Results of investigations and assessment of air pollution by cadmium, lead, and arsenic using Italian ryegrass are presented in this paper. The experiment was carried out in the 2011 growing season in Poznań city and surroundings areas. Lolium multiflorum L. ‘Lema’ exhibits several properties useful for active biomonitoring of air pollution. Plants were exposed at sites varying in environmental characteristics. High cadmium and lead concentrations in leaves were noted in plants exposed within the city area. Canonical variate analysis illustrated variability in concentrations of elements in certain exposure series. The highest arsenic concentrations were observed in the first exposure series, while the highest lead concentrations were observed during the second series. Comparison of trace element concentrations at exposure sites to the control site revealed that comparable levels occurred in the city sites and the Agro-ecological Landscape Park. This was an effect of high cadmium and lead levels at city sites, and arsenic at the rural site. The lowest level of measured trace elements was observed at an exposure site located 15 km from Poznań in a rural area.