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NO2 population Exposure Mapping based on APEX hyperspectral Data (BUMBA)

Research project SR/00/310 (Research action SR)

Persons :

Description :


As human exposure and the associated health effects in hot spot areas are particularly affected by pollutants that have a strong local character and that exhibit strong concentration gradients at relatively small scales, such as nitrogen dioxide (NO2), there is a strong need for high-resolution operational NO2 exposure models. The currently available RIO-IFDM modeling tool seems to perform moderately with regard to high-resolution spatial patterns. However, it can still be improved and needs to be validated extensively. Up to now no suitable observations with high spatial resolution are available to validate the RIO-IFDM model. The validation of the RIO-IFDM model with the spatial urban patterns of NO2 concentrations derived from APEX measurements above Brussels, Antwerp and Liège is unique in that way that before models were compared to point measurements.
Hence, the most important objectives of the BUMBA proposal are:
1) the exploitation of the existing expertise at VITO-TAP and BIRA to further develop and optimize a high-resolution APEX-based NO2 column mapping system, (2) the conversion of these values to high-resolution surface layer NO2 concentrations, (3) the use of these NO2 maps to validate and improve the high-resolution RIO-IFDM modelling system, (4) the development of a near-real time high-resolution operational NO2 model and high resolution exposure calculations at IRCEL. The results of this exposure calculations will be published in near-real time on the IRCEL-CELINE-website and used in annual assessments in reports on Belgian air quality. (5) the disposition of a validated operational NO2 product as integrated end-product within the APEX processing chain for future APEX users.


In order to achieve its objectives, the project will count 5 main collaborative tasks. In a first step, an innovative processing chain will be developed for the APEX instruments allowing for the mapping of NO2 distributions at the scale of traffic roads and city streets. The retrieval of NO2 column densities from APEX will be improved through an optimization of APEX operation and retrieval algoritms. This will be based on existing APEX data acquired in unbinned mode above Antwerp, and then consequently applied on three new flight campaigns above the cities of Antwerp, Brussels and Liège. Secondly, parallel to the new flight campaigns, correlative observations will be performed from the ground using the BIRA DOAS instruments. In addition, all available in-situ observations from the measurement surface network of the Environment Agencies will be gathered and aerosol information form operational CIMEL sunphotometers will be used. Thirdly, the retrieved vertical column values will be transformed into surface concentrations, usable for validation purposes. Fourthly, the high-resolution exposure model RIO-IFDM will be optimized and validated using the overall data set acquired. Finally, the optimized RIO-IFDM chain will be implemented in near-real time at IRCEL to use for exposure analysis and risk assessment.


Scientific results that can be expected from the BUMBA project are a.o.
- optimized spectral retrieval algorithms to retrieve NO2 columns from APEX data
- High resolution maps of total NO2 column values above the cities of Antwerp, Brussels and Liège.
- Correlative comparison statistics between the different types of observations
- NO2 surface concentrations from APEX hyperspectral data
- Validation statistics between the observations and RIO-IFDM model output
- Improved RIO-IFDM model chain
- Updated, more accurate exposure maps of NO2


The final expected outcomes are high resolution exposure maps of NO2 for the Belgian regions. These exposure maps will be produced hourly in near-real time by an improved and validated RIO-IFDM model chain installed at the IRCEL-CELINE servers and made available through the IRCEL-CELINE website. The hourly model results will be saved in a compressed format to be able to calculate daily, monthly and annual means and exceedance metrics if appropriate. Aggregated results are then subsequently used for assessment and reporting in the IRCEL-CELINE Belgian annual air quality report.
Next to the operational model chain, also some instantaneous NO2 exposure maps for the three major agglomerations in Belgium, i.e. Brussels, Antwerp and Liège will be derived through the APEX measurement campaign, hereby covering the largest and most heavily polluted cities in the Flemish, Brussels and Walloon region. Liège, situated in the Meuse river valley, differs from the other two cities by its topology, posing likely a higher uncertainty on the RIO-IFDM model results. These maps provide an independent view on air quality and exposure over these three cities. It is proposed to acquire APEX data during clear winter days, because NO2 concentrations are generally higher on such days due to bad atmospheric dispersion conditions.

Finally, the optimized NO2 extraction chain will be implemented into the APEX operational processing chain at VITO and offered to the user community as a validated operational end-product.

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