Proposed Short-Lived Climate Pollutant Reduction Strategy

IV.
Reducing Black Carbon Emissions
Black carbon is the light-absorbing component of fine particulate matter (PM) produced
during incomplete combustion of fuels. Black carbon does not account for the warming
effects of brown carbon. The lifetime of black carbon is very short, from days to weeks,
compared to other SLCPs, which may remain in the atmosphere for a few decades.
California has done more than any other jurisdiction in the world to reduce PM and
black carbon emissions. As a result, ambient levels of black carbon in California are
now 90 percent lower than in the early 1960s, despite the use of diesel fuel more than
tripling over the same time period. 83 If the rest of the world achieved similar reductions,
it could substantially improve health and slow global warming. California’s actions can
serve as a blue print for other jurisdictions to reduce SLCP emissions and improve
public health. California is continuing to explore additional ways to reduce black carbon
emissions. Complying with federal air quality standards and reducing localized risk will
require substantial reductions in smog-forming and PM emissions from mobile sources
and other source categories.
For purposes of this report, black carbon emissions are discussed in two categories,
anthropogenic (non-forest) sources and forest-related sources. Anthropogenic sources
include on- and off-road transportation, residential wood burning, fuel combustion, and
industrial processes. Forest-related sources include prescribed fire and wildfire and are
separated to account for the unique challenges associated with inventorying and
mitigating these sources. In a typical year, wildfires account for approximately twothirds
of California’s black carbon emissions, but this varies from year to year.
Prescribed fires also emit black carbon, but are an important tool for forest managers to
help restore and maintain forest health, which in turn can reduce wildfire severity and
the associated black carbon emissions from catastrophic wildfires.
A. Anthropogenic (Non-Forest) Sources of Black Carbon Emissions
California’s major anthropogenic sources of black carbon include off-road
transportation, on-road transportation, residential wood burning, fuel combustion, and
industrial processes (Figure 1). The fuel combustion and industrial source categories
include a variety of stationary and portable equipment such as boilers, turbines, and
steam generators, as well as process emissions from industrial operations, such as
cement and asphalt production and pulp and paper mills. Sources in the miscellaneous
category include dust, waste disposal, unplanned structure and car fires, residential
natural gas combustion, and non-agricultural open burning (mostly residential green
waste burning).
83 V. Ramanathan et al. 2013. Black Carbon and the Regional Climate of California. Report to the
California Air Resources Board No. 08-323. http://www.arb.ca.gov/research/apr/past/08-323.pdf
40 April 11, 2016