Air quality and human health - Air Pollution Modeling and Its Application - page 462

7.2 Computational Scheme Accounting for
Heterogeneous Surface Emissions in CTMs
Myrto Valari and Laurent Menut
Laboratoire de Météorologie Dynamique/IPSL 91128 Palaiseau, France
Abstract Chemistry transport models (CTMs) have been widely used for urban
air-quality forecast over the last 10 years but rarely for human exposure studies or
health impact assessment (HIA). Exposure models require information on
pollutant concentration at the neighborhood scale (sub-kilometer resolution). High
resolution modelling applications may look appealing but their high computational
cost makes them inappropriate for this purpose. Spatio-temporal analysis of
monitor data is used in most cases in exposure studies (Georgopoulos et al., 2005).
On the other hand, traditional HIA methods use area-aggregated monitor data. Not
taking into account the spatial variability of pollutant concentrations has been
shown to lead to significant bias in health risk estimates in HIA methods (Smith,
1997). It becomes clear that CTMs should adapt to the needs of such studies and
provide information on small scale concentration variability.
We applied an emission scheme to the CHIMERE CTM that allows to extract
information on the variability of pollutant concentrations at sub-grid scale. The
application is based on the split of grid-averaged emission into separate contri-
butions of emitting activities co-existing over the same grid-cell area (e.g. traffic
transportation, residential emissions, etc.). Different concentrations are calculated
for each emission scenario allowing the evaluation of concentration variability
between source-specific areas inside grid-cells. The advantage of the application is
that modelled concentrations are directly associated to human-activities during the
day and are therefore, easily adapted to human exposure models.
Keywords Urban air-quality, heterogeneous emissions, small-scale pollutant
variability
1. Methodology
In cities people live and move over areas of highly variable pollutant concentration
fields. This variability is due, at a large degree, to heterogeneous surface emissions.
In common CTMs small scale emission variability is not accounted for since
emissions are averaged over grid-cell areas, beforehand. However, grid resolution
is of some square kilometers and sub-grid scale effects have been proved to