Real-world emissions of in-use off-road vehicles in Mexico

ABSTRACT

Off-road vehicles used in construction and agricultural activities can contribute substantially to emissions of gaseous pollutants and can be a major source of submicrometer carbonaceous particles in many parts of the world. However, there have been relatively few efforts in quantifying the emission factors (EFs) and for estimating the potential emission reduction benefits using emission control technologies for these vehicles. This study characterized the black carbon (BC) component of particulate matter and NOx, CO, and CO₂ EFs of selected diesel-powered off-road mobile sources in Mexico under real-world operating conditions using on-board portable emissions measurements systems (PEMS). The vehicles sampled included two backhoes, one tractor, a crane, an excavator, two front loaders, two bulldozers, an air compressor, and a power generator used in the construction and agricultural activities. For a selected number of these vehicles the emissions were further characterized with wall-flow diesel particle filters (DPFs) and partial-flow DPFs (p-DPFs) installed. Fuel-based EFs presented less variability than time-based emission rates, particularly for the BC. Average baseline EFs 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 EFs by operation mode are proposed as an alternative method for characterizing the variability of off-road vehicles emissions under real-world conditions. Mass-based reductions for black carbon EFs were substantially large (above 99%) when DPFs were installed and the vehicles were idling, and the reductions were moderate (in the 20–60% range) for p-DPFs in working operating conditions. The observed high variability in measured EFs also indicates the need for detailed vehicle operation data for accurately estimating emissions from off-road vehicles in emissions inventories.

Implications: Measurements of off-road vehicles used in construction and agricultural activities in Mexico using on-board portable emissions measurements systems (PEMS) showed that these vehicles can be major sources of black carbon and NO_X. Emission factors varied significantly under real-world operating conditions, suggesting the need for detailed vehicle operation data for accurately estimating emissions inventories. Tests conducted in a selected number of sampled vehicles indicated that diesel particle filters (DPFs) are an effective technology for control of diesel particulate emissions and can provide potentially large emissions reduction in Mexico if widely implemented.

Acknowledgment

The authors thank the California Air Resources Board for its strong support and collaboration in this project. Special thanks to Reyes Martinez Cordero of the Planta de Asfalto del Distrito Federal, Jaqueline de la Cruz of Geo-Construction, and Antonio Nava of Sistema Maiz for providing their off-road vehicles for testing. We thank the anonymous reviewers for their valuable comments.

Funding

The funding provided by the U.S. Agency for International Development (USAID) and the support from Tetra-Tech are gratefully acknowledged. The Project Team also acknowledges the Instituto Nacional de Ecología y Cambio Climático (INECC) for providing funding for the emissions control devices and Sergio Zirath and Francisco Guardado for their support.

Disclaimer

The use of the U.S. EPA NONROAD model in this paper is for illustrative purposes and should not be considered as an evaluation of the model’s performance.

Supplemental data

Supplemental data for this paper can be accessed on the publisher’s website.

Additional information

Funding

The funding provided by the U.S. Agency for International Development (USAID) and the support from Tetra-Tech are gratefully acknowledged. The Project Team also acknowledges the Instituto Nacional de Ecología y Cambio Climático (INECC) for providing funding for the emissions control devices and Sergio Zirath and Francisco Guardado for their support.

Notes on contributors

Miguel Zavala

Miguel Zavala is a research scientist at the Molina Center for Energy and the Environment in La Jolla, CA.

Jose Ignacio Huertas

Jose Ignacio Huertas is a research professor at the Instituto Tecnológico de Monterrey, Monterrey, NL, Mexico.

Daniel Prato

Daniel Prato is a PhD student at the Instituto Tecnológico de Monterrey, Monterrey, NL, Mexico.

Aron Jazcilevich

Aron Jazcilevich is a research professor at the Universidad Nacional Autónoma de México, Mexico City, Mexico.

Andrés Aguilar

Andrés Aguilar is a researcher at the Instituto Nacional de Ecología y Cambio Climático, Mexico City, Mexico.

Marco Balam

Marco Balam is an environmental consultant at Ambientalis, Mexico City, Mexico.

Chandan Misra

Chandan Misra is a researcher at the California Air Resources Board, Sacramento, CA.

Luisa T. Molina

Luisa T. Molina is the president of the Molina Center for Energy and the Environment in La Jolla, CA.