California's targeted, sector-based policies could reduce diesel emissions nationwide

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE

Research News

 

Compared to the rest of the United States, California has drastically reduced emissions of diesel particulate matter (DPM) from diesel-powered vehicles. The state has achieved this by systematically targeting high-emitting sectors with stringent and effective policies that go beyond federal standards. In a Policy Forum, Meagan Schwarzman and colleagues argue that a similar approach to emissions standards could serve as a model for reducing DPM emissions nationwide and improve health in the communities disproportionately impacted by diesel particulate pollution. While diesel is the fuel that drives much of the modern economy, powering trucks, buses, trains, ships and agricultural equipment, diesel exhaust is a known carcinogen and a significant contributor to harmful particulate air pollution in urban areas. Due to these public health impacts, efforts to reduce DPM emissions have been implemented in countries worldwide. Recently, however, the U.S. federal administration has attempted to roll back, weaken or eliminate the policies and standards that govern diesel emissions at the federal level and is moving to limit the ability of individual states to set their own emissions standards that go beyond the federal guidelines. Here, Schwarzman et al. show that California - the U.S.'s most populous state and the world's 5th largest economy - has continued to reduce DPM emissions for more than 30 years by regulating DPM air pollution more stringently than the federal government through targeted, sector-based policy. To understand the impact of California's policies, the authors evaluated DPM emissions data from the Environmental Protection Agency's national emissions inventory to compare mobile-source DPM emissions in California versus in the rest of the U.S. for the period spanning 1990 to 2014. Despite a steady rise in diesel fuel consumption, California reduced overall mobile-source DPM emissions by 78% compared to a 51% reduction in the rest of the U.S. The analysis highlights opportunities for the U.S. to reduce DPM emissions by adopting policies similar to California's. The findings also underscore the need to protect states' authority to set their own emissions standards.