A collaborative project that intends to map the diversity of lichens in the city of Barcelona and carry out long-term monitoring of them. Lichens are great bioindicators, natural sentinels of atmospheric quality, and the making of maps with the Natusfera app allows us to know the quality of the atmosphere in Barcelona. The mapping is done thanks to collaboration between citizens and experts. Observations of lichens are part of the GBIF open data network (Global Biodiversity Information Facility).