Sustained Reductions of Bay Area CO₂ Emissions 2018-2022

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Urban Ecology

Background:

• Cities are major contributors to global carbon dioxide (CO2) emissions, necessitating accurate quantification of urban emissions and trends.
• Evaluating emission reduction policies and understanding urban biosphere dynamics requires robust methods for measuring, reporting, and verifying (MRV) urban CO2.
• Existing MRV approaches for urban CO2 emissions have limitations in cost-effectiveness and accuracy.

Purpose of the Study:

• To demonstrate a cost-effective and accurate method for assessing urban CO2 emissions trends using a dense sensor network and Bayesian inversions.
• To quantify the interannual trend of urban CO2 emissions in the San Francisco Bay Area over a five-year period.
• To attribute observed CO2 emission trends to specific sectors, such as passenger vehicle electrification.

Main Methods:

• Deployment of the Berkeley Environmental Air Quality and CO2 Network (BEACO2N), a spatially dense network of sensors, for continuous CO2 observations.
• Integration of sensor-derived CO2 concentration data with meteorological information.
• Application of Bayesian inversion techniques to synthesize measurements and estimate CO2 emissions.

Main Results:

• Continuous CO2 observations were collected over nearly five years (2018-2022) in the San Francisco Bay Area.
• Bayesian inversion analysis indicated a modest interannual decrease in urban CO2 emissions of 1.8 ± 0.3% per year.
• On-road emissions from passenger vehicles showed a greater decrease, at a rate of 2.6 ± 0.7% per year, suggesting a primary contribution to the overall trend.

Conclusions:

• A dense sensor network combined with Bayesian inversions provides an effective and cost-efficient approach for monitoring urban CO2 emissions.
• The San Francisco Bay Area experienced a significant reduction in urban CO2 emissions, primarily driven by the electrification of passenger vehicles.
• This methodology offers a scalable solution for tracking the efficacy of climate policies and understanding urban carbon cycles.