The article discusses the results of bench tests that monitor the increase of NO2 emissions in the heavy duty vehicles engines exhausts as a result of the use of particulate matter filters. The use of passive particulate matter filters inevitably leads to an increase in NO2 emissions from the engine. The particularly intensive increase in the emissions occurs when SCR reactors are shut off, which is still a common practice among drivers. NO2 concentrations in exhaust gases of DPF-equipped engines reach concentration dangerous for human health and life. The causes of the NO2 formation in the vehicles’ exhaust systems, the harmfulness of this chemical, and the results of NO2 measurements in different tests, are discussed. In addition, the effect of the presence of this compound on the accuracy of opacity measurement is discussed.