Developing a novel warning-informative system as a tool for environmental decision-making based on biomonitoring

•National monitoring of air pollution is a mandatory requirement for many countries.•New, green methodologies are needed for the environmental decision-making process.•Common tree species were used in an innovative national biomonitoring programme.•Concentration of lead (Pb), cadmium (Cd), nickel (Ni) and arsenic (As) was measured.•BioMonRo software is a novel functional warning-informing and decision-making tool.