Naomi Zimmerman and colleagues analyzed four scenarios based on reported black carbon emissions from both traditional port fuel injection engines and newer gasoline direct injection (GDI) engines. They determined that installing efficient particulate filters in vehicles with GDI engines -- even if they slightly lower fuel efficiency -- could likely balance this trade-off and benefit the climate. But this outcome is not a given and depends on a variety of factors that can impact black carbon emissions such as engine design, fuel composition and geographic location.