Method and sensing module for sensing pollution of outside air. The sensing module (1) comprises an electro chemical sensing element (3), and a processor (2). A sensing module output signal is provided based on the measurement signal and a baseline signal level. The baseline signal level is adapted depending on two threshold levels (13-15). A pollution concentration value is determined from the measurement signal and a classification level of air pollution is provided as sensing module output signal. A classification level is determined using a plurality of classification threshold values and the pollution concentration values. The plurality of classification threshold values are dynamically adjustable.