Analysis of the St. Petersburg Traffic Data using the OSPM Model

Since October 1998 two DOAS instruments were installed at the level of the first floor and at the top of a building located in St. Petersburg at Pestelya Street. The collected datacovers the time period of December 1998–March 2001, and include concentrations of benzene, toluene, NO and NO₂, ozone and SO₂. There is also an additional information about the traffic intensity and meteorological conditions. The results of the analysis of this data set, using the OSPM model, are presented here with the goal to understand the features of the air pollution dispersion in this street canyon and to analyse the information about the emission factors of the vehicles. In particular, the model results are used for the solution of the inverse problem of reconstructing the emission factors from measured concentrations. The results obtained indicate that most of the concentrations are well inside the Russian standards with the only exception of NO₂ (mean and 98-th percentile are equal to 57.8 and 119.2 g m^-3 for the street level). The same values for benzene are 18.5 and 62.6, respectively. Emission estimates show that there is a possibility that the NO_x and benzene basic emission factors recommended by the Russian national guidelines could result in overestimating the traffic emissions. These considerations are supplemented with the model sensitivity tests carried out in connection with the problem of predictability of NO₂ concentrations in the street canyon. Tests indicate that NO₂ concentrations are not very sensitive to NO_x emissions because of the usually low urban background ozone levels.     

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.     

Characteristics of NO2 Pollution in the City of Gothenburg, South-West Sweden—Relation to NO x and O3 Levels, Photochemistry and Monitoring Location

Concentrations of NO₂, NO, and O₃ from a rooftop monitoring station in Gothenburg, Sweden (2002–2006) were analysed to characterise NO₂ pollution. [NO₂] was shown to correlate strongly and non-linearly with [NO _x ] (NO _x ?=?NO?+?NO₂), in line with observations in other cities. The [NO₂] to [NO _x ] fraction fell initially with increasing [NO _x ]. At [NO _x ] levels >200 ppb, the decline in [NO₂]/[NO _x ] with increasing [NO _x ] levelled out and [NO₂]/[NO _x ] converged towards approximately 0.15–0.16, independent of [NO _x ]. Data from a traffic route site showed the same pattern. This value of [NO₂]/[NO _x ] at high [NO _x ] can be interpreted as the NO₂ fraction of the NO _x emissions from vehicle exhaust. Situations with high NO _x pollution and minimum [NO₂]/[NO _x ] were always associated with [O₃] close to zero. Plotting [Ox] (Ox?=?NO₂?+?O₃) vs. [NO _x ] provided a strong linear correlation for situations dominated by local pollution ([NO]/[NO₂]>1). The slope of the regression, a measure of the primary NO₂ fraction in NO _x emissions, was 0.13 during the day and 0.14 during the night. With stronger winds, the rooftop monitoring station became more similar, in terms of NO₂ pollution, to a city street site and a traffic route site, although [NO₂] was almost always higher at the street/traffic route locations. The EU standard for the annual average of [NO₂] (40 μg m^?3) was exceeded, while the hourly standard (200 μg m^?3, not to be exceeded more than 18 times per year by 2010) was not exceeded at any of the sites.     

Three-Dimensional Numerical Simulation of Air Pollutant Dispersion in Street Canyons

The PHOENICS Computational Fluid Dynamics (CFD) software package has been used with a standard k- turbulence model to simulate the three-dimensional dispersion of air pollutants in an urban street canyon. In all cases, a vortex was formed within the street canyon, characterized by updrafts near the upwind buildings and down-drafts near the downwind buildings. Contours of pollutant concentrations over a transverse vertical plane at mid-canyon show pollutants circulating within the vortex, with higher concentrations at the leeward face than at the windward faces, and higher concentrations above downwind buildings than above upwind buildings. Longitudinal distributions of pollutant concentrations at leeward and windward faces are characterized by higher concentrations at mid-block and lower concentrations at the ends. These results agree qualitatively with previous wind tunnel findings such as those of Hoydysh and Dabberdt (1988) and Wedding et al. (1977). The results also suggest that the k- turbulence model is satisfactory for simulating the effect of turbulence on dispersion of pollutants in street canyons     

Measurements of Traffic-Induced Turbulence within a Street Canyon during the Nantes'99 Experiment

A full scale experiment has been performed in a streetcanyon, the Rue de Strasbourg in Nantes (France). Thiscampaign, the Nantes'99 experiment, provided a detaileddata base documenting, amongst others, the production ofturbulent kinetic energy (TKE) by vehicles within thestreet. Airflow and CO concentration measurements have beenanalysed during days with low wind perpendicular to thestreet axis, i.e. for conditions expected to greatly favourthe enhancement of the turbulence produced by traffic onflow and dispersion within the street canyon. It is shownthat traffic is associated with an increase in turbulentkinetic energy at the lowest levels of the street,especially at the leeward side of the street. It issuggested that turbulent kinetic energy increases with thenumber of vehicles up to a threshold value and thendecreases when vehicles form a `block' shape that limitsthe additional production of turbulence. Moreover, it issuggested that traffic-produced turbulence affectspollutant dispersion reducing CO concentration at the lowerlevels of the leeward side of the street from a thresholdvalue of TKE equal to about 0.15 m² s^-2. On the other hand, high traffic density generates less turbulencewhich in turn leads to a lower pollutant dispersion.     

Atmospheric Levels of Nitrogen Oxides at a Greek Oil Refinery Compared with the Urban Measurements in Athens

Oil refining is among the industrial activities that emit considerable amounts of air pollutants into the atmosphere. Nitrogen oxides are important air pollutants that are emitted by oil refineries as products of combustion processes. The ambient air concentrations of nitrogen oxide (NO) and nitrogen dioxide (NO₂) were monitored continuously at a site close to an oil refinery, near the city of Corinth in Greece, during autumn 1997 together with the main meteorological parameters. The contribution of the oil refinery to the measured atmospheric levels of nitrogen oxides was estimated. The ambient air concentration of nitrogen oxides in the area surrounding the oil refinery were generally lower than the ambient air concentrations in the urban area of Athens in Greece, and the NO₂ levels were always below the existing air quality standards. The influence of the refinery emitted NO_x in the photochemical production of ozone seems to be more important in terms of human and vegetation exposure given the high ozone backgrounds measured in the area.     

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.     

Characteristics of air pollution in Beijing during sand-dust storm periods

In the Beijing area, March and April have the highest frequency of sand-dust weather. Floating dust, blowing sand, and dust storms, primarily from Mongolia, account for 71%, 20%, and 9% of sand-dust weather, respectively. Ambient air monitoring and analysis of recent meteorological data from Beijing sand-dust storm periods revealed that PM₁₀ mass concentrations during dust storm events remained at 1500 μg m⁻³, which is five to ten times higher than during non-dust storm periods, for fourteen hours on both April 6 and 25, 2000. During the same period, the concentrations in urban areas were comparable to those in suburban areas, while the concentrations of gaseous pollutants, such as SO₂, NO _x , NO₂, and O₃, remained at low levels, owing to strong winds. Furthermore, during sand-dust storm periods, aerosols were created that consisted not only of many coarse particles, but also of a large quantity of fine particles. The PM_2.5 concentration was approximately 230 μg m⁻³, accounting for 28% of the total PM₁₀ mass concentration. Crustal elements accounted for 60–70% of the chemical composition of PM_2.5, and sulfate and nitrate for much less, unlike the chemical composition of PM_2.5 on pollution days, which was primarily composed of sulfates, nitrates, and organic material. Although the very large particle specific surface area provided by dust storms would normally be conducive to heterogeneous reactions, the conversion rate from SO₂ to SO₄ ²⁻ was very low, because the relative humidity, less than 30%, was not high enough.     

A New Concept for Air Quality Modelling in Street Canyons

We present an analytical model that predicts concentrations in street canyons assuming a uniform distribution within a street, dimensioned by its length and width and the height of the surrounding built-up area. Using the Prandtl-Taylor hypothesis, the concentration in the street is determined from a mass flux balance between a horizontal advective flux, a turbulent diffusive vertical flux and a continuous road transport emission source. The model does not necessarily assume re-circulation of the flow in the street canyon, but rather considers the turbulent intermittency in the shear layer shed from the upwind roof level as the driving force. This concept is in agreement with recent measurements and observations. The model has been applied to compute benzene concentrations based on hourly emissions obtained for 1963 streets and road segments in the City of Antwerp, Belgium. The results are compared with diffusive sampler measurements carried out at 101 locations in several streets of Antwerp, during 4 periods of 5 days in 1998. When averaged over periods of 5 days, the calculated benzene concentrations show a very good agreement with the results obtained by the diffusive sampler measurements.     

Modelling of Air Quality with CAMx: A Case Study in Switzerland

The three-dimensional Eulerian model CAMx (Comprehensive Air QualityModel with Extensions) was applied for the first time to simulate bothgaseous and particulate photochemical air pollution in Switzerland during July 28–30, 1993. The meteorological input data were prepared using the Systems Applications International Mesoscale Model (SAIMM). The CAMx model results were compared with the measurements carried out at ground level andfrom airborne measuring platforms within the frame of the Swiss POLLUMET research programme. In general, the CAMx performance for gaseous species wasfound to be better than that of the previously used Urban Airshed Model (UAM)and the Variable Grid Urban Airshed Model (UAM-V). The most significant improvement for the gaseous species is in the prediction of HNO₃ concentrations, due to the inclusion of aerosol chemistry. Aerosol species such as NO₃ ^-, NH₄ ⁺, SO₄ ^2-, and secondary organic aerosols were calculated in one particle size range (0.04–2.5 m) and compared with a few measurements available. Although July 29 was reasonably well simulated, overestimated wind speeds by SAIMM for July 30 caused a too fast transport of pollutants. Similarly to measurements, significant spatial correlation of the secondarily formed aerosols with ozone and formaldehyde is found in the afternoon.     

Analysis of the recycling system for aluminum cans,focusing on collection,transportation, and the intermediate processing methods

In this article, the systems for the collection and intermediate processing of used beverage cans (UBCs) are compared and analyzed, focusing on the time taken and the cost of processing, the energy consumption, and the emissions of CO₂, SO _x , and NO _x , during the process. We found that cases where the UBCs were crushed in the discharging process gave better results, and how the UBCs were collected was the most important factor. It was more desirable to treat UBCs in one place than in two places. When the transportation distance was longer, the pressed form of UBCs was more convenient. When the transportation distance was short, the original form, the crushed form, and the shredded form of UBCs were all suitable. That is, the contribution of the transportation process to the evaluation was large when the transport distance was long, and the contribution of the treatment process was large when the transport distance was short.     

Simulations of Atmospheric Dispersion Following a Spillage of Petroleum at Sea

In January 1997 7000 t of refined petrol were spilled into the English Channel following a collision in dense fog off Ostend. The following day reports of petrol odours were recorded throughout central England at distances up to 300 km from the spill site. One possibility is that mass hysteria was induced by media reports of the accident coupled with the publicised wind direction. Indeed, the simulated gas cloud trajectory does not pass over central England if the petrol is assumed to have evaporated over a period of about 3 h. However, a feasible advection path can be reproduced by assuming that the water/atmosphere exchange of vapours occurred on a time scale of 12 h, the extended evaporation being due to the formation of subsurface droplets by wave action. Evidence to support the simulated trajectory has been obtained from the UK National Air Quality Information Archive which contains hourly data for benzene and NO_x concentrations. By regressing the benzene concentration against NO_x which is assumed to be an indicator of traffic density, it is shown that an increase in benzene concentrations on the day following the spillage was consistent with the simulated movement of the vapour cloud.     

A Wind Tunnel Investigation of the Influence of Solar-Induced Wall-Heating on the Flow Regime within a Simulated Urban Street Canyon

A wind tunnel study has been undertaken to assess theinfluence of solar-induced wall heating on the airflowpattern within a street canyon under low-speed windconditions. This flow is normally dominated by large-scalevortical motion, such that the wind moves downwards at thedownstream wall. In the present work the aim has been toexamine whether the buoyancy forces generated at this wallby solar-induced heating are of sufficient strength tooppose the downward inertial forces and, thereby, changethe canyon flow pattern. Such changes will also influencethe dispersion of pollutants within the street. In theexperiments the windward-facing wall of a canyon has beenuniformly heated to simulate the effect of solar radiation.Four different test cases, representing different degreesof buoyancy (defined by a test Froude number, Fr), havebeen examined using a simple, 2-D, square-section canyonmodel in a wind tunnel. For reference purposes, the neutralcase (no wall heating), has also been studied. The approachflow boundary layer conditions have been well defined, withthe wind normal to the main canyon axis, and measurementshave been taken of canyon wall and air temperatures andprofiles of mean velocities and turbulence intensities.Analysis of the results shows clear differences in the flowpatterns. As Fr decreases from the neutral case there arereductions of up to 50% in the magnitudes of the reverseflow velocities near the ground and in the upward motionnear the upstream wall. A marked transition occurs at Fr 1, where the single dominant vortex, existing at higher Fr values, weakens and moves upwards whilst a lower region of relatively stagnant flow appears. This transition hadpreviously been observed in numerical model predictions butat a Fr at least an order of magnitude higher.     

Influence of Traffic Emissions Estimation Variability on Urban Air Quality Modelling

The main objective of this work is to analyse how uncertainties in emission data of nitrogen oxides (NO_x) and volatile organic compounds (VOC), originated from road traffic, influence the model prediction of ozone (O₃) concentration fields. Different methods to estimate emissions were applied and results were compared in order to obtain their variability. Based on these data, different emission scenarios were compiled for each pollutant considering the minimum and the maximum values of the estimated emission range. These scenarios were used as input to the MAR-IV mesoscale modelling system. Simulations have been performed for a summer day in the Northern Region of Portugal. The different approaches to estimate NO_x and VOC traffic emissions show a significant variability of absolute values and of their spatial distribution. Comparison of modelling results obtained from the two scenarios presents a dissimilarity of 37% for ozone concentration fields as a response of the system to a variation in the input emission data of 63% for NO_x and 59% for VOC. Far beyond all difficulties and approximations, the developed methodology to build up an emission data base shows to be consistent and an useful tool in order to turn applicable an air quality model. Nevertheless, the sensitivity of the model to input data should be considered when it is used as a decision support tool.     

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.     

Effects of Duststorms on the Air Pollution in Beijing

The objective of this study was to investigate the air pollutionin Beijing before, during, and after duststorms occur. There aretwo different phenomena of air pollution in Beijing during a duststorm; one being related to the concentration of particulatematter and the second related to gaseous chemical pollutant concentrations. In this study, the concentrations of the chemicalpollutants, such as SO₂, NO_x and CO, were high prior to the occurrence of the duststorms. At the beginning of the two duststorms studied, the air quality related to these chemicalconstituents was improved due to a strong wind blowing away the chemical pollutants, which caused a decrease in the concentrations of SO₂, CO and NO_x. During the duststorm, the concentration of particulate matter, quantified by PM₁₀, wasobserved to increase and the atmospheric visibility decreased.     

Long Term Trends in Concentration of Major Pollutants (SO<Subscript>2</Subscript>, CO,NO, NO<Subscript>2</Subscript>, O<Subscript>3</Subscript> and PM<Subscript>10</Subscript>) in Prague – Czech Republic (Analysis of Data Between 1992 and 2005)

To assess the effect of changes in traffic density and fuels used for heating at the beginning of the 1990s, 1992–2005 monthly averages of PM₁₀, SO₂, NO₂, NO, CO and O₃ from Prague, the Czech capital, were analyzed together with long term trends in emissions of major pollutants, fuel consumption and number of vehicles registered in Prague. The data from all monitoring stations were retrieved from the database of the state automated monitoring system. Correlation coefficients between ambient monthly averaged temperature and all pollutants of concern showed distinct seasonal trends. The results showed that while SO₂ and to some extent also CO concentrations dropped namely in the first half of the analyzed period (1992–1997) as a result decreased fossil fuel consumption for local heating, the behaviour of other pollutant concentrations followed a different pattern. PM₁₀ concentrations decreased during the beginning of the 1990s but showed a sign of increase after 2000. Concentrations of ozone and NO₂ did not reveal any significant change throughout the whole studied period. It can be concluded that during the studied period traditional urban sources of pollution, such as coal and oil combustion, lost their importance but were simultaneously substituted by pollutants from automotive transport (namely PM and NO₂) making the problem of air quality even worse.     

Thermal Effects on the Airflow in a Street Canyon – Nantes'99 Experimental Results and Model Simulations

The thermal effects on the airflow within a street canyon, which are produced by the variation of direct solar heating of the street sides and ground, are examined in this article. The investigation is based on the experimental results of the Nantes'99 campaign and numerical simulations performed with the Computational Fluid Dynamics (CFD) code CHENSI using the standard k- model. The Nantes'99 experimental campaign was performed in a North-to-South oriented central street canyon of Nantes, France. It was observed that a thin thermal layer develops locally within a few centimetres from the heated wall. It is anticipated that, the convective flow close to the windward wall, which was visualised during the experiment, carries air masses from the street level upwards, where normally cleaner air is transported. Consequently, thermal effects may be important for the air quality in the street.Based on the temperature and wind flow measurements, the flow and temperature fields were simulated first in two dimensions with the CFD code CHENSI. It was found that CHENSI overestimates the thermal effects on the canyon airflow showing the main re-circulation simulated in the isothermal case to change into two counter-rotating vortices after the inclusion of the heating of the windward wall. A reason for this overestimation is possibly the temperature wall function implemented for such thin thermal boundary layers in conjunction with the limitations in grid resolution.     

Life cycle assessment of selective non-catalytic reduction (SNCR) of nitrous oxides in a full-scale municipal solid waste incinerator

Selective non-catalytic reduction (SNCR) of nitrous oxides in a full-scale municipal solid waste incinerator was investigated using LCA. The relationship between NO_x-cleaning and ammonia dosage was measured at the plant. Un-reacted ammonia - the ammonia slip - leaving the flue-gas cleaning system adsorbed to fly-ash or in the effluent of the acidic scrubber was quantified from the stoichiometric reaction of NO_x and ammonia assuming no other reaction products was formed. Of the ammonia slip, 37% was associated with the fly-ash and 63% was in the effluent of the acidic scrubber. Based on NO_x-cleaning efficiency, the fate of the ammonia slip as well as the environmental impact from ammonia production, the potential acidification and nutrient enrichment from NO_x-cleaning was calculated as a function of ammonia dosage. Since the exact fate of the ammonia slip could not be measured directly, a number of scenarios were set up ranging from “best case” with no ammonia from the slip ending up in the environment to “worst case” where all the ammonia slip eventually ended up in the environment and contributed to environmental pollution. In the “best case” scenario the highest ammonia dosage was most beneficial demonstrating that the environmental load associated with ammonia production is of minor importance. In contrast, in a “worst case” scenario” NO_x-cleaning using SNCR is not recommendable at all, since the impacts from the ammonia slip exceed the saved impacts from the NO_x removal. Increased dosage of ammonia for removal of NO_x is recommendable as long as less than 10-20% of the ammonia slip to the effluent of the acidic scrubber ends up in the environment and less than 40% of the slip to the fly-ash ends up in the environment. The study suggests that the actual fate of the ammonia slip is crucial, but since the release of the ammonia may take place during transport and at the facilities that treat the wastewater and treat the fly-ash this factor depends strongly on local conditions and may be hard to determine. Thus, LCA-modeling proved useful in assessing the balance between ammonia dosage and NO_x-removal in flue-gas cleaning from waste incineration.     

Dioxin emissions: Possible techniques for maintaining the limit of 0.1 ng TE m−3 (as of 1990/91)

Processes which will achieve up to 100-fold reduction of exhaust gas emissions of dioxin as proposed for the new German Standards are reviewed. A combination of processes which remove fly ash, NO_x, SO_x, HCl and other pollutants will also remove dioxins. Reduction of chlorinated compounds fed to the incinerator is not likely to make any significant difference. Good turbulence with elimination of cold spots in the firebox will ensure initial thermal destruction. Dioxins are synthesized on fly ash particles at temperatures between 200 and 400° C. Rapid temperature reduction across this range by water injection will greatly reduce dioxin levels. Catalytic inhibitors can also be used. Since dioxin is adsorbed on fly ash, efficient scrubbing is essential for high removal efficiency. Sorption on active carbon beds is also being evaluated.