Evaluation of the Air Quality and Greenhouse Gas Benefits of an Advanced Low‐NOx Compressed Natural Gas (CNG) Engine in Medium and Heavy‐Duty Vehicles in California

Research Team: Scott Samuelson (lead), Michael MacKinnon, Brendan Shaffer, and Alejandra Cervantes

UC Campus(es): UC Irvine

Problem Statement: The recent commercialization of advanced Compressed Natural Gas (CNG) engines for medium-duty vehicles (MDV) and heavy-duty vehicles (HDV) that can dramatically reduce emissions of NOx relative to baseline technologies has garnered significant interest due to the potential for air quality benefits. Furthermore, the co‐utilization of renewable natural gas (RNG) from pathways including biomass/biogas and power‐to‐gas can achieve deep reductions in greenhouse gas (GHG) emissions relative to both diesel and CNG. However, the regional air quality and GHG impacts of large‐scale deployment are currently unclear and require quantification, including both primary and secondary pollutants including ground-level ozone and PM2.5.

Project Description: The goal of this research is to assess the greenhouse gas (GHG) emissions and air quality (AQ) impacts of transitions to advanced low‐NOx Compressed Natural Gas (CNG) engines in medium-duty vehicle (MDV) and heavy-duty vehicle (HDV) applications in California with a particular emphasis on renewable natural gas (RNG) as a fueling pathway. To evaluate regional AQ impacts in 2035, pollutant emissions from all end-use sectors are projected from current levels and spatially and temporally resolved. Scenarios are constructed beginning with both a conservative (Base Case) and more optimistic (SIP) case regarding advanced vehicle technology and fuels integration to provide spanning of potential impacts. To capture the impact of seasonal dynamics on pollutant formation and fate, two modeling periods are conducted including a winter and summer episode. To estimate the potential GHG impacts of transitions to advanced CNG engines in HDV and MDV, scenarios are evaluated under various assumptions regarding fuel pathways to meet CNG demand from a life cycle perspective. Scenarios are compared to the baseline cases assuming (1) all CNG is provided from conventional fossil natural gas and (2) under a range of possible resource availabilities associated with RNG and renewable synthetic natural gas (RSNG) from in-state resources. Key findings include: i) expanding the deployment of advanced CNG MDV and HDV can reduce summer ground-level ozone concentrations and groundlevel PM2.5 in key regions of California; ii) the largest AQ benefits are associated with reducing emissions from HDV; iii) in-state RNG pathways can meet the CNG demand estimated for both baseline cases; iv) in-state resources are unable to entirely meet CNG demand for the high total CNG demand estimated for the majority of Base alternative cases, and v) advanced CNG HDV and MDV can moderately reduce GHG emissions if fossil natural gas is used (14 to 26%).

Status: Completed

Budget: $57,150

Project Partner(s): California Air Resources Board (CARB), South Coast Air Resources Board

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