Validating Urban Air Pollution and Microclimatic ENVI-met Models Using Lichen Biomonitoring: A Case Study of Avenida da Liberdade, Lisbon

Urban air pollution and microclimatic conditions significantly influence public health. This study validates pollutant dispersion and microclimatic conditions simulated in ENVI-met using lichen biomonitoring data. The case study focuses on Avenida da Liberdade, an urban canyon in Lisbon, Portugal, characterized by high traffic and dense tree coverage. ENVI-met simulations of NO₂ and PM10 dispersion, along with microclimatic conditions (wind speed, solar radiation, and humidity), were performed under current conditions. To validate the simulations, changes in lichen species composition on Celtis australis trees were assessed using a European standard methodology. A total of 82 trees were surveyed, recording lichen abundance and species diversity across four cardinal orientations. Non-metric multidimensional scaling (NMDS) was applied to identify gradients in lichen species composition associated with pollution and microclimatic factors. The ordination analysis revealed significant correlations between NMDS axes and simulated environmental variables, such as NO₂, PM10 concentrations, and wind speed. The spatial distribution of NMDS scores closely mirrored the ENVI-met outputs, with axis 3 reflecting pollution gradients and axis 2 aligning with wind patterns.  This integrated approach demonstrates the efficacy of combining CFD-based simulations with biological indicators to assess urban microclimates and pollutant dispersion. The results highlight the potential of lichen biomonitoring as a cost-effective tool for validating environmental models, contributing to more accurate urban environmental management strategies. Future research may explore extending this methodology to diverse urban contexts and a broader range of climatic conditions and pollutant types.