The objective of this work was to investigate the viability of using the land mollusk Cantareus aspersus (Müller, 1774) as biomonitor and the Comet Assay as biomarker, exposing organisms to atmospheric pollutants. Organisms were exposed to air at the Ulbra University campus climatic control station (Canoas, RS) for 7, 15 and 30 days, in the winter/2004 and in the summer/2005. Our control group, not exposed, was kept in the laboratory, under controlled conditions. Lung cells and hemolymph cells were evaluated through Comet Assay, which shows sensitive results in a short time in quantifying lesions and detecting DNA repair effects. 100 cells/individual/tissue were analyzed and visually classified into five classes (0 – no effect to 4 – maximum damage). Results show that pulmonary cells are more sensitive than hemolymph cells. Longer exposition time produced more DNA damage. Considering climatic seasons, no significant differences were detected between them. Both organisms and method showed to be cheap, effective and sensitive in our study, for biomonitoring atmospheric pollution.