Atmospheric Environment (v.35, #12)

“Haagen-Smit Award” by Hanwant B. Singh; Peter Brimblecombe; Jacques Kiebert (iii).

Environmental tobacco smoke (ETS) is a major source of human exposure to airborne particles. To better understand the factors that affect exposure, and to investigate the potential effectiveness of technical control measures, a series of experiments was conducted in a two-room test facility. Particle concentrations, size distributions, and airflow rates were measured during and after combustion of a cigarette. Experiments were varied to obtain information about the effects on exposure of smoker segregation, ventilation modification, and air filtration. The experimental data were used to test the performance of an analytical model of the two-zone environment and a numerical multizone aerosol dynamics model. A respiratory tract particle deposition model was also applied to the results to estimate the mass of ETS particles that would be deposited in the lungs of a nonsmoker exposed in either the smoking or nonsmoking room. Comparisons between the experimental data and model predictions showed good agreement. For time-averaged particle mass concentration, the average bias between model and experiments was less than 10%. The average absolute error was typically 35%, probably because of variability in particle emission rates from cigarettes. For the conditions tested, the use of a portable air filtration unit yielded 65–90% reductions in predicted lung deposition relative to the baseline scenario. The use of exhaust ventilation in the smoking room reduced predicted lung deposition in the nonsmoking room by more than 80%, as did segregating the smoker from nonsmokers with a closed door.
Keywords: Experiments; Exposure; Aerosol; Indoor environment; Modeling;

Measurements of biogenic VOC emissions: sampling, analysis and calibration by M. Komenda; E. Parusel; A. Wedel; R. Koppmann (2069-2080).
We describe an experimental system and techniques for sampling and analyzing biogenic emissions of volatile organic compounds (VOC). The system uses a Teflon chamber to enclose a single branch of a tree. Temperature, photosynthetic active radiation (PAR), relative humidity and carbon dioxide concentration are continuously monitored with a time resolution of five minutes. VOCs are sampled on tubes containing solid adsorbents (Tenax TA and Carbotrap) with a time resolution of 1 h. Composition and concentration of VOC emissions are measured with a gas chromatographic system equipped with a flame ionization detector (FID) for quantitative and a mass spectrometer (MS) for qualitative analysis. To calibrate the system, a diffusion source was built to produce standard mixtures of up to 36 different compounds with mixing ratios at low concentrations and high accuracy. The diffusion rates were monitored over 17 months and showed variations between 0.2 and 7.6% for monoterpenes (expect for α-phellandrene, α-terpinene and γ-terpinene) and between 10.6 and 22.6% for sesquiterpenes. FID response factors calculated from calibration measurements were corrected using correction factors based on the effective carbon number concept. The individual response factors of 23 compounds were combined to a mean response factor (RFm) with a value of 23,100 μV s ng−1 and a standard deviation of 9%. The system described here was used to measure VOC emission rates of Scots pine (Pinus sylvestris) in 1998 and 1999.
Keywords: Monoterpenes; Enclosure chamber; Diffusion device;

This paper presents correlations between the logarithm of the rate constants of the reaction between RO2+NO and RO2+HO2 (and possibly RO2+CH3O2) and the singly occupied molecular orbital (SOMO) energy of the organic peroxy radical, RO2. These reactions are of the utmost importance in the tropospheric oxidation cycle of organic compounds. A correlation such as this may allow the prediction of rate constants for the reactions of organic peroxy radicals, RO2, with species such as NO, HO2 and CH3O2 where no previous experimental determination has been undertaken. The mathematical form of the correlation for the reactions of RO2 with NO and HO2 is −ln  k  (cm 3  molecule −1  s −1)=mE SOMO (RO 2)+c, where m=1.14 and −1.45 eV−1, c=28.80 and 21.16 for NO and HO2, respectively; E SOMO(RO2) is the SOMO energy of the organic RO2 radical in eV. The origin of the correlation is explained in terms of frontier orbital theory. Six previously unmeasured rate constants are predicted for reactions between RO2 and NO, and 20 rate constants are predicted for the reactions between RO2 and HO2. This appears to be the first time that such a correlation has been applied to a series of radical–radical reactions, and the method holds promise for further chemical systems.
Keywords: Correlation; Peroxy radical; Frontier molecular orbital theory; Hydroperoxy (radical); Nitrogen monoxide; Methyl peroxy (radical); Rate constants;

Development of an improved optical transmission technique for black carbon (BC) analysis by J Ballach; R Hitzenberger; E Schultz; W Jaeschke (2089-2100).
A new optical transmission technique for black carbon (BC) analysis was developed to minimize interferences due to scattering effects in filter samples. A standard thermal analysis method (VDI, 1999) is used to link light attenuation by the filter samples to elemental carbon (EC) concentration. Scattering effects are minimized by immersion of the filters in oil of a similar refractive index, as is often done for microscopy purposes. Light attenuation was measured using both a white light source and a red LED of 650 nm. The usual increase in overestimation of BC concentrations with decreasing BC amount in filter samples was found considerably reduced. Some effects of BC properties (e.g. fractal dimension, microstructure and size distribution) on the specific attenuation coefficient B ATN, however, are still present for the treated samples. B ATN was found close to 1 m2  g−1 for dry-dispersed industrial BC and 7 m2  g−1 for nebulized BC. Good agreement was found between the oil immersion, integrating sphere and a polar photometer technique and Mie calculations. The average specific attenuation coefficient of ambient samples in oil varied between 7 and 11 m2  g−1 for white light and 6 and 9 m2  g−1 for red light (LED). B ATN was found to have much less site variation for the treated than for the untreated samples. The oil immersion technique improved also the correlation with thermally analyzed EC. This new immersion technique therefore presents a considerable improvement over conventional optical transmission techniques and may therefore serve as a simple, fast and cost-effective alternative to thermal methods.
Keywords: Black carbon; Optical analysis; Scattering effects; Immersion technique; Specific attenuation coefficient;

Modelling plume rise and dispersion from pool fires by B.E.A. Fisher; E. Metcalfe; I. Vince; A. Yates (2101-2110).
This paper describes an investigation into the behaviour of smoke plumes from pool fires, and the subsequent generation of empirical models to predict plume rise and dispersion from such a combustion source. Synchronous video records of plumes were taken from a series of small-scale (0.06–0.25m2) outdoor methanol/toluene pool fire experiments, and used to produce sets of images from which plume dimensions could be derived. Three models were used as a basis for the multiple regression analysis of the data set, in order to produce new equations for improved prediction. Actual plume observations from a large (20.7 m×14.2 m) aviation fuel pool fire were also used to test the predictions. The two theoretically based models were found to give a better representation of plume rise and dispersion than the empirical model based on measurements of small-scale fires. It is concluded that theoretical models tested on small-scale fires (heat output ≈70 kW) can be used to predict plume behaviour from much larger combustion sources (heat output ≈70 MW) under near neutral atmospheric conditions.
Keywords: Plume rise; Dispersion; Models; Pool fires;

Results of the “carbon conference” international aerosol carbon round robin test stage I by Heidrun Schmid; Lothar Laskus; Hans Jürgen Abraham; Urs Baltensperger; Vincent Lavanchy; Mirko Bizjak; Peter Burba; Helene Cachier; Dale Crow; Judith Chow; Thomas Gnauk; Arja Even; H.M ten Brink; Klaus-Peter Giesen; Regina Hitzenberger; Christoph Hueglin; Willy Maenhaut; Casimiro Pio; Abel Carvalho; Jean-Philippe Putaud; Desiree Toom-Sauntry; Hans Puxbaum (2111-2121).
An international round robin test on the analysis of carbonaceous aerosols on quartz fiber filters sampled at an urban site was organized by the Vienna University of Technology. Seventeen laboratories participated using nine different thermal and optical methods. For the analysis of total carbon (TC), a good agreement of the values obtained by all laboratories was found (7 and 9% r.s.d.) with only two outliers in the complete data set. In contrast the results of the determination of elemental carbon (EC) in two not pre-extracted samples were highly variable ranging over more than one order of magnitude and the relative standard deviations (r.s.d.) of the means were 36.6 and 45.5%. The laboratories that obtained similar results by using methods which reduce the charring artifact were put together to a new data set in order to approach a “real EC” value. The new data set consisting of the results of 10 laboratories using seven different methods showed 16 and 24% lower averages and r.s.d. of 14 and 24% for the two not pre-extracted samples. Taking the current filters as “equivalents” for urban aerosol samples we conclude that the following methods can be used for the analysis of EC in carbonaceous aerosols: thermal methods with an optical feature to correct for charring during pyrolysis, two-step thermal procedures reducing charring during pyrolysis, the VDI 2465/1 method (removal of OC by solvent extraction and thermodesorption in nitrogen) and the VDI 2465/2 method (combustion of OC and EC at different temperatures) with an additional pre-extraction with a dimethyl formamide (DMF)/toluene mixture. Only thermal methods without any correction for charring during pyrolysis and the VDI 2465/2 method were outside the range of twice the standard deviation of the new data set. For a filter sample pre-extracted with the DMF/toluene mixture the average and r.s.d. from all laboratories (20.7 μgC; 24.4% r.s.d.) was very similar as for the laboratory set reduced to 10 laboratories (20.6 μgC; 19% r.s.d.). Thus DMF pre-extraction appears to improve the performance of the thermal methods without charring during pyrolysis control, e.g. the VDI 2465/2 methods.
Keywords: Intercomparison; Thermal–optical method; Pyrolysis; Elemental carbon; Soot;

Evaluation of a Gaussian and a Lagrangian model against a roadside data set, with emphasis on low wind speed conditions by Dietmar Oettl; Jaakko Kukkonen; Raimund Alfons Almbauer; Peter Johann Sturm; Mia Pohjola; Jari Härkönen (2123-2132).
The evaluation of the high percentiles of concentration distributions is required by most national air quality guidelines, as well as the EU directives. However, it is problematic to compute such high percentiles in stable, low wind speed or calm conditions. This study utilizes the results of a previous measurement campaign near a major road at Elimäki in southern Finland in 1995, a campaign specifically designed for model evaluation purposes. In this study, numerical simulations were performed with a Gaussian finite line source dispersion model CAR-FMI and a Lagrangian dispersion model GRAL, and model predictions were compared with the field measurements. In comparison with corresponding results presented previously in the literature, the agreement of measured and predicted data sets was good for both models considered, as measured using various statistical parameters. For instance, considering all NO x data (N=587), the so-called index of agreement values varied from 0.76 to 0.87 and from 0.81 to 1.00 for the CAR-FMI and GRAL models, respectively. The CAR-FMI model tends to slightly overestimate the NO x concentrations (fractional bias FB=+14%), while the GRAL model has a tendency to underestimate NO x concentrations (FB=−16%). The GRAL model provides special treatment to account for enhanced horizontal dispersion in low wind speed conditions; while such adjustments have not been included in the CAR-FMI model. This type of Lagrangian model therefore predicts lower concentrations, in conditions of low wind speeds and stable stratification, in comparison with a standard Lagrangian model. In low wind speed conditions the meandering of the flow can be quite significant, leading to enhanced horizontal dispersion. We also analyzed the difference between the model predictions and measured data in terms of the wind speed and direction. The performance of the CAR-FMI model deteriorated as the wind direction approached a direction parallel to the road, and for the lowest wind speeds. However, the performance of the GRAL model varied less with wind speed and direction; the model simulated better the cases of low wind speed and those with the wind nearly parallel to the road.
Keywords: Line source model; Low wind speed; High percentile; EU directive 99/30/EC; Road traffic; Lagrangian dispersion model; Gaussian dispersion model;

The kinetics of sensitized photolysis for four pesticides, deltamethrin (Decis), acrinathrin (Rufast), s-fenvalerate (Sumialpha), and propiconazol (Tilt) in thin films and aerosol particles was investigated under sunlight or the irradiation from halogen or mercury lamp. The peculiarities of principle of the photochemistry of pesticides in high disperse substance state were discussed. The quantum yields of sensitized and direct photolysis were measured, and the phenomenological kinetic mechanism of photolysis was proposed and examined. Four relations between six rate constants of reaction steps of the kinetic mechanism were determined. The use of sensitizers to accelerate the decomposition rates of pesticide pollutants under sunlight could minimize the contamination of agricultural commodities and the adjacent environment. The Shirvanol 2 sensitizer (a by-product of the full treatment of Caspian oils) can regulate decomposition of many pesticides in a wide range of photolysis rates, so that practically any desired lifetime could be really available for either pesticide residues on plant foliage or pesticide aerosol particles in the air.
Keywords: Aerosol; Atmosphere; Photolysis; Sensitizer; Kinetics; Pesticide;

Ozone emission rate testing and ranking method using environmental chamber by Jianlei Niu; Thomas C.W. Tung; J. Burnett (2143-2151).
Ionization-based air cleaners can emit high concentrations of ozone. With the aim to limit the ozone concentration below the standard value in actual use conditions, we propose a standard procedure for testing and ranking the ozone emission of air cleaners. It is demonstrated by testing 27 samples of air cleaners that ozone emission rate can be measured in an airtight environmental chamber, by applying a generation-decay model to the concentration increase curve. The results indicate that deposition velocities v d on chamber wall surfaces need to be better characterized so that the ozone emission of a tested product could be characterized by a three-parameter model. The model takes into account actual room sizes and surface material deposition effects to predict ozone concentrations in indoor applications. This procedure accounts for ozone decay effect in an explicit manner and allows using alternative testing chamber sizes other than as specified in the current Underwriters Laboratory standard.
Keywords: Air exchange rate; Domestic environment; Indoor sources; Deposition experiment; Modeling;

In this study, the BC aerosol measured at two very different urban sites is compared in terms of concentration, seasonal variation, and size distribution. During a 14 month study, one impactor sample was performed each month on a day with typical meteorological conditions. One (Vienna) or three (Uji) filter samples were obtained during the sampling time of the impactors. BC concentration in both the filter and impactor samples was analyzed with an optical technique (integrating sphere technique), where a calibration curve obtained from commercial carbon black is used to convert the optical signal to BC mass. Gravimetric mass concentration was measured at both sites. The gravimetric mass size distribution was measured only in Vienna. At both sites, the yearly average of the BC concentration on the sampling days was around 5 μg m−3. In Vienna, some seasonal trend with high concentrations during the cold season was observed, while in Uji, no pronounced seasonal trend was found. The BC size distribution in Uji was distinctly bimodal in the submicron size range. Log-normal distributions were fitted through the impactor data. The average BC mass median diameters (MMD) of the two submicron modes were 0.15 and 0.39 μm. Each mode contained about the same amount of BC mass. In Vienna only one submicron BC mode (average MMD 0.3 μm) was found because of the low size resolution of the impactor. An analysis of humidity effects on the MMDs of BC (both sites) and gravimetric mass (Vienna only) indicates that the Vienna aerosol is partly mixed internally with respect to BC, while the Uji aerosol seems to be externally mixed.
Keywords: Urban aerosol; Black carbon size distribution; Mass size distribution; Integrating sphere technique;

Release of iodine in the atmospheric oxidation of alkyl iodides and the fates of iodinated alkoxy radicals by E.S.N. Cotter; N.J. Booth; C.E. Canosa-Mas; R.P. Wayne (2169-2178).
This paper describes a study of the products of the Cl-atom-initiated oxidation of three alkyl iodides, RI=CH3I, C2H5I, and 2-C3H7I, carried out in synthetic air at atmospheric pressure and at room temperature. Fourier-transform infrared spectroscopy was used to follow the decay of reactants and subsequent formation of products. The primary step proceeds via two channels, one of which yields HCl and an iodinated alkyl radical, and the other I atoms and an alkyl chloride. Quantitative analysis of the product yields, together with an assessment of the formation of HCl in secondary processes, allowed the fractional branching into the two channels to be calculated. The channel yielding HCl from RI constitutes a fraction 0.59, 0.93, and 0.68 for R=CH3, C2H5, and 2-C3H7. The iodinated alkyl radical forms first a peroxy, and then an alkoxy, radical in the presence of air. The final products CH2O, CH3CHO, and CH3COCH3 were observed as expected for the decomposition of these radicals with RI=CH3I, C2H5I, and 2-C3H7I, and the fractions of the alkoxy radicals fragmenting to the carbonyl compounds were 0.88, 0.57, and 0.86, respectively. Atomic iodine is formed concomitantly with the carbonyl species, so that these fractions also indicate the yield of I atoms in the secondary process. Alternative reaction pathways for the iodinated alkoxy radicals, in particular reaction with O2, are evaluated and discussed. The yields of I atoms in the primary and secondary steps, taken in combination with kinetic data, make it possible to estimate the contribution of the Cl-initiated oxidation of the alkyl halides to I-atom production in the atmosphere (and, making certain assumptions, the analogous contribution from OH-initiated oxidation). Radical-initiated processes might augment the photolytic yield of I atoms from simple alkyl iodides: the maximum enhancements lie between 5% (CH3I) and more than 30% (2-C3H7I).
Keywords: Alkyl iodides; Cl oxidation; Iodine; Fourier-transform infrared spectroscopy (FTIR); Reaction channels; Unimolecular decompostion;

At two sites in the Armenhof district, 10 km east of Fulda, Germany, dew samples were collected from June 1996 to June 1997 and investigated for free and protein-bound amino acids. On account of the high pollen content, at the beginning of June 1996 and in May 1997 total amino acid concentrations were 53–390 μmol l−1, in one sample 922 μmol l−1. At other times the concentration in dew was 8–164 μmol l−1. On 4 and 5 June 1996 the diluted free amino acid fraction (DFAA) of the total hydrolysed amino acids (THAA) at both sites amounted to 35–44% and was predominantly arginine, proline and glutamine/glutamate. Likewise on 11 March 1997 the fraction of DFAA was found to be 39.5% with extremely high arginine and proline fractions. At other times the DFAA-fraction was in the range 14–26%. From July 1996 to June 1997 the amino acid concentrations in the vapours rising from a meadow were also measured and it ranged from 8 to 51 μmol l−1. From July to October 1996 the amino acid composition in the hydrolysates of dew samples and meadow vapours collected overnight were almost identical. The DFAA fraction in the condensation water collected overnight from the meadow varied from 18 to 40%. From 4 to 6 June 1996, on 11 and 13 March 1997 and in the period 16–20 May 1997, the amino acid distribution in dew showed much variation. The percentage fraction of arginine and proline in the hydrolysate increased greatly, whereas that of glycine and serine decreased. The large increase in proline and arginine in hydrolysate is attributable solely to the large amounts of free arginine and proline. This effect occurred in both 1996 and 1997 over several days at both sites at any one time and therefore appears confirmed.
Keywords: Soil evaporation; Dewfall; Vapour of soil organic nitrogen cycling; Amino acids wet deposition;

Characterisation of polar organic compounds in fog water by Gyula Kiss; Bálint Varga; András Gelencsér; Zoltán Krivácsy; Ágnes Molnár; Tomas Alsberg; Linn Persson; Hans-Christen Hansson; Maria Cristina Facchini (2193-2200).
In this paper the results of a systematic liquid chromatographic investigation are described to characterise water-soluble organic compounds in fog. A diode array detector is used to record the UV spectrum of the components during separation and a mass spectrometer is applied to obtain information on the ion masses of the constituents. The combination of UV and mass spectra reveal that the organic carbon content of fog water is distributed among a great number of acidic compounds which have polar functional groups and polyconjugated systems absorbing up to 500 nm. Due to the complexity of the organic fraction in fog water an unresolved hump of ions was recorded by the mass spectrometer from m/z=100–600 the most intense peaks being detected around m/z=200–250. Tannin and fulvic acid were also examined under the same conditions. In terms of complexity and ion distribution the mass spectrum of the organic fraction was similar to that of a fulvic acid reference material rather than to that of tannin.
Keywords: Water-soluble organic compounds; Fog; Liquid chromatography; Mass spectrometry; Diode array detection;

In-residence, multiple route exposures to chlorpyrifos and diazinon estimated by indirect method models by D.J. Moschandreas; Y. Kim; S. Karuchit; H. Ari; M.D. Lebowitz; M.K. O’Rourke; S. Gordon; G. Robertson (2201-2213).
One of the objectives of the National Human Exposure Assessment Survey (NHEXAS) is to estimate exposures to several pollutants in multiple media and determine their distributions for the population of Arizona. This paper presents modeling methods used to estimate exposure distributions of chlorpyrifos and diazinon in the residential microenvironment using the database generated in Arizona (NHEXAS-AZ). A four-stage probability sampling design was used for sample selection. Exposures to pesticides were estimated using the indirect method of exposure calculation by combining measured concentrations of the two pesticides in multiple media with questionnaire information such as time subjects spent indoors, dietary and non-dietary items they consumed, and areas they touched. Most distributions of in-residence exposure to chlorpyrifos and diazinon were log-normal or nearly log-normal. Exposures to chlorpyrifos and diazinon vary by pesticide and route as well as by various demographic characteristics of the subjects. Comparisons of exposure to pesticides were investigated among subgroups of demographic categories, including gender, age, minority status, education, family income, household dwelling type, year the dwelling was built, pesticide use, and carpeted areas within dwellings. Residents with large carpeted areas within their dwellings have higher exposures to both pesticides for all routes than those in less carpet-covered areas. Depending on the route, several other determinants of exposure to pesticides were identified, but a clear pattern could not be established regarding the exposure differences between several subpopulation groups.
Keywords: Multi-stage probability sampling design; Censored data; Sampling weights; Weighting adjustment; Exposure models;

Fine-scale layering on the edge of a stratospheric intrusion by G. Vaughan; H. Gouget; F.M. O’Connor; D. Wier (2215-2221).
Observations of vertical profiles of ozone, humidity, static stability and VHF radar vertical power at Aberystwyth (52°N, 4°W) on 21 June 1996 revealed a pronounced layered structure at the western edge of a stratospheric intrusion, in a location where one would expect to see a tropopause fold. Despite the 3 km depth of the observed ozone anomaly, it was not represented as a fold in the ECMWF potential vorticity analyses; nor was it evident as a layer of enhanced wind shear. Ozone lidar measurements suggest that the fine-scale layering gave way to a single layer as the day progressed. Weak sporadic turbulence observed by the radar at the edge of the fold showed some mixing between stratospheric and tropospheric air.