Black Carbon

AuthorMelissa Powers
Page 846 Legal Pathways to Deep Decarbonization in the United States
I. Introduction
Black carbon is a type of pa rticulate matter (PM) that con-
tributes to global warming by direc tly absorbing solar radi-
ation, by reducing albedo through deposition on surfaces
covered in snow and ice that would otherwise reect lig ht
back out of the earth’s atmosphere, and through complex
cloud interactions.1 A 2013 scientic review calculated
that black carbon is the second most importa nt contribu-
Author's Note: e author thanks Nathan Borgford-Parnell for
his initial help with this chapter. anks also go to Jessica Jetter
and Elias Kohn for their research assistance. Lev Blumenstein,
Natascha Smith, and Casille Systermans also provided excellent
research and analytical assistance through their work on the Green
Energy Institute’s diesel project. e extremely helpful feedback and
recommendations of Michael Gerrard, John Dernbach, and the
peer reviewers, Hannah Chang and Michael Geller, improved this
chapter a great deal. Finally, thanks to Mark Riskedahl and Amelia
Schlusser for helpful advice about how to eectively implement many
of the recommendations in this chapter.
1. T.C. Bond et al., Bounding the Role of Black Carbon in the Climate System: A
Scientic Assessment, 118 J. G R.: A 5380, 5388,
5390 (2013).
tor to warming the climate—less than carbon dioxide
(CO2), but more than methane and other greenhouse gas-
es.2 Black carbon is short-lived in the atmosphere, how-
ever, and reducing black carbon emissions could have a
quick and profound impact on climate change mitigation
by avoiding as much as one-half a degree Celsius (or nearly
one degree Fahrenheit) of warming and potentially giv-
ing the global community additional time to reduce CO2
emissions.3 Reductions of black carbon from diesel, coal,
and wood combustion could also provide additional cli-
mate and public health co-benets from reduced emissions
of CO2 and decreased exposu re to PM emissions.4 Includ-
ing black carbon in an overall decarbonization strategy
thus enhances the li kelihood that the Deep Decarboniza-
2. Id. at 5388.
3. Press Release, International Geosphere-Biosphere Programme, Black Car-
bon Larger Cause of Climate Change an Previously Assessed (Jan. 15,
4. U.S. E P A, R  C 
B C 11 (2012) [hereinafter EPA B C R].
Chapter 32
Black Carbon
by Melissa Powers
Black carbon (or soot) is a potent climate forcer that may rank second only to CO2 in warming the planet.
Reducing black carbon emissions could avoid as much as .5°C (or nearly 1° Fahrenheit) of warming. In the
United States, the major sources of black carbon emissions are diesel combustion from the transportation sector,
diesel combustion from stationary sources, coal combustion, and biomass combustion. is chapter discusses
key strategies and obstacles to reducing black carbon emissions, with a particular focus on reducing diesel fuel
use. e chapter explains how several Clean Air Act (CA A) programs that regulate emissions of ne particulate
matter, including the mobile source standards program, several stationary source programs, national ambient air
quality standards, and state implementation plans, could help reduce or eliminate black carbon emissions. e
chapter also examines programs that state and local governments could use independent of the CAA to reduce
black carbon emissions. Finally, the chapter identies obstacles to successful regulation, proposes strategies to
overcome obstacles, identies areas of uncertainty, and briey identies measures discussed in other chapters in
the book that would complement or accelerate the black carbon reduction strategies identied here.
Page 847
tion Pathways Project’s (DDPP’s) 80% reduction goal for
greenhouse gases ca n be met by 2050.5
is chapter will discuss the most viable legal strategies
to quickly reduce black carbon emissions from the tra ns-
portation, energy, and industrial sectors, as well as from
biomass combustion. Because black carbon is a compo-
nent of ne particulate matter (PM2.5), and because the
Clean Air Act (CA A) provides the most useful and expan-
sive regulatory structures for reducing PM emissions, this
chapter will focus primarily on programs under the CA A
that could reduce black carbon emissions. W here relevant,
the chapter will also identif y regulatory tools that state and
local governments can deploy—either under or indepen-
dent of the CAA—to reduce black carbon emissions. e
majority of this chapter focuses on reductions of black car-
bon from the transportation sector, and specically black
carbon emissions from diesel.
Section II of this chapter provides an overview of the
current science regarding black carbon, its contribution to
climate change, and areas of uncertainty t hat may aect
regulatory strategies. Scientists broadly recognize that
black carbon has a potent warming eect through direct
absorption of solar radiation and by reducing the albedo of
snow and ice.6 However, as Section II explains, scientists
are still learning about black carbon’s impacts on clouds
and the complex interactions between black carbon, which
has a warming eect, and other ne particles, which have
cooling eects and are often co-emitted with black car-
bon.7 As scientists develop a clearer understa nding of the
interactions between black carbon and other pollutants,
new regulatory tools may become available to spur fur-
ther reductions in black carbon. Even with this scientic
uncertainty in mind, it makes sense to reduce black car-
bon from certain sectors right away. In particula r, because
black carbon accounts for a high proportion of the PM2.5
emitted f rom diesel,8 policies focused on reducing diesel
use, particula rly from the transportation sector, could have
clear climate benets.
Section III of this chapter provides a detailed overview
of the ways in which the CA A’s mobile source programs
5. See Jessica Seddon Wallack & Veerabhadran Ramanathan, e Other Climate
Changers: Why Black Carbon and Ozone Also Matter, 88 F A. 105,
106 (2009) (describing black carbon mitigation as the “lowest hanging of the
low-hanging fruit”). e DDPP, like the Kyoto Protocol, focuses on green-
house gas reductions and does not discuss black carbon, which is a climate
forcer, but not a greenhouse gas. e recommendations in this chapter aim
to complement strategies in the DDPP to reduce greenhouse gases.
6. EPA B C R, supra note 4, at 3, 36.
7. Id. at 3, 37.
8. Id. at 7.
could reduce black carbon emissions from passenger vehi-
cles, heavy-duty trucks, and other transportation sources
that use diesel fuels. is section will also explore pre-
emption of state vehicle regulation, which is a potentially
signicant obstacle, depending upon how the U.S. Envi-
ronmental Protection Agency (EPA) under the Trump
Administration proceeds. e C AA gives the federal gov-
ernment exclusive authority over some aspects of mobile
source regulation, creates a power-sharing structure over
some other aspects of mobile source regulation, and gives
states primary authority over yet other aspects.9 As this
section will show, EPA has traditionally given states (spe-
cically, California) substantia l discretion to enact vehicle
standards. However, early signs from the Trump Admin-
istration suggest that EPA may limit the ability of states
to regulate vehicle emissions.10 Navigating the preemption
issues is a key legal ch allenge, and this section will identify
ways for states and local governments to regulate black c ar-
bon emissions without facing preemption. Finally, Section
III will also e xplore economic tools and incentives that
could support a quick transition away from diesel engines,
or at least the use of more ecient, lower emitting engines.
Section IV then discusses strategies to reduce black
carbon emissions from stationary sources, such as power
plants and industrial faci lities, primarily through C AA
programs that regulate PM. Several of the CAA’s station-
ary source programs, a ll of which already regu late PM
emissions from various types of sources, create tools to
reduce black carbon emissions.11 However, grandfather-
ing weakens the eectiveness of most stationary source
program s,12 and states are often reluctant to establish
regulatory requirements for existing sources. is section
therefore proposes ways for the federal government to limit
grandfathering and identies strategies that states can use
to regulate sources that mig ht otherwise be grandfat hered
under the federal stationary source programs.
Next, Section V focuses on regulatory strategies to
reduce black carbon emissions from residential wood burn-
ing. e CAA a gain serves as a regulatory tool, through
stationary source standards that require new woodstoves
to meet advanced technology standa rds, and through state
implementation plans (SIPs), which states must develop
9. See infra Section III.
10. See Chris Megerian, President Trump and California Soon Could Spar Over Air
Quality Rules, L.A. T, May 9, 2017,
11. See infra Section IV.
12. See infra Section IV; see also Jonathan Nash & Richard L. Revesz, Grandfa-
thering and Environmental Regulation: e Law and Economics of New Source
Review, 101 N. U. L. R. 1677 (2007).
Page 848 Legal Pathways to Deep Decarbonization in the United States
and implement to maintain air quality. Stove retrots and
replacements are other important black carbon mitigation
strategies, and funding is a critical aspect of ensuring that
older stoves are replaced.
Section VI then discusses means to limit open biomass
burning from agricultural elds and forest res. Once
again, the CA A’s SIP requirements create a federal regula-
tory tool, and states and local governments may also use
other means, such as eld burning bans and wildre pre-
vention strategies, to prevent open burns. As this section
explains, however, attempts to reduce black carbon emis-
sions from forest res present some technical challenge s, as
forest res release both warming black carbon and light-
reecting particles t hat have a cooling eect on the climate
(at least in the short term). While forest res also release
massive amounts of CO2, and preventing these emissions
is a wise long-term strategy for deep decarboniz ation,13 this
section suggests that polic ymakers should consider the net
climate impacts of using wild re prevention to reduce
black carbon emissions.
is chapter will conclude with a brief description of
other strategies that could help eliminate use of some
fuels, particularly diesel, that emit black carbon. It will
then refer the reader to other chapters in this book that
provide detailed discussions of these programs, including
those related to vehicle electrication (Chapter 14), alter-
native fuels (Chapter 27), forest management (Chapter
31), and transitioning to a carbon-free energy economy
(Chapter 24).
II. Black Carbon’s Climate Impacts and
Recommended Emissions Reduction
Unlike the other pollutants addressed in this book, black
carbon is not a greenhouse gas. Rather, black carbon is a
short-lived, but potent, climate forcer that absorbs solar
radiation and reduces albedo.14 Reductions in black car-
bon could oer signicant and almost immediate climate
mitigat ion benets .15 Although scientists are still work-
ing to understand how black carbon interacts with other
species of PM and with clouds,16 scientists recogni ze
that black carbon reductions could prevent a substantial
amount of warming.17 is section provides an overview
of how black carbon emissions aect the cli mate, identies
the major sources of black carbon emissions in the United
States, and summarizes the climate and non-climate ben-
ets that black carbon reductions could provide. is sec-
13. For a discussion of forest management strategies to promote deep decarbon-
ization, see Chapter 31.
14. EPA B C R, supra note 4, at 3.
15. Id. at 27.
16. Id. at 33.
17. Id. at 11.
tion also describes the technologies that are available to
reduce black carbon emissions, and it proposes ambitious
reduction objectives for the transportation, energy, and
residential sectors.
A. Black Carbon and Climate Change
Black carbon is the darkest and most potent light-absorb-
ing species of PM emitted from incomplete combustion
of fossil fuels and biomass.18 In the United States, the
major sources of black carbon are mobile sources (52%
total; approximately 93% of this is diesel), open biomass
combustion (35%), energy/power production (6.8%), resi-
dential sources (3.6%), industrial sources (1%), and other
sectors (the remaining 0.6%).19 Within t he mobile sourc e
category, vehicles, trains, ships, and ai rplanes that burn die-
sel for fuel emit the vast majority—93%— of black carbon,
while gasoline engines account for most of the remaining
7%.20 Of these mobile sources, older, heavy-duty on-road
and nonroad vehicles produce many more emissions than
their modern counterpar ts.21 Addressing eet turnover is
thus a key component of eective black carbon reductions.
e sources of open biomass combustion are wildres,
prescribed burning, and agricultural burning.22 Wild res
contribute about 60% of the black carbon emissions from
open combustion, with Alaskan wildres accounting for
33% of total U.S. open combustion emissions. Residen-
tial sources include wood burning for cooking and heat-
ing. Finally, the energy/power production and industrial
sources include power plants, industrial plants, and other
facilities that combust coal, diesel, and wood.23
Black carbon inuences the cli mate in three ways: (1) by
directly absorbing solar radiat ion; (2) by reducing albedo—
the amount of sunlight that is reected from earth back to
space—through deposition on lighter ground, snow, and
ice; and (3) through complex cloud interactions. First,
unlike greenhouse ga ses, which contribute to climate
change by trapping outgoing infra red radiation (or heat) in
the earth ’s atmosphere, black carbon “absorbs both incom-
ing and outgoing radiation of all wavelengths.”24 Second,
albedo reduction results from black carbon par ticles falling
on and darkening otherwi se reective surfaces such as snow
and ice. e deposition of black carbon on ice and snow
creates a dangerous feedback loop, as surfaces that would
otherwise reect sunlight out to space instead absorb it,
increasing the amount of infrared radiation available for
trapping by greenhouse gases and black c arbon.25 Trapped
18. Id. at 17.
19. Id. at 85, 88 g. 4-3.
20. Id. at 92.
21. Id. at 177.
22. Id. at 88.
23. Id. at 90 tbl. 4-2.
24. Id. at 3.
25. Id.

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