Atmospheric Environment (v.36, #5)

A chemical speciation of trace metals for fine urban particles by Antonio J. Fernández Espinosa; Miguel Ternero Rodrı́guez; Francisco J. Barragán de la Rosa; Juan C. Jiménez Sánchez (773-780).
The chemical speciation of 11 metals in aerosols has been studied in 12 areas of the city of Seville (Spain). Urban particles were collected with a high-volume sampling system equipped with a cascade impactor, which effectively separates the particulate matter into six size ranges. Forty-one samples were collected in the spring of 1996. The chemical speciation was studied in the finest particles of the impactor system (<0.61 μm), those that can penetrate into the alveolar region of the lung. This speciation scheme is specific for urban particles and consisted of four fractions: 1. soluble and exchangeable metals; 2. carbonates, oxides and reducible metals; 3. bound to organic matter, oxidisable and sulphidic metals; and 4. residual metals. The sample extractions were analysed for 11 metals by inductively coupled plasma atomic emission spectrometry (ICP-AES). The chemical speciation of metals showed that the metals with highest percentages in the different fractions are vanadium (50.4%) in the soluble and exchangeable fraction, calcium (39.7%) in the carbonates, oxides and reducible fraction, magnesium (59.2%) in the bound to organic matter, oxidisable and sulphidic fraction, and iron (54.6%) in the residual fraction. Correlations between all the variables have been studied and the results showed common sources to the metal fractions correlated in relation to the industrial activities and mainly the vehicular traffic.
Keywords: Chemical speciation; Speciation scheme; Trace metals; Air pollution; Urban particles; Fine particles; Inductively coupled plasma atomic emission spectrometry;

Emission of polycyclic aromatic hydrocarbons from medical waste incinerators by Wen-Jhy Lee; Ming-Chu Liow; Perng-Jy Tsai; Lien-Te Hsieh (781-790).
This study was conducted on two batch-type medical waste incinerators (MWIs), including the one with a mechanical grate (MG-MWI) and the other with a fixed grate (FG-MWI) for the disposal of general medical waste and special medical waste, respectively. Both incinerators shared the same air-pollution control devices which were installed in series, including one electrostatic precipitator (ESP) and one wet scrubber (WSB). In addition to the investigated emissions of polycyclic aromatic hydrocarbons (PAHs) from both types of MWIs, the PAH removal efficiencies of air-pollution control devices were also included. In this study, the GC/MS technique was used to analyze the concentrations of 21 PAH species contained in the stack flue gas, ESP fly ash, WSB effluent, and incinerating ash. Results show that total-PAHs (i.e., the sum of 21 PAH species) in stack flue gas were dominated by LM-PAHs (i.e., two- to three-ringed PAHs), but in incinerating ash, ESP fly ash and WSB effluent we found that they were dominated by MM-PAHs (i.e., four-ringed PAHs) and HM-PAHs (i.e., five- to seven-ringed PAHs) for both types of MWIs. The above results due to air-pollution control devices used in both types of MWIs had much higher removal efficiencies on both MM-PAHs and HM-PAHs (>78%) than on LM-PAHs (<5%). The emission factors of total-PAHs for MG-MWI (=252,000 μg/kg-waste) were lower than FG-MWI (=856,000 μg/kg-waste), which was probably due to more complete combustion involved in the combustion process of the former than the latter. Nevertheless, the above two emission factors were found consistently higher than the only municipal waste incinerator that was located in the same city (=871 μg/kg-waste, respectively). The above results warrant the need for seeking better technologies for disposing medical waste in the future.
Keywords: PAHs; Medical waste incinerator; Removal efficiency; Air-pollution control devices; Emission factor;

Direct measurements and parameterisation of aerosol flux, concentration and emission velocity above a city by J.R. Dorsey; E. Nemitz; M.W. Gallagher; D. Fowler; P.I. Williams; K.N. Bower; K.M. Beswick (791-800).
Articles have recently been published on aerosol size distributions and number concentrations in cities, however there have been no studies on transport of these particles. Eddy covariance measurements of vertical transport of aerosol in the size range 11 nm<D p<3 μm are presented here. The analysis shows that typical average aerosol number fluxes in this size range vary between 9000 and 90,000 cm−2  s−1. With concentrations between 3000 and 20,000 cm−3 this leads to estimates of particle emission velocity between 20 and 75 mm s−1. The relationships between number flux and traffic activity, along with emission velocity and boundary layer stability are demonstrated and parameterised. These are used to derive an empirical parameterisation for aerosol concentration in terms of traffic activity and stability. The main processes determining urban aerosol fluxes and concentrations are discussed and quantified where possible. The difficulties in parameterising urban activity are discussed.
Keywords: Urban; Pollution; Parameterisation; Eddy covariance; Measurement;

Cigarette smoking is a major cause of indoor aerosol pollution. Determination of exposure to environmental tobacco smoke (ETS) aerosol is critical to understanding health effects. Sizing studies have shown that ETS has a size distribution that is efficiently deposited into the lungs and can therefore provide effective delivery of carcinogenic compounds into the human body. Two-step laser mass spectrometry is used to analyze aromatic compounds on aerosols collected from a smoking lobby. The determination and suitability of ETS tracers on aerosols is examined. Additionally, the transport of aerosol from the smoking lobby is examined to determine what effect deposition and dilution have on the mass spectrum observed.Results from the analysis of ETS, both from lobby samples and direct cigarette sampling, show that several unique peaks are present in the mass spectrum when compared to other combustion sources, such as automobiles and diesel trucks. In particular, ions at m/z 118, 132, 146, and 160 are consistently present and are not found in other combustion sources. For the indoor environment, where chemical transformation is much less rapid than in the outdoor environment, these ions were found to be present as soon as the first smokers appeared and persisted over the course of the day. Aerosol samples taken in the morning prior to the presence of smokers in the lobby reveal the presence of skeletal PAHs, indicative of outdoor urban traffic aerosol penetration into the building.
Keywords: Health effects; Particle; Indoor pollution; Time-of-flight mass spectrometry; PAH;

Atmospheric behaviour of oil-shale combustion fly ash in a chamber study by Erik Teinemaa; Uuve Kirso; Michael R. Strommen; Richard M. Kamens (813-824).
There are huge world deposits of oil shale, however, little is known about the fate of atmospheric oil-shale combustion fly ash. In the present work, oil-shale combustion fly-ash aerosol was investigated under simulated daytime and nighttime conditions. Fly-ash particles collected from the Baltic Power Plant (Estonia) were injected directly to a 190 m3 outdoor Teflon film chamber. The initial concentration of particles was in the range from 15 to 20 mg/m3. Particle size distributions were monitored continuously by various optical and electrical devices. During the course of an experiment the particle phase was collected on filters, and the gas phase was collected using denuders. The initial aerosol mass concentration decreased quickly due to the deposition of larger particles. Since fine particles dominated the count distribution, the change in aerosol number concentration was less significiant than the mass concentration over time. Experimental data showed a bimodal particle size distribution with maximums at about 0.07 and 4 μm. SEM images of aerosol particles also provided particle shape and size distribution information. The respirable fraction of particles, which contributes most to the health effects of the aerosol, significantly increased during the experiment, being 25% by mass immediately after the injection of fly ash and achieving 65% at the end of the experiment. Results of CG/MS analysis confirm the presence of different polycyclic aromatic hydrocarbons (PAHs) in the particle phase of the aerosol. Some of the individual compounds included phenanthrene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, and benzo(a)pyrene. Several PAHs were found in the gas phase of the chamber after fly ash had aged for 2 h, indicating that PAHs desorbed from the particles over time.
Keywords: Oil-shale fly ash; Aerosol; Particle deposition; Atmospheric fate; PAHs;

Field observations of regional and urban impacts on NO2, ozone, UVB, and nitrate radical production rates in the Phoenix air basin by Jeffrey S. Gaffney; Nancy A. Marley; Paul J. Drayton; Paul V. Doskey; V.Rao Kotamarthi; Mary M. Cunningham; J.Christopher Baird; Julie Dintaman; Heather L. Hart (825-833).
In the May and June of 1998, field measurements were taken at a site near the Usery Pass Recreation Area, ∼27 miles from the downtown Phoenix area, overlooking Phoenix and Mesa, Arizona. This site was selected to examine the impacts of the Phoenix urban plume on the Usery Pass Recreation Area and surrounding regions. Data were obtained for ultraviolet-B (UVB) radiation, nitrogen dioxide (NO2), peroxyacetyl nitrate (PAN), ozone (O3), and carbon monoxide (CO). Nocturnal plumes of NO2 (in tens of ppb), observed near midnight, were correlated with CO and anti-correlated with O3. This behavior was consistent with the titration of locally generated NO by boundary layer O3 to form the nighttime NO2 plumes that were subsequently transported into the Usery Pass Recreation area. Nitrate radical (NO3) production rates were calculated to be very high on the edges of these nocturnal plumes. Examination of O3 and PAN data also indicates that Phoenix is being affected by long-range transport of pollutants from the Los Angeles to San Diego areas. A regional smoke episode was observed in May, accompanied by a decrease in UVB of factor of two and a decrease in O3 and an increase in methyl chloride. Low level back trajectories and chemical evidence confirm that the smoke event originated in northern Mexico and that the reduced O3 levels observed at Usery Pass could be partially due to reduced photolysis rates caused by carbonaceous soot aerosols transported in the smoke plume. The results are discussed with regard to potential effects of local pollution transport from the Phoenix air basin as well as an assessment of the contributions from long-range transport of pollutants to the background levels in the Phoenix-Usery Pass area.
Keywords: UVB; Nitrate radical; PAN; Ozone formation; Biomass burning; Smoke aerosols; Transport; Atmospheric chemistry; Nightime chemistry;

A two-resistance exchange interface model (TREIM) was developed to simulate gaseous mercury (Hg) emissions from soils measured by dynamic flux chamber (DFC) operations. The model is based on mass balance principles and a Hg air/soil exchange theory that considers the influence of flushing flow rate on Hg air/soil exchange. We used this model to examine the effect of the flushing flow rate and understand the optimum conditions for DFC measurements of Hg emission fluxes over soils. Our model simulations indicate that the flushing flow rate is a most critical operation condition. We recommend adoption of high flushing flow rates (e.g., ∼15–40 l min−1 for DFCs of common design) based on our simulation findings that underestimation of actual emission fluxes can occur at low flushing flow rates. The biased low fluxes are caused by suppression of emission potential resulting from internal accumulation of emitted Hg and by higher exchange resistance both at low flushing flow rates. This model provides a useful means for estimating maximum steady-state fluxes and soil air Hg concentrations and for adjustment of the fluxes measured under different operating conditions. The model also finds its value in understanding mechanical processes of Hg emissions from soils.
Keywords: Air/soil exchange; Biogeochemical cycling; Boundary layer; Global Hg chemodynamics; Trace gases;

Both field and laboratory tests demonstrated that soil Hg emission fluxes measured by dynamic flux chamber (DFC) operations strongly depend on the flushing air flow rates used. The general trend is an increase in the fluxes with increasing flushing flow rates followed by an asymptotic approach to flux maximum at sufficiently high (optimum) flushing flow rates. This study indicates that the DFC measurements performed at low flushing flow rates can underestimate Hg emission fluxes over soils, especially Hg-enriched soils. High flushing flow rates therefore are recommended for accurate estimation of soil Hg emission fluxes by DFC operations. The dependence of DFC-measured soil Hg emission fluxes on flushing flow rate is a physical phenomenon inherent in DFC operations, regardless of DFC design and soil physical characteristics. Laboratory tests using DFCs over different soils confirmed the predictions of a two-resistance exchange interface model and demonstrated the capability of this model in quantitatively simulating Hg emissions from soils measured by DFC operations.
Keywords: Atmosphere/surface exchange; Biogeochemical cycling; Terrestrial surface; Trace gas;

Validation of a two-dimensional pollutant dispersion model in an isolated street canyon by T.L. Chan; G. Dong; C.W. Leung; C.S. Cheung; W.T. Hung (861-872).
A two-dimensional numerical model based on Reynolds-averaged Navier–Stokes equations coupled with a series of standard, Renormalization Group (RNG) and realizable kε turbulence models was developed to simulate the fluid-flow development and pollutant dispersion within an isolated street canyon using the FLUENT code. In the present study, the validation of the numerical model was evaluated using an extensive experimental database obtained from the atmospheric boundary layer wind tunnel at the Meteorological Institute of Hamburg University, Germany (J. Wind Eng. Ind. Aerodyn. 62 (1996) 37). Among the studied turbulence models, the RNG kε turbulence model was found to be the most optimum turbulence model coupled with the two-dimensional street canyon model developed in the present study. Both the calculated and measured dimensionless pollutant concentrations have been shown to be less dependent on the variation of wind speed and source strength conditions for the studied street canyon aspect ratio of the B/H=1 case. However, the street canyon configuration has significant influence on the pollutant dispersion. The wider street and lower height of the buildings are favorable to pollutant dilution within the street canyon. The fluid-flow development has demonstrated that the rotative vortex or vortices generated within the urban street canyon can transport the pollutants from a line source to the wall surfaces of the buildings.
Keywords: Street canyon; Two-dimensional pollutant dispersion model; kε turbulence models; Vehicle emissions; Wind tunnel data;

We present in this article an efficient numerical solver for the time integration of atmospheric multiphase chemical kinetics. This solver is based on a second-order Rosenbrock scheme, that has been proposed by Verwer et al. (SIAM J. Sci. Comput. 20 (4) (1999) 1456) for gas-phase chemical kinetics. We show that the stiff time dependence of cloudy events (through liquid water content) has to be solved by the numerical scheme and a non-autonomous version has to be used. We benchmark our non-autonomous ROS2 scheme with the classical LSODE solver for two kinetic schemes. For detailed schemes such as RADM2, the speed-up is of magnitude 5 for the same accuracy.
Keywords: Box models; Air pollution modelling; Multiphase chemistry; Lumping; Time integration;

Hg localisation in Tillandsia usneoides L. (Bromeliaceae), an atmospheric biomonitor by G.M Amado Filho; L.R Andrade; M Farina; O Malm (881-887).
The Spanish moss, Tillandsia usneoides, has been applied as an atmospheric biomonitor of Hg contamination, although the mechanism of metal plant accumulation has not been understood until now. In the present work, analytical scanning electron microscopy (SEM) was used to localize Hg in T. usneoides exposed to a Hg–air-contaminated area during 15 days. After this period, Hg was determined by the flow injection mercury system, and plants were prepared for SEM observation and energy-dispersive X-ray analysis. A concentration of 2702±318 μg Hg g−1 was determined in exposed plants. The presented microanalytical results demonstrated that Hg was partly associated with atmospheric particles deposited upon the plant surface, but it was highly absorbed by the scales, stem and leaves surfaces and less absorbed by epidermal cells of T. usneoides. No Hg was detected in mesophyll parenchyma or in vascular system cells. The great surface adsorption area provided by the scales, in addition to the characteristics of T. usneoides morphology, especially of the node region, are suggested to confer the great capability of T. usneoides in Hg holding.
Keywords: Spanish moss; Atmospheric contamination; Hg; Scanning electron microscopy; EDXA;

Development and evaluation of a new personal sampler for culturable airborne microorganisms by Igor E Agranovski; Victoria Agranovski; Tiina Reponen; Klaus Willeke; Sergey A Grinshpun (889-898).
The objective of this study was to develop a new personal sampler for viable airborne microorganisms and to evaluate its performance under controlled laboratory conditions and in a field. In the sampler, air is bubbled through a porous medium submerged in a liquid layer, as has earlier been demonstrated to be highly efficient for air purification. The prototype had the physical collection efficiency >95% for particles >0.32 μm in aerodynamic diameter during 8 h of continuous operation. The pressure drop across the sampler was below 1700 Pa, much lower than that of most conventional bioaerosol samplers. The collection liquid losses due to evaporation and aerosolization did not exceed 18% in 8 h and the culturability of sampled microorganisms remained high: the recovery rate of stress-sensitive gram-negative P. fluorescens bacteria was 61±20%; for stress-resistant B. subtilis bacteria and A. versicolor fungal spores it was 95±9% and 97±6%, respectively. Six identical personal samplers were tested simultaneously on a simplified human manikin in an office environment. The culturable microbial concentration data obtained during 2, 4 and 8-h sampling were not affected by the sampling time. Inter-sample variation did not exceed 30%. The laboratory and field evaluations have demonstrated that the new sampler is capable of long-term personal sampling of airborne culturable microorganisms. The estimation of the detection limits has indicated that the sampler is capable of monitoring microbial exposure in the environments with the bacterial concentrations above 15 CFU/m3 and fungal concentrations above 5 CFU/m3 when using a sampling time of 8 h.
Keywords: Bioaerosol; Personal sampling; Viable microorganisms; Liquid collection; Collection efficiency;

Static secondary ion mass spectrometry as a new analytical tool for measuring atmospheric particles on insulating substrates by Rita Van Ham; Annemie Adriaens; Paolo Prati; Alessandro Zucchiatti; Luc Van Vaeck; Freddy Adams (899-909).
The paper presents static secondary ion mass spectrometry (S-SIMS) analyses of aerosol particles, which have been collected on an insulating polycarbonate filter (nuclepore) using a two-stage streaker sampler. A method was developed to analyze one streaker sample in its entirety without the need of cutting the filter. The latter allows the analysis of the same sample set with complementary techniques. Simultaneous detection of low Z atomic ions (Z<11) together with mean Z atomic ions (11<Z<82) and molecular fragment ions (e.g. HSO4 ,NO2 ,NH4 +) has shown to be feasible and has proven to be a major advantage of this technique. The large amounts of spectral data received were reduced by statistical clustering and were interpreted. A separate group of positive ions, e.g. Fe, K, Mn, Al, and Mg showed correlation with the PO2 ion in the negative mode and were identified as particle emission from the steel plant. Practical problems of sample introduction and spectral effects due to charge compensation were solved and will be discussed. Despite the lack of quantitative analysis, static SIMS can be used to determine the relative abundance of compounds present in the sample and the correlation between them. In addition, the technique has been proven to provide complementary information to particle induced X-ray emission results of the same sample.
Keywords: ToF-SIMS; Inorganic speciation; Streaker sampler; Nuclepore filter; Charging;

Preservation of atmospheric dimethyl sulphide samples on Tenax in sea-to-air flux measurements by H.J Zemmelink; W.W.C Gieskes; P.M Holland; J.W.H Dacey (911-916).
The low concentration of dimethyl sulphide (DMS) in the atmosphere makes it necessary to concentrate the gas before gas-chromatographic analysis. One of the preferred methods has been to use a cold Tenax adsorbent in this concentration step. DMS concentration onto Tenax-TA traps is shown to be sensitive to temperature and to humidity. Implementation of cooling and concentration devices for the measurement of DMS over the air–sea interface is difficult since these measurements are typically made in exposed conditions where temperature control can be problematic. Instead of concentrating DMS in traps, collecting bulk air in Tedlar bags allows storage for at least one week without loss of DMS. This approach allows the concentration and analysis to be postponed until return to the laboratory where analytical conditions can be much better controlled—improving precision and accuracy in DMS measurement needed for gas flux estimation.
Keywords: Dimethyl sulphide; DMS; Air sampling;