California Air Resources Board

CARB develops and conducts policy-relevant in-house and extramural research to advance the science and to support CARB mobile source programs and policies. Current research includes efforts to better understand the discrepancy between certification and real-world emission levels, achieve further emission reductions from on-road vehicles and off-road equipment, track and model the effect of various regulatory options to achieve real-world emission reduction targets using laboratory, portable emissions monitoring systems (PEMS), remote-sensing, and engine and activity data-logging technologies, and understand non-tailpipe emissions such as brake-wear, tire-wear, and resuspended roadside dust. CARB is also responsible for programs to reduce emissions of high global warming potential greenhouse gases from mobile air conditioners and to investigate the effect on emissions from advanced vehicle and low carbon fuel technologies. Some activities include conducting large data-driven technical analyses, providing expert opinions to decision-makers, networking with internal, national and international stakeholders, and publishing research findings.

For specific projects see the following links:

Some major topics of concern that drive CARB's research needs are described in greater detail below.

Mobile Source Control Strategy Research

Mobile source emissions of criteria pollutants, especially NO_X and PM, are controlled using after-treatment devices such as catalytic converters and diesel particle filters (DPF). These devices have significantly reduced the pollutants emitted by both light duty vehicles and heavy duty vehicles. They are typically tested in a laboratory setting under standard certification cycles to determine their effectiveness. However, it is much more challenging to determine their effectiveness under various operational conditions which may lead to conditions which prevent the proper functioning of these devices. Additionally, some vehicles and equipment which are not required to have after-treatment could benefit from pilot projects to study their compatibility with these devices and any potential emissions reductions.

Another method for controlling emissions is to alter operational parameters. Although not currently required, some benefit could be derived from vehicle speed limiters, which help to reduce fuel consumption and hence greenhouse gas emissions.

CARB is currently undertaking various project which specifically examine the efficacy and durability of aftertreatment devices operating under real-world conditions.

Fleet Deterioration and Durability

Mobile source durability and deterioration have a high impact on emissions as vehicles age. Engines and engine aftertreatment devices are highly complex systems and maintenance programs are incredibly important for maintaining proper function. CARB's emissions inventory model, EMFAC, provides an estimate of expected deterioration rates for vehicles which is reflected in emissions results. This information is based on real-world measurements but new data is always needed to ensure model fidelity. CARB focuses significant effort toward measuring real-world vehicle emissions deterioration.

Mobile Source Greenhouse Gas Emissions Mitigation

One of the most important goals of the Mobile Source Emissions Research Program is to support CARB programs and regulations. CARB has set ambitious goals to reduce greenhouse gases (GHGs) and mitigate the worst effects of climate change in the coming years. This will require technological advancements in the transportation sector and innovative strategies to reduce overall energy consumption and increase in efficiencies. Already some regulations have been put into place to curb the CO₂ emissions from heavy duty vehicles and various programs are in place to incentivize the use of partially or fully electrified vehicles. In an effort to support these programs, the Vehicle Emissions Research Program is pursuing various avenues of inquiry including real-world emissions measurements to determine how well regulations are working to curb these emissions and feasibility studies to chart the most effective path toward a sustainable transportation sector.

Real-world Vehicle, Engine and Trailer Operations

CARB is mandated to improve air quality and reduce emissions that impact the climate. The transportation sector is a major source of both criteria pollutants and greenhouse gases (GHGs) but this sector is highly complex. Although engines and vehicles are certified before being allowed on the road, their real-world emissions may vary significantly from their certification emissions. This may depend on their operational behavior which can affect on-board emissions controls and after-treatment devices. In order to better understand the major factors affecting in-use emissions, the real-world behavior of on-road vehicles has to be measured and linked to their characteristic emissions.

Our understanding of fleet emissions relies upon limited information because directly measuring emissions from individual vehicles is costly and time consuming. However, new methods which rely on real-time vehicle diagnostics and remote sensing have provided us with a breakthrough resource to mine large data sets and gain a better understanding of vehicle operational parameters and emissions.

The Mobile Source Emissions Research Program is taking active steps in using these tools and create databases with extensive real-world activity data.

In-Use Emissions

The Mobile Source Emissions Research Program includes various programs and projects to measure real-world in-use emissions from all on-road and off-road vehicles. These measurements are compared to emissions testing used during the certification process as well as to emissions estimates derived from models and emissions inventories. This work is important for verifying the fidelity of models and testing the relevance of standardized drive cycles.

Emissions data can be collected using sophisticated instrumentation where single vehicles are measured on-road, or using lower cost sensors. In some instances, on-board diagnostic (OBD) data is used to leverage information gathered by on-board sensors.