Spatial representativeness of an air quality monitoring station. Application to NO2 in urban areas

International audienceThe present study aims at setting up a geostatistical methodology that could be implemented in an operational context to assess the spatial representativeness of a measurement station. In the proposed definition, a point is considered as belonging to the area of representativeness of a station if its concentration differs from the station measurement by less than a given threshold. Additional criteria related to distance or environmental characteristics may also be introduced. Concentrations are first estimated at each point of the domain applying kriging techniques to passive sampling data obtained from measurement surveys. The standard deviation of the estimation error is then used, making a hypothesis on the error distribution, to select the points, at a fixed risk, where the difference of concentration with respect to the station is below the threshold. The methodology is then applied to NO2 experimental datasets for different French cities

Estimation of the areas of air quality limit value exceedances on national and local scales. A geostatistical approach

International audienceEach year Member States have to report to the European Commission on the exceedances of air quality limit values which occurred on their territory. Quantitative information is required about the areas and population exposed to such exceedances. A probabilistic methodology for defining exceedance zones has been developed, based on preliminary air quality mapping. Atmospheric concentration fields estimated by kriging and the corresponding kriging variance are used to identify areas where the exceedance or non-exceedance can be considered as certain and areas where the situation with respect to the limit value is indeterminate. The methodology is applied on national and urban scales focusing on exceedances of PM10 daily limit value and NO2 annual limit value. Results are discussed from operational perspectives

Evaluation of the chimere model at high resolution over Europe : focus on urban area

International audienc

Evaluation of numerical models used to simulate atmospheric pollution near roadways

International audienceNumerical modelling of traffic-related pollution can be useful to check compliance with regulatory thresholds, compare the atmospheric impact of various traffic scenarios or represent roadside concentrations in air quality maps. Because of operational constraints, local actors usually make use of parametrised models which are easy to implement but require caution and rigour in their application. Since 2007 an Internet information base including data sets, technical information and reference methodologies, has been built up by the French Central Laboratory for Air Quality Monitoring (LCSQA) to help local actors in evaluating their modelling tools. In addition, simulations have been performed for different types of streets to provide examples of model evaluation studies and draw some indications about the application framework of a few commonly used models. The results of those tests are presented and discussed for two street canyons and one semi-open street located in the French city of Nante

Evaluation of numerical models used to simulate atmospheric pollution near roadways

International audienceNumerical modelling of traffic-related pollution can be useful to check compliance with regulatory thresholds, compare the atmospheric impact of various traffic scenarios or represent roadside concentrations in air quality maps. Because of operational constraints, local actors usually make use of parametrised models which are easy to implement but require caution and rigour in their application. Since 2007 an Internet information base including data sets, technical information and reference methodologies, has been built up by the French Central Laboratory for Air Quality Monitoring (LCSQA) to help local actors in evaluating their modelling tools. In addition, simulations have been performed for different types of streets to provide examples of model evaluation studies and draw some indications about the application framework of a few commonly used models. The results of those tests are presented and discussed for two street canyons and one semi-open street located in the French city of Nante

Spatial representativeness of an air quality monitoring station. Application to NO2 in urban areas

International audienceThe present study aims at setting up a geostatistical methodology that could be implemented in an operational context to assess the spatial representativeness of a measurement station. In the proposed definition, a point is considered as belonging to the area of representativeness of a station if its concentration differs from the station measurement by less than a given threshold. Additional criteria related to distance or environmental characteristics may also be introduced. Concentrations are first estimated at each point of the domain applying kriging techniques to passive sampling data obtained from measurement surveys. The standard deviation of the estimation error is then used, making a hypothesis on the error distribution, to select the points, at a fixed risk, where the difference of concentration with respect to the station is below the threshold. The methodology is then applied to NO2 experimental datasets for different French cities

Evaluation of numerical models used to simulate atmospheric pollution near roadways

International audienceNumerical modelling of traffic-related pollution can be useful to check compliance with regulatory thresholds, compare the atmospheric impact of various traffic scenarios or represent roadside concentrations in air quality maps. Because of operational constraints, local actors usually make use of parametrised models which are easy to implement but require caution and rigour in their application. Since 2007 an Internet information base including data sets, technical information and reference methodologies, has been built up by the French Central Laboratory for Air Quality Monitoring (LCSQA) to help local actors in evaluating their modelling tools. In addition, simulations have been performed for different types of streets to provide examples of model evaluation studies and draw some indications about the application framework of a few commonly used models. The results of those tests are presented and discussed for two street canyons and one semi-open street located in the French city of Nante

A necessary distinction between spatial representativeness of an air quality monitoring station and the delimitation of exceedance areas

International audienceThe European legislation on ambient air quality introduces the concepts of spatial representativeness of a monitoring station and spatial extent of an exceedance zone. Spatial representativeness is an essential macro-scale siting criterion which should be evaluated before the setting-up and during the life of a monitoring point. As for the exceedance area, it has to be defined each time an environmental objective is exceeded in an assessment zone. No specific approach is prescribed to delimit such areas. A probabilistic methodology is presented, based on a preliminary kriging estimation of atmospheric concentrations at each point of the domain. It is applied to NO2 pollution on the urban scale. In the proposed approach, a point belongs to the area of representativeness of a station if its concentration differs from the station measurement by less than a given threshold. To take the estimation uncertainty into account, the standard deviation of the kriging error is used in a probabilistic framework. The choice of the criteria used to deal with overlapping areas is first tested on NO2 annual mean concentration maps of France, built by combining surface monitoring observations and outputs from the CHIMERE chemistry transport model. At the local scale, data from passive sampling surveys and high -resolution auxiliary variables are used to provide a more precise estimation of the background pollution in different French cities. The traffic-related pollution can also be accounted for in the map by additional predictors such as distance to the road, and traffic-related NOx emissions. Similarly, the proposed approach is implemented to identify the points, at a given statistical risk, where the NO2 concentration is above the annual limit value

An exponential external drift modeling for urban scale

International audienc