California’s “Going Zero” policy, which strives for 100 percent zero-emission vehicle sales by 2035, will reduce ozone pollution and carbon dioxide emissions in Los Angeles, according to recent CIRES-led work.

Gas- and diesel-burning vehicles emit volatile organic compounds (VOCs) and nitrogen oxides. When it’s hot and sunny, these chemicals react, forming ground-level ozone, which creates smog and increases the risk of respiratory issues.

Los Angeles has been plagued with air quality issues for decades and experiences some of the most extreme ozone pollution in the country. The CIRES-led research, published in Environmental Science & Technology, shows California’s zero-emission vehicle policy would lead to fewer summer days with dangerous levels of ozone pollution.

“We wanted to provide a timely evaluation of what this policy means for urban air quality as well as climate change,” said Qindan Zhu, a former CIRES researcher at NOAA’s Chemical Sciences Laboratory and lead author of the study.

In the new study, Zhu and her colleagues used a chemical transport model to simulate the evolution of VOCs and nitrogen oxides released by gas- and diesel-burning vehicles and how they react to produce ozone. The model also incorporates the most up-to-date information about cooking source VOC emissions, which had not been well-constrained in previous work.

“It’s probably the first time scientists have focused on the impact of cooking emissions in urban air quality modeling,” Zhu said. “Incorporating cooking emissions significantly improved the representation of how VOCs contribute to ozone formation in the model.”

The team found that adopting a zero-emission policy for on-road gasoline cars and trucks would reduce human-caused emissions of nitrogen oxides by 28 percent and carbon dioxide by 41 percent.

The drop in nitrogen oxides leads to a reduction in ozone production rate, which decreases the average number of days when ozone reaches dangerous levels for people in Los Angeles from 9 to 6 days in August. When the team simulated zero-emission adoption for on-road diesel vehicles and off-road gasoline vehicles to the model, the number of ozone exceedance days in August dropped to 1.

The researchers hope their approach can be expanded and applied to other regions in the U.S. and across the world to help inform policy-makers.

“Our study highlights the potential of electric and zero-emission vehicle adoption as a good strategy to simultaneously address climate change and air quality challenges,” Zhu said.