Using dispersion models at microscale to assess long-term air pollution in urban hot spots: A FAIRMODE joint intercomparison exercise for a case study in Antwerp.

In the framework of the Forum for Air Quality Modelling in Europe (FAIRMODE), a modelling intercomparison exercise for computing NO2 long-term average concentrations in urban districts with a very high spatial resolution was carried out. This exercise was undertaken for a district of Antwerp (Belgium). Air quality data includes data recorded in air quality monitoring stations and 73 passive samplers deployed during one-month period in 2016. The modelling domain was 800 × 800 m2. Nine modelling teams participated in this exercise providing results from fifteen different modelling applications based on different kinds of model approaches (CFD - Computational Fluid Dynamics-, Lagrangian, Gaussian, and Artificial Intelligence). Some approaches consisted of models running the complete one-month period on an hourly basis, but most others used a scenario approach, which relies on simulations of scenarios representative of wind conditions combined with post-processing to retrieve a one-month average of NO2 concentrations. The objective of this study is to evaluate what type of modelling system is better suited to get a good estimate of long-term averages in complex urban districts. This is very important for air quality assessment under the European ambient air quality directives. The time evolution of NO2 hourly concentrations during a day of relative high pollution was rather well estimated by all models. Relative to high resolution spatial distribution of one-month NO2 averaged concentrations, Gaussian models were not able to give detailed information, unless they include building data and street-canyon parameterizations. The models that account for complex urban geometries (i.e. CFD, Lagrangian, and AI models) appear to provide better estimates of the spatial distribution of one-month NO2 averages concentrations in the urban canopy. Approaches based on steady CFD-RANS (Reynolds Averaged Navier Stokes) model simulations of meteorological scenarios seem to provide good results with similar quality to those obtained with an unsteady one-month period CFD-RANS simulations.

Multizone airflow and pollution simulations of indoor emission sources.

A health impact assessment of the indoor pollution was performed for various indoor sources: oven for heating, cooking, photocopy machine and smoke cigarettes. The mortality levels and hospital admissions associated with exposure to PM2.5 and NO2 concentrations have been calculated. We have modelled a two level house in Madrid city center where the office and the living floors are in the same building. The people follow a predefined activity patterns (time profiles) in the outdoor and indoor environments. In this experiment, we have performed a full year simulation using the EnergyPlus model to obtain the following parameters: building energy use, thermal behavior, airflow and indoor air quality simultaneously. Outdoor air quality and meteorological conditions were provided by the output of running the very well-known model WRF/Chem. The health impacts of the indoor emitting sources are higher in the warm months due to the operation of the air conditioning system. The largest impact on health is produced by the emissions that are released during cooking. The results also show a high correlation between indoor and outdoor concentrations when indoor emissions are not considered.