Observing Annual Trends in Vehicular CO₂ Emissions

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Climate Change Research

Background:

• Transportation is the largest source of greenhouse gas (GHG) emissions globally.
• Reducing transportation-related emissions is critical for climate change mitigation policies.
• Urban CO2 emission monitoring requires high spatial and temporal resolution.

Purpose of the Study:

• To develop and validate an approach for inferring vehicular CO2 emissions using atmospheric observations.
• To track annual trends in urban CO2 emissions with high precision.
• To independently verify policy-driven reductions in transportation GHG emissions.

Main Methods:

• Utilized data from 26 Berkeley Environmental Air-quality and CO2 Observation Network (BEACO2N) sites.
• Employed a Gaussian plume model to synthesize and analyze CO2 measurements.
• Removed biogenic emission signals to isolate vehicular CO2 contributions.

Main Results:

• Inferred a 7.6 ± 3.5% reduction in vehicular CO2 emissions in the San Francisco Bay Area between 2018 and 2020.
• Observed emission reduction is slightly larger than estimates from the California Air Resources Board EMFAC model (4.7%).
• Demonstrated the feasibility of using atmospheric observations to constrain annual emission trends.

Conclusions:

• Atmospheric CO2 monitoring networks can effectively track and verify emission reductions from the transportation sector.
• This approach provides an independent method for assessing the impact of climate policies.
• High-resolution urban CO2 monitoring is crucial for understanding and managing emission sources.