Potential and Shortcomings of Numerical Weather Prediction Models in Providing Meteorological Data for Urban Air Pollution Forecasting

The last decade progress in numericalweather prediction (NWP) modelling and studies of urbanatmospheric processes for providing meteorological data forurban air pollution forecasting is analysed on examples ofseveral European meteorological centres. Modern nested NWP models are utilising land-use databasesdown to 1 km resolution or finer, and are approaching thenecessary horizontal and vertical resolution suitable forcity scale. The recent scientific developments in the fieldof urban atmospheric physics and the growing availabilityof high-resolution urban surface characteristics datapromise further improvements of the capability of NWPmodels for this aim. A strategy to improve NWP data forthe urban air pollution forecasting is suggested.     

Modelling of Flow and Pollution Dispersion in a Two Dimensional Urban Street Canyon

The wind-driven flow patterns and the dispersion of vehicle exhaust pollutants released at street level has been simulated with the three-dimensional (3-D) dispersion model ADREA-HF (Andronopoulos et al., 1993), for idealised two-dimensional urban fetches occupied by buildings with slanted roofs. The simulation used oncoming atmospheric boundary layer characteristics corresponding to realistic above-town wind characteristics, as measured in reference wind tunnel experiments (Rafailidis, 1997). At that stage, analysis was limited to neutral stability conditions only. Firstly, the quality assurance of the numerical model was investigated in terms of the sensitivity to different grid allocations. The modelling results were corroborated by comparison with wind tunnel measurements in a similar two-dimensional domain (Pavageau et al., 1997). The numerical modelling replicated well the high degree of non-uniformity in the dispersion field in the test street, and the results agreed satisfactorily with the experimental measurements. The reasons for the differences observed have been investigated. With the model thus validated, three different exhaust release scenarios have been tested, keeping the same overall emission rate but different spatial patterns of street-release. The effect of the different street-release scenarios was found to be only marginal, with the dispersion patterns on the sidewalls affected only locally, close to the street level.     

CFD Prediction of Air Quality in the Area between Two City Vehicular Tunnels Considering Moving Cars

Concentration fields of different pollutants that spread outside two roadtunnels predicted with a CFD code will be presented. The solution domain represents the city area located between two tunnel outlets – tunnel Strahov and tunnel Mrazovka in Prague. The vicinity of both tunnels is a heavily built up area with tall buildings forming typical street canyons. The CFD modelling predicts the situation after the tunnel Mrazovka will be finished and traffic will increase considerably between both tunnels. Namely, an interest was given to the prediction of dispersion of emissions leaving both tunnel and the area touched by the traffic. For the CFD predictions, a method previously developed for moving vehicles was used. The method uses combination of Eulerian and Lagrangian approaches to moving objects and is capable of modeling different speeds and traffic rates of cars as well as traffic-induced turbulence. Influence of several meteorological parameters was studied, namely wind speed and direction and traffic parameters, like traffic rates and speed of cars. The method separates contributions from different sources to the total concentration field, namely from background, tunnel outlet and roadway. Results are presented in the form of horizontal and vertical concentration fields of NO_x.     

Ozone Episode in the Milan Metropolitan Area A Comparative Evaluation of UAM-V and CALGRID Models

Data from an ozone episode (2–5 June, 1998) in the Milan metropolitan area were used for an application of two photochemical grid models: UAM-V and CALGRID. To assure a fair comparison, the models were run on the same domain and grid size, with same source emission inputs, CALMET diagnostic meteorology, and initial and boundary conditions taken from air quality data and literature values. Hourly emissions were derived from the AutoOil-II programme inventory except for on-road mobile source emissions; a new traffic emission inventory, based on both COPERT II methodology and road classification has been developed. NO_x and O₃ concentration results were compared to local network monitoring data. Results indicate that both models predict the highest ozone values along the north-east direction and are able to reproduce the ozone daytime trend though differences can be found between the two models on ozone spatial distribution. Average normalised bias for both models is about 50%, peak daily ozone concentrations are underestimated, with simulated peak shapes broader than the observed ones and a temporal shift between the two models. Night-time concentration levels of pollutants were not successfully reproduced due to an incorrect parameterisation of vertical turbulence calling for further work.     

Intercomparison of Numerical Urban Dispersion Models – Part I: Street Canyon and Single Building Configurations

Microscale Computational Fluid Dynamics (CFD) models havebecome an efficient and common simulation tool forassessment and prediction of air quality in urban areas.The proper validation of such a model is a crucialprerequisite for its practical application. Within theframework of the European research network TRAPOS a workinggroup on computational fluid dynamics modelling wasestablished and model intercomparison exercises werelaunched. Different Computational Fluid Dynamics Codes wereapplied for simulating the wind flow and pollutantconcentration patterns in several test cases. The aim ofthe present model intercomparison is (1) to assess andallocate the source of differences that appear whendifferent CFD codes using the same turbulence model areapplied to well defined test cases and (2) to improve theknowledge base for model development and application.Throughout the series of model applications coveringmanifold urban configurations, the overall agreementbetween the various models and experimental data is fair.In spite of quantitative differences between the variousnumerical results, the models are capable of reproducingthe flow patterns and dispersion characteristics observedin urban areas but they show significant differences forthe turbulent kinetic energy field that controls thedispersion of pollutants.     

An Evaluation of Daumod Model in Estimating Urban Background Concentrations

This article presents an evaluation of the performance of the urban atmospheric dispersion model (DAUMOD) in estimating nitrogen oxides (NO_x) background concentrations in Copenhagen. Estimations of hourly average (averaged over a year), mean daily and mean monthly concentrations of NO_x are compared with observed values for two years of data. The model slightly underestimates low hourly average values and overestimates high values. The cumulative frequency distribution of mean daily concentration obtained from model estimations is in good agreement with the obtained from observed data. We performed a statistical analysis to determine the agreement between estimated and observed concentration values. The results show that 95.8% of hourly average estimations, 86.8% of mean daily and 100% of monthly average concentrations are within a factor of two of the observed values. The normalised mean square error of predictions is +0.13 for hourly average estimations, +0.22 for mean daily values and +0.02 for monthly mean concentrations. The fractional bias values are: –0.049 for hourly mean estimations, –0.047 for mean daily values and –0.053 for monthly average estimations. The values of the statistical parameters allow us to consider that though estimations are lightly larger than the observed values, the model performance is acceptable.     

Measurement of Traffic Related Toxic Air Pollutants in an Urban Atmosphere

Nose-level measurements of air toxics were made along a busy urban street in Ottawa, Canada for 2 hr periods during morning, noon, and afternoon rush hours in the winter and summer of 2000. Measurements were also made in a commuter car and a transit bus during morning and afternoon commutes in 2000. The main objectives of the study were to establish a database, to determine temporal and seasonal variations and to determine the contribution of motor vehicle traffic to the measured toxic substance concentrations. Ottawa is an appropriate choice of location for the measurement of motor vehicle related toxic and reactive compounds, as it has virtually no industrial sources that could be contributing to the ambient loadings. Samples were collected for a total of 165 volatile organic compounds and 25 carbonyl compounds. Sampling and analytical methodologyare discussed and results are presented. Toluene, ethylene andformaldehyde were the most abundant pollutants in Ottawa during both winter and summer. Total non-methane hydrocarbon concentrationwas measured as 100 g m^-3 at nose-level measurements in Ottawa.     

ICAROS: An Integrated Computational Environment for the Assimilation of Environmental Data and Models for Urban and Regional Air Quality

Integrated environmental management in urban areas is nowadaysconsidered a sine qua non objective of Community and nationalenvironmental and development policies. A large amount ofscientific information on the state of the environment is nowavailable from a large pool of data sources. This work presentsan innovative method for integration of these data sources andeffective coupling of environmental information with appropriatemodels and decision-support tools. State-of-the-art Earthobservation techniques, ground-based air quality measurements,atmospheric transport and chemical modelling, and multi-criteriadecision-aid systems are used in an integrated information fusionenvironment in support of environmental and health impactassessment and decision-making at the urban and regional scales. Results of the pilot application of the method in the area ofLombardy in Northern Italy demonstrate the validity andusefulness of this novel approach.     

Integrated Assessment of Air Pollution Abatement Strategies in Urban Areas: Application to the Greater Athens Area

This paper presents an integrated system for the assessmentof technical and non-technical measures that are putforward in order to reduce air pollution levels in urbanareas. In contrast to the majority of the currentlyemployed assessment tools, this system allows for theevaluation of any proposed air pollution control measure interms of its combined impact on air quality and socialwelfare, by correlating the environmental and economicaspects of alternative air pollution abatement solutions.Based on the multi-pollutant, multi-effect concept, thesystem presented aims in providing policy-makers with areliable tool for the objective assessment of the mostcost-effective packages of measures, the latter beingallocated according to the particular features and needs ofthe areas examined.     

The Spatial and Temporal Variation of Measured Urban PM10 and PM2.5 in the Helsinki Metropolitan Area

We have studied particulate matter (PM) concentrations,PM₁₀ and PM_2.5, measured in an urban air qualitymonitoring network in the Helsinki Metropolitan Area during1997–1999. The data includes PM₁₀ concentrationsmeasured at five locations (two urban traffic, one suburbantraffic, one urban background and one regional backgroundsite) and PM_2.5 concentrations measured at twolocations (urban traffic and urban background sites). Theconcentrations of PM₁₀ show a clear diurnal variation,as well as a spatial variation within the area. Bycontrast, both the spatial and temporal variation of thePM_2.5 concentrations was moderate. We have analysedthe evolution of urban PM concentrations in terms of therelevant meteorological parameters in the course of oneselected peak pollution episode during 21–31 March, 1998.The meteorological variables considered included wind speedand direction, ambient temperature, precipitation, relativehumidity, atmospheric pressure at the ground level,atmospheric stability and mixing height. The elevated PMconcentrations during the 1998 March episode were clearlyrelated to conditions of high atmospheric pressure,relatively low ambient temperatures and low wind speeds inpredominantly stable atmospheric conditions. The resultsprovide indirect evidence indicating that the PM₁₀concentrations originate mainly from local vehiculartraffic (direct emissions and resuspension), while thePM_2.5 concentrations are mostly of regionally andlong-range transported origin.     

Results from Three Field Tracer Experiments on the Neighbourhood Scale in the City of Birmingham UK

The physical processes governing flow and pollutantdispersion at the neighbourhood scale, a spatial scaleintermediate between the street scale and the city scale, is notwell understood. Furthermore, it is not clear whether a traditional approach using averaged characteristics such as theaerodynamic roughness length is sufficient to predict the concentration field at this scale. To investigate pollutant dispersion in a real urban area, three field experiments were designed within the UK-URGENT programme sponsored by NERC. Theexperiments were performed in the City of Birmingham using a finite duration release of inert, non-toxic and non-depositingtracers, vis. perfluoromethylcyclohexane (PMCH) and perfluoromethylcyclopentane (PMCP). Measurements were taken using air bag samplers placedin an arc at 3.5 km (first experiment) and 1 km (second andthird experiments) from the source; some trap samplers wereplaced outside the main arc in the outskirts of the city. Measurements were analysed in the laboratory using anovel gas-chromatography technique. Data so obtained werecompared with predictions from a simple steady-state modeland a time-dependent model. The concentration-time serieswere very asymmetrical with a sharp rise, a plateau followedby a relatively slow decrease and finally a long-livedplateau above (or possibly very slow decrease to) thebackground level.     

Integrated Assessment of Abatement Strategies to Improve Air Quality in Urban Environments, the USIAM Model

Planning effective strategies to combat air pollution in amajor city such as London requires integration ofinformation on atmospheric concentrations and where theyexceed prescribed air quality standards, detailed data onemissions and potential measures to reduce them includingcosts, and a good understanding of the relativecontributions of different emission sources to pollutantconcentrations plus the remaining background. The UrbanScale Integrated Assessment Model (USIAM) is designed as atool to integrate such information, and to explore andassess a variety of potential strategies for improving airquality. It is based on the same principles as theAbatement Strategies Assessment Model (ASAM) that has beenused in the UN Economic Commission for Europe. To startwith the USIAM model is being developed with respect to theparticulate PM₁₀ only, and in particular the primaryparticulate contribution. The secondary particulate istreated as part of the background superimposed on theprimary particulate concentrations; this may need to betreated more specifically at a later stage, particularlywith respect to nitrate formation over the city. The USIAMmodel therefore sets out to examine a selection of severeepisode conditions as well as long-term annual averageconcentrations, and aims to find strategies that aresuccessful in eliminating exceedance of the prescribedtarget concentrations. By ranking different options forabatement of emissions, for example in terms of cost orease of implementation, the USIAM model can also select andprioritise different potential strategies.     

Influence of Inversion Layers on the Distribution of Air Pollutants in Urban Areas

The air quality in urban areas is on the one hand determined by the intensity of emissions. On the other hand atmospheric dispersion and chemical transformation conditions as well as topographic location have great influence on the ambient air concentrations. Within, this study the correlation between pollutant concentrations and the dynamics of atmospheric barrier and mixing layers has been experimentally investigated by tethered balloon soundings.The most important barrier layer is the surface inversion. During clear sky it develops in the late afternoon and is dissolved by warm air from the heated ground in the morning. Emitted pollutants are kept beneath this inversion. But, at the same time, the component ozone is depleted below and stored above the layer within the so called `ozone reservoir layer'. During night elevated mountain sites are decoupled from the ground conditions and stay within this reservoir without a remarkable nocturnal decrease of ozone concentration. The regularly observed ground level ozone increase in the morning hours is firstly caused by down mixing from the reservoir. The conditions and dynamics are illustratively depicted by vertical profiles of the different components and diagrams of temperature and concentration isopleths over the height and the experiment time lasting over five days.     

The Relative Influences of Primary and Secondary Particulates to Urban Air Quality in the United Kingdom

This study uses a combination of data from U.K. monitoringstations and from modelling undertaken with the U.K.Meteorological Office's NAME Model to investigate therelative influences of primary and secondary particulateson total PM₁₀ levels at sites in the United Kingdom. Co-located PM₁₀ and sulphate aerosol measurementsindicate that sulphate has a disproportionately largeinfluence on the variation of PM₁₀ levels incomparison to its contribution to their total mass.Comparisons of measured PM₁₀ at urban centre, roadsideand rural sites suggest that local primary sources havevery little influence on daily mean levels. NAME has beenused to model both primary particles and sulphate aerosolfrom sources across the whole of Europe. The discrepanciesbetween modelled and observed PM₁₀ suggest that coarseparticles, such as windblown dust and resuspended roaddust,may comprise a very large, if not dominant, proportion ofobserved PM₁₀ levels. The apparently minor role ofprimary particles (especially locally-sourced ones) raisesa number of issues regarding the suitability of current U.K.and European legislation to addressing the particle problem.     

Urban Land-Use Influences on Transport of Heavy Metals to Lakes and Concentrations in Fish

Water, Air, &; Soil Pollution: Focus - To investigate the urban land-useinfluences on transport of heavy metals to lakesand metal concentrations in fish liver (perch andcrucian carp), ten lakes...     

中国大气环境质量现状及趋势分析

近年来我国经济的快速发展在引起能源消费急剧增长的同时带来了严重的环境污染问题.回顾近年来我国大气环境质量的基本状况,综合分析造成我国大气污染的主要原因,对造成我国大气污染的主要污染源火电行业的污染现状做了具体阐述,并在此基础上预测大气环境质量的变化趋势.