Off-road vehicles used in construction and agricultural activities can hugely contribute to emissions of gaseous pollutants and can be a major source of submicrometer carbonaceous particles in many parts of the world. The black carbon (BC) component of particulate matter and NOx, CO, and CO2 emission factors (EF) of selected diesel-powered off-road mobile sources in Mexico were assessed under real-world operating conditions using on-board portable emissions measurements systems. For a selected number of vehicles, the emissions were further characterized with wall-flow diesel particle filters (DPF) and partial-flow DPFs (p-DPF) installed. Fuel-based EF showed less variability than time-based emission rates, particularly for the BC. Average baseline EF in working conditions for BC, NOx, and CO ranged from 0.04 to 5.7, from 12.6 to 81.8, and from 7.9 to 285.7 g/kg-fuel, respectively, and a high dependency by operation mode and by vehicle type was observed. Measurement-base frequency distributions of EF by operation mode were proposed as an alternative method for characterizing the variability of off-road vehicles emissions under real-world conditions. Mass-based reductions for black carbon EF were significantly large (above 99%) when DPF were installed and the vehicles were idling, and the reductions were moderate (in the 20%-60% range) for p-DPF in working operating conditions. The observed high variability in measured EF also suggests the need for detailed vehicle operation data for accurately estimating emissions from off-road vehicles in emissions inventories.
