constantly changing air quality. When agents are traveling, the in-traffic exposure model is applied taking into
account transport mode, timing, location and duration of the trip. For touring activities, the in-traffic exposure model
for active modes is used (these are activities where people are in transport but without a specific destination and
with the same start and end point). The activity-based model is not specifically built for air pollution exposure
assessment: for example there is no formal distinction between indoor and outdoor activities and trips by public
transport are grouped in one category (although concentrations inside buses are a factor 2-3 higher than exposure in
trains). As a simplification, all activities are assumed to be indoors except for travel.
Dynamic exposure is calculated making full use of the AB²C model, i.e. by including population mobility. The
FEATHERS model simulates one diary for every agent in the population, for every day of the week, and the AB²C
model can calculate exposures from these data.
The final outcome of the AB²C model, i.e. personal exposure to BC, was validated using weeklong personal
monitoring in 62 subjects (Fig. 1) [7]. All volunteers were living in Flanders, some in urban areas and some in more
rural areas. Participants were asked to carry a micro-aethalometer measuring BC, an electronic diary to register their
time-activity pattern, and a GPS logger. Personal measurements were done in 2010-2011, and were rescaled to
account for changing background concentrations. For each participant in the monitoring campaign, a synthetic
population of 100 model-agents per day was made up with all agents having the same characteristics (age, work
situation, household composition, home location subzone, etc.) as each real-life agent. When these model-agents
pass through AB²C, it results in a distribution of potential exposures for each individual. The AB²C model estimates
average personal exposure more accurately compared to ambient concentrations as predicted for the home subzone;
however the added value of a dynamic model lies in the potential for detecting short term patterns and peak
exposures, e.g. while traveling, rather than modeling average exposures [7].