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Black Carbon

What is black carbon?

Black carbon (BC) is a component of particulate matter that is highly efficient at absorbing heat, and a major element of soot. BC is formed through incomplete combustion of fossil fuels, biomass and biofuels, and enters the air as fine particulate (PM2.5).

Where does it come from?

Primary sources of black carbon include emissions from diesel engines and vehicles, biomass burning such as cook stoves and domestic wood burning, and forest fires. Other sources include domestic heating and industry.

The majority of black carbon emissions come from the developing world: China and India together contribute 25-35% of the world’s BC emissions, compared with the US as 7th highest contributor, emitting 8%.

How does it affect our health?

Black carbon contributes to the negative health impacts posed by PM2.5: respiratory and cardiovascular effects, and sometimes premature death.

Over the past decade, the scientific community has made efforts to distinguish the different health effects of different components of PM2.5, such as black carbon. However, as of yet there is insufficient evidence to differentiate individual health effects, so the present assumption is that many different components contribute to the adverse health effects of PM2.5. Of existing evidence, BC is most consistently associated with cardiovascular effects.

Environmental effects?

Locally, black carbon as a component of PM2.5 can damage ecosystems and reduce agricultural yield.

However, black carbon is becoming increasingly recognised for its previously understated role in contributing to climate change. By some estimates, black carbon vies with methane for contributing the second largest emissions toward global warming after carbon dioxide. It has a direct warming effect through absorbing light and radiating this as heat; it also has severe indirect warming effects in the Arctic. When black carbon settles on snow or ice it accelerates melting; in this way BC reduces the white space in the Arctic which reflects light away from the Earth, thus further contributing to warming.

Interestingly, BC has a very short atmospheric life span: it will stay in the air for a matter of days to weeks, unlike CO2 which remains for over a hundred years. This property has identified BC as a significant opportunity to be able to mitigate climate change quickly – and potentially make crucial headway in slowing the melting of the Arctic.

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