4 The record articles

“Black Carbon” Emissions

Posted: January 18th, 2012

Author: All4 Staff 


Four sessions at the U.S. EPA – AWMA Information Exchange that was held in Research Triangle Park, North Carolina this past December were either directly or indirectly related to Black Carbon emissions.  There is growing momentum both domestically and internationally to regulate emissions of Black Carbon from a climate change perspective as well as a human health perspective.

What Is Black Carbon?

The term “Black Carbon” is essentially a fancier name for soot.  Soot, as defined by Merriam-Webster Online is “a black substance formed by combustion or separated from fuel during combustion, rising in fine particles, and adhering to the sides of the chimney or pipe conveying the smoke; especially: the fine powder consisting chiefly of carbon that colors smoke.”   A more technical definition of Black Carbon can be found in Climate Change 2001: Working Group I: The Scientific Basis as “operationally defined species based on measurement of light absorption and chemical reactivity and/or thermal stability; consists of soot, charcoal, and/or possible light-absorbing refractory organic matter.”  In essence, Black Carbon or soot emissions have been around as long as fire has.

Why are There Concerns Regarding Black Carbon Emissions?

Climate Change Concerns – Black Carbon emissions are viewed by some as the second largest source of global warming and are understood to play an important, but evolving, role in understanding climate change.  Aerosols, including Black Carbon, contribute to radiative forcing in the atmosphere by both scattering and absorbing infrared radiation. In addition, Black Carbon emissions deposited on snow and ice absorb solar radiation and accelerate the melting of snow and ice caps.

Health Concerns – Black Carbon is a primary component of fine particulate matter (PM2.5) emissions, typically comprising 3 to 12% of PM2.5 emissions in U.S. urban areas.    Human exposure to PM2.5 emissions has been associated with a range of health effects.  PM2.5 emissions are capable of traveling deep into the lungs.  Long term exposure to PM2.5 emissions is suspected to aggravate existing conditions, such as asthma, and has been linked to increased rates of chronic bronchitis, reduced lung function, and increased mortality from lung cancer and heart disease.  In addition, Black Carbon is generally a by-product of fossil fuel and biomass combustion and consists of many complex organic chemical compounds thereby adding to concerns regarding toxicity.  Polycyclic Aromatic Hydrocarbons (PAHs) are intermediates in the formation of soot and are currently regulated as hazardous air pollutants (HAPs) as Polycyclic Organic Matter (POM).

What are Typical Sources of Black Carbon Emissions?

Domestically, emissions of Black Carbon originate primarily from mobile source diesel emissions (~ 50%), biomass burning (~ 32%), and fossil fuel combustion (~ 13%). Biomass burning is broadly characterized as wildfires, agricultural burning, and residential wood combustion.  The distribution of domestic Black Carbon emissions is expected to shift to primarily biomass burning over the next 20 years as controls are implemented on mobile diesel combustion emissions.  The U.S. currently emits approximately 6% of the global Black Carbon emissions.

The international profile of Black Carbon emissions differs from that of the U.S. In the developed countries, the Black Carbon profile mimics that of the U.S.  However, in many undeveloped areas of Africa, Asia, and South America, the bulk of the Black Carbon emissions are associated with the combustion of biomass (e.g., forest, savanna, agricultural waste, and biofuel).  The broad variety of Black Carbon emission sources across various global regions will result in varying mitigation strategies.

Why Mitigate Black Carbon Emissions?

Black Carbon emissions are increasingly viewed as an easy target for regulation that will result in multiple environmental and human health benefits.  U.S. EPA believes that reducing Black Carbon emissions can lead to “immediate” climate benefits.  As mentioned above, reducing emissions of Black Carbon will reduce PM2.5 emissions, which will also impact regional haze programs.  Reducing Black Carbon emissions is also viewed as reducing emissions of HAPs, since PAHs (regulated as POM) are believed to be a constituent of Black Carbon. U.S. EPA also believes that reducing emissions of Black Carbon can slow the rate of glacial and polar ice cap melting over the next several decades.

When Can We Expect Black Carbon Emissions to be Regulated?

Black Carbon emissions are already indirectly regulated as PM2.5 and as HAPs (i.e., POM).  Explicit regulations that target Black Carbon emissions are likely years away.  However, there is growing interest in mitigating Black Carbon emissions domestically and internationally.  The Waxman-Markey Climate and Energy Bill requires a report to Congress along with domestic and international recommendations for Black Carbon emission mitigation. There is also signed appropriations language that mandates a Black Carbon report to Congress by April 2011.


Based on the multiple benefits that U.S. EPA believes will result from mitigating Black Carbon emissions, it seems logical that an effort to regulate emissions of Black Carbon cannot be far behind.  Stay tuned.


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