Alain Clappier

Effect of Sea Breeze on Air Pollution in the Greater Athens Area. Part I: Numerical Simulations and Field Observations

Abstract Numerical simulations compared with field measurements are used to explain the effect of sea breezes on photochemical smog episodes in Athens during the Mediterranean Campaign of Photochemical Tracers on 12–14 September 1994. The numerical simulations, performed using a nonhydrostatic vorticity mesoscale model coupled to the Lurmann–Carter–Coyner photochemical module, are compared with ground-based lidar and aircraft measurements. The current analysis shows that the three selected days include the two main summertime flow patterns characteristic of the Athens peninsula, each of which lead to significantly different pollution amounts. On 12 and 13 September, a strong, northerly synoptic wind reduces the inland penetration of the sea breeze so that ozone concentrations within the greater Athens area remained low. In contrast, the weaker synoptic forcing on 14 September allowed the development of sea breezes over the whole peninsula and high ozone concentrations were found north and east of the city...

Effect of Sea Breeze on Air Pollution in the Greater Athens Area. Part II: Analysis of Different Emission Scenarios

Abstract The Mediterranean Campaign of Photochemical Tracers–Transport and Chemical Evolution that took place in the greater Athens area from 20 August to 20 September 1994 has confirmed the role of sea-breeze circulation in photochemical smog episodes that had been suggested already by a number of experiments and numerical studies. The meteorological and photochemical modeling of this campaign were discussed in Part I. Part II focuses on the study of the 14 September photochemical smog event associated with a sea-breeze circulation. The objective of the study is to identify and to understand better the nonlinear processes that produce high ozone concentrations. In particular, the effect of land and sea breezes is investigated by isolating the effect of nighttime and daytime emissions on ozone concentrations. The same principle then is used to isolate the effect on ozone concentrations of the two main sources of emissions in the greater Athens area: the industrial area around Elefsis and the Athens urban ...

Validation of an Urban Surface Exchange Parameterization for Mesoscale Models— 1D Case in a Street Canyon

Abstract A detailed urban parameterization scheme is used in and above a street canyon. To validate this new scheme, the model is run offline on a vertical column (one-dimensional simulations), using measurements from a 30-m-high tower for upper boundary conditions. Measurements were obtained during the intensive observation period of the Basel Urban Boundary Layer Experiment (BUBBLE). Vertical profiles of meteorological variables are simulated in the street canyon. The validation of the parameterization is made with measurements from the tower in the street canyon and directly above roof height. The results show that the urban parameterization scheme is able to catch most of the typical processes that are induced by an urban surface near the ground. The fit to measured profiles is improved in comparison with a model using the traditional approach for urban parameterization (variation of z0 to take into account the presence of a city).

A new approach to design source-receptor relationships for air quality modelling

Air quality models are often used to simulate how emission scenarios influence the concentration of primary as well as secondary pollutants in the atmosphere. In some cases, it is necessary to replace these air quality models with source-receptor relationships, to mimic in a faster way the link between emissions and concentrations. Source-receptor relationships are therefore also used in Integrated Assessment Models, when scenario responses need to be known in very short time. The objective of this work is to present a novel approach to design a source-receptor relationship for air quality modeling. Overall the proposed approach is shown to significantly reduce the number of simulations required for the training step and to bring flexibility in terms of emission source definition. A regional domain application is also presented, to test the performances of the proposed approach. A novel approach to design source-receptor relationships for air quality is proposed.It needs a small number of simulations to be implemented.It also brings flexibility in terms of application in Integrated Assessment Models.A case study on a regional domain is presented.

Exploring trade-offs between air pollutants through an Integrated Assessment Model.

When designing air pollution reduction policies, regional decision makers face a limited budget to choose the most efficient measures which will have impacts on several pollutants in different ways. RIAT+ is a regional integrated assessment tool that supports the policy maker in this selection of the optimal emission reduction technologies, to improve air quality at minimum costs. In this paper, this tool is formalized and applied to the specific case of a French region (Alsace), to illustrate how focusing on one single pollutant may exacerbate problems related to other pollutants, on top of conflicts related to budget allocation. In our case, results are shown for possible trade-offs between NO2 and O3 control policies. The paper suggests an approach to prioritize policy maker objectives when planning air pollution policies at regional scale.

On the design and assessment of regional air quality plans: The SHERPA approach

Although significant progress has been made in Europe regarding air quality, problems still remain acute for some pollutants, notably NO2 and Particulate Matter (fine and coarse fractions) in specific regions/cities. One issue regarding air quality management is governance, i.e. the selection of appropriate and cost effective strategies over the area controlled by policy makers. In this work we present a new approach to integrated assessment modelling focusing on regional and urban aspects. One of the key added values is spatial flexibility, namely the possibility to assess the contributions from different regions to air quality at any given location. The SHERPA tool is shown to be particularly helpful in addressing the following tasks: source allocation, governance and the assessment of scenario impacts. Application of the methodology over the London area for yearly averaged PM2.5 concentrations demonstrates these features. Given that it is possible to use the SHERPA interface with other types of data, SHERPA can also be seen as a means to foster harmonization in the field of model evaluation.

On the Coherence in the Boundary Layer: Development of a Canopy Interface Model

A 1D Canopy Interface Model (CIM) is developed to act as an interface between a meso-scale and a micro-scale atmospheric model and to better resolve the surface turbulent fluxes in the urban canopy layer. A new discretisation is proposed to solve the TKE equation finding solutions that remain fully concordant with the surface layer theories developed for neutral flows over flat surfaces. A correction is added in the buoyancy term of the TKE equation to improve consistency with the Monin-Obukhov surface layer theory. Obstacles of varying heights and dimensions are taken into account by introducing specific terms in the equations and by modifying the mixing length formulation in the canopy layer. The results produced by CIM are then compared with wind and TKE profiles simulated with a LES experiment and results obtained during the BUBBLE meteorological intensive observation campaign. It is shown that the CIM computations are in good agreement with the results simulated by the LES as well as the measurements from BUBBLE. The applicability of the correction term in an urban canopy layer and to further validate CIM in multiple stability conditions and various urban configurations is discussed.

A novel approach to screen and compare emission inventories.

A methodology is proposed to support the evaluation and comparison of different types of emission inventories. The strengths and weaknesses of the methodology are presented and discussed based on an example. The approach results in a “diamond” diagram useful to flag out anomalous behaviors in the emission inventories and to get insight in possible explanations. In particular, the “diamond” diagram is shown to provide meaningful information in terms of: discrepancies between the total emissions reported by macro-sector and pollutant, contribution of each macro-sector to the total amount of emissions released by pollutant, and the identification and quantification of the different factors causing the discrepancies between total emissions. A practical example in Barcelona is used for testing and to provide relevant information for the analyzed emission datasets. The tests show the capability of the proposed methodology to flag inconsistencies in the existing inventories. The proposed methodology system may be useful for regional and urban inventory developers as an initial evaluation of the consistency of their inventories.

A benchmarking tool to screen and compare bottom-up and top-down atmospheric emission inventories

This paper describes the Δ-Emis tool for emission inventories, recently developed in the framework of Forum for Air Quality Modelling in Europe (FAIRMODE). The Δ-Emis tool consists of a set of indicators and diagrams that support the comparison of bottom-up and top-down emission inventories. Four different comparison methods are proposed: (1) pollutant emission comparisons across sectors (bar plot), (2) quantification of the differences between inventories allocated in terms of activity data and emission factors (diamond diagram), (3) emission per capita comparisons (per-capita diagram) and (4) comparison of pollutant ratios (pollutant ratio diagram). The methodology has been tested for an urban emission inventory in Barcelona, and results show the capability of the system to flag inconsistencies in the existing inventories. The strengths and limitations of the tool are presented. The proposed methodology may be useful for regional and urban inventory developers as an initial evaluation of the consistency of their inventories.

Modelling of air pollution in the area of Algiers City, Algeria

Algiers is the political and economic capital of Algeria. The city drains a large part of the activities of the country with intense road traffic. This road traffic is the main source of air pollution, followed by industry and waste combustion. An application of the new road traffic emission model, called EMISENS, is performed to build road traffic emission inventories for the Algiers region. These emission inventories are then used as input to the MM5/CHIMERE system to estimate air pollution. The objective of this study is to propose a methodology to improve the quality of emission inventories, and to validate results. First, by studying the correlation between observed measurements and data concerning cadastre of primary pollutants emitted mainly by road traffic, then by comparing the pollutants concentrations from observed measures with the simulated concentrations with the model of chemistry-transport CHIMERE.