Environmental Impact of Real Gaseous Pollutants Emission of Agricultural Tractors

The gaseous pollutants produced by the internal combustion engines fitted on vehicles powered with fossil fuels are considered one of the main sources causing the global warming and consequently the climate change. In this scenario, the agricultural self-propelled machinery, in particular tractors, are believed to have a significant role, due to the generalized fitting of diesel engines. Trying to improve the situation, from 1996 for non road vehicles (therefore also for self-propelled agricultural machinery) some Standards were issued, based on steps referred to the time, defining progressively stringent emission limits, from Stage I to Stage V (in Europe), roughly correspondent to Tier 1 to Tier 5 in USA. The compliance of an engine to a given step is referred to dedicated homologation tests, on the basis of a series of defined running conditions. At present, no subsequent tests are provided to check the conformity of the engine along its service life. Consequently, there is no assurance that the engine is respecting the emission limits provided by its homologation step, especially in case it is heavily used and/or is not submitted to a diligent periodical maintenance. To ascertain the real pollutants gaseous emission of used tractors, a model equipped with an engine compliant to the Stage IIIA level was tested, using PEMS (Portable Emission Measurement System), measuring NOx, CO, HC and PM emissions, in comparison with the limits established by its homologation stage.