Switch to GDI Engine Will Cause More Climate Warming in U.S. Urban Areas

A study performed by researchers at the University of Georgia College of Engineering reports that new automotive technology that offers increased fuel efficiency could have severe negative implications, such as major impacts on public health and climate.

One of the leading technologies used by car manufacturers to realize the carbon dioxide emission and fuel economy goals set by the U.S. Environmental Protection Agency, in 2012, is the gasoline direct injection (GDI) engine.

The market share of GDI-fitted vehicles in the model year 2008 was 2.3%, which increased to 51% in the model year 2018. According to the EPA estimates, by 2025, 93% of vehicles in the United States will be fitted with GDI engines.

Although GDI engines have been shown to reduce CO₂ emissions and increase fuel efficiency, compared to conventional port fuel injection engines, this technology generates more black carbon aerosols. Black carbon absorbs solar radiation strongly and has high climate warming properties.

In a research paper published recently in the Environmental Science and Technology journal, a research team from UGA has predicted that a rise in the emission of black carbon from GDI-equipped vehicles will add to climate warming in urban areas of the United States that considerably exceeds the cooling related to a drop in CO₂ levels.

Moreover, they suppose the change will make the premature mortality rate due to vehicle emissions almost double, from 855 deaths per year to 1,599. According to the team, the estimated annual social cost of these premature deaths will be $5.95 billion.

Even though emissions from gasoline vehicles constitute a small fraction of the black carbon in the atmosphere, the vehicle emissions are concentrated in regions with high population densities, which magnifies their effect.

Rawad Saleh, Assistant Professor, School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia

Saleh is the principal investigator of the study.

The rise in black carbon levels is an undesirable result of the switch to GDI-powered vehicles that some researchers suspect was based on experimental data, says Saleh. He added that the UGA research is the first of its kind to set up the experimental outcomes in a complex modeling framework to examine the trade-off between an increase in black carbon and CO₂ reduction.

Earlier studies have reported that the switch to GDI engines will lead to evident benefits for the global climate. However, according to the UGA team, these benefits are relatively small and can only be achieved on decadal timescales. However, the negative effect of black carbon can be sensed immediately.

Our research shows the climate trade-off is much different on the regional scale, especially in areas with high vehicle densities. In these regions, the climate burden induced by the increase in black carbon dominates over the climate benefits of the reduction in CO₂.

Rawad Saleh, Assistant Professor, School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia

Saleh continued, “The study concludes the social cost associated with the acute localized climate burden and public health impacts induced by GDI vehicles largely overweigh their marginal global climate benefits.”

The interdisciplinary research was the result of a collaboration between the UGA College of Engineering, the Department of Geography in UGA’s Franklin College of Arts and Sciences, and the National Center for Atmospheric Research. The study was financially supported by the National Science Foundation, the U.S. Department of Energy, and the UGA President’s Interdisciplinary Seed Grant Program.