Guido Cosemans

Dynamic modelling of transient emissions and concentrations from traffic in street canyons

In the EU 5th framework project DECADE (2001–2003), a new methodology has been developed to calculate in detail the engine power required to drive a given vehicle over any particular route. It includes the rapidly changing (transient) demands placed on the engine, an area that has proved an obstacle to accurate simulations in the past. Together with the associated speed profiles, the actual power demands allow a detailed calculation of emissions and ambient air concentrations in street canyons. This makes the methodology a valuable tool for detailed assessments of the ambient air quality impact of e.g., street design (traffic lights, road bumps, busy crossings), driving patterns, driving behaviour and fleet composition.

Simulating Building Downwash of Heavy Metals by Using Virtual Sources: Methodology and Results

There is a discrepancy in data quality between the highly detailed concentration measurements in the surroundings of industrial plants emitting heavy metals and the registered emission data at these sites. When simulating the concentration fields in the direct vicinity of the emitting plants by using the bi-gaussian model IFDM and the reported emissions, the simulated concentrations were much lower than the measured concentrations. Originally, this was thought to be due to diffuse, wind-fugitive emissions not reported in the official inventories. Therefore, inverse modeling was performed to get the emission data and wind dependency of these emissions. It was expected that the emissions coming out of the inverse modeling would follow a power law of the wind speed except for very low and very high wind speeds. In the latter case, a constant emission was expected, while in the former case, no emissions were expected to be found. However, this lower threshold did not seem to exist in the modeled emissions. Furthermore, these emissions seemed to have their source in spots not used for storage of heavy metals such as parking lots. Detailed analysis of these results showed that another effect, known as building downwash, is responsible for this behavior. Thereafter, it was shown that it is possible for a bi-gaussian model that lacks a building downwash module, to simulate correct concentration levels by putting in virtual sources just behind the buildings causing the building downwash phenomenon. By using half of the available concentration data for the inverse modeling and half for the validation, it was shown that this technique can be used to produce detailed and validated concentration maps of the surroundings of the industrial site. Finally, it was shown that in this case study building downwash has an important effect on local concentrations and that a better representation of building downwash is needed in bi-gaussian models to describe the complex dispersion patterns in the wake of industrial sites.

Reverse modelling for the determination of fugitive sources of PM10

Time-series of half-hourly PM10 concentrations and meteorological data measured near industrial sites where dusty materials are processed can be used to estimate PM10 source strengths for these activities using reverse modelling. Reverse modelling starts with building an over-determined system of linear equations: Observed_Cmj = Computed_Cmj(known sources)+ Σ i=1, NComputed_Cmj(Qi) where the N values of Qi are determined by least squares regression. The paper focuses on regression solutions tainted by noise fitting that are physically meaningless, on rules to reduce the risk for noise fitting, and on how to use cumulative frequency distributions, time series for different averaging times and pollutant roses to obtain a physically sound solution.

Assessing Uncontrolled Emissions Near a Lead Works

The study revealed the impact of the fugitive emissions at the lead works. The existing monitoring network can not be replaced by modelling only. Some monitoring sites will be needed to assess the evolution in time and space of the diffuse emissions of airborne lead in the vicinity of the lead works.

Presentation and Validation of a New Building Downwash Model

Olesen et al. (Bound Layer Meteorol 131(1):73–83, 2009) have shown that current building downwash parameterizations, which are essential in the vicinity of build up areas, perform poorly at very short distances. Therefore, a new building downwash model has been developed based on the Thompson-wind tunnel dataset. The model consists of the Gaussian transport and diffusion equation, in which the variables xR (distance source-receptor) and Hs (stack height) have been replaced with functions that define a receptor dependent virtual origin. The virtual source functions account for the impact of building downwash (1) by changing the height of the plume to account for the vertical displacement of the plume and the extra turbulence around the building, (2) by using an upwind displacement of the plume origin to simulate the impact of the wind-upward displacement of the plume and (3) by accounting for the entrainment of clean air into the plume by increasing the distance between the virtual source and the receptor point. The model results are compared to the several measurement time series in Flanders, Belgium, at industrial locations where building downwash plays an important role. We have shown an increased modeling ability in all cases: for instance, biases ranging from −4 to −33 ng/m3 (−46 to −77 %) improve to values ranging from 1.3 to −7.5 ng/m3 (−29 to +14 %) and R2 values improve dramatically (up to 0.83 from 0.65 in cases with a strong building downwash effect).

A New Approach to Building Downwash Modelling

Thompson (1991, 1993) measured ground-level concentrations profiles (GLCPs) for 330 combinations of stack height, building type and distance between stack and building. Cosemans and Lefebvre (Dispersion parameters in a wind tunnel and in the field: analysing Thompson’s 1991 wind tunnel data for isolated stacks with IFDM, and its application to building downwash. In: Preprints of the 13th international conference on harmonisation within atmospheric dispersion for regulatory purposes, Paris, pp 304–308, 2010) derived dispersion parameters needed by the bi-Gaussian transport and dispersion equation to reproduce the GLCPs measured for nine isolated stacks. Now, we present a formula to reproduce the 321 other GLCPs, measured. Basically, the plume affected by building downwash is replaced by a set of plumes that have a modified lognormal distribution of height and pollutant mass. The different phenomena that influence plume growth subject to building downwash are modelled by virtual origin functions. Incorporating this in a regulatory plume model could strongly increase the capacity of such model to predict the pollutant concentrations in the vicinity of buildings neighbouring emission sources

Comparing the impact of a road tunnel vs. a road viaduct by means of an integrated exposure assessment

Using the MOBILEE methodology, we performed a detailed air quality assessment for three scenarios for the ring road around Antwerp, a major city in Belgium, using PM10 and NOx emission inventories for 2003 (reference) and 2015 (projected future situation), followed by an assessment of the exposure of the population living in the vicinity of the planned constructions. PM10 turned out to be the dominant parameter in exposure assessment. Compared with the impact of the viaduct, a tunnel with an exhaust at a height of 5 or 30 m shows respectively a 40% increase or a 5% decrease in total exposure.

Environmental Impact Assessment by Means of Two Different (National) Models: IFDM in Belgium and Pluimplus in the Netherlands

Unless the use of atmospheric dispersion models for permit granting is strictly regulated, consultants will use a wide variety of those models. Authorities, as well as industry might thus wonder how the output of the different models can be compared. In order to investigate this problem, the following approach has been used:

EMIAD, For Evaluating Alternative SO2/NOxEmission Reductions In The Antwerp RegionDuring Air Pollution Episodes

EMIAD is a computer program allowing for a fast and easy investigation of the immission and meteorological quantities measured by the ambient air quality monitoring network in the Antwerp (Belgium) region. Three atmospheric transport and dispersion models (puff, segmented plume, steady state plume) allow to calculate the air pollution levels over the Antwerp region in a greater spatial detail than can be obtained from measurements. Modelling also allows for the determination of the contribution of different source categories to the global pollution, so that, during episodes of high pollution, the most effective emission reduction measures can be imposed. EMIAD is intended to be used daily by the operators of the ambient air quality monitoring network. Contacts with the operators during the early stages of the program conception and implementation lead to a system satisfying the needs of modellers, operators and air quality managers.