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Atmospheric Environment (v.41, #6)

Editorial board (pp. i).

Comparison of multi-receptor and single-receptor trajectory source apportionment (TSA) methods using artificial sources by Stephanie Lee; Lowell Ashbaugh (pp. 1119-1127).

Two trajectory source apportionment methods were tested using an artificially generated data set to determine their ability to detect the known sources. The residence time or conditional probability method developed by Ashbaugh et al. [1985. A residence time probability analysis of sulfur concentrations at Grand Canyon National Park. Atmospheric Environment 19(8), 1263–1270] uses a single receptor at a time, whereas the new multi-receptor (MURA) method developed here uses several receptors at once in an attempt to detect the sources with higher accuracy. The methods were first tested using a simulation with a single source and then with another simulation using four sources. The ability of the methods to detect the sources was quantified for each simulation. The MURA trajectory method proved to be superior at identifying sources for these simulations.

Keywords: Residence time analysis; Trajectory analysis; HYSPLIT; Source apportionment

An improved algorithm for locating a gas source using inverse methods by Laura C. Thomson; Bill Hirst; Graham Gibson; Steve Gillespie; Philip Jonathan; Kenneth D. Skeldon; Miles J. Padgett (pp. 1128-1134).

We apply an inverse problem approach to locating a known gas source in a desert setting from simultaneous measurements of gas concentration and wind data. We use a random search algorithm with simulated annealing to generate candidate distributions of source strengths and positions. These distributions are then assessed by means of a cost function, which quantifies the degree to which the postulated source distribution accounts for the measured gas concentrations. We present results from using three cost functions with differing regularisation terms. We assess the robustness of these and the differing regularisation terms by the progressive addition of random noise and systematic offsets to the concentration data. We show that for our application, the best reconstructions are obtained by using a multiplicative regularisation parameter defined to minimise the total gas emissions.

Keywords: Inverse problem; Gas dispersion; Random search; Simulated annealing; Cost function

Modeling of mercury emission, transport and deposition in North America by Philip K. Gbor; Deyong Wen; Fan Meng; Fuquan Yang; James J. Sloan (pp. 1135-1149).

Most studies on the atmospheric behaviour of mercury in North America have excluded a detailed treatment of natural mercury emissions. The objective of this work is to report a detailed simulation of the atmospheric mercury in a domain that covers a significant part of North America and includes not only anthropogenic mercury emissions but also those from natural sources including vegetation, soil and water.The simulations were done using a natural mercury emission model coupled with the US EPA's SMOKE/CMAQ modelling system. The domain contained 132×90 grid cells at a resolution of 36km, covering the continental United States, and major parts of Canada and Mexico. The simulation was carried out for 2002, using boundary conditions from a global mercury model. Estimated total natural mercury emission in the domain was 230 tonnes (1 tonne=1000kg) and the ratio of natural to anthropogenic emissions varied from 0.7 in January to 3.2 in July. Average total gaseous mercury (TGM) concentration ranged between 1 and 4ngm⁻³. Good agreement was found between the modelled results and measurements at three Ontario sites for ambient mercury concentrations, and at 72 mercury deposition network sites in the domain for wet deposition. The correlation coefficient between the simulated and the measured values of the daily average TGM at three monitoring sites varied between 0.48 and 0.64. When natural emissions were omitted, the correlation coefficients dropped to between 0.15 and 0.40. About 335 tonnes of mercury were deposited in the domain during the simulation period but overall, it acted as a net source of mercury and contributed about 21 tonnes to the global pool. The net deposition of mercury to the Great Lakes was estimated to be about 2.4 tonnes. The estimated deposition values were similar to those reported by other researchers.

Keywords: Mercury; Modelling; Natural emission; CMAQ; Great Lakes

Light-absorbing aldol condensation products in acidic aerosols: Spectra, kinetics, and contribution to the absorption index by Noziere Barbara Nozière; William Esteve (pp. 1150-1163).

The radiative properties of aerosols that are transparent to light in the near-UV and visible, such as sulfate aerosols, can be dramatically modified when mixed with absorbing material such as soot. In a previous work we had shown that the aldol condensation of carbonyl compounds produces light-absorbing compounds in sulfuric acid solutions. In this work we report the spectroscopic and kinetic parameters necessary to estimate the effects of these reactions on the absorption index of sulfuric acid aerosols in the atmosphere. The absorption spectra obtained from the reactions of six different carbonyl compounds (acetaldehyde, acetone, propanal, butanal, 2-butanone, and trifluoroacetone) and their mixtures were compared over 190–1100nm. The results indicated that most carbonyl compounds should be able to undergo aldol condensation. The products are oligomers absorbing light in the 300–500nm region where few other compounds absorb, making them important for the radiative properties of aerosols. Kinetic experiments in 96–75wt% H₂SO₄ solutions and between 273 and 314K gave an activation energy for the rate constant of formation of the aldol products of acetaldehyde of −(70±15)kJmol⁻¹ in 96wt% solution and showed that the effect of acid concentration was exponential. A complete expression for this rate constant is proposed where the absolute value in 96wt% H₂SO₄ and at 298K is scaled to the Henry's law coefficient for acetaldehyde and the absorption cross-section for the aldol products assumed in this work. The absorption index of stratospheric sulfuric acid aerosols after a 2-year residence time was estimated to 2×10⁻⁴, optically equivalent to a content of 0.5% of soot and potentially significant for the radiative forcing of these aerosols and for satellite observations in channels where the aldol products absorb.

A new detailed chemical model for indoor air pollution by Nicola Carslaw (pp. 1164-1179).

A detailed chemical box model has been constructed based on a comprehensive chemical mechanism (the Master Chemical Mechanism) to investigate indoor air chemistry in a typical urban residence in the UK. Unlike previous modelling studies of indoor air chemistry, the mechanism adopted contains no simplifications such as lumping or the use of surrogate species, allowing more insight into indoor air chemistry than previously possible. The chemical mechanism, which has been modified to include the degradation reactions of key indoor air pollutants, contains around 15,400 reactions and 4700 species. The results show a predicted indoor OH radical concentration up to 4.0×10⁵moleculecm⁻³, only a factor of 10–20 less than typically observed outdoors and sufficient for significant chemical cycling to take place. Concentrations of PAN-type species and organic nitrates are found to be important indoors, reaching concentrations of a few ppb. Sensitivity tests highlight that the most crucial parameters for modelling the concentration of OH are the light-intensity levels and the air exchange rate. Outdoor concentrations of O₃ and NO _X are also important in determining radical concentrations indoors. The reactions of ozone with alkenes and monoterpenes play a major role in producing new radicals, unlike outdoors where photolysis reactions are pivotal radical initiators. In terms of radical propagation, the reaction of HO₂ with NO has the most profound influence on OH concentrations indoors. Cycling between OH and RO₂ is dominated by reaction with the monoterpene species, whilst alcohols play a major role in converting OH to HO₂. Surprisingly, the absolute reaction rates are similar to those observed outdoors in a suburban environment in the UK during the summer. The results from this study highlight the importance of tailoring a model for its particular location and the need for future indoor air measurements of radical species, nitrated species such as PANs and organic nitrates, photolysis rates of key species over the range of wavelengths observed indoors and concurrent measurements of outdoor air pollutant concentrations.

Keywords: Hydroxyl radical; Ozone; VOCs; Indoor air pollution

Elemental composition of aerosol in the Nam Co region, Tibetan Plateau, during summer monsoon season by Zhiyuan Cong; Shichang Kang; Xiande Liu; Guangfu Wang (pp. 1180-1187).

In order to investigate the chemical characteristics of atmospheric aerosols in a remote region of the Tibetan Plateau, total suspended particles were collected continuously at the Nam Co Comprehensive Observation and Research Station from July to October 2005. The PIXE analytical results showed that Si, Ca, Fe, Al, K, and S were the major components of aerosols, ranging from 82 (K)–550 (Si)ngm⁻³. The mean elemental concentrations were comparable with those from other remote sites and significantly lower than those from megacities (e.g. Beijing). The very low presence of anthropogenic elements demonstrates that the Nam Co region is an ideal background site for atmospheric monitoring. Crustal enrichment factor (EF) calculation indicated that several anthropogenic heavy metals (Cr, Ni, Cu, Zn, As) are transported long distances atmospherically. The backward air mass trajectory analysis suggests that South Asia may be the source region of those pollutants.

Keywords: Aerosol; PIXE; Nam Co; Tibetan Plateau; Summer monsoon season

Geraniol (2,6-dimethyl-2,6-octadien-8-ol) reactions with ozone and OH radical: Rate constants and gas-phase products by Crystal D. Forester; Jason E. Ham; J.R. Wells (pp. 1188-1199).

The bimolecular rate constants, k_OH+geraniol, (231±58)×10⁻¹²cm³molecule⁻¹s⁻¹ andkO3+geraniol, (9.3±2.3)×10⁻¹⁶cm³molecule⁻¹s⁻¹, were measured using the relative rate technique for the reaction of the hydroxyl radical (OH) and ozone (O₃) with 2,6-dimethyl-2,6-octadien-8-ol (geraniol) at (297±3)K and 1 atmosphere total pressure. To more clearly define part of geraniol's indoor environment degradation mechanism, the products of the geraniol+OH and geraniol+O₃ reactions were also investigated. The identified geraniol+OH and geraniol+O₃ reaction products were: acetone, hydroxyacetaldehyde (glycolaldehyde, HC(O)CH₂OH), ethanedial (glyoxal, HC(O)C(O)H), and 2-oxopropanal (methylglyoxal, CH₃C(O)C(O)H). The use of derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to propose 4-oxopentanal as the other major geraniol+OH and geraniol+O₃ reaction product. The elucidation of this other reaction product was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible geraniol+OH and geraniol+O₃ reaction mechanisms based on previously published volatile organic compound+OH and volatile organic compound+O₃ gas-phase reaction mechanisms.

Keywords: Geraniol; 2,6-dimethyl-2,6-octadien-8-ol; Reaction products; Kinetics; Oxygenated organic compounds

Coarse particulate matter concentrations from residential outdoor sites associated with the North Carolina Asthma and Children's Environment Studies (NC-ACES) by Fu-Lin Chen; Ronald Williams; Erik Svendsen; Karin Yeatts; John Creason; James Scott; Dock Terrell; Martin Case (pp. 1200-1208).

Coarse particulate matter (PM10-2.5) concentration data from residential outdoor sites were collected using portable samplers as part of an exposure assessment for the North Carolina Asthma and Children's Environment Studies (NC-ACES). PM10-2.5 values were estimated using the differential between independent PM10 and PM2.5 collocated MiniVol measurements. Repeated daily 24-h integrated PM10 and PM2.5 residential outdoor monitoring was performed at a total of 26 homes during September 2003–June 2004 in the Research Triangle Park, NC area. This effort resulted in the collection of 73 total daily measurements. This assessment was conducted to provide data needed to investigate the association of exposures to coarse particle PM mass concentrations with observed human health effects. Potential instrument bias between the differential MiniVol methodology and a dichotomous sampler were investigated. Results indicated that minimal bias of PM10-2.5 mass concentration estimates (slope= 0.8, intercept=0.36μgm-3) existed between the dichotomous and differential MiniVol procedures. Residential outdoor PM10-2.5 mass concentrations were observed to be highly variable across measurement days and ranged from 1.1 to12.6μgm-3 (mean of5.4μgm-3). An average correlation coefficient ofr=0.75 existed between residential outdoor PM10-2.5 mass concentrations and those obtained from the central ambient monitoring site. Temporal and spatial variability of PM10-2.5 mass concentrations during the study were observed and are described in this report.

Keywords: PM; 10; -; 2.5; Dichot; MiniVol sampler; Spatial variability; Coarse particulate matter

Emissions of polycyclic aromatic hydrocarbons (PAHs) from the pyrolysis of scrap tires by S.-J. Shui-Jen Chen; H.-B. Hung-Bin Su; J.E. Juu-En Chang; W.-J. Wen-Jhy Lee; K.L. Kuo-Lin Huang; L.-T. Lien-Te Hsieh; Y.-C. Yi-Chu Huang; W.-Y. Wen-Yinn Lin; C.-C. Chih-Chung Lin (pp. 1209-1220).

This work investigated the PAHs generated in a waste-tire pyrolysis process and the PAHs removal by a wet scrubber (WSB) and a flare. IND, DBA, and BaP were found to dominate in the powders of scrap tires before the pyrolysis. The PAHs in the carbon blacks formed in the pyrolysis were mainly 2-, 3-, 6-, and 7-ring PAHs. Nap was the most predominant water-phase PAH in the WSB effluent. About 40% of the water-phase total-PAHs in the WSB effluent were contributed by nine carcinogenic PAHs. NaP, IND, and COR displayed higher mean gas- and particulate-phase concentrations than the other PAHs in the flare exhaust. The mean removal efficiencies of individual PAHs, total-PAHs, and high carcinogenic BaP+IND+DBA were 39.1–90.4%, 76.2%, and 84.9%, respectively for the WSB. For the flare, the mean removal efficiencies of gaseous, particulate, and combined (gaseous+particulate) total-PAHs were 59.8%, 91.2%, and 66.8%, respectively, whereas the removal efficiencies were 91.0%, 80.1%, and 89.1%, respectively for the total-BaPeq. However, the gaseous BaA displayed a negative mean removal efficiency. The total PAH emission rate and factor estimated for the scrap tire pyrolysis plant were 42.3gd⁻¹ and 4.00mgkg-tire⁻¹, respectively.

Keywords: PAHs; Pyrolysis; Tires; Air pollution control devices (APCDs)

A mass transfer based method for measuring the reaction coefficients of a photocatalyst by Rui Yang; Yinping Zhang; Qiujian Xu; Jinhan Mo (pp. 1221-1229).

We have developed a new method, the mass transfer based (MTB) method, for measuring the Langmuir–Hinshelwood (L–H) rate form reaction coefficients of photocatalysts. The conventional method for determining the reaction coefficients disregards the effect of mass transfer on the reaction surface by designing and controlling a reaction process to be reaction-limited. In contrast, the new MTB method takes the mass transfer effect into account by using a computational fluid dynamics (CFD) method. The reaction coefficients can be regressed by the measured reaction rates and the calculated VOC concentrations in the air adjacent to the reaction surface. Thus, by using the new method, the reaction coefficient of a reaction process can be accurately determined even if it is not reaction-limited. This is very important in cases where it is difficult to realize reaction-limited processes, such as photocatalytic oxidation of VOCs with strong UV radiation intensity. The relative error of the regressed reaction coefficients obtained by the new method is analyzed. To illustrate, we apply this method to measuring the reaction coefficients of TiO₂ photocatalytic decomposing formaldehyde. This method is very useful in determining the reaction coefficients of the photocatalytic oxidation of various VOCs simultaneously.

Keywords: Indoor air quality; Formaldehyde; Titania; Photocatalytic oxidation; Air purification

The effects of evaporating essential oils on indoor air quality by Huey-Jen Su; Chung-Jen Chao; Ho-Yuan Chang; Pei-Chih Wu (pp. 1230-1236).

Essential oils, predominantly comprised of a group of aromatic chemicals, have attracted increasing attention as they are introduced into indoor environments through various forms of consumer products via different venues. Our study aimed to characterize the profiles and concentrations of emitted volatile organic compounds (VOCs) when evaporating essential oils indoors. Three popular essential oils in the market, lavender, eucalyptus, and tea tree, based on a nation-wide questionnaire survey, were tested. Specific aromatic compounds of interest were sampled during evaporating the essential oils, and analyzed by GC-MS. Indoor carbon monoxide (CO), carbon dioxide (CO₂), total volatile organic compounds (TVOCs), and particulate matters (PM₁₀) were measured by real-time, continuous monitors, and duplicate samples for airborne fungi and bacteria were collected in different periods of the evaporation. Indoor CO (average concentration 1.48 vs. 0.47ppm at test vs. background), CO₂ (543.21 vs. 435.47ppm), and TVOCs (0.74 vs. 0.48ppm) levels have increased significantly after evaporating essential oils, but not the PM₁₀ (2.45 vs. 2.42ppm). The anti-microbial activity on airborne microbes, an effect claimed by the use of many essential oils, could only be found at the first 30–60min after the evaporation began as the highest levels of volatile components in these essential oils appeared to emit into the air, especially in the case of tea tree oil. High emissions of linalool (0.092–0.787mgm⁻³), eucalyptol (0.007–0.856mgm⁻³),d-limonene (0.004–0.153mgm⁻³), ρ-cymene (0.019–0.141mgm⁻³), and terpinene-4-ol-1 (0.029–0.978mgm⁻³), all from the family of terpenes, were observed, and warranted for further examination for their health implications, especially for their potential contribution to the increasing indoor levels of secondary pollutants such as formaldehyde and secondary organic aerosols (SOAs) in the presence of ozone.

Keywords: Essential oils; Indoor air quality; Airborne microbes; Terpenes; Formaldehyde; Secondary organic aerosols

An integrated MM5–CMAQ modeling approach for assessing trans-boundary PM₁₀ contribution to the host city of 2008 Olympic summer games—Beijing, China by D.S. Chen; S.Y. Cheng; L. Liu; T. Chen; X.R. Guo (pp. 1237-1250).

In this paper, an integrated MM5–CMAQ modeling approach was employed to investigate the PM₁₀ air pollution issue in Beijing, China, with a focus on assessing pollution contributions from surrounding provinces. A 2-level-nested grid domain with spatial resolutions of 36 and 12km was designed for the study region. Seven monitoring stations across Beijing municipality were selected to provide hourly PM₁₀ measurement data. The months of January, April, July and October in 2002 were taken as target periods for model performance evaluation. Five emission scenarios were designed and run in order to quantitatively assess the trans-boundary PM₁₀ contributions. The results show that, while Beijing needs to take positive steps to reduce its own pollution emissions, much effort should also be placed on demanding more pollution reduction and better environmental performance from surrounding provinces.

Keywords: Air quality; CMAQ; MM5; Model; Simulation

The impact of transpacific transport of mineral dust in the United States by T. Duncan Fairlie; Daniel J. Jacob; Rokjin J. Park (pp. 1251-1266).

We use a global chemical transport model (GEOS-Chem) to estimate the impact of transpacific transport of mineral dust on aerosol concentrations in North America during 2001. We have implemented two dust mobilization schemes in the model (GOCART and DEAD) and find that the best simulation of North American surface observations with GEOS-Chem is achieved by combining the topographic source used in GOCART with the entrainment scheme used in DEAD. This combination restricts dust emissions to year-round arid areas but includes a significant wind threshold for dust mobilization. The model captures the magnitude and seasonal cycle of observed surface dust concentrations over the northern Pacific. It simulates the free tropospheric outflow of dust from Asia observed in the TRACE-P and ACE-Asia aircraft campaigns of spring 2001. It reproduces the timing and distribution of Asian dust outbreaks in North America during April–May. Beyond these outbreaks we find persistent Asian fine dust (averaging 1.2μgm⁻³) in surface air over the western United States in spring, with much weaker influence (0.25μgm⁻³) in summer and fall. Asian influence over the eastern United States is 30–50% lower. We find that transpacific sources accounted for 41% of the worst dust days in the western United States in 2001.

Keywords: Transpacific; Transport; Mineral; Dust

Model evidence for a significant source of secondary organic aerosol from isoprene by Aaron van Donkelaar; Randall V. Martin; Rokjin J. Park; Colette L. Heald; T.-M. Tzung-May Fu; Hong Liao; Alex Guenther (pp. 1267-1274).

We investigate how a recently suggested pathway for production of secondary organic aerosol (SOA) affects the consistency of simulated organic aerosol (OA) mass in a global three-dimensional model of oxidant-aerosol chemistry (GEOS-Chem) versus surface measurements from the interagency monitoring of protected visual environments (IMPROVE) network. Simulations in which isoprene oxidation products contribute to SOA formation, with a yield of 2.0% by mass reduce a model bias versus measured OA surface mass concentrations. The resultant increase in simulated OA mass concentrations during summer of 0.6–1.0μgm⁻³ in the southeastern United States reduces the regional RMSE to 0.88μgm⁻³ from 1.26μgm⁻³. Spring and fall biases are also reduced, with little change in winter when isoprene emissions are negligible.

Keywords: Isoprene; Secondary organic aerosol; Organic carbon

Ammonia fluxes and derived canopy compensation points over non-fertilized agricultural grassland in The Netherlands using the new gradient ammonia—high accuracy—monitor (GRAHAM) by R.J. R.J. (Roy) Wichink Kruit; W.A.J. van Pul; R.P. Otjes; P. Hofschreuder; A.F.G. Jacobs; A.A.M. Holtslag (pp. 1275-1287).

During a measurement period from June till November 2004, ammonia fluxes above non-fertilized managed grassland in The Netherlands were measured with a Gradient Ammonia—High Accuracy—Monitor (GRAHAM). Compared with earlier ammonia measurement systems, the GRAHAM has higher accuracy and a quality control system.Flux measurements are presented for two different periods, i.e. a warm, dry summer period (from 18 July till 15 August) and a wet, cool autumn period (23 September till 23 October). From these measurements canopy compensation points were derived. The canopy compensation point is defined as the effective surface concentration of ammonia. In the summer period (negative) deposition fluxes are observed in the evening, night and early morning due to leaf surface wetness, while in the afternoon emission fluxes are observed due to high canopy compensation points. The mean NH₃-flux in this period was 4ngm⁻²s⁻¹, which corresponds to a net emission of 0.10kgNha⁻¹ over the 28 day sampling period. The NH₃-flux in the autumn period mainly shows (negative) deposition fluxes due to small canopy compensation points caused by low temperatures and a generally wet surface. The mean NH₃-flux in this period is −24ngm⁻²s⁻¹, which corresponds to a net deposition of 0.65kgNha⁻¹ over the 31 day sampling period.Frequency distributions of the NH₃-concentration and flux show that despite higher average ambient NH₃-concentrations (13.3μgm⁻³ in the summer period vs. 6.4μgm⁻³ in the autumn period) there are more emission events in the summer period than in the autumn period (about 50% of the time in summer vs. 20% in autumn). This is caused by the high canopy compensation points in summer due to high temperatures and a dry surface. In autumn, deposition dominates due to a generally wet surface that induces low canopy compensation points.For our non-fertilized agricultural grassland site, the derived canopy compensation points (at temperatures between 7 and 29°C) varied from 0.5 to 29.7μgm⁻³ and were on an average 7.0μgm⁻³, which is quite high for non-fertilized conditions and probably caused by high nitrogen inputs in the past or high dry deposition amounts from local sources. The average value for the ratio between NH₄⁺ and H⁺ concentration in the canopy, Γ_c, that was derived from our data was 2200.

Keywords: Ammonia; Flux; Distribution; Compensation point

Dry deposition fluxes and deposition velocities of PAHs at an urban site in Turkey by Y. Yücel Tasdemir; Fatma Esen (pp. 1288-1301).

Even though dry deposition and air–water exchange of semivolatile organic compounds (SOCs) are important for surfaces in and around the urban areas, there is still no generally accepted direct measurement technique for dry deposition. In this study, a modified water surface sampler (WSS) configuration, including a filter holder and an XAD-2 resin column, was employed to investigate the polycyclic aromatic hydrocarbon (PAH) dry deposition in an urban area. The measured total (particle+dissolved) PAH fluxes to the WSS averaged to be 34960±16540ngm⁻²d⁻¹. Average particulate PAH flux, determined by analyzing the filter in the WSS, was about 8% of the total PAH flux. Temporal flux variations indicated that colder months (October–April) had the highest PAH fluxes. This increase could be attributed to the residential heating as well as meteorological effects including lower mixing height. A high volume air sampler was concurrently employed to collect ambient air concentrations. The average total (gas+particle) atmospheric PAH concentration (456±524ngm⁻³) was within the range of previously measured values at different urban locations. PAH concentrations in urban areas are more than two orders of magnitude higher than those measured in pristine areas and this result may indicate that urban areas have major source sectors and greater deposition rates are expected near to these areas. The average contribution of particle phase was about 10% in total concentration. Simultaneous particulate phase dry deposition and ambient air samples were collected in this study. Then, particulate phase apparent dry deposition velocities were calculated using the fluxes and concentrations for each PAH compound and they ranged from 0.1 to 1.2cms⁻¹. These values are in good agreement with previously reported values.

Keywords: SOCs; Water surface sampler; Air–water exchange; Bursa; Turkey

Ground-level ozone and ozone vertical profile measurements close to the foothills of the Guadarrama mountain range (Spain) by M.L. Sanchez; B. de Torre; Garcia M.A. García; Perez I. Pérez (pp. 1302-1314).

Continuous measurements of ozone vertical profiles, OVP, in the low troposphere (around 500–2400m) using an unattended commercial ozone profiler DIAL, were conducted during June–July 2004 in Segovia, SG, a small city in the upper plateau located close to the foothills of the Guadarrama mountain range, Guadarrama, in the Central Massif. The data obtained over almost 37 complete days have enabled us to characterise the ozone vertical exchange, describe the phenomenology of the main ozone peaks, OP, recorded in the city and their relationship with ozone transport/formation from the gas precursor emissions of the greater Madrid area across Guadarrama. To achieve the last objective concurrent measurements of ground-level ozone in SG and a representative monitoring station upwind from Guadarrama, Buitrago de Lozoya, BL, have been used. 72.2% of the concurrent maximum diurnal ozone peaks exceeding the 95 percentile hourly value in SG (OPSG) and BL (OPBL) were linked to ozone transport and formation from the greater Madrid area towards Guadarrama. An estimate of the contribution of the greater Madrid area on OPSG yielded 28μgm⁻³.The most prominent ozone vertical stratification was linked to the mixing height, MH, and a frequent nocturnal stable layer formed, NSL. Three small ozone enriched-layers were identified at mean heights of 500, 700 and 1000m, respectively. Ozone tended to decline versus altitude. The hourly patterns of the three layers showed two peak occurrences of similar amplitude in the early morning, 7–8h, and mid-afternoon, 14–16h. A minimum was also observed during daytime, 10–11h, its origin being attributed to a dilution process induced by the “chimney effect” caused by the slopes heating during this period.The comparison between OPSG, and the maximum diurnal ozone peaks in the first layer, OL1P, showed a satisfactory relationship, correlation coefficient, r, of the linear fit 0.77, and comparable mean values, 127 and 130μgm⁻³, respectively, revealing the presence of an uniform ozone vertical distribution in the 500m atmospheric layer above ground level during mid-afternoon.

Keywords: Ozone ground level; Ozone vertical profiles; Ozone vertical exchange; Ozone episodes; Ozone laser remote-sensing technology

Long-term atmospheric bulk deposition of polycyclic aromatic hydrocarbons (PAHs) in rural areas of Southern Germany by Tilman Gocht; Otto Klemm; Peter Grathwohl (pp. 1315-1327).

A novel passive sampling technique using a funnel–adsorber–cartridge device was adopted and validated in the field during a long-term monitoring program on the atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) in three rural regions of southern Germany. Apart from seasonal variations, fairly stable annual deposition rates around 200μgm⁻²yr⁻¹ for the sum of PAHs were obtained. The time-integrating passive samplers showed that spatial variability due to topography was negligible and differences between open-field and forest deposition were within a factor of 2. Based on correlations with ambient temperature, advection was identified as the most important factor that controls the atmospheric deposition of PAHs. Gas-adsorption contributes significantly to the deposition of the semivolatile compounds in forests, but particle deposition seems to be the major pathway for all PAHs.

Keywords: Passive sampler; Monitoring; Deposition processes; Open-field; Forest

Prediction of atmospheric dispersion of pollutants in an airport environment by S.K. Das; P.A. Durbin (pp. 1328-1341).

In this article we discuss the development of a methodology to predict atmospheric turbulent dispersion of pollutants generated from air traffic in an airport. It is based on the Lagrangian stochastic model (LSM), developed by Das and Durbin [2005. A Lagrangian stochastic model for dispersion in stratified turbulence, Physics of Fluids 17, 025109]. The approach is via the backward trajectory formulation of the model. The sources and receptors in an airport type problem are modeled as spheres and procedures have been derived for concentration calculation by both forward and backward trajectory methods. Some tests are performed to highlight certain features of the method. The turbulence statistics that are required as input are provided in terms of similarity profiles. The airport domain is partitioned to make the required search algorithms efficient. Pollutant concentration profiles are calculated over a range of meteorological data.

Keywords: Lagrangian stochastic model; Turbulence; Backward trajectory; Air-traffic pollutants; Environmental flows

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Atmospheric Environment (v.41, #6)