances; CPMAS 13C NMR spectroscopy; FTIR-ATR spectroscopy;

A combined Lagrangian stochastic model with a micromixing sub-model is used to estimate the fluctuating concentrations observed in two wind tunnel experiments. The Lagrangian stochastic model allows fluid trajectories to be simulated in the inhomogeneous flow, while the mixing model accounts for the dissipation of fluctuations using the interaction by exchange with the mean (IEM) mechanism. The model is first tested against the open terrain, wind tunnel data of Fackrell, J.E. and Robins, A.E. [1982. Concentration fluctuations and fluxes in plumes from point sources in a turbulent boundary layer. Journal of Fluid Mechanics 117, 1–26] and shows good agreement with the observed mean concentrations and fluctuation intensities. The model is then compared with the wind tunnel simulation of a two-dimensional street canyon by Pavageau, M. and Schatzmann, M. [1999. Wind tunnel measurements of concentration fluctuations in an urban street canyon. Atmospheric Environment 33, 3961–3971]. Despite the limitations of the k–ε turbulence scheme and the IEM mixing mechanism, the model reproduces the fluctuation intensity pattern within the canyon well. Overall, the comparison with both sets of wind tunnel experiments are encouraging, and the simplicity of the model means that predictions in a complex, three-dimensional geometry can be produced in a practicable amount of time.
Keywords: Concentration fluctuations; Lagrangian stochastic; Mixing model; Pollution; Urban;

The effects of roadside structures on the transport and dispersion of ultrafine particles from highways by George E. Bowker; Richard Baldauf; Vlad Isakov; Andrey Khlystov; William Petersen (8128-8139).
Understanding local-scale transport and dispersion of pollutants emitted from traffic sources is important for urban planning and air quality assessments. Predicting pollutant concentration patterns in complex environments depends on accurate representations of local features (e.g., noise barriers, trees, buildings) affecting near-field air flows. This study examined the effects of roadside barriers on the flow patterns and dispersion of pollutants from a high-traffic highway in Raleigh, North Carolina, USA. The effects of the structures were analyzed using the Quick Urban & Industrial Complex (QUIC) model, an empirically based diagnostic tool which simulates fine-scale wind field and dispersion patterns around obstacles. Model simulations were compared with the spatial distributions of ultrafine particles (UFP) from vehicular emissions measured using a passenger van equipped with a Differential Mobility Analyzer/Condensation Particle Counter. The field site allowed for an evaluation of pollutant concentrations in open terrain, with a noise barrier present near the road, and with a noise barrier and vegetation present near the road.Results indicated that air pollutant concentrations near the road were generally higher in open terrain situations with no barriers present; however, concentrations for this case decreased faster with distance than when roadside barriers were present. The presence of a noise barrier and vegetation resulted in the lowest downwind pollutant concentrations, indicating that the plume under this condition was relatively uniform and vertically well-mixed. Comparison of the QUIC model with the mobile UFP measurements indicated that QUIC reasonably represented pollutant transport and dispersion for each of the study configurations.
Keywords: Air quality; Dispersion modeling; Noise barriers; Vegetation; Mobile sources; QUIC;

Fungal fragments in moldy houses: A field study in homes in New Orleans and Southern Ohio by Tiina Reponen; Sung-Chul Seo; Faye Grimsley; Taekhee Lee; Carlos Crawford; Sergey A. Grinshpun (8140-8149).
Smaller-sized fungal fragments (<1 μm) may contribute to mold-related health effects. Previous laboratory-based studies have shown that the number concentration of fungal fragments can be up to 500 times higher than that of fungal spores, but this has not yet been confirmed in a field study due to lack of suitable methodology. We have recently developed a field-compatible method for the sampling and analysis of airborne fungal fragments. The new methodology was utilized for characterizing fungal fragment exposures in mold-contaminated homes selected in New Orleans, Louisiana and Southern Ohio. Airborne fungal particles were separated into three distinct size fractions: (i) >2.25 μm (spores), (ii) 1.05–2.25 μm (mixture), and (iii) <1.0 μm (submicrometer-sized fragments). Samples were collected in five homes in summer and winter and analyzed for (1→3)-β-d-glucan.The total (1→3)-β-d-glucan varied from 0.2 to 16.0 ng m−3. The ratio of (1→3)-β-d-glucan mass in fragment size fraction to that in spore size fraction (F/S) varied from 0.011 to 2.163. The mass ratio was higher in winter (average=1.017) than in summer (0.227) coinciding with a lower relative humidity in the winter. Assuming a mass-based F/S-ratio=1 and the spore size=3 μm, the corresponding number-based F/S-ratio (fragment number/spore number) would be 103 and 106, for the fragment sizes of 0.3 and 0.03 μm, respectively. These results indicate that the actual (field) contribution of fungal fragments to the overall exposure may be very high, even much greater than that estimated in our earlier laboratory-based studies.
Keywords: Mold; Beta-glucan; Particle size; Exposure assessment;

Effects of soil fumigants on methanotrophic activity by K. Spokas; J. King; D. Wang; S. Papiernik (8150-8162).
Negative impacts on methane (CH4) oxidation capacity have already been observed for a variety of agronomic practices, but the effect of soil fumigation on CH4 oxidation has not been investigated. Fumigation is a common practice in agricultural crop and nursery seedling protection. Soils from various agricultural experiment stations, forest nurseries, and a landfill were evaluated for effects of 1,3-dichloropropene (1,3-D), methyl isothiocyanate (MITC), and chloropicrin (CP) on CH4 oxidation capacities. All three fumigants significantly reduced CH4 oxidation rates in historically non-fumigated soils (>50%). 1,3-D enhanced CH4 oxidation in 3 out of 5 previously fumigated soils and MITC increased CH4 oxidation rates in all historically MITC-fumigated soils compared to controls. CP universally decreased oxidation capacity regardless of fumigation history. These results support the conclusion that CH4 oxidation effects are fumigant specific and that prior fumigation history plays a vital role in determining the impact on CH4 oxidizer community functionality, which may have implications on the global CH4 cycle.
Keywords: Methanotrophs; Enhanced biodegradation; Fumigation history; Methane oxidation;

The molecular distribution of fine particulate organic matter emitted from Western-style fast food cooking by Yunliang Zhao; Min Hu; Sjaak Slanina; Yuanhang Zhang (8163-8171).
The emissions from food cooking could be a significant contributor to atmospheric particulate organic matter (POM) and its chemical composition would vary with different cooking styles. In this study, the chemical composition of POM emitted from Western-style fast food cooking was investigated. A total of six PM2.5 samples was collected from a commercial restaurant and determined by gas chromatography–mass spectrometry (GC–MS). It is found that the total amount of quantified compounds of per mg POM in Western-style fast food cooking is much higher than that in Chinese cooking. The predominant homologue is fatty acids, accounting for 78% of total quantified POM, with the predominant one being palmitic acid. Dicarboxylic acids display the second highest concentration in the quantified homologues with hexanedioic acid being predominant, followed by nonanedioic acid. C max of n-alkanes occurs at C25, but they still appear relative higher concentrations at C29 and C31. In addition, both levoglucosan and cholesterol are quantified. The relationship of concentrations of unsaturated fatty acids (C16 and C18) with a double bond at C9 position and C9 acids indicates the reduction of the unsaturated fatty acids in the emissions could form the C9 acids. Moreover, the nonlinear fit indicates that other C9 species or other compounds are also produced, except for the C9 acids. The potential candidates of tracers for the emissions from Western-fast food cooking could be: tetradecanoic acid, hexadecanoic acid, octadecanoic acid, 9-octadecenoic acid, nonanal, lactones, levoglucosan, hexanedioic acid and nonanedioic acid.
Keywords: Food cooking; Particulate organic matter; Organic tracers; Fatty acids;

Aerosol–cloud condensation nuclei (CCN) closure was studied in a semi-rural location 80 km north of Toronto, Canada at the Centre for Atmospheric Research Experiments outside of Egbert, Ontario during the fall of 2005. This site is subject to both polluted air from southern Ontario and clean air from the north. The purpose of the investigation was to evaluate the degree to which closure is attained at a supersaturation of 0.32% when size-resolved aerosol compositions from an Aerodyne Quadrupole Aerosol Mass Spectrometer are made alongside measurements of CCN number density and aerosol size distribution. Attention was given to assessing the sensitivity of closure to assumptions made concerning the water solubility and surface tension of the organic fraction of the aerosol in the Köhler analysis. By assuming that the organics are insoluble and that the growing droplet has the surface tension of water, a good overall degree of closure is attained throughout the analysis time period, with the predicted numbers of CCN within 15% of the modelled numbers, which is within our estimated systematic uncertainties. However, for the specific periods during which the organic content of the aerosol is high, the degree of closure is significantly lower. Sensitivity analyses indicate that some degree of organic water solubility and/or surface tension reduction is necessary to achieve the best agreement and least variance between the modelled and measured numbers of CCN. A general conclusion is that significant uncertainties arise in predicting CCN levels only when the level of soluble inorganic species is below approximately 25% by mass.
Keywords: Cloud condensation nuclei; Organic aerosols; Köhler theory; Closure study;

Fugitive dust from the erosion of arid and fallow land, after harvest and during agricultural activities, can at times be the dominant source of airborne particulate matter. In order to assess the source contributions to a given site, chemical mass balance (CMB) modeling is typically used together with source-specific profiles for organic and inorganic constituents. Yet, the mass balance closure can be achieved only if emission profiles for all major sources are considered. While a higher degree of mass balance closure has been achieved by adding individual organic marker compounds to elements, ions, EC, and organic carbon (OC), major source profiles for fugitive dust are not available. Consequently, neither the exposure of the population living near fugitive dust sources from farm land, nor its chemical composition is known. Surface soils from crop fields are enriched in plant detritus from both above and below ground plant parts; therefore, surface soil dust contains natural organic compounds from the crops and soil microbiota. Here, surface soils derived from fields growing cotton, safflower, tomato, almonds, and grapes have been analyzed for more than 180 organic compounds, including natural lipids, saccharides, pesticides, herbicides, and polycyclic aromatic hydrocarbon (PAH). The major result of this study is that selective biogenically derived organic compounds are suitable markers of fugitive dust from major agricultural crop fields in the San Joaquin Valley. Aliphatic homologs exhibit the typical biogenic signatures of epicuticular plant waxes and are therefore indicative of fugitive dust emissions and mechanical abrasion of wax protrusions from leaf surfaces. Saccharides, among which α- and β-glucose, sucrose, and mycose show the highest concentrations in surface soils, have been proposed to be generic markers for fugitive dust from cultivated land. Similarly, steroids are strongly indicative of fugitive dust. Yet, triterpenoids reveal the most pronounced distribution differences for all types of cultivated soils examined here and are by themselves powerful markers for fugitive dust that allow differentiation between the types of crops cultivated. PAHs are also found in some surface soils, as well as persistent pesticides, e.g., DDE, Fosfall, and others.
Keywords: San Joaquin Valley; Soils; Saccharides; Triterpenoids; Steroids; Aliphatic lipids; PAH; Pesticides;

Estimation of mercury loadings to Lake Ontario: Results from the Lake Ontario atmospheric deposition study (LOADS) by Soon-Onn Lai; Thomas M. Holsen; Young-Ji Han; Philip P. Hopke; Seung-Muk Yi; Pierrette Blanchard; James J. Pagano; Michael Milligan (8205-8218).
Atmospheric mercury (Hg) loadings to Lake Ontario were estimated using data measured at two land-based sites: Sterling, NY and Point Petre, Ont., as part of the Lake Ontario air deposition study (LOADS) between April 2002 and March 2003. These loadings were compared with those estimated using intensive data measured onboard the R/V Lake Guardian in April 2002, September 2002, and July 2003 (each approximately one week). Measured concentrations and modeled mass transfer coefficients of elemental mercury (Hg0), reactive gaseous mercury (RGM) and particulate mercury (Hg(p)) in air and total Hg in precipitation were incorporated into a total deposition model including wet deposition, air–water gas exchange and particle dry deposition. Urban/rural Hg concentration ratios were assumed based on literature values. Assuming that 10% of the lake was influenced by urban areas, the annual net Hg atmospheric loadings of wet deposition, net air–water gas exchange of Hg0 (deposition=300 kg yr−1 and emission=410 kg yr−1) and RGM, and Hg(p) dry deposition to Lake Ontario were estimated to be 170, −110, 68, and 20 kg, respectively, resulting in a net loading of 150 kg yr−1. Net Hg loadings were largest in the fall (46 kg) and smallest in the summer (20 kg). Hg0, wet, RGM and Hg(p) deposition contributed 55%, 30%, 12%, and 3.6% of the total Hg deposition, respectively. The net loading was found to be most sensitive to the assumed urban/rural concentration ratios, wind speed, DGM concentration and Hg0 transfer velocity. An increase in the influence of urban areas from 0% to 30% resulted in a 90% increase in the total loading demonstrating the complexity and non-linearity of the atmospheric deposition of mercury to Lake Ontario and the importance of quantifying the urban footprint.
Keywords: Mercury; Atmospheric deposition; Wet deposition; Dry deposition; Air–water exchange; Great Lakes;

Heterogeneous ice nucleation on synthetic silver iodide, natural kaolinite and montmorillonite particles via condensation, freezing and deposition modes was studied by environmental scanning electron microscopy (ESEM) in the temperature range of 250–270 K. By increasing the H2O pressure in the sample chamber at constant temperature, ice formation can be studied in situ and can be related to the chemical composition of the particles that can be determined simultaneously. For silver iodide and kaolinite, supersaturation values of first ice formation are in good agreement (1–2% absolute) with diffusion chamber experiments. For both substances, threshold temperatures for the condensation, freezing and deposition modes are also in good agreement (within 2 K) with previous literature data. For montmorillonite, ESEM results for the supersaturation value of first ice formation and for threshold temperatures of condensation freezing and deposition mode lie within the large range reported in the literature.
Keywords: Environmental scanning electron microscopy; Ice nucleation; Deposition freezing; Condensation freezing;

Isocyanatocyclohexane and isothiocyanatocyclohexane levels in urban and industrial areas and possible emission-related activities by E. Gallego; F.X. Roca; F. Perales; A. Ribes; G. Carrera; X. Guardino; M.J. Berenguer (8228-8240).
Isocyanatocyclohexane and isothiocyanatocyclohexane are becoming relevant compounds in urban and industrial air, as they are used in important amounts in automobile industry and building insulation, as well as in the manufacture of foams, rubber, paints and varnishes. Glass multi-sorbent tubes (Carbotrap, Carbopack, Carboxen) were connected to LCMA-UPC pump samplers for the retention of iso- and isothiocyanatocyclohexanes. The analysis was performed by automatic thermal desorption (ATD) coupled with capillary gas chromatography (GC)/mass spectrometry detector (MSD). TD-GC/MS was chosen as analytical method due to its versatility and the possibility of analysis of a wide range of volatility and polarity VOC in air samples. The method was satisfactory sensitive, selective and reproducible for the studied compounds. The concentrations of iso- and isothioisocyanatocyclohexanes were evaluated in different urban, residential and industrial locations from extensive VOC air quality and odour episode studies in several cities in the Northeastern edge of Spain. Around 200–300 VOC were determined qualitatively in each sample. Higher values of iso- and isothiocyanatocyclohexane were found in industrial areas than in urban or residential locations. The concentrations ranged between n.d.−246 and n.d.−29 μg m−3 for isocyanatocyclohexane and isothiocyanatocyclohexane, respectively, for industrial areas. On the other hand, urban and residential locations showed concentrations ranging between n.d.−164 and n.d.−29 μg m−3 for isocyanatocyclohexane and isothiocyanatocyclohexane, respectively. The site location (urban or industrial), the kind and nearness of possible iso- and isothiocyanatocyclohexane emission activities (industrial or building construction) and the changes of wind regimes throughout the year have been found the most important factors influencing the concentrations of these compounds in the different places.
Keywords: Isocyanatocyclohexane; Isothiocyanaotcyclohexane; VOC; Air quality; Immission level; TD-GC/MS; Ambient air;

Equilibrium sorption of gaseous organic chemicals to fiber filters used for aerosol studies by Hans Peter H. Arp; René P. Schwarzenbach; Kai-Uwe Goss (8241-8252).
Fiber filters commonly used to collect aerosols for various analyses also collect gaseous organic chemicals during sampling. These sorbed chemicals can lead to serious artifacts, particularly when analyzing aerosols for organic compounds and organic carbonaceous material. To date, this sorption process has only been looked at for a few types of filters and compound classes. This work presents a comprehensive study of this sorption process for various, widely used fiber filters and a broad variety of compound classes. Furthermore, important factors have been investigated, including relative humidity, temperature, baking and exposure to ambient air during sampling. From these data, poly-parameter linear-free energy relationships were derived that allow for estimations of sorption constants of gaseous organic compounds on different filter types. Based on the results, recommendations are provided to help predict, minimize and ensure reproducibility of artifacts caused by gaseous organic compounds sorbing to fiber filters.
Keywords: Filter; Sorption; Artifacts; Aerosol; OC;

An important oceanic source of micro-organisms for cloud water at the Puy de Dôme (France) by Pierre Amato; Marius Parazols; Martine Sancelme; Gilles Mailhot; Paolo Laj; Anne-Marie Delort (8253-8263).
A description of the microbial content of cloud water based on samples collected along an almost 2-year-period is presented. Cloud water from 14 events was sampled at the Puy de Dôme summit (1465 m a.s.l.). Total bacterial and fungal cells were about, respectively, 8.1×104 and 5.9×103  mL−1, with more than 10% of the fungi but <1% of bacteria recovered by cultivation at 15 or 27 °C. However, ATP concentration of about 0.40 pmol mL−1 shows that a large majority of these cells are likely viable but not cultivable and remain alive in clouds. A high variability is noticed in the microbial content, and local meteorological variations are not involved. A seasonal effect is shown, with a general increase in the concentrations of cultivable micro-organism and of total fungal cells during summer and autumn. Moreover, psychrotolerant micro-organisms, with respect to those growing only at 27 °C, are more numerous during winter. The concentrations of micro-organisms (total and cultivable) were clearly linked to the chemical composition of cloud water: an increase with increasing oceanic contribution is pointed, and bacteria concentration decreases with increasing anthropic influence. A preferential integration of micro-organisms emitted by the ocean into cloud droplets, compared to micro-organisms from other sources, is likely to occur, making the ocean a major source of micro-organisms for cloud water. It also suggests that the toxicity of polluted cloud water could disturb an eventual multiplication of cells in atmospheric droplets.
Keywords: Cloud water; Microorganisms; Bacteria; Fungi; Oceanic source;

An evaluation of the protein mass of particulate matter by M.Y. Menetrez; K.K. Foarde; T.R. Dean; D.A. Betancourt; S.A. Moore (8264-8274).
This research study provides the characterization of mass percent of protein-based particulate matter in total ambient particulate matter collected in a metropolitan area of NC. The project determined the percentages of protein-based ambient bioaerosols for particles in the 2.5–10 μm range and for particles in the range of 2.5 μm or less in 298 samples taken over a six-month period. The analysis of total protein mass was used as an all-inclusive indicator of biologically based aerosols. These organic bioaerosols may have nucleated with inorganic non-biological aerosols, or they may be combined with inert aerosols. The source of these bioaerosols may be any combination of pollen, mold, bacteria, insect debris, fecal matter, or dander, and they may induce irritational, allergic, infectious, and chemical responses in exposed individuals. Ambient samples of PM2.5 and PM10−2.5 were analyzed for gravimetric mass and total protein mass. The results for 19 of 24 sample periods indicated that between 1% and 4% of PM10−2.5 and between 1% and 2% of PM2.5 mass concentrations were made of ambient protein bioaerosols. (The remaining 5 of 24 sample periods yielded protein results which were below detectable limits.)
Keywords: Bioaerosols; Allergens; Total protein; PM;

Boundary layer photochemistry simulated with a two-stream convection scheme by Robert Vautard; Mohamed Maidi; Laurent Menut; Matthias Beekmann; Augustin Colette (8275-8287).
We explore the sensitivity of the simulation of photochemical smog to the turbulent mixing scheme, using two diffusion schemes and an original two-stream model (TSM) scheme, assuming in the column an updraft and a downdraft. In this latter scheme both updraft and downdraft concentrations are prognostic variables, unlike in previously proposed schemes. The comparisons are made using a one-dimensional column model, in a Eulerian or a Lagrangian mode. The diffusion schemes produce tilted concentration profiles for primary species, with higher concentrations near the surface and lower values at the top of the boundary layer, while TSM profiles yield more homogeneous concentrations in the planetary boundary layer (PBL). Ozone concentrations are also more homogeneous in the TSM PBL than in the diffusive PBL. Only deposition makes ozone concentrations slightly lower near the surface, while in diffusive case ozone is lower also due to titration by higher nitrogen oxide concentrations. The overall differences between the schemes remain small for ozone.Also, the development time and amplitude of an ozone city plume is not very sensitive to the choice of the mixing scheme. In the urban framework ozone build-up is slightly delayed by higher nitrogen oxide concentrations near the surface in the diffusive cases, but the plume development is similar to that of the TSM once the plume travels away from the emission area. Results also show that the sensitivity of ozone to nitrogen oxide and non-methane volatile organic compounds is itself not very sensitive to the mixing scheme.
Keywords: Photochemical smog; Boundary layer; Mixing; Turbulence; Ozone; Modelling;

Estimates of the contributions of biogenic and anthropogenic hydrocarbons to secondary organic aerosol at a southeastern US location by Tadeusz E. Kleindienst; Mohammed Jaoui; Michael Lewandowski; John H. Offenberg; Charles W. Lewis; Prakash V. Bhave; Edward O. Edney (8288-8300).
An organic tracer-based method containing laboratory and field study components was used to estimate the secondary organic aerosol (SOA) contributions of biogenic and anthropogenic hydrocarbons to ambient organic carbon (OC) concentrations in PM2.5 during 2003 in Research Triangle Park, NC. In the laboratory, smog chamber experiments were conducted where isoprene, α-pinene, β-caryophyllene, and toluene were individually irradiated in the presence of NO X . In each experiment, SOA was collected and analyzed for potential tracer compounds, whose concentrations were used to calculate a mass fraction of tracer compounds for each hydrocarbon. In the field, 33 PM2.5 samples were collected and analyzed for (1) tracer compounds observed in the laboratory irradiations, (2) levoglucosan, a biomass burning tracer, and (3) total OC. For each of the four hydrocarbons, the SOA contributions to ambient OC concentrations were estimated using the tracer concentrations and the laboratory-derived mass fractions. The estimates show SOA formation from isoprene, α-pinene, β-caryophyllene, and toluene contributed significantly to the ambient OC concentrations. The relative contributions were highly seasonal with biomass burning in the winter accounting for more than 50% of the OC concentrations, while SOA contributions remained low. However, during the 6-month period between May and October, SOA from the precursor hydrocarbons contributed more than 40% of the measured OC concentration. Although the tracer-based method is subject to considerable uncertainty due to the simplification of replacing the complex set of chemical reactions responsible for SOA with a laboratory-derived single-valued mass fraction, the results suggest this approach can be used to identify major sources of SOA which can assist in the development of air quality models.
Keywords: SOA; Organic aerosol; Biogenic hydrocarbons; Anthropogenic hydrocarbons;

The long-range atmospheric transport (LRT) of polycyclic aromatic hydrocarbons (PAHs) is not fully understood and has hardly been addressed by model studies. By model experiments the LRT of PAH emissions into air from Europe and Russia is studied testing several scenarios of gas–particle partitioning and degradability by reaction with ozone and the hydroxyl and nitrate radicals for two PAHs, benzo[a]pyrene (BAP) and fluoranthene (FLT). The model used is the atmosphere general circulation model ECHAM5 with a dynamic modal aerosol sub-model, HAM, ozone and sulfur species chemistry and bidirectional mass exchange on 2D marine (ocean surface mixed layer) and terrestrial surfaces (top soil layer and vegetation surfaces). After 5 years the substances are found to be mostly distributed to the soil compartment (64–97% as the global mean, varying with substance and season), which after 10 years is still filling; 1–5% are found in air and 2–33% in ocean. It is found that the lifetime and vertical distribution of the substances in the atmosphere and the LRT potential are all significantly influenced by the partitioning and degradation scenario. The total environmental burden is higher when sorption to organic matter and black carbon are considered to determine gas–particle partitioning rather than adsorption to the surface of particulate matter. The effect is + 20 % for BAP but sevenfold for FLT. Concentrations in Arctic air are mostly underestimated by the model, which is partly explained by emissions not considered in the simulation. The comparison shows, however, that degradation of the sorbed BAP and FLT molecules should be significantly slower than the respective gaseous molecules and that absorptive partitioning is necessary to explain the LRT potential of FLT.
Keywords: Polycyclic aromatic hydrocarbons; Global fate; Long-range transport potential; Gas–particle partitioning; Multicompartmental model;

Simulations of pollutant dispersion within idealised urban-type geometries with CFD and integral models by Silvana Di Sabatino; Riccardo Buccolieri; Beatrice Pulvirenti; Rex Britter (8316-8329).
Until recently, urban air quality modelling has been based on operational models of an integral nature. The use of computational fluid dynamics (CFD) models to address the same problems is increasing rapidly. Operational models e.g. OSPM, AERMOD, ADMS-Urban have undergone many comprehensive formal evaluations as to their “fitness for purpose” while CFD models do not have such an evaluation record in the urban air quality context. This paper looks at the application of both approaches to common problems. In particular, pollutant dispersion from point and line sources in the simplest neutral atmospheric boundary layer and line sources placed within different regular building geometries is studied with the CFD code FLUENT and the atmospheric dispersion model ADMS-Urban. Both the effect of street canyons of different aspect ratios and various obstacle array configurations consisting of cubical buildings are investigated. The standard k – ε turbulence model and the advection–diffusion (AD) method (in contrast to the Lagrangian particle tracking method) are used for the CFD simulations. Results from the two approaches are compared. Overall CFD simulations with the appropriate choice of coefficients produce similar concentration fields to those predicted by the integral approach. However, some quantitative differences are observed. These differences can be explained by investigating the role of the Schmidt number in the CFD simulations. A further interpretation of the differences between the two approaches is given by quantifying the exchange velocities linked to the mass fluxes between the in-canopy and above-canopy layers.
Keywords: Pollutant dispersion modelling; Urban areas; CFD models; Operational dispersion models; Street canyons; Building packing density;

A novel field measurement method for determining fine particle and gas emissions from residential wood combustion by Jarkko Tissari; Kati Hytönen; Jussi Lyyränen; Jorma Jokiniemi (8330-8344).
Emission data from residential wood combustion are usually obtained on test stands in the laboratory but these measurements do not correspond to the operational conditions in the field because of the technological boundary conditions (e.g. testing protocol, environmental and draught conditions). The field measurements take into account the habitual practice of the operators and provide the more reliable results needed for emission inventories. In this study, a workable and compact method for measuring emissions from residential wood combustion in winter conditions was developed. The emissions for fine particle, gaseous and PAH compounds as well as particle composition in real operational conditions were measured from seven different appliances. The measurement technique worked well and was evidently suitable for winter conditions. It was easy and fast to use, and no construction scaffold was needed. The dilution of the sample with the combination of a porous tube diluter and an ejector diluter was well suited to field measurement. The results indicate that the emissions of total volatile organic carbon (TVOC) (17 g kg−1 (of dry wood burned)), carbon monoxide (CO) (120 g kg−1) and fine particle mass (PM1) (2.7 g kg−1) from the sauna stove were higher than in the other measured appliances. In the masonry heaters, baking oven and stove, the emissions were 2.9–9 g kg−1 TVOC, 28–68 g kg−1 CO and 0.6–1.6 g kg−1 PM1. The emission of 12 PAHs (PAH12) from the sauna stove was 164 mg kg−1 and consisted mainly of PAHs with four benzene rings in their structure. PAH12 emission from other appliances was, on average, 21 mg kg−1 and was dominated by 2-ring PAHs. These results indicate that despite the non-optimal operational practices in the field, the emissions did not differ markedly from the laboratory measurements.
Keywords: Emission; Fine particles; Field measurement method; Residential combustion;

An on-line technique has been developed for analysis of gas-phase oxidation products formed in a reaction flow tube using different reaction times, concentrations and humidities. Products of ozonolysis, including thermally labile secondary ozonides (SOZ), were directly introduced into an atmospheric sampling townsend discharge ionization (ASTDI) source coupled to a triple quadrupole mass spectrometer (MS). Instant changes in the product composition were monitored in the total-ion chromatogram, or by fragment ions in the collision activated dissociation mass spectra by use of MS/MS scan techniques. Assignment of the individual ions was accomplished by inspection of the products’ mass spectra obtained by pre-concentration of the gas phase on a dedicated short column followed by chromatographic analysis. The observed reaction products correspond to those identified with other techniques. Of relevance for future mechanistic modelling, is the point that conditions of excess d-limonene favoured the formation of the d-limonene SOZ (major product), which was observed to be quite stable in dry and humid air, without oxidants. The d-limonene/ozone ratio was observed to be crucial for the stability of the SOZ, because it is prone to ozonolysis, and no SOZ could be detected in completely reacted 1:1 mixtures.
Keywords: On-line; Townsend discharge; Cyclohexene; d-Limonene; Secondary ozonide;

Road vehicle emissions of molecular hydrogen (H2) from a tunnel study by Martin K. Vollmer; Niklas Juergens; Martin Steinbacher; Stefan Reimann; Martin Weilenmann; Brigitte Buchmann (8355-8369).
Motor vehicle combustion emissions of molecular hydrogen (H2), carbon monoxide (CO), and carbon dioxide (CO2) were measured during a 6-week period from November 2004 to January 2005 in Gubrist Tunnel, Switzerland, to determine vehicle emission factors for these trace gases and the ratios of the concentration growths Δ H 2 / Δ CO and Δ H 2 / Δ CO 2 in the tunnel under real-world highway driving conditions. For H2, molar mixing ratios at the tunnel exit were found to be 7–10 ppm (parts-per-million, 10 - 6 ) during rush hours. Mean emission factors of E H 2 = 49.7 ( ± 16.5 ) mg km - 1 , E CO = 1.46 ( ± 0.54 ) g km - 1 , and E CO 2 = 266 ( ± 69 ) g km - 1 were calculated. E H 2 was largest during weekday rush-hour traffic, a consequence of the more frequent accelerations in congested traffic when fuel combustion is not optimal. E H 2 was smaller for heavy-duty vehicles (HDV) compared to light-duty vehicles (LDV), a finding which was attributed to the diesel vs. gasoline engine technology. The mean Δ H 2 / Δ CO molecular ratio was 0.48 ± 0.12 . This ratio increased to ∼ 0.6 during rush hours, suggesting that H2 yield is favored relative to CO under fuel-rich conditions, presumably a consequence of an increasing contribution of the water–gas-shift reaction. The mean Δ H 2 / Δ CO 2 molecular ratio was 4.4 × 10 - 3 but reduced to 2.5 × 10 - 3 when the relative HDV abundance was at maximum. Using three different approaches, road traffic H2 emissions were estimated for 2004 for Switzerland at 5.0–6.6 Gg and globally at 4.2–8.1 Tg. Despite projections of increasing traffic, Swiss H2 emissions are not expected to change significantly in the near future, and global emissions are likely to decrease due to improved exhaust gas clean-up technologies.
Keywords: Emission factor; H2/CO ratio; H2/CO2 ratio; Global emissions; Traffic emission;

Seasonal variation of polycyclic aromatic hydrocarbons (PAHs) in Pearl River Delta region, China by Chang Lang; Shu Tao; Xuejun Wang; Gang Zhang; Jun Li; Jiamo Fu (8370-8379).
A level IV fugacity model was applied to simulate the seasonal variation of polycyclic aromatic hydrocarbons (PAHs) in various bulk media in Pearl River Delta (PRD), China. The predictions were validated against monthly observed concentrations of gaseous and particulate phase PAHs in air and annual mean concentrations of all other bulk media. The uncertainty of the predictions was evaluated using Monte Carlo simulation. The influential parameters were identified using sensitivity analysis on both media concentrations and seasonal variations. The predicted concentrations and the patterns of seasonal variation generally agreed with the field observations. Concentrations of gaseous phase PAHs in air increased in the summer and decreased in the winter while concentrations of particulate phase PAHs in summer were lower than those in the winter. The relative variations of PAHs in the other bulk media were not as profound as those in air and the variation patterns were chemical compound dependent. Temperature and precipitation were the most important parameters leading to the seasonalities of PAH concentrations. Other key parameters included dry precipitation rate, advective water flow from upstream, and solid fractions in air and water.
Keywords: Seasonal variations; PAHs; Pearl River Delta; Fugacity model;

Impact of biomass burning on urban air quality estimated by organic tracers: Guangzhou and Beijing as cases by Qiaoqiao Wang; Min Shao; Ying Liu; Kuster William; Goldan Paul; Xiaohua Li; Yuan Liu; Sihua Lu (8380-8390).
The impacts of biomass burning have not been adequately studied in China. In this work, chemical compositions of volatile organic compounds and particulate organic matters were measured in August 2005 in Beijing and in October 2004 in Guangzhou city. The performance of several possible tracers for biomass burning is compared by using acetonitrile as a reference compound. The correlations between the possible tracers and acetonitrile show that the use of K+ as a tracer could result in bias because of the existence of other K+ sources in urban areas, while chloromethane is not reliable due to its wide use as industrial chemical. The impact of biomass burning on air quality is estimated using acetonitrile and levoglucosan as tracers. The results show that the impact of biomass burning is ubiquitous in both suburban and urban Guangzhou, and the frequencies of air pollution episodes significantly influenced by biomass burning were 100% for Xinken and 58% for downtown Guangzhou city. Fortunately, the air quality in only 2 out of 22 days was partly impacted by biomass burning in August in Beijing, the month that 2008 Olympic games will take place. The quantitative contribution of biomass burning to ambient PM2.5 concentrations in Guangzhou city was also estimated by the ratio of levoglocusan to PM2.5 in both the ambient air and biomass burning plumes. The results show that biomass burning contributes 3.0–16.8% and 4.0–19.0% of PM2.5 concentrations in Xinken and Guangzhou downtown, respectively.
Keywords: Biomass burning; Tracer; Acetonitrile; PM2.5; Air quality;

Aerosol samples were collected using a stacked filter unit (SFU) for PM10-2.0 and PM2.0 size fractions on the platform of a metropolitan underground railway station in downtown Budapest. Temporal variations in the PM10 mass concentration and wind speed and direction were determined with time resolutions of 30 and 4 s using a tapered-element oscillating microbalance (TEOM) and a wind monitor, respectively. Sample analysis involved gravimetry for particulate mass, and particle-induced X-ray emission spectrometry (PIXE) for elemental composition. Diurnal variation of the PM10 mass concentration exhibited two peaks, one at approximately 07:00 h and the other at approximately 17:00 h. The mean±SD PM10 mass concentration for working hours was 155±55 μg m−3. Iron, Mn, Ni, Cu, and Cr concentrations were higher than in outdoor air by factors between 5 and 20, showing substantial enrichment compared to both the average crustal rock composition and the average outdoor aerosol composition. Iron accounted for 40% and 46% of the PM10-2.0 and PM2.0 masses, respectively, and 72% of the PM10 mass was associated with the PM10-2.0 size fraction. The aerosol composition in the metro station (in particular the abundance of the metals mentioned above) is quite different from the average outdoor downtown composition. Mechanical wear and friction of electric conducting rails and bow sliding collectors, ordinary rails and wheels, as well as resuspension, were identified as the primary sources. Possible health implications based on comparison to various limit values and to data available for other underground railways are discussed.
Keywords: Rail wear; Steel dust; Diurnal variation; Indoor aerosol; Transition metals; Metro; Subway;