Polycyclic aromatic hydrocarbons (PAHs) are a large group of persistent organic pollutants (POPs), which have received increased attention in recent decades in air pollution studies due to their carcinogenicity and mutagenicity. Air monitoring of PAHs is performed measuring compounds in the particulate- and gas-phase of air using active air samplers, which show several constraints, notably: a) reflect a short-term indicator that varies considerably in space and time; b) samplers are expensive and require physical installation and energy supply, meaning that less samplers can be installed; c) don’t provide information on the long-term impact on ecosystem. To overcome these constraints, Directive 2004/107/EC recommends the use of other monitoring methods, notably biomonitors (living organisms), to complement data and to assess spatial deposition of PAHs. Biomonitoring methods have been developed during the last decades for this purpose. Within biomonitors, lichens (symbiosis between fungi and algae) are the most used organisms to monitor atmospheric deposition of several air pollutants. However, one of the main drawbacks of using lichens to monitor atmospheric PAHs has been reported as the impossibility to translate PAH values in lichens into the atmospheric equivalents ones, in order to use this information for regulatory purposes. Moreover, it’s still missing an understanding of the mechanisms through which lichens intercept and accumulate PAHs, as well as a calibration between PAHs in lichens and in vapor- and different particulate-phases of air. It’s also missing a critical level for PAHs in lichens – lowest level that will affect lichen structures and functions, which will be valuable when identifying areas with high ecological/environmental risk. POPLAIR aims to fulfill these gaps of knowledge and to study the feasibility of introducing lichens in the market as a well-known tool to be applied in environmental monitoring assessments.