oEPA
United States
Environmental
Protection Agency
Report to Congress on Black Carbon:
Executive Summary
Department of the Interior, Environment, and Related Agencies Appropriations Act, 2010
March 2012
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Printed on 100% recycled/recyclable process chlorine-free paper with 100% post-consumer fiber using vegetable oil-based ink.
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EPA-450/S-12-001
March 2012
Report to Congress on Black Carbon:
Executive Summary
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Office of Atmospheric Programs
Office of Radiation and Indoor Air
Office of Research and Development
Office of Transportation and Air Quality
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The full Report to Congress on Black Carbon
(EPA-450/R-12-001) is available online at
http://www.epa.gov/blackcarbon.
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Highlights
Black carbon (BC) is the most strongly light-
absorbing component of particulate matter (PM),
and is formed by the incomplete combustion of
fossil fuels, biofuels, and biomass.
BC is emitted directly into the atmosphere in the
form of fine particles (PM2.5). The United States
contributes about 8% of the global emissions of
BC. Within the United States, BC is estimated to
account for approximately 12% of all direct PM2.5
emissions in 2005.
BC contributes to the adverse impacts on human
health, ecosystems, and visibility associated with
PM2.5.
BC influences climate by: 1) directly absorbing
light, 2) reducing the reflectivity ("albedo")
of snow and ice through deposition, and 3)
interacting with clouds.
The direct and snow/ice albedo effects of BC are
widely understood to lead to climate warming.
However, the globally averaged net climate effect
of BC also includes the effects associated with
cloud interactions, which are not well quantified
and may cause either warming or cooling.
Therefore, though most estimates indicate that BC
has a net warming influence, a net cooling effect
cannot be ruled out.
Sensitive regions such as the Arctic and the
Himalayas are particularly vulnerable to the
warming and melting effects of BC.
BC is emitted with other particles and gases,
many of which exert a cooling influence on
climate. Therefore, estimates of the net effect
of BC emissions sources on climate should
include the offsetting effects of these co-emitted
pollutants. This is particularly important for
evaluating mitigation options.
BC's short atmospheric lifetime (days to weeks),
combined with its strong warming potential,
means that targeted strategies to reduce BC
emissions can be expected to provide climate
benefits within the next several decades.
The different climate attributes of BC and
long-lived greenhouse gases make it difficult to
interpret comparisons of their relative climate
impacts based on common metrics.
Based on recent emissions inventories, the
majority of global BC emissions come from Asia,
Latin America, and Africa. Emissions patterns and
trends across regions, countries and sources vary
significantly.
Control technologies are available to reduce BC
emissions from a number of source categories.
BC mitigation strategies, which lead to reductions
in PM2.5, can provide substantial public health and
environmental benefits.
Considering the location and timing of emissions
and accounting for co-emissions will improve the
likelihood that mitigation strategies will be
Report to Congress on Black Carbon
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Highlights
properly guided by the balance of climate and
public health objectives.
Achieving further BC reductions, both
domestically and globally, will require adding a
specific focus on reducing direct PM2.5 emissions
to overarching fine particle control programs.
The most promising mitigation options identified
in this report for reducing BC (and related
"soot") emissions are consistent with control
opportunities emphasized in other recent
assessments.
- United States: The United States will achieve
substantial BC emissions reductions by 2030,
largely due to controls on new mobile diesel
engines. Other source categories in the United
States, including stationary sources, residential
wood combustion, and open biomass burning
also offer potential opportunities.
- Global: The most important BC emissions
reduction opportunities globally include
residential cookstoves in all regions; brick kilns
and coke ovens in Asia; and mobile diesels in
all regions.
- Sensitive Regions: To address impacts in
the Arctic, other assessments have identified
the transportation sector; residential heating;
and forest, grassland and agricultural
burning as primary mitigation opportunities.
In the Himalayas, studies have focused
on residential cooking; industrial sources;
and transportation, primarily on-road and
off-road diesel engines.
A variety of other options may also be suitable
and cost-effective for reducing BC emissions,
but these can only be identified with a tailored
assessment that accounts for individual countries'
resources and needs.
Despite some remaining uncertainties about BC
that require further research, currently available
scientific and technical information provides
a strong foundation for making mitigation
decisions to achieve lasting benefits for public
health, the environment, and climate.
Report to Congress on Black Carbon
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Executive Summary
Black carbon (BC) emissions have important
impacts on public health, the environment, and
the Earth's climate. BC is a significant component of
particle pollution, which has been linked to adverse
health and environmental impacts through decades
of scientific research. Recent work indicates that
BC also plays an important role in climate change,
although there is more uncertainty about its effects
on climate than for greenhouse gases (GHG), such
as carbon dioxide and methane. BC has been linked
to a range of climate impacts, including increased
temperatures, accelerated ice and snow melt, and
disruptions to precipitation patterns. Importantly,
reducing current emissions of BC may help slow
the near-term rate of climate change, particularly
in sensitive regions such as the Arctic. However,
BC reductions cannot substitute for reductions in
long-lived GHGs, which are necessary for mitigating
climate change in the long run.
Despite the rapidly expanding body of scientific
literature on BC, there is a need for a more
comprehensive evaluation of both the magnitude
of particular global and regional climate effects due
to BC and the impact of emissions mixtures from
different source categories. To advance efforts to
understand the role of BC in climate change, on
October 29, 2009, Congress requested the U.S.
Environmental Protection Agency (EPA) conduct a BC
study as part of /-/./?. 2996: Department of the Interior,
Environment, and Related Agencies Appropriations
Act, 2010. Specifically, the legislation stated that:
"Not later than 18 months after the date of
enactment of this Act, the Administrator, in
consultation with other Federal agencies, shall
carry out and submit to Congress the results of a
study on domestic and international black carbon
emissions that shall include
• an inventory of the major sources of black carbon,
• an assessment of the impacts of black carbon on
global and regional climate,
• an assessment of potential metrics and
approaches for quantifying the climatic effects
of black carbon emissions (including its radiative
forcing and warming effects) and comparing
those effects to the effects of carbon dioxide and
other greenhouse gases,
• an identification of the most cost-effective
approaches to reduce black carbon emissions,
and
• an analysis of the climatic effects and other
environmental and public health benefits of
those approaches."
To fulfill this charge, EPA has conducted an intensive
effort to compile, assess, and summarize available
scientific information on the current and future
impacts of BC, and to evaluate the effectiveness of
available BC mitigation approaches and technologies
for protecting climate, public health, and the
environment. As requested by Congress, EPA
has consulted with other federal agencies on key
elements of this report, including inventories, health
and climate science, and mitigation options. The
report draws from recent BC assessments, including
work under the United Nations Environment
Programme (UNEP) and the World Meteorological
Organization (WMO), the Convention on Long
Range Transboundary Air Pollution (CLRTAP), and
the Arctic Council. Each of these individual efforts
provides important information about particular
sectors, regions, or issues. The task outlined for EPA
by Congress is broader and more encompassing,
requiring a synthesis of currently available
information about BC across numerous bodies
of scientific inquiry. The results are presented in
this Report to Congress on Black Carbon. The key
messages of this report can be summarized as
follows.
1. Black carbon is the most strongly light-
absorbing component of particulate matter
(PM), and is formed by the incomplete
combustion of fossil fuels, biofuels, and
biomass.
BC can be defined specifically as a solid form of
mostly pure carbon that absorbs solar radiation
(light) at all wavelengths. BC is the most effective
form of PM, by mass, at absorbing solar energy;
Report to Congress on Black Carbon
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Executive Summary
Global BC Emissions, 2000 (7,600 Gg)
0.5% 0.7%
19.3%
U.S. BC Emissions in 2005 (0.64 Million Tons)
1.1%
35.5%
52.3%
19.0%
35.3%
25.1%
1.0%
6.8%
• Open Biomass Burning Domestic/Residential
1 (Includes Wildfires)
Transp°rt Other
• Energy/Power
Figure A. BC Emissions by Major Source Category. (Source: Lamarque et al., 2010 and U.S. EPA)
other types of particles, including sulfates, nitrates
and organic carbon (OC), generally reflect light. BC
is a major component of "soot," a complex light-
absorbing mixture that also contains organic carbon.
Recent estimates of BC emissions by source category
in the United States and globally are shown in Figure
A.
2. BC is emitted directly into the atmosphere in
the form of fine particles (PM2.S). The United
States contributes about 8% of the global
emissions of BC. Within the United States,
BC is estimated to account for approximately
12% of all direct PM2_5 emissions in 2005.
Many countries have significantly higher
PM2.S emissions than the United States,
and countries with a different portfolio of
emissions sources might have a significantly
higher percentage of BC.
3. BC contributes to the adverse impacts on
human health, ecosystems, and visibility
associated with PM2.S.
Short-term and long-term exposures to PM2.5 are
associated with a broad range of human health
impacts, including respiratory and cardiovascular
effects, as well as premature death. PM2.5, both
ambient and indoor, is estimated to result in millions
of premature deaths worldwide, the majority of
which occur in developing countries. The World
Health Organization estimates that indoor smoke
from solid fuels is the 10th major mortality risk
factor globally, contributing to approximately 2
million deaths annually. Women and children are
particularly at risk. Ambient air pollution is also a
significant health threat: according to the WHO,
urban air pollution is among the top ten risk factors
in medium- and high-income countries. Urban air
pollution is not ranked in the top ten major risk
factors in low-income countries since other risk
factors (e.g., childhood underweight and unsafe
water, sanitation and hygiene) are so substantial;
however, a much larger portion of the total deaths
related to ambient PM2.5 globally are expected to
occur in developing regions, partly due to the size of
exposed populations in those regions. PM2.5 is also
linked to adverse impacts on ecosystems, to visibility
impairment, to reduced agricultural production in
some parts of the world, and to materials soiling and
damage.
Over the past decade, the scientific community
has focused increasingly on trying to identify the
health impacts of particular PM2.5 constituents, such
as BC. However, EPA has determined that there is
insufficient information at present to differentiate
the health effects of the various constituents of
PM25; thus, EPA assumes that many constituents
are associated with adverse health impacts. It
is noteworthy that emissions and ambient
concentrations of directly emitted PM2.5 are often
highest in urban areas, where large numbers of
people live.
Report to Congress on Black Carbon
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Executive Summary
4. BC influences climate through multiple
mechanisms:
• Direct effect: BC absorbs both incoming and
outgoing radiation of all wavelengths, which
contributes to warming of the atmosphere and
dimming at the surface.
• Snow/ice albedo effect: BC deposited on snow and
ice darkens the surface and decreases reflectivity,
thereby increasing absorption and accelerating
melting.
• Other effects: BC also alters the properties of
clouds, affecting cloud reflectivity and lifetime
("indirect effects"), stability ("semi-direct effect")
and precipitation.
5. The direct and snow/ice albedo effects of
BC are widely understood to lead to climate
warming. However, the globally averaged net
climate effect of BC also includes the effects
associated with cloud interactions, which
are not well quantified and may cause either
warming or cooling. Therefore, though most
estimates indicate that BC has a net warming
influence, a net cooling effect cannot be ruled
out. It is also important to note that the net
radiative effect of all aerosols combined
(including sulfates, nitrates, BC and OC) is
widely understood to be negative (cooling) on
a global average basis.
The direct radiative forcing effect of BC is the best
quantified and appears to be positive and significant
Black carbon direct TOA forcing (W nr2)
90,= , , , =, —5
45
0
-45
-90
90
45
-45
-90
Black carbon cryosphere forcing (W rrr2)
5
2
1
0.5
0.25
0.1
0.05
0.025
Figure B. Regional Variability in Direct Radiative Forcing and Snow/Ice Albedo Forcing for BC from All
Sources, simulated with the Community Atmosphere Model. (Source: Bond et al., 2011)
Report to Congress on Black Carbon
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Executive Summary
on both global and regional scales. This warming
effect is augmented by deposition of BC on snow and
ice. These effects are shown in Figure B. The central
estimates of global average direct forcing by BC from
surveyed studies range from +0.34 to +1.0 Watts
per square meter (W rrr2). A recent UNEP/WMO
assessment presented a narrower central range of
+0.3 to +0.6 W m2. These estimates are generally
higher than the 2007 Intergovernmental Panel on
Climate Change (IPCC) estimate of +0.34 (±0.25) W
m2.
The snow/ice albedo effect from BC has been
estimated in recent studies to add about +0.05
W m-2, generally less than the +0.1 (±0.1) W m-2
estimated by the IPCC; however, UNEP/WMO found
that when the snow/ice albedo forcing estimates are
adjusted to account for the greater warming efficacy
of the snow/ice deposition mechanism, the snow/
ice albedo effect could add +0.05 to +0.25 W m2 of
forcing. The sum of the direct and snow/ice albedo
effects of BC on the global scale is likely comparable
to or larger than the forcing effect from methane,
but less than the effect of carbon dioxide;1 however,
there is more uncertainty in the forcing estimates for
BC.
The climate effects of BC via interactions with clouds
are more uncertain, and their net climate influence
is not yet clear. All aerosols (including BC) affect
climate indirectly by changing the reflectivity
(albedo) and lifetime of clouds. The net indirect
effect of all aerosols is very uncertain but is thought
to have a net cooling influence. The IPCC estimated
the global average cloud albedo forcing from all
aerosols as -0.7 W m2 (with a 5 to 95% confidence
range of -0.3 W m2 to -1.80 W rrr2). The IPCC did
not provide quantitative estimates of the effect of
aerosols on cloud lifetime, and the contribution of
BC to these indirect effects has not been explicitly
quantified to date. BC has additional effects on
clouds—including changes to cloud stability and
enhanced precipitation from colder clouds—that
can lead to either warming or cooling. However, few
quantitative estimates of these effects are available,
and significant uncertainty remains. Due to all of
the remaining gaps in scientific knowledge, it is
difficult to place quantitative bounds on the forcing
attributable to BC impacts on clouds at present;
however, UNEP/WMO have provided a central
forcing estimate of -0.4 to +0.4 W rrr2 for all of the
cloud effects of BC combined.
The sign and magnitude of the net climate forcing
from BC emissions are not fully known at present,
1 The IPCC's radiative forcing estimates for elevated concentrations
of CO2 and methane are +1.66 W m 2 and +0.48 W m 2, respectively.
largely due to remaining uncertainties regarding the
effects of BC on clouds. There is inconsistency among
reported observational and modeling results,
and many studies do not provide quantitative
estimates of cloud impacts. In the absence of a full
quantitative assessment, the current scientific basis
for understanding BC climate effects is incomplete.
Based on a limited number of modeling studies,
the recent UNEP/WMO assessment estimated that
global average net BC forcing is likely to be positive
and in the range of 0.0 to +1.0 W rrr2, with a best
estimate of +0.6 W rrr2; however, further work is
needed to refine these estimates.
6. Sensitive regions such as the Arctic and the
Himalayas are particularly vulnerable to the
warming and melting effects of BC.
Studies have shown that BC has especially strong
impacts in the Arctic, contributing to earlier spring
melting and sea ice decline. All particle mixtures
reaching the Arctic are a concern, because even
emissions mixtures that contain more reflective
(cooling) aerosols can lead to warming if they are
darker than the underlying ice or snow. Studies
indicate that the effect of BC on seasonal snow
cover duration in some regions can be substantial,
and that BC deposited on ice and snow will continue
to have radiative effects as long as the BC remains
exposed (until the snow melts away or fresh snow
falls). BC has also been shown to be a significant
factor in the observed increase in melting rates of
some glaciers and snowpack in parts of the Hindu
Kush-Himalayan-Tibetan (HKHT) region (the "third
pole").
7. BC contributes to surface dimming, the
formation of Atmospheric Brown Clouds
(ABCs), and changes in the pattern and
intensity of precipitation.
The absorption and scattering of incoming solar
radiation by BC and other particles cause surface
dimming by reducing the amount of solar radiation
reaching the Earth's surface. In some regions,
especially Asia, southern Africa, and the Amazon
Basin, BC, sulfates, organics, dust and other
components combine to form pollution clouds
known as Atmospheric Brown Clouds (ABCs). ABCs
have been linked to surface dimming and a decrease
in vertical mixing, which exacerbates air pollution
episodes. ABCs also contribute to changes in the
pattern and intensity of rainfall, and to observed
changes in monsoon circulation in South Asia. In
general, regional changes in precipitation due to BC
and other aerosols are likely to be highly variable,
with some regions seeing increases while others
experience decreases.
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Executive Summary
BC, 2000
0.1 0.2 0.5 1 2 5 10 20
Figure C. BC Emissions, 2000, Gg. (Courtesy of Tami Bond, produced based on data from Bond et al., 2007)
8. BC is emitted with other particles and gases,
many of which exert a cooling influence
on climate. Therefore, estimates of the net
effect of BC emissions sources on climate
should include the offsetting effects of these
co-emitted pollutants. This is particularly
important for evaluating mitigation options.
Some combustion sources emit more BC
than others relative to the amount of co-
pollutants; reductions from these sources have
the greatest likelihood of providing climate
benefits.
The same combustion processes that produce BC
also produce other pollutants, such as sulfur dioxide
(SO2), nitrogen oxides (NOX), OC and CO2. Some of
these co-emitted pollutants result in "scattering" or
reflecting particles (e.g. sulfate, nitrate, OC) which
exert a cooling effect on climate. The sign and
magnitude of the forcing resulting from particular
emissions mixtures depend on their composition.
For example, the particles emitted by mobile diesel
engines are about 75% BC, while particle emissions
from biomass burning are dominated by OC. Sources
rich in BC have a greater likelihood of contributing to
climate warming, and this may affect climate-related
mitigation choices. Although OC generally leads to
cooling, some portion of co-emitted OC, notably
brown carbon (BrC), partially absorbs solar radiation.
The net contribution of BrC to climate is presently
unknown.
Atmospheric processes that occur after BC is
emitted, such as mixing, aging, and coating, can also
affect the net influence on climate.
9. BC's short atmospheric lifetime (days to
weeks), combined with its strong warming
potential, means that targeted strategies
to reduce BC emissions can be expected to
provide climate benefits within the next
several decades.
Because the duration of radiative forcing by BC is
very limited, the climate will respond quickly to BC
emissions reductions, and this can help slow the
rate of climate change in the near term. In contrast,
long-lived GHGs may persist in the atmosphere
for centuries. Therefore, reductions in GHG
emissions will take longer to influence atmospheric
concentrations and will have less impact on climate
on a short timescale. However, since GHGs are the
largest contributor to current and future climate
change, and because GHGs accumulate in the
atmosphere, deep reductions in these pollutants are
necessary for limiting climate change over the long-
term.
Emissions sources and ambient concentrations of
BC vary geographically and temporally (Figure C),
resulting in climate effects that are more regional
and seasonal than the more uniform effects of
long-lived, well-mixed GHGs. Likewise, mitigation
actions for BC will produce different climate results
depending on the region, season, and sources in the
area where emissions reductions occur.
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Executive Summary
10. The different climate attributes of BC and
long-lived GHGs make it difficult to interpret
comparisons of their relative climate impacts
based on common metrics.
Due in large part to the difference in lifetime
between BC and CO2, a comparison between the
relative climate impacts of BC and CO2 (or other
climate forcers) is very sensitive to the metric used.
There is currently no single metric (e.g., Global
Warming Potential or GWP) that is widely accepted
by the science and research community for this
purpose. However, new metrics designed specifically
for short-lived climate forcers like BC have recently
been developed, and these metrics may enable
better prioritization among mitigation options with
regard to potential net climate effects.
11. Based on recent emissions inventories (2000
for global and 2005 for the United States), the
majority of global BC emissions come from
Asia, Latin America, and Africa. The United
States currently accounts for approximately
8% of the global total, and this fraction is
declining. Emissions patterns and trends
across regions, countries and sources vary
significantly.
Though there is significant uncertainty in global BC
emissions inventories, recent studies indicate that
global BC emissions have been increasing for many
decades. However, emissions of BC in North America
and Europe have declined substantially since the
early 1900s and are expected to decline further in
the next several decades due to pollution controls
and use of cleaner fuels. Elsewhere, BC emissions
have been increasing, with most of the increase
coming from developing countries in Asia, Africa
and Latin America. According to available estimates,
these regions currently contribute more than 75%
of total global BC emissions, with the majority
of emissions coming from the residential sector
(cookstoves) and open biomass burning. Current
emissions from the United States, OECD Europe,
the Middle East, and Japan come mainly from the
transportation sector, particularly from mobile diesel
engines. In the United States, nearly 50% of BC
emissions came from mobile diesel engines in 2005.
12. Control technologies are available to reduce
BC emissions from a number of source
categories.
BC emissions reductions are generally achieved by
applying technologies and strategies to improve
combustion and/or control direct PM2.5 emissions
from sources. Though the costs of such mitigation
approaches vary, many reductions can be achieved at
reasonable costs. Controls applied to reduce BC will
help reduce total PM2.5 and other co-pollutants.
13. BC mitigation strategies, which lead to
reductions in fine particles, can provide
substantial public health and environmental
benefits.
Strategies to reduce BC generally lead to reductions
in emissions of all particles from a particular source.
Thus, while it is not easy to reduce BC in isolation
from other constituents, most mitigation strategies
will provide substantial benefits in the form of
PM2.5 reductions. Reductions in directly emitted
PM25 can substantially reduce human exposure,
providing large public health benefits that often
exceed the costs of control. In the United States,
the average public health benefits associated with
reducing directly emitted PM2.5 are estimated to
range from $290,000 to $1.2 million per ton PM2.5
in 2030 (2010$). The cost of the controls necessary
to achieve these reductions is generally far lower.
For example, the costs of PM controls for new diesel
engines are estimated to be about $14,000 per ton
PM2.5 (2010$). BC reduction strategies implemented
at the global scale could provide very large benefits:
the PM25 reductions resulting from BC mitigation
measures could potentially result in hundreds of
thousands of avoided premature deaths each year.
14. Mitigating BC can also make a difference
in the short term for climate, at least in
sensitive regions.
Benefits in sensitive regions like the Arctic, or in
regions of high emissions such as Asia, may include
reductions in warming and melting (ice, snow,
glaciers) and reversal of changes in precipitation
patterns. BC reductions could help reduce the
rate of warming soon after they are implemented.
However, available studies also suggest that BC
mitigation alone would be insufficient to change
the long-term trajectory of global warming (which is
driven by GHGs).
15. Selecting optimal BC mitigation measures
requires taking into account the full suite
of impacts and attempting to maximize
co-benefits and minimize unintended
consequences across all objectives (health,
climate, and environment).
With a defined set of goals, policymakers can
evaluate the "mitigation potential" within each
country or region. The mitigation potential depends
on total BC emissions and key emitting sectors,
and also depends on the availability of control
technologies or alternative mitigation strategies.
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POTENTIAL BENEFITS = MITIGATION POTENTIAL +/- CONSTRAINING FACTORS
Goals
Climate
Radiative Forcing
Temperature
Ice/Snow Melt
Precipitation
Health
Ambient Exposures
Indoor Exposures
Environment
Surface Dimming
Visibility
Emissions sources
Stationary
Sources
Brick Kilns
Coke Ovens
Diesel Generator:
Utilities
Flaring
Mobile
Sources
On-Road Diesel
On-Road Gasoline
Construction Equip.
Agricultural Equip.
Locomotives
Marine
Open Biomass
Burning
Agricultural Burning
Prescribed Burning
Residential
Cooking and
Heating
Cookstoves
Wood stoves
Hydronic Heaters
Mitigation options
Available Control
Technologies
e.g. Diesel
Participate Filters
Alternative Strategies
to Reduce Emissions
e.g. Efficiency
Improvements, Substitution
Timing
Location
Atmospheric
Transport
Co-Emitted
Pollutants
Cost
Existing Regulatory
Programs
Implementation
Barriers
Uncertainty
Figure D. Policy Framework for Black Carbon Mitigation Decisions. (Source: U.S. EPA.)
As illustrated in Figure D, the ideal emissions
reduction strategies will also depend on a range of
constraining factors, including:
• Timing
• Location
• Atmospheric Transport
• Co-emitted Pollutants
• Cost
• Existing Regulatory Programs
• Implementation Barriers
• Uncertainty
16. Considering the location and timing of
emissions and accounting for co-emissions
will improve the likelihood that mitigation
strategies will be properly guided by the
balance of climate and public health
objectives.
PM mitigation strategies that focus on sources
known to emit large amounts of BC—especially
those with a high ratio of BC to OC, like diesel
emissions—will maximize climate co-benefits. The
timing and location of the reductions are also very
important. Some of the most significant climate
benefits of BC-focused control strategies may
come from reducing emissions affecting the Arctic,
Himalayas and other ice and snow-covered regions.
The effect of BC emissions reductions on human
health is a function of changing exposure and the
size of the affected population. The largest health
benefits from BC-focused control strategies will
occur locally near the emissions source and where
exposure affects a large population.
17. Achieving further BC reductions, both
domestically and globally, will require adding
a specific focus on reducing direct PM2.S
emissions to overarching fine particle control
programs.
BC reductions that have occurred to date (largely
in developed countries) are mainly due to control
programs aimed at PM2.5, not targeted efforts to
reduce BC per se. Greater attention to BC-focused
strategies has the potential to help protect the
climate (via the BC reductions achieved through
Report to Congress on Black Carbon
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Executive Summary
direct PM2.5 controls) while ensuring continued
improvements in public health (via control of direct
PM2.5in highly populated areas). Even if such controls
are more costly than controls on secondary PM
precursors, the combined public health and climate
benefits may justify the expense.
18. The most promising mitigation options
identified in this report for reducing BC (and
related "soot") emissions are consistent with
control opportunities emphasized in other
recent assessments.
• United States: The United States will achieve
substantial BC emissions reductions by 2030,
largely due to controls on new mobile diesel
engines. Diesel retrofit programs for in-use
mobile sources are a valuable complement to new
engine standards for reducing emissions. Other
source categories in the United States, including
stationary sources (industrial, commercial and
institutional boilers, stationary diesel engines,
uncontrolled coal-fired electric generating units),
residential wood combustion (hydronic heaters
and woodstoves), and open biomass burning also
offer potential opportunities but have more limited
mitigation potential due to smaller remaining
emissions in these categories, or limits on the
availability of effective BC control strategies.
- Total mobile source BC emissions are
projected to decline by 86% by 2030 due
to regulations already promulgated. BC
emissions from mobile diesel engines
(including on-road, non road, locomotive, and
commercial marine engines) in the United
States are being controlled through two
primary mechanisms: (1) emissions standards
for new engines, including requirements
resulting in use of diesel particulate filters
(DPFs) in conjunction with ultra low sulfur
diesel fuel; and (2) retrofit programs for
in-use mobile diesel engines, such as EPA's
National Clean Diesel Campaign and the
SmartWay Transport Partnership Program.
Substantial future reductions in mobile diesel
emissions are anticipated through new engine
requirements and diesel retrofit programs.
- BC emissions from stationary sources in the
United States have declined dramatically in
the last century, with remaining emissions
coming primarily from coal combustion
(utilities, industrial/commercial boilers, other
industrial processes) and stationary diesel
engines. Available control technologies and
strategies include use of cleaner fuels and
direct PM2.5 reduction technologies such
as fabric filters (baghouses), electrostatic
precipitators (ESPs), and DPFs.
- Emissions of all pollutants from residential
wood combustion (RWC) are currently
being evaluated as part of EPA's ongoing
review of emissions standards for residential
wood heaters, including hydronic heaters,
woodstoves, and furnaces. Mitigation options
include providing alternatives to wood,
replacing inefficient units or retrofitting
existing units.
- Open biomass burning, including both
prescribed fires and wildfires, represents a
potentially large but less certain portion of
the U.S. BC inventory. These sources emit
much larger amounts of OC compared to
BC. The percent of land area affected by
different types of burning is uncertain, as are
emissions estimates. Appropriate mitigation
measures depend on the timing and location
of burning, resource management objectives,
vegetation type, and available resources. For
wildfires, expanding domestic fire prevention
efforts may help to reduce BC emissions.
Global: The most important BC emissions
reduction opportunities globally include residential
cookstoves in all regions; brick kilns and coke ovens
in Asia; and mobile diesels in all regions. A variety
of other opportunities may exist in individual
countries or regions.
- Other developed countries have emissions
patterns and control programs that are
similar to the United States, though the
timing of planned emissions reductions may
vary. Developing countries have a higher
concentration of emissions in the residential
and industrial sectors, but the growth of
the mobile source sector in these countries
may lead to an increase in their overall
BC emissions and a shift in the relative
importance of specific BC-emitting sources
over the next several decades.
- For mobile sources, both new engine
standards and retrofits of existing engines/
vehicles may help reduce BC emissions in
the future. While many other countries have
already begun phasing in emissions and fuel
standards, BC emissions in this category
in developing countries are expected to
continue to increase. Emissions control
requirements lag behind in some regions,
as does on-the-ground deployment of DPFs
and low sulfur fuels. Further or more rapid
10
Report to Congress on Black Carbon
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Executive Summary
reductions in BC will depend on accelerated
deployment of clean engines and fuels.
Emissions from residential cookstoves are
both a large source of BC globally and a
major threat to public health. Approximately
3 billion people worldwide cook their food or
heat their homes by burning biomass or coal
in rudimentary stoves or open fires, resulting
in pollution exposures that lead to 2 million
deaths each year. Mitigation in this sector
represents the area of largest potential public
health benefit of any of the sectors considered
in this report. Significant expansion of current
clean cookstove programs would be necessary
to achieve large-scale climate and health
benefits. A wide range of improved stove
technologies is available, but the potential
climate and health benefits vary substantially
by technology and fuel. Setting BC emissions
reductions as a policy priority would drive
cookstove efforts toward solutions that
achieve this goal. A number of factors point to
much greater potential to achieve large-scale
success in this sector today.
The largest stationary sources of BC
emissions internationally include brick
kilns, coke ovens (largely from iron/
steel production), and industrial boilers.
Replacement or retrofit options already exist
for many of these source categories.
Open biomass burning is the largest source
of BC emissions globally. However, emissions
of OC (including potentially light absorbing
BrC) are approximately seven times higher
than BC emissions from this sector, and
more complete emissions inventory data are
needed to characterize impacts of biomass
burning and evaluate the effectiveness
of mitigation measures at reducing BC.
Expanded wildfire prevention efforts may
help to reduce BC emissions globally.
Successful implementation of mitigation
approaches in world regions where biomass
burning is widespread will require training
in proper burning techniques and tools to
ensure effective use of prescribed fire.
• Sensitive Regions: To address impacts in the
Arctic, other assessments have identified the
transportation sector (land-based diesel engines
and Arctic shipping); residential heating (wood-
fired stoves and boilers); and forest, grassland
and agricultural burning as primary mitigation
opportunities. In the Himalayas, studies have
focused on residential cooking; industrial
sources (especially coal-fired brick kilns); and
transportation, primarily on-road and off-road
diesel engines.
19. A variety of other options may also be
suitable and cost-effective for reducing BC
emissions, but these can only be identified
with a tailored assessment that accounts for
individual countries' resources and needs.
Some potential sectors of interest for further
exploration include agricultural burning, oil and gas
flaring, and stationary diesel engines in the Arctic far
north.
20. Despite some remaining uncertainties about
BC that require further research, currently
available scientific and technical information
provides a strong foundation for making
mitigation decisions to achieve lasting
benefits for public health, the environment,
and climate.
Report to Congress on Black Carbon
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Acknowledgments
Lead Authors
Erika Sasser (Chair)
James Hemby (Vice-Chair)
Ken Adler
Susan Anenberg
Chad Bailey
Larry Brockman
Linda Chappell
Benjamin DeAngelo
Rich Damberg
Contributing Authors
Farhan Akhtar
Bryan Bloomer
Edmund Coe
Amanda Curry Brown
Penny Carey (retired)
Jason DeWees
Pat Dolwick
Robin Dunkins
Dale Evarts
Brian Gullett
John Guy (retired)
Beth Hassett-Sipple
Michael Hays
John Dawson
Neil Frank
Michael Geller
Gayle Hagler
Brooke Hemming
Lesley Jantarasami
Thomas Luben
John Mitchell
Jacob Moss
Carey Jang
Jim Jetter
Terry Keating
John Kinsey
Amy Lamson
Robin Langdon
Bill Linak
Bryan Manning
Allison Mayer
Harvey Michaels
Andy Miller
Ron Myers
Glenn Passavant
Venkatesh Rao
Joann Rice
Marcus Sarofim
Joseph Somers
Charlene Spells
Sara Terry
Matthew Witosky
Rob Pinder
Marc Pitchford
Adam Reff
Michael Rizzo
Charles Schenk
Darrell Sonntag
Larry Sorrels
Lauren Steele
Nicholas Swanson
Lori Tussey
Karen Wesson
Gil Wood
Rosa Yu
Additional Contributions to the Report
Jamie Bowers
Devin Hartman
Project Support
Lourdes Morales
Joseph Dougherty
Megan Melamed
Joseph Tikvart
Report Production
Sonoma Technology, Inc.
Steve Brown
Chelsea Jennings
Marina Michaels
Jana Schwartz
Editorial Support
Stratus Consulting
Nimmi Damodaran
Joe Donahue
Report to Congress on Black Carbon
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Acknowledgments
Peer Review
Council on Clean Air Compliance Analysis, Black Carbon Review Panel
C. Arden Pope, III (Chair) Ivan J. Fernandez Denise Mauzerall
Alberto Ayala H. Christopher Frey Surabi Menon
Michelle Bell Jan Fuglestvedt Richard L Poirot
Kevin J. Boyle D. Alan Hansen Armistead (Ted) Russell
Sylvia Brandt Joseph Helble Michael Walsh
Linda Bui MarkJacobson John Watson
James J. Corbett Jonathan Levy
EPA Science Advisory Board Staff
Stephanie Sanzone
Vanessa Vu
Contributing Federal Departments and Agencies
Centers for Disease Control and Prevention
Council on Environmental Quality
Department of Energy
Department of Transportation
Federal Highway Administration
Federal Aviation Administration
National Aeronautics and Space Administration
National Institute of Child Health and Human Development
National Institute of Environmental Health Sciences
National Institute of Standards and Technology
National Oceanic and Atmospheric Administration
Natural Resources Conservation Service
Office of Management and Budget
Office of Science and Technology Policy
United States Department of State
United States Agency for International Development
United States Department of Agriculture
United States Forest Service
Special Photo Credits
Cookstove in Guatemala (Cover): Nigel Bruce, University of Liverpool, UK
Brick Kiln in Kathmandu (Highlights): Sara Terry, U.S. Environmental Protection Agency
Outdoor Wood Boiler (Highlights): Philip Etter, Vermont Department of Environmental Conservation
74 Report to Congress on Black Carbon
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