Epidemic spreading in a heterogeneous population can be influenced by spatial differences in population distribution, mobility, and environmental conditions. In this work, an existing metapopulation epidemic model based on the GLeAM framework is adapted to study influenza spreading in the Community of Madrid and its surrounding areas. The model is extended by introducing a dependence of the transmission rate on the local PM2.5 concentration, controlled by a parameter D. The model is first studied without pollution dependence to analyse the influence of population and mobility on the epidemic dynamics. The pollution-dependent model is then used to study how increasing the dependence on PM2.5 modifies the epidemic evolution and its spatial distribution. A second study was also performed for COVID-19 by introducing modifications to the established influenza model. The results show that population and mobility contribute to the spatial heterogeneity of the epidemic outcome.