Air Quality Part II: Crunching the Numbers for San Diego County

The last segment looked at air quality in the U.S. and how zero emission vehicles (ZEVs) might contribute to reducing pollution and health risks. San Diego County is an early adopter of electric vehicles (EVs) and home to the country’s first large scale all-electric car sharing program. It has substantial electric vehicle charging infrastructure. The County’s Climate Action Plan also includes alternative fuel vehicles as part of its long-term mitigation strategy. Looking at EV adoption data for San Diego may shed light on how electric vehicles can improve air quality more broadly.

ZEV Adoption Goals

By 2025, San Diego will have 3.1 million registered vehicles. For its share of Governor Brown’s California target of 1.5 million ZEVs in 2025, the County should have 141,000 ZEVs, or 4.5% of its registered vehicles. This is an increase of 126,000 ZEVs from current levels, and requires a quick and sustained ramp-up over the next decade.

San Diego Air Quality

Today, over half of San Diego’s NOx emissions come from on-road vehicles, with heavy-duty vehicles causing about two-thirds. NOx emissions have significantly decreased over the last decade. On-road vehicles emitted over 115 tons/day of NOx in 2002 and just under 70 tons/day in 2012. The San Diego Air Pollution Control District aims to decrease emissions further, to 38 tons/day in 2020 and 30 tons/day in 2025. The County’s regional plan similarly aims to continue reducing carbon monoxide, volatile organic compounds (VOCs, contributors to ozone formation), and particulate matter through 2035.

Impact of Electric Vehicle Adoption on Air Quality

The California Air Resources Board’s transportation model helps California predict air quality as vehicles are replaced over time. The current model predicts a 4% adoption for the County of San Diego by 2025, 73% of the level needed to meet its share of the state goal. Including the additional 40,000 ZEVs in the model predicts a significant  decrease in carbon monoxide, NOx and volatile organic compounds (VOCs). Carbon monoxide would decrease by about 25 tons/day and NOx and VOCs would decrease by about 2 tons/day for light-duty vehicle replacement. With air quality goals of about 15 tons/day reduction of NOx and 200 tons/day of VOCs, ZEVs offer a moderate but clear  contribution. And these improvements are achieved with ZEVs accounting for only 4.5% of all registered vehicles.

Looking Forward

Not all counties have the advantages of San Diego for adopting ZEVs. California emissions, transportation and urban planning policies help, as do popular support and early deployment of electric charging infrastructure. But more states are adopting transportation and emissions goals that align with ZEV adoption benefits. In addition, ZEV prices are decreasing, battery range is improving, and more models are being introduced.

The main appeal of electric vehicles remains their low  greenhouse gas emissions- as long as electricity is generated from low-carbon sources- low fuel cost, and contribution to U.S. energy security. Even with low levels of adoption, ZEVs can also help improve air quality, reduce peak day-time ozone, decrease health and economic impacts, help meet federal and state air quality standards, and improve visibility. With all of these benefits, hopefully California’s executive order calling for 1.5 million ZEVs will become reality rather than just an ambitious goal.

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