California ARB releases concept paper on short-lived climate pollutants

8 May 2015

The California Air Resources Board (ARB) released a concept paper describing ways to reduce emissions of short-lived climate pollutants (SLCPs) including methane, black carbon (BC) and fluorinated gases (refrigerants, insulating foam and aerosol propellants). Due to their high climate forcing potential, these chemicals may be responsible for as much as 40% of the global warming to date, said the ARB. These pollutants also tend to have a shorter duration in the atmosphere than CO₂, making their most dramatic climate impact over a period of days to about 10 years.

The concept paper will be discussed at a public workshop on May 27, 2015. The comments received on the paper will inform the development of a draft Strategy that the ARB expects to release for public comment later this summer.

The use of natural gas in the transportation sector is increasing—says the paper—and it could potentially play an important role in helping many parts of the state comply with federal air quality standards over the next 20 years, especially if ultra-low NOx natural gas engines become commercially available for heavy-duty trucks within the next few years.

The critical issues with natural gas include (1) increasing supplies of renewable natural gas, such as from landfills, wastewater treatment plants, commercial food waste facilities, or agricultural operations and (2) minimizing fugitive emissions of methane from natural gas infrastructure. Due to its high global warming potential, relatively small levels of methane emissions throughout the supply chain can overwhelm any reduction in CO₂ emissions from the use of fossil or renewable natural gas, compared to diesel fuel used in transportation.

California has done more than any other jurisdiction to reduce the emissions of PM and black carbon, states the paper. Through a combination of emission regulations and programs, such as the Diesel Risk Reduction Plan, ambient BC levels in California are now 90% lower than in the early 1960s, while the use of diesel fuel more than tripled over the same time period. In spite of the emission reductions, many areas in the state still suffer from poor air quality.

In developing the Strategy, the ARB will identify any additional diesel BC-specific measures that may not otherwise be captured through existing efforts. While existing policies and processes effectively target PM and black carbon emissions from onroad sources—says the paper—additional efforts are needed to drive reductions from off-road sources, including farm and construction equipment, trains and railroad operations, cargo handling equipment, and shipping.

Source: California ARB