Atmospheric Environment (v.36, #22)

Quantification of source region influences on the ozone burden by Renate Treffeisen; Katja Grunow; Detlev Möller; Andreas Hainsch (3565-3582).
A project was performed to quantify different influences on the ozone burden. It could be shown that large-scale meteorological influences determine a very large percentage of the ozone concentration. Local measures intended to reduce peak ozone concentrations in summer turn out to be not very effective as a result. The aim of this paper is to quantify regional emission influences on the ozone burden. The investigation of these influences is possible by comparison of the ozone (O3) and oxidant (O x =O3+NO2) concentrations at high-elevation sites downwind and upwind of a source region by using back trajectories. It has been shown that a separation between large-scale influenced meteorological and regional ozone burdens at these sites is possible. This method is applied for an important emission area in Germany—the Ruhrgebiet. On average, no significant ozone contribution of this area to the regional ozone concentration could be found. A large part of the ozone concentration is highly correlated with synoptic weather systems, which exhibit a dominant influence on the local ozone concentrations. Significant contributions of related photochemical ozone formation of the source area of 13–15% have been found only during favourable meteorological situations, identified by the hourly maximum day temperature being above 25°C. This is important with respect to the EU daughter directive to EU 96/62/EC (Official Journal L296 (1996) 55) because Member States should explore the possibilities of local measures to avoid the exceedance of threshold values and, if effective local measures exist, to implement them.
Keywords: Local ozone contribution; Ozone transport; Meteorological influence; Synoptic weather system;

Total, labile and bioaccessible concentrations of heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) were determined in the airborne particulate matter (d<7.2 μm) from various urban and industrial sites in the Greater Thessaloniki area, N. Greece. Particle mass concentrations were similar at the two site types; however, total Mn, Ni, Zn and Cd exhibited higher concentrations in the industrial area. Urban particles were found to contain higher labile fractions of Cd, Cu, Ni and Zn than industrial particles suggesting that they are emitted from different sources and in different, more soluble, chemical forms. The bioaccessible fractions of Mn, Ni and Zn were also higher at the urban area, therefore, posing a potentially higher health risk. The daily respiratory uptakes of heavy metals were calculated.
Keywords: Airborne particles; Bioaccessible fraction; Inhalation exposure; Heavy metals; Labile fraction; PM7.2; Respiratory uptake;

Occurrence and photostability of 3-nitrobenzanthrone associated with atmospheric particles by Anders Feilberg; Takeshi Ohura; Torben Nielsen; Morten West Bach Poulsen; Takashi Amagai (3591-3600).
The occurrence of the carcinogenic and extremely mutagenic compound, 3-nitrobenzanthrone, in extracts of ambient particulate matter has been investigated at a semi-rural sampling location. A total of seventeen 24-h samples and fourteen 12-h samples were analyzed for their content of 3-nitrobenzanthrone. 3-Nitrobenzanthrone was unambiguously detected in one-fourth of the samples in the lower pg m−3 range (mean=17.1±14.8 or 9.8±4.2 pg m−3 excluding one high value), but in the majority of the samples no signal due to 3-nitrobenzanthrone was observed. By comparison with the levels of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) and other air pollution components, it is suggested that 3-nitrobenzanthrone is a directly emitted primary pollutant and that it is not formed in the atmosphere to a significant degree. The photodegradation of 3-nitrobenzanthrone was studied in order to understand the low levels of this compound in ambient air. In the presence of a radical sensitizer, anthraquinone, the degradation rate of 3-nitrobenzanthrone is comparable to that of 1-nitropyrene (NP), a directly emitted nitro-PAH present in ambient air in significantly higher levels than 3-nitrobenzanthrone. The rate of direct photolysis is slightly smaller than that for 1NP. The conclusion of this study is that the dominant sources of 3-nitrobenzanthrone are unidentified combustion processes from which it is emitted in relatively small amounts. Accordingly, 3-nitrobenzanthrone should mainly be considered a health problem at locations close to these sources.
Keywords: 3-Nitrobenzanthrone; Polycyclic aromatic compounds; Aerosols; Photodegradation; Sources in ambient air;

Large-eddy simulations (LESs) are applied to the problem of pollution dispersion within the urban canopy layer, specifically street canyons. The objective is to study the turbulence structure and hence the physical dispersion mechanisms of pollutants. LESs are implemented by incorporating the dynamic sub-grid scale stress model into the commercial computational fluids dynamics code CFX. To gain confidence in the approach, simulations are performed for a canyon-like geometry (roof garden) for which experimental measurements were also made. The experimental campaign consisted of using sonic anemometers to measure mean flow and turbulence intensities at a high sample rate of 60 Hz. Good agreement between simulations and experimental data are obtained. Real geometric features, such as non-uniform wall heights, result in a very much three-dimensional flow distribution. Comparisons with the kε model show that LESs are able to predict more accurately the turbulence statistics of the flow.
Keywords: Turbulence statistics; Dynamic sub-grid scale model; Canyon-like geometry; CFX commercial code implementation;

Three-dimensional large-eddy simulations are performed with the dynamic sub-grid scale model for an idealised urban canyon with pollution modelled as a passive scalar. In addition to concentration distributions, turbulence statistics for the canyon are presented. Higher turbulence intensities are predicted in the core of the vortex compared to the widely used kε model. This results in a more homogeneous distribution of pollutants, in agreement with experimental studies reported in the literature. Regions of enhanced turbulence are also observed near the walls leading to a lateral dispersion of pollutants along the canyon. The centre of the vortex is observed to precess around the canyon and also meanders along the length of the canyon. Puffs of pollution are ejected from the top of canyons intermittently rather than smoothly, with a characteristic time scale of the order of 30–60 s.
Keywords: Dynamic sub-grid scale model; CFX commercial code implementation; Turbulence statistics; Vortex migration;

Source apportionment of exposures to volatile organic compounds. I. Evaluation of receptor models using simulated exposure data by Shelly L. Miller; Melissa J. Anderson; Eileen P. Daly; Jana B. Milford (3629-3641).
Four receptor-oriented source apportionment models were evaluated by applying them to simulated personal exposure data for select volatile organic compounds (VOCs) that were generated by Monte Carlo sampling from known source contributions and profiles. The exposure sources modeled are environmental tobacco smoke, paint emissions, cleaning and/or pesticide products, gasoline vapors, automobile exhaust, and wastewater treatment plant emissions. The receptor models analyzed are chemical mass balance, principal component analysis/absolute principal component scores, positive matrix factorization (PMF), and graphical ratio analysis for composition estimates/source apportionment by factors with explicit restriction, incorporated in the UNMIX model. All models identified only the major contributors to total exposure concentrations. PMF extracted factor profiles that most closely represented the major sources used to generate the simulated data. None of the models were able to distinguish between sources with similar chemical profiles. Sources that contributed <5% to the average total VOC exposure were not identified.
Keywords: Hazardous air pollutants; Air toxics; Source attribution;

Source apportionment of exposures to volatile organic compounds: II. Application of receptor models to TEAM study data by Melissa J Anderson; Eileen P Daly; Shelly L Miller; Jana B Milford (3643-3658).
Four receptor-oriented source apportionment models were applied to personal exposure measurements for toxic volatile organic compounds (VOCs). The measurements are from the total exposure assessment methodology studies conducted from 1980 to 1984 in New Jersey (NJ) and California (CA) and the 1987–1990 CA Indoor Exposure study. The receptor models applied are the Chemical Mass Balance model, Principal Component Analysis/Absolute Principal Component Scores, Positive Matrix Factorization, and Graphical Ratio Analysis for Composition Estimates/Source Apportionment by Factors with Explicit Restriction. Major sources of personal exposure to toxic VOCs appear to have been aromatic sources resembling automobile exhaust, gasoline vapor, or environmental tobacco smoke, and a 1,1,1-trichloroethane-dominated source that may be associated with solvent or pesticide use. Drycleaning chemicals, deodorizers or mothballs, and building materials or carpet emissions also appear to have been significant sources of exposure. Source apportionment results from the four models agreed reasonably well for the NJ data. The performance of the models was generally poorer for the CA data, and the corresponding source apportionment results were less consistent across the models.
Keywords: Hazardous air pollutants; Air toxics; Source attribution;

Uncertainty in emissions projections for climate models by M.D. Webster; M. Babiker; M. Mayer; J.M. Reilly; J. Harnisch; R. Hyman; M.C. Sarofim; C. Wang (3659-3670).
Future global climate projections are subject to large uncertainties. Major sources of this uncertainty are projections of anthropogenic emissions. We evaluate the uncertainty in future anthropogenic emissions using a computable general equilibrium model of the world economy. Results are simulated through 2100 for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6), sulfur dioxide (SO2), black carbon (BC) and organic carbon (OC), nitrogen oxides (NO x ), carbon monoxide (CO), ammonia (NH3) and non-methane volatile organic compounds (NMVOCs). We construct mean and upper and lower 95% emissions scenarios (available from the authors at 1°×1° latitude–longitude grid). Using the MIT Integrated Global System Model (IGSM), we find a temperature change range in 2100 of 0.9 to 4.0°C, compared with the Intergovernmental Panel on Climate Change emissions scenarios that result in a range of 1.3 to 3.6°C when simulated through MIT IGSM.
Keywords: Atmospheric chemistry; Monte Carlo simulation; Air pollution; Economic models; Greenhouse gases; Earth systems modeling;

Gas absorption by a liquid aerosol in the absence of flow is analyzed, in which three different methods, including the perfect absorption model (PAM), rapid diffusion model (RDM), and fully numerical method (FNM), are carried out. By introducing a mass diffusion number, which represents the driving-force ratio between the external and the internal mass transfers, solute uptake characteristics of a variety of gaseous species (CO2, SO2, HCl, and NH3) of interest are elucidated. The analyzed results indicate that, over the investigated range of the mass diffusion number (D m≒10−4–0.12), the gas phase and the interfacial concentrations are highly relevant to the number. Specifically, when the mass diffusion number is small, such as CO2 and SO2, the mass transfer processes in the gas phase and at the interface can be approximated well by the RDM all the time. In contrast, when the number is large to a certain extent, say, NH3, the PAM is capable of providing a fundamental insight into the gas-phase mass transport phenomenon in the initial absorption period. With regard to the aerosol interior, because the liquid phase controls the two-phase mass transfer, the internal transport and absorption processes are merely affected by the mass diffusion number slightly. As a result, for the investigated gas the RDM is also applicable in predicting the solute uptake process in the liquid phase, no matter what the gas.

FT–IR study of the ring-retaining products from the reaction of OH radicals with phenol, o-, m-, and p-cresol by Romeo Iulian Olariu; Björn Klotz; Ian Barnes; Karl Heinz Becker; Raluca Mocanu (3685-3697).
The ring-retaining products of the OH-initiated degradation of phenol and o-, m-, and p-cresol in the presence of NO x have been investigated and their formation yields determined. The experiments were carried out in a large volume reactor at (298±2) K and 1000 mbar total pressure of synthetic air using FT–IR spectroscopy for the analysis of reactants and products.The products observed and their respective molar yields were: from phenol: 1,2-dihydroxybenzene (80.4±12.1)%, 1,4-benzoquinone (3.7±1.2)% and 2-nitrophenol (5.8±1.0)%; from o-cresol: 3-methyl-1,2-dihydroxybenzene (73.4±14.6)%, methyl-1,4-benzoquinone (6.8±1.0)% and 6-methyl-2-nitrophenol (6.8±1.5)%; from m-cresol: 3-methyl-1,2-dihydroxybenzene (68.6±13.4)%, 4-methyl-1,2-dihydroxybenzene (9.7±2.7)%, methyl-1,4-benzoquinone (11.3±2.5)%, 5-methyl-2-nitrophenol (4.4±1.5)% and 3-methyl-2-nitrophenol (4.3±1.6)% and from p-cresol: 4-methyl-1,2-dihydroxybenzene (64.1±11.3)% and 4-methyl-2-nitrophenol (7.6±2.2)%.Reaction pathways leading to the observed products are proposed and potential ramifications for the atmospheric reaction mechanisms of aromatic hydrocarbons are considered.
Keywords: Phenols; Atmospheric photochemistry; OH-radical; Dihydroxybenzenes; Benzoquinones;

A model to estimate mixing height and its effects on ozone modeling by Ouattara Fatogoma; Robert B Jacko (3699-3708).
A mixing height estimation model (PMH) whose output can be used in air quality models, especially the Urban Airshed Model (UAM-IV), is developed. The evaluation of the performance of the PMH shows that the predictions match the observations very well. The average geometric mean of the predicted to observed hourly mixing height ratios is equal to 0.99. The outputs of the PMH along with those of the mixing height model incorporated in the UAM-IV package (RAMMETX) are used in the UAM-IV to simulate hourly average concentrations of tropospheric ozone (O3) in the Indianapolis metropolitan statistical area (MSA). A comparative study performed to assess the effects of mixing height shows that the UAM-IV performs better when the mixing height fields are from the PMH. For example, the episodic mean of the average normalized bias and the average normalized absolute bias of predicted to observed O3 concentrations are 1.2% and 18.6%, respectively, when the mixing height fields are from the PMH. They are 6.6% and 20.1%, respectively, when the mixing height fields are from RAMMETX.
Keywords: Ozone; Mixing height; Air quality; Dispersion modeling; Urban airshed; UAM; PMH; RAMMETX;

In wind-tunnel studies of atmospheric dispersion, the pollutant emission by traffic is usually considered as ground-level line source. The source performance under different flow conditions is therefore important for the adequate description of pollutant dispersion. The dispersion from a line source in the wind-tunnel model of the atmospheric boundary layer has been investigated in the present study. Specially conducted mean flow and turbulence measurements have proved the similarity between the wind-tunnel flow and the flow in the lower portion of the atmospheric boundary layer. Lateral and vertical distributions of mean concentration downwind of the source have been measured with varying source parameters and wind velocities. The concentration pattern has not revealed a significant dependence on the parameter variations. The wind-tunnel results have been further evaluated by means of analytical and numerical dispersion models. The evaluation has shown a good general agreement of measured and calculated concentration fields. Two alternative sets of equations with different parameterizations of eddy diffusivity and different values of the turbulent Schmidt number have been employed in the analytical model calculations. A better agreement with the wind-tunnel results has been achieved with a similarity-theory expression for eddy diffusivity rather than with the eddy diffusivity parameterization based on the conjugate-power-law formula. The numerical model has provided the best match for the wind-tunnel concentration data at large distances from the source. However, certain discrepancies between the wind-tunnel and numerical predictions have been marked out close to the source.
Keywords: Dispersion; Vehicle emissions; Surface layer; Numerical modeling; Analytical model;