Atmospheric Environment (v.40, #6)

Particulate emissions from wheat and Kentucky bluegrass stubble burning in eastern Washington and northern Idaho by Ranil Dhammapala; Candis Claiborn; Jeff Corkill; Brian Gullett (1007-1015).
The PM2.5 emission factors (EF) in smoke from post-harvest wheat and Kentucky bluegrass (KBG) stubble burning were quantified in the United States Environmental Protection Agency test burn facility. The PM2.5 EFs from high and low combustion efficiency (CE) wheat burns were 0.8±0.4 and 4.7±0.4 g kg−1, respectively, and decreased with increasing CE. While these EFs are generally in agreement with literature, it is difficult to compare the PM2.5 EFs from KBG burns (12.1±1.4 g kg−1) due to the scarcity of published data. Wheat burns conducted with randomly piled stubble resulted in PM2.5 EFs different to those where the stubble was oriented as found in the field post harvest. Two separate methods for estimating EFs were employed and found to be in good agreement. The carbon in the biomass was almost quantitatively accounted for by measuring CO2, CO, total hydrocarbons (THC) and PM2.5 emissions. The PM2.5/CO emission ratios for wheat (0.05±0.01) agree with literature data, while the same ratio for KBG (0.23±0.02) was slightly higher than data reported. These ratios exhibit low dependence on CE and can be used to predict the level of one pollutant in a plume, when the concentration of the other is known. Wheat and KBG fields in 18 counties of eastern Washington and northern Idaho are burned on less than a tenth of the days of the year. Yet the fires were estimated to have produced between 0.04% and 34.5% of the total PM2.5 and CO emissions within the respective counties, during 2002.
Keywords: PM2.5; Emission factor; Combustion efficiency; Carbon mass balance; Emission ratio;

Parameters for the assessment of odour impacts on communities by Paul Henshaw; James Nicell; Anamika Sikdar (1016-1029).
Odorous emissions are the cause of most air pollution complaints that are made by the public to regulatory agencies. Methods need to be developed to objectively access the impact of odours so that odour-producing facilities have a pro-active means of reducing their impact on surrounding communities. These methods must consider the sub- and supra-threshold effects of odour over the range of concentrations that can be experienced as the odour disperses over a community. In addition, the influence of local meteorological and terrain conditions can be accommodated through conventional dispersion models. However, metrics of odour impact need to be developed which take into account the concentration and frequency of odours at receptors, as well as the population density at those receptors. This paper proposes and demonstrates the use of six impact parameters that may be used as metrics of the impact of a stationary odour source on a community. These odour impact parameters are maximum concentration, maximum probability of response, footprint area, concentration-weighted footprint area, probability-weighted footprint area and population impact. The utility of these parameters were demonstrated by evaluating them to quantify the impact of an industrial facility that produces an odorous chemical.
Keywords: Odor; Impact; Dispersion; Population response;

The effect of nitrogen dioxide on particle formation during ozonolysis of two abundant monoterpenes indoors by Jacob Klenø Nøjgaard; Merete Bilde; Charlotte Stenby; Ole John Nielsen; Peder Wolkoff (1030-1042).
The effect of the nitrogen dioxide (NO2) concentration on particle formation during ozonolysis of two abundant monoterpenes indoors, α-pinene and d-limonene, was studied in dry air in 1000 l Tedlar bags at 21±2 °C and ambient pressure. Particle size distributions were measured during 1 h after the reaction was initiated. In mixtures of 50 parts per billion volume (ppbv) of monoterpene and 50 ppbv of ozone (O3), d-limonene produced about five times as many particles (10–350 nm) as α-pinene after 60 min. The presence of NO2 introduced an additional loss term for O3, resulting in formation of the nitrate radical. This affected particle formation, since the nucleation potential of NO3 is much lower than O3. Modeling showed that the observed decrease in particle concentration from d-limonene/O3/NO2 mixtures was likely to be ascribed to the O3/NO2 reaction at NO2 concentrations <150 ppb, above which unknown mechanisms additionally reduced the particle formation. In similar experiments with α-pinene, the particle concentration and volume were substantially reduced in the presence of NO2, e.g. 162 ppbv NO2 reduced the particle number concentration by a factor of 10. In addition, the detection of particle formation was delayed as the NO2 concentration increased, but the additional loss of O3 in the O3/NO2 reaction could not explain the observation. The particle mode progressively increased with the NO2 concentration for both monoterpenes. Oxidation of d-limonene may be highly relevant for new particle formation in indoor air, whereas ozonolysis products of α-pinene seem less likely to nucleate in indoor environments.
Keywords: Nitrogen dioxide; Ozone; d-Limonene; α-Pinene; Secondary organic aerosols;

Quantitative measurements of the generation of hydroxyl radicals by soot particles in a surrogate lung fluid by Heejung Jung; Bing Guo; Cort Anastasio; Ian M. Kennedy (1043-1052).
Epidemiological and toxicological studies have shown a relation between the inhalation of atmospheric particles and adverse cardiopulmonary health effects. The generation of reactive oxygen species (ROS) by particles is one current hypothesis for their toxic effects. Thus a quantitative measurement of ROS is important since that will be an index to assess the oxidative stress that particles may cause in the lung. We have developed a technique to quantitatively and specifically measure OH (the strongest biological ROS) in an aqueous, buffered extract solution as a surrogate lung fluid (SLF). Using this technique we quantitatively measured OH formation in SLF containing hydrogen peroxide (HOOH) for samples of flame soot particles, carbon black, and ambient fine particles (PM2.5). We have found that OH is formed by flame soot, independent of transition metals, with a dose-dependent linear response that depends upon HOOH concentration. Experiments with carbon black revealed that its mass-normalized OH generation was ∼10 times lower than that of flame soot, suggesting that carbon black is not a good surrogate for soot particles in health effect studies, at least in terms of oxidative stress. Mass-normalized OH generation by ambient PM2.5 was 6–30 times larger than that of flame soot. While much of the PM2.5 reactivity was suppressed by pretreating samples with a transition metal chelator, there was a significant fraction of reactivity which was not affected. Our results suggest that the in vivo generation of free radicals, specifically OH, by inhalation of PM2.5 is partially due to carbonaceous soot as well as transition metals.
Keywords: Reactive oxygen species (ROS); Transition metal; Health effect; Oxidative stress; Soot; PM2.5; Combustion;

Epidemiological studies relating air pollution to health effects often estimate personal exposure to particulate matter using values from a central ambient monitoring site as a proxy. However, when there is a significant amount of variation in particulate concentrations across an urban area, the use of central sites may result in exposure misclassification that induces error in long-term cohort epidemiological study designs. When spatially dense monitoring data are not available, advanced dispersion models may offer one solution to the problem of accurately characterising intraurban particulate concentrations across an area. This study presents results from an intraurban assessment of The Air Pollution Model (TAPM)—an Integrated Meteorological-Emission (IME) Model. Particles less than 10 μm in aerodynamic diameter (PM10) were modelled and compared with a dense intraurban monitoring network in Christchurch, New Zealand, a city with high winter levels of particulate air pollution. Despite the area's high intraurban concentration variability, and meteorological and topographical complexity, the model performed satisfactorily overall, with mean observed and modelled concentrations of 42.9 and 43.4 μg m−3, respectively, while the mean Index of Agreement (IOA) between individual sites was 0.60 and the mean systematic RMSE was 16.9 μg m−3. Most of the systematic error in the model was due to coarse spatial resolution of the local emission inventory and complex meteorology attributed to localised convergence of drainage flows, especially on the western and southern fringes of the urban area. Given further improvements in site-specific estimates within urban areas, IME models such as TAPM may be a viable alternative to central sites for estimating personal exposure in longer-term (monthly or annual) cohort epidemiological studies.
Keywords: Spatial epidemiology; Exposure assessment; TAPM; Mesoscale;

With a new retrieval method, the mixed layer height (MLH) over the urban area of Beijing is studied using data observed by an eye-safe, compact micro pulse lidar (MPL). The retrieval results show that the retrieved MLH agrees well with that from radiosonde data. The MLH and its growth rate are estimated from the MPL measurements. Entrainment zone thickness (EZT) is extracted from MPL datasets. Entrainment ratio calculated from MLH and EZT is about 0.24. Regional surface sensible heat fluxes are retrieved with a common thermodynamic model. The contribution of mechanical production on MLH evolution is also studied. These results determined from lidar remote sense are useful for modeling air pollution diffusion and transportation.
Keywords: Micro-pulse lidar; Mixed layer height; Entrainment ratio; Sensible heat flux; Mechanical production;

Micromixing effects in a reacting plume by the Stochastic Fields method by A. Garmory; E.S. Richardson; E. Mastorakos (1078-1091).
The Stochastic Fields method for turbulent reacting flows has been used for a reacting plume. The method simulates macromixing with an eddy diffusivity and micromixing by a random walk in scalar space with appropriate models for the scalar dissipation. The numerical technique used for the solution of the stochastic partial differential equation that arises from the stochastic fields method is discussed. The predictions are very close to experimental data for a plume of NO in a O 3 -doped turbulent air flow for a range of Damköhler numbers.
Keywords: Micromixing; Turbulent reacting flows; Stochastic fields;

An industrial district with polluting factories operating inside poses a potential threat to the air quality in the surrounding areas. Therefore, establishing a proper air quality monitoring network (AQMN) is essential for assessing the effectiveness of imposed pollution controls, strategies, and facilities in reducing pollutants. The geographic layout of such an AQMN should assure the quality of the monitored data. Monitoring stations located at inappropriate sites will likely affect data validity. In this study, a multiobjective approach was explored for configuring an AQMN for an industrial district. A dispersion model was employed to simulate hourly distribution of pollutant concentrations in the study area. Models optimizing pollution detection, dosage, coverage, and population protection were established. Alternative AQMNs with varied station numbers and spatial distributions were obtained using the models. The resulting AQMNs were compared and evaluated for effectiveness in monitoring the temporal and spatial variation of pollutants. Discussion of the differences among the AQMNs is provided. This multiobjective analysis is expected to facilitate a decision-making process for determining an appropriate AQMN.
Keywords: Optimization; Detection; Coverage; Environmental systems analysis; Decision analysis;

A three-dimensional large eddy simulation (LES) of flow structures and pollutant dispersion in the near-wake region of a light-duty diesel vehicle for both high and low idling conditions within the urban road microenvironments was performed. Four different grid resolutions with and without coordinate transformation were used for evaluating the grid independence on computational results of the LES approach. Time-averaged velocities, temperatures and pollutant concentrations along the centreline of the vehicular exhaust plume have been calculated for both high and low idling conditions. The computational results show that the finer grid cell provides a better agreement with the experimental results for both idling conditions. Furthermore, the computational work has been extended to investigate the effect of ambient wind conditions (i.e., wind speed and direction) on the flow dynamics and pollutant dispersion in the near-wake region of a light-duty diesel vehicle for high idling condition. For the low ambient wind speed case, the vehicular exhaust jet plume dominates the flow structures and the pollutant dispersion patterns. On the other hand, for the higher ambient wind speed case, the vortices and turbulence mixing induced by the interaction between the vehicular exhaust jet and the ambient wind dilute the pollutant concentration, while the oblique ambient wind may alter the spreading direction of the vehicular exhaust jet plume.
Keywords: Large eddy simulation; Pollutant dispersion; Flow structures; Near-wake region; Vehicular exhaust jet plume; Urban road microenvironments; Ambient wind condition;

It is premature to include non-CO2 effects of aviation in emission trading schemes by Piers M. de F. Forster; Keith P. Shine; Nicola Stuber (1117-1121).
Keywords: Aviation; Climate; Emission trading schemes; Contrails; Global warming potentials; Radiative forcing;

The contents of heavy metal accumulated by air pollution in the cedar tree needles from the green area of Konya city centre were measured by chemical analyses. The needle samples were collected from two types of trees (about 10–15 and 20–25-years-old trees) from eight different pollution regions for two different sampling periods. Results of sulphur dioxide and particle matter analyses were used for measurement of air pollution effect on accumulation of heavy metals in the vegetation. Contents of heavy metals (Pb, Cu, Zn, Co, Cr, Cd and V) were determined for sampling periods, tree ages and sampling places. Results of the present study showed that accumulations of heavy metals in the old trees were generally higher than those of young trees. Similarly, heavy metal contents of needles collected in spring 2004 were higher than those of needles collected in autumn 2003. Accumulation of heavy metals via sulphur dioxide pollution and particle matter originated from usage of low quality fossil fuels, which might affect the living organisms in the city centre. On the other hand, Pb levels in the samples from Karatay Industry Park (3.53 ppm in 2004) showed that people are health living around the industry, and heavy traffic area is under risk. According to the other sampling areas, the chromium levels were also very high around the Chrome–Magnesite Factory Garden (87.15 ppm in 2004); it could be a toxic risk for people working around the factory. The heavy metal levels obtained from the other samples were not as high a risk level for the living organisms in the sampling areas.
Keywords: Air pollution; Sulphur dioxide; Heavy metals; Cedar tree; Konya city; Health;

Estimation of secondary organic aerosol formation from semi-continuous OC–EC measurements in a Madrid suburban area by J. Plaza; F.J. Gómez-Moreno; L. Núñez; M. Pujadas; B. Artíñano (1134-1147).
An analysis of hourly measurements of gaseous pollutants and fine carbonaceous aerosol (PM2.5) divided into two fractions, elemental and organic carbon (EC and OC), in a suburban Madrid metropolitan area site is presented. Data were obtained using a semi-continuous thermal analyser for two periods of time during the summer and late autumn–early winter of 2003. In the summer period, correlation between EC and OC was poor ( r = 0.4 6 ), and high OC/EC ratios were usually found. In contrast, during the late autumn–early winter period the two carbonaceous aerosol fractions showed a high degree of correlation ( r = 0.9 4 ). Coincident peaks of OC and secondary gases (NO2+O3) were observed during summer episodes and also on some winter episodic days, suggesting a significant non-primary contribution to OC in fine aerosol, linked to photochemical oxidation of gaseous pollutants. OC apportionment between primary and secondary origins has been attempted for the two measuring periods using the EC tracer model. In the summer period, the results of this apportionment were very dependent on the y-intercept value (considered as the non-combustion OC background concentration) of selected linear regressions. Calculation of the secondary contribution to the OC fraction during polluted days gave diurnal maximum hourly estimations in a range from 35% to 55% and daily estimations averaged during the 10–19 h period ranging from 25% to 45%. Thus, this would confirm a daily urban photochemical origin for the secondary organic aerosol, although biogenic contribution to both the OC background and the SOA formation may be significant in the area during summer. During late autumn–early winter episodes primary contribution to OC was more prevailing, although the model also estimated maximum hourly values of secondary OC in the order of 35% of the measured OC.
Keywords: PM2.5; Carbonaceous aerosol; Semi-continuous EC–OC measurements; EC tracer model; Secondary organic aerosol (SOA);

Low emissions from wood burning in an ecolabelled residential boiler by Maria Olsson; Jennica Kjällstrand (1148-1158).
Emissions of organic compounds from wood burning in a modern ecolabelled residential boiler (30 kW) were studied. Smoke was collected in the chimney outlet at different times during the burning cycle for subsequent analysis by gas chromatography.The studied ecolabelled wood boiler had high combustion efficiency, and the flaming phase emissions were very low. The greenhouse gas methane (CH4) was determined in low concentrations of about a few mg m−3 and was the major volatile hydrocarbon emitted. The CH4 emission factor was calculated to 0.04 g kg−1  dry fuel. Benzene, in the range 0.1–1 mg m−3, was the predominant aromatic compound emitted. Other major aromatic compounds were methylbenzene, dimethylbenzenes and ethenylbenzene. The concentrations of the studied polycyclic aromatic compounds were generally low, except for naphthalene, which was the third most prominent aromatic compound. However, the total emissions of these health and environmentally hazardous compounds were low.The already low emissions of most of the organic compounds decreased further towards the end of the burning cycle, although the concentration of carbon monoxide (CO) increased. This indicates that large CO emissions are not necessarily linked to large emissions of organic compounds. Relative to benzene, the concentrations of many of the aromatic compounds studied were higher in the glowing combustion phase, than in the flaming combustion phase.The total environmental and health impact of the studied emissions from the ecolabelled boiler is considered to be low. This wood boiler can be recommended as an environmentally sound residential heating alternative.
Keywords: Air pollution; Biofuel; GC-MS; Hydrocarbon; PAH;

The passive and active release of bioaerosols during green waste composting, measured at source is reported for a commercial composting facility in South East (SE) England as part of a research programme focused on improving risk assessments at composting facilities. Aspergillus fumigatus and actinomycetes concentrations of 9.8–36.8×106 and 18.9–36.0×106  cfu m−3, respectively, measured during the active turning of green waste compost, were typically 3-log higher than previously reported concentrations from static compost windrows. Source depletion curves constructed for A. fumigatus during compost turning and modelled using SCREEN3 suggest that bioaerosol concentrations could reduce to background concentrations of 103  cfu m−3 within 100 m of this site. Authentic source term data produced from this study will help to refine the risk assessment methodologies that support improved permitting of compost facilities.
Keywords: Bioaerosols; Compost; Actinomycetes; Aspergillus fumigatus; Risk; Assessment;

Correlations for gas-phase reactions of NO3, OH and O3 with alkenes: An update by Christian Pfrang; Martin D. King; Carlos E. Canosa-Mas; Richard P. Wayne (1170-1179).
Methods are developed for predicting rate coefficients for reactions of initiators of tropospheric oxidation with unsaturated compounds that are abundant in the atmosphere; prognostic tools of this kind are essential for atmospheric chemists and modellers. To pursue the aim of exploring such tools, the kinetics of reactions of NO3, OH and O3 with a series of alkenes are examined for correlations relating the logarithms of the rate coefficients to the energies of the highest occupied molecular orbitals (HOMOs) of the alkenes. A comparison of the values predicted by the correlations with experimental data (where the latter exist) allowed us to assess the reliability of our method. We used a series of theoretical methods to calculate the HOMO energies, and found that higher computational effort improves the agreement of the predicted rate coefficients with experimental values, especially for reactions of NO3 with alkenes that possess vinyllic halogen substituents. As a consequence, it is expedient to suggest new correlations to replace those presented by us and others that were based on the lower level of theory. We propose the following correlations for the reactions of NO3, OH and O3 with alkenes: ln( k NO 3 /cm3  molecule−1  s−1)=6.40(E HOMO/eV)+31.69, ln(k OH/cm3  molecule−1  s−1)=1.21(E HOMO/eV)−12.34 and ln( k O 3 /cm3  molecule−1  s−1)=3.28(E HOMO/eV)−6.78. These new correlations have been developed using the larger experimental data sets now available, and the impact of the extended data on the quality of the correlations is examined in the paper. Atmospheric lifetimes have been calculated from both experimental and estimated rate coefficients to provide an overview of removal efficiencies for different classes of alkenes with respect to oxidative processes initiated by NO3, OH and O3. A figure is presented to show the spatial scales over which alkenes may survive transport in competition with attack by NO3, OH and O3. Removal by NO3 or OH is always more important than removal by O3, and reactions with NO3 dominate for scales up to a few hundred metres.
Keywords: Lifetimes; Halogens; Troposphere; MP2; B3LYP; HOMO;

Structure–activity relations (SARs) for gas-phase reactions of NO3, OH and O3 with alkenes: An update by Christian Pfrang; Martin D. King; Carlos E. Canosa-Mas; Richard P. Wayne (1180-1186).
We present updated structure–activity relations (SARs) for the prediction of rate coefficients for gas-phase reactions with alkenes of the major atmospheric oxidants NO3, OH and O3. Such SARs provide one way of incorporating essential information about reactivity into atmospheric models. Rate coefficients obtained from correlations relating the logarithms of the rate coefficients to the energies of the highest occupied molecular orbitals (HOMOs) of the alkenes were used to refine the SARs. SARs have an advantage for the user over the direct application of the correlations in that knowledge of the structure of the alkene of interest is sufficient to estimate rate coefficients, and no quantum-mechanical calculations need to be performed. A comparison of the values predicted by the SARs with experimental data where they exist allowed us to assess the reliability of our method.
Keywords: Prediction; Correlation; Troposphere; HF; MP2; HOMO;