Characterization of Physical and Chemical Properties of Particulate Emissions of a Modern Diesel-Powered Tractor under Real Driving Conditions

In this study, tailpipe-sampling was used to sample the exhaust aerosol of a Stage IV tractor equipped with Diesel Oxidation Catalyst (DOC) and Selective Catalytic Reduction (SCR) aftertreatment systems. The particle emissions were characterized in terms of number concentration (particle size of > 2.5 nm), mass concentration (particle size of 6-612 nm) BC mass concentration and chemical composition (particle size of > 30 nm). The measurements were conducted on-road by setting a mobile laboratory on a trailer and pulling it with the tractor. In addition to driving, heavy-lift work cycles were tested, where separate lifts of a 1000 kg weight were conducted with the front fork of the tractor with two minutes of idling between consecutive lifts. Both a Porous Tube Diluter (PTD) with ambient temperature dilution air as well as an ejector diluter with hot dilution air were used to sample the exhaust aerosol. Emission factors for particle number, particle mass and BC (mass) were calculated in three engine operating conditions: road driving, during load-lifting and engine idling. During heavy-lifts, the calculated emission factors were approximately eight times higher for particle number and 20-30 times higher for particle mass, when compared to emission factors obtained from road-driving. The particle number size distribution of exhaust was typically dominated by soot mode mostly in sub-100 nanometer particle size range. However, the exhaust particle concentrations varied significantly, depending on driving parameters and engine loading. The differences in emission factors and size distributions between the diluter setups were very small. The particulate mass consisted mostly of BC and organic compounds, but also small traces of sulphates and nitrates were detected during road-driving.