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Atmospheric Environment (v.39, #15)

List for forthcoming papers (pp. i-ii).

Editorial board (pp. i).

Fourth international conference on urban air quality—measurement, modelling and management, 25–28 March 2003, Prague, Czech Republic by Ranjeet S. Sokhi Conference Chair (pp. 2695-2696).

Personal carbon monoxide exposure in Helsinki, Finland by Greta Scotto di Marco; Stylianos Kephalopoulos; Juhani Ruuskanen; Matti Jantunen (pp. 2697-2707).

Personal exposure concentrations of carbon monoxide (CO) were measured for the adult urban population of Helsinki, Finland, as part of the multi-centre European EXPOLIS study. The arithmetic mean of the 48h average personal CO exposure concentration was 1.3mgm⁻³ for participants not exposed to environmental tobacco smoke (ETS) and 1.6mgm⁻³ for those exposed to ETS at any time and in any microenvironment. The maximum 8 and 1h exposure values were 2.0 and 2.6mgm⁻³, and 4.3 and 5.7mgm⁻³, respectively. As tobacco smoke is one of the major sources of CO, therefore the personal mean exposures of ETS participants were higher than the non-ETS participants for all averaging times. The long- and short-term personal exposures were higher in winter than in summer for all participants. In order to analyse in more detail the correlation between the time-activity patterns and exposure levels, cluster analysis was performed using 24h personal exposure profiles of 1h moving averages. The results showed clearly that the major source of CO for non-ETS exposed participants are traffic emissions. The majority of the diurnal exposure profiles showed two notable exposure peaks corresponding to the morning and evening traffic rush hours. The time spent in street traffic was the most relevant factor for describing the short-term personal exposures. The more time was spent commuting by car the higher were the exposures. The long-term exposure levels were linked both to the time spent commuting and home location. People living in low-traffic suburban areas and working in downtown spent more time commuting and ended up experiencing similar long-term exposure levels than people who lived in heavy-traffic downtown areas, but spent little time commuting. For ETS exposed participants the personal exposure profiles were dominated by both tobacco smoke and traffic emissions.

Keywords: Microenvironment; Seasonal variation; Exposure profile; Environmental tobacco smoke (ETS); Traffic emissions; Cluster analysis

Inter-comparison of interpolated background nitrogen dioxide concentrations across Greater Manchester, UK by S.J. Lindley; T. Walsh (pp. 2709-2724).

There are many modelling methods dedicated to the estimation of spatial patterns in pollutant concentrations, each with their distinctive advantages and disadvantages. The derivation of a surface of air quality values from monitoring data alone requires the conversion of point-based data from a limited number of monitoring stations to a continuous surface using interpolation. Since interpolation techniques involve the estimation of data at un-sampled points based on calculated relationships between data measured at a number of known sample points, they are subject to some uncertainty, both in terms of the values estimated and their spatial distribution. These uncertainties, which are incorporated into many empirical and semi-empirical mapping methodologies, could be recognised in any further usage of the data and also in the assessment of the extent of an exceedence of an air quality standard and the degree of exposure this may represent. There is a wide range of available interpolation techniques and the differences in the characteristics of these result in variations in the output surfaces estimated from the same set of input points. The work presented in this paper provides an examination of uncertainties through the application of a number of interpolation techniques available in standard GIS packages to a case study nitrogen dioxide data set for the Greater Manchester conurbation in northern England. The implications of the use of different techniques are discussed through application to hourly concentrations during an air quality episode and annual average concentrations in 2001. Patterns of concentrations demonstrate considerable differences in the estimated spatial pattern of maxima as the combined effects of chemical processes, topography and meteorology. In the case of air quality episodes, the considerable spatial variability of concentrations results in large uncertainties in the surfaces produced but these uncertainties vary widely from area to area. In view of the uncertainties with classical techniques research is ongoing to develop alternative methods which should in time help improve the suite of tools available to air quality managers.

Keywords: Mapping; Episode; GIS

Spatial variability of air pollution in the vicinity of a permanent monitoring station in central Paris by Sotiris Vardoulakis; Norbert Gonzalez-Flesca; Bernard E.A. Fisher; Koulis Pericleous (pp. 2725-2736).

The strong spatial and temporal variability of traffic-related air pollution detected at roadside locations in a number of European cities has raised the question of how representative the site and time period of air quality measurements actually can be. To address this question, a 7-month sampling campaign was carried out on a major road axis (Avenue Leclerc) leading to a very busy intersection (Place Basch) in central Paris, covering the surroundings of a permanent air quality monitoring station. This station has recorded the highest CO and NO _x concentrations during recent years in the region of Paris.Diffusive BTX samplers as well as a mobile monitoring unit equipped with real-time CO, NO _x and O₃ analysers and meteorological instruments were used to reveal the small-scale pollution gradients and their temporal trends near the permanent monitoring station. The diffusive measurements provided 7-day averages of benzene, toluene, xylene and other hydrocarbons at different heights above the ground and distances from the kerb covering summer and winter periods. Relevant traffic and meteorological data were also obtained on an hourly basis. Furthermore, three semi-empirical dispersion models (STREET-SRI, OSPM and AEOLIUS) were tested for an asymmetric canyon location in Av. Leclerc. The analysis of this comprehensive data set has helped to assess the representativeness of air quality monitoring information.

Keywords: Passive sampling; Traffic emissions; Urban intersection; Asymmetric canyon; Dispersion modelling

Wind tunnel modelling of urban building exposure to outdoor pollution by A.M. Mfula; V. Kukadia; R.F. Griffiths; D.J. Hall (pp. 2737-2745).

The effects of the position of air pollution sources on the magnitude and spatial variation in concentrations on a building model were investigated in a boundary layer wind tunnel. The aim was to determine the region around the building from which pollution sources affect the building (region of influence of sources) and generate concentration patterns on its surface. The tests were carried out at a nominal building model scale of 1:100 and used continuous releases of a tracer gas at different locations within arrays of cubes representative of urban areas.The region of influence of sources around the test building was found to be variable in size depending on the area density of the array of buildings. The region of influence across the wind increased in size with increasing area density of the array. There was a limiting area density, however, beyond which this sensitivity of the region to the area density diminished. Sources closest to the test building generated the highest variation in concentrations on the building. This variation decreased with increasing source distance from the building and was sensitive to the area density of the array. Generally, the decay in the spatial variation in concentrations with increasing upwind source distance was smaller in higher density arrays.

Keywords: Ingress; Outdoor pollution; Plume; Ventilation; Wind tunnel

Joint analysis of air pollution in street canyons in St. Petersburg and Copenhagen by E.L. Genikhovich; A.D. Ziv; E.A. Iakovleva; F. Palmgren; R. Berkowicz (pp. 2747-2757).

The bi-annual data set of concentrations of several traffic-related air pollutants, measured continuously in street canyons in St. Petersburg and Copenhagen, is analysed jointly using different statistical techniques. Annual mean concentrations of NO₂, NO _x and, especially, benzene are found systematically higher in St. Petersburg than in Copenhagen but for ozone the situation is opposite. In both cities probability distribution functions (PDFs) of concentrations and their daily or weekly extrema are fitted with the Weibull and double exponential distributions, respectively. Sample estimates of bi-variate distributions of concentrations, concentration roses, and probabilities of concentration of one pollutant being extreme given that another one reaches its extremum are presented in this paper as well as auto- and co-spectra. It is demonstrated that there is a reasonably high correlation between seasonally averaged concentrations of pollutants in St. Petersburg and Copenhagen.

Keywords: Keyword; Urban air pollution; Statistical analysis; Interurban correlation; Concentration extrema

Analysis and evaluation of selected local-scale PM₁₀ air pollution episodes in four European cities: Helsinki, London, Milan and Oslo by Jaakko Kukkonen; Mia Pohjola; Ranjeet S Sokhi; Lakhu Luhana; Nutthida Kitwiroon; Lia Fragkou; Rantamaki Minna Rantam�ki; Erik Berge; Odegaard Viel �degaard; Havard Slordal Leiv H�vard Sl�rdal; Bruce Denby; Sandro Finardi (pp. 2759-2773).

We have analysed in detail four selected episodes involving substantially high concentrations of PM₁₀ that occurred in Oslo on 4–10 January 2003, in Helsinki on 3–14 April 2002, in London on 18–27 February 2003 and in Milan on 14–19 December 1998. We have also utilised a more extensive dataset containing relevant information regarding 21 episodes from seven cities in six countries. The four episodes analysed in detail were recently occurring cases that were at least partly caused by various local emission sources. In particular, we have addressed the evolution of the measured concentrations in terms of the measured, meteorologically pre-processed and predicted (using numerical weather prediction models and a meso-scale meteorological model) meteorological variables. All the four episodes addressed were associated with areas of high pressure (Oslo, Helsinki and London) or a high-pressure ridge (Milan). The best meteorological prediction variables were found to be the temporal evolution of the temperature inversions and atmospheric stability and, in some of the cases, wind speed. Strong ground-based or slightly elevated temperature inversions prevailed in the course of the episodes in Oslo, Helsinki and Milan, and there was a slight ground-based inversion also in London; their occurrence coinciding with the highest PM₁₀ concentrations. The same result was also obtained by considering an additional set of seven PM₁₀ episodes from the larger dataset. The inversions in Oslo and Milan were mainly caused by the advection of warmer air above a relatively colder surface, and that in Helsinki by radiation cooling of snow-covered ground. It was also found that a low wind speed is not necessarily a good indicator of episodes; this is the case, e.g., in the Po valley, due to the frequently occurring calm and low wind speed conditions there.

Keywords: Episode; Urban; PM; ₁₀; Inversion; Forecasting

Evaluation of two versions of the HIRLAM numerical weather prediction model during an air pollution episode in southern Finland by Rantamaki Minna Rantam�ki; Mia A Pohjola; Priit Tisler; Pia Bremer; Jaakko Kukkonen; Ari Karppinen (pp. 2775-2786).

The main objective of this work is to evaluate the performance of two operational versions of the numerical weather prediction model HIRLAM ( HIgh Resolution Limited Area Model) in severe wintertime air pollution conditions. The evaluation has been done by comparing the predicted temperature, wind speed and relative humidity with observational data during one specific episode in December 1995. Simulations were executed with versions 4.6.2 (operational 1999–2003) and 6.2.1 (operational since 2004) of the HIRLAM model. During 27–29 December 1995, an area of high pressure was formed over Southern Scandinavia and Finland, leading to the formation of an exceptionally strong ground-based temperature inversion. According to radiosonde measurements, the maximum strength of the inversion was 18°C at Jokioinen. These conditions caused poor air quality for 2 days, especially in the Helsinki Metropolitan Area. The simulations with both model versions were able to predict the occurrence of the inversions, but the surface temperatures and wind speeds near the surface were generally overestimated, thus leading to underestimation of the strength of the inversion. However, the more recent model version performed better in predicting the ground-based inversions. The improved performance of the more recent model version is probably due to both the improved surface parameterisation and the better vertical resolution in the lowest atmospheric layers, compared with those of the older model version.

Keywords: Air quality; Ground-based inversion; Winter; Numerical weather prediction; HIRLAM

The conceptual development of a simple scale-adaptive reactive pollutant dispersion model by M.K. Neophytou; D.A. Goussis; E. Mastorakos; R.E. Britter (pp. 2787-2794).

The paper develops the basis for a self-consistent, operationally useful, reactive pollutant dispersion model, for application in urban environments. The model addresses the multi-scale nature of the physical and chemical processes and the interaction between the different scales. The methodology builds on existing techniques of source apportionment in pollutant dispersion and on reduction techniques of detailed chemical mechanisms.

Keywords: Dispersion model; Chemical reactions; Space–time scales; Reactive pollutant

Seasonal modelling assessment of ozone sensitivity to precursors in northern Italy by Veronica Gabusi; Marialuisa Volta (pp. 2795-2804).

One of the major thrusts of model application is to assess the relative importance ofNOx and VOC controls in reducing ozone levels; in this paper, the long-term assessment of ozone exposure and sensitivity toNOx and VOC emissions, in terms of mean values and seasonal indicators, has been investigated over a complex domain in northern Italy, including Milan metropolitan area. The analysis has been carried out comparing eight seasonal simulations performed by the Gas Aerosol Modelling Evaluation System (GAMES): the summer season 1996, selected as reference case, and seven simulations obtained feeding the modelling system with increasing or decreasing precursor emissions. The study allowed to: (1) recognize the photochemical regimes of the domain, (2) investigate the influence of Milan plume in ozone production and accumulation processes over neighbouring suburban and rural areas, (3) identify parts of the domain where local emission reduction strategies are not effective, (4) provide a support system for local Air Quality Authorities in selecting effective emission reduction strategies.

Keywords: Ozone; Long-term modelling simulation; Sensitivity analysis; AOT40; Photochemical regimes

Quantitative assessment of uncertainties for a model of tropospheric ethene oxidation using the European Photoreactor (EUPHORE) by Zador Judit Z�dor; Volker Wagner; Klaus Wirtz; Michael J. Pilling (pp. 2805-2817).

Methods of uncertainty analysis were used for comparison of the Master Chemical Mechanism version 3 (MCMv3) with measurements made in the European Photoreactor (EUPHORE) at Valencia (Spain) to investigate model–measurement discrepancies and to obtain information on the importance of wall effects. Two EUPHORE smog chamber measurements of ethene oxidation, under high and low NO _x conditions were analysed by the following methods: (i) local uncertainty analysis, (ii) the global screening method of Morris and (iii) Monte Carlo (MC) analysis with Latin hypercube sampling. For both experiments, ozone (by 25% and 30%, respectively) and formaldehyde (by 34% and 40%, respectively) are significantly over-predicted by the model calculations, while the disagreement for other species is less substantial. According to the local uncertainty analysis and the Morris method, the most important contributor to ozone uncertainty under low NO _x conditions is HOCH₂CH₂O₂+NO→HOCH₂CH₂O+NO₂, while under high NO _x conditions OH+NO₂→HNO₃ is the main contributor. The MC simulations give an estimate of the 2σ uncertainty for ozone as ∼20% in both scenarios at the end of the experiment. The results suggest systematic disagreement between measurements and model calculations, although the origin of this is not clear. It seems that chamber effects alone are not responsible for the observed discrepancies.

Keywords: Uncertainty analysis; European photoreactor; Master chemical mechanism; Ethene; Smog chamber; Wall effects; Monte Carlo; Morris method

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Atmospheric Environment (v.39, #15)