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Soot

Another nice paper from PEW.

Abstract: Over the last decade, a growing body of evidence indicates that soot and smoke from incomplete combustion are major contributors to climate change. Black carbon (BC), a soot component, is a potent climate driver that absorbs sunlight in the atmosphere, changes rainfall patterns, and when deposited on snow and ice, accelerates melting. In addition, soot can cause direct effects on health and agriculture. Climate and other effects of soot are magnified in broad regions where the strongest source emissions occur, but transported soot is also a major concern in the Arctic. The short atmospheric lifetime of soot particles also means that emissions reductions produce nearly immediate results, in contrast to most greenhouse gases (GHGs).

The argument: The principal source categories include diesel engines, small industrial sources, residential coal and solid biofuels for heating and cooking, and open biomass burning for agriculture and forestry. Control and mitigation approaches exist, but the small size and wide dispersion of these sources provide challenges. The available evidence suggests that appropriately targeted soot controls have the potential to accelerate and enhance climate and air quality when used as a complement to overall climate strategies centered on greenhouse gases. Consideration of such controls is, however, subject to a number of scientific and technical uncertainties and complexities regarding emissions, controls, and the net effect of addressing some soot sources on both global and regional scales. This paper summarizes current knowledge on the effects of soot components—BC and organic particles—on climate, and identifies sources and technologies to mitigate their impacts. It also presents perspectives on the potential role of soot mitigation approaches in developing more comprehensive climate strategies.

Here is the PEW background blog post on the issue and on the paper.  This refers to the work of  V. Ramanathan’s  and his article “The Other Climate Changers,”.  A US House Select Committee on Energy Independence and Global Warming held a hearing last Tuesday to investigate the impacts of BC pollution. The upshot is that BC policies should be complementary to efforts to reduce GHG gases. Reductions in emissions of BC would have near-term effects on reducing global warming that are impossible from actions directed at CO2 and other long-lived gases. Reducing BC is good for the environment, public health, and creates jobs.

A growing body of evidence indicates that soot and smoke are major contributors, possibly second only to carbon dioxide, to human-induced global warming. BC warms the air by absorbing sunlight in the atmosphere, changes rainfall patterns and, when deposited on snow and ice, accelerates melting. According to Ramanathan, BC’s warming effect is around 40-70% of that of CO2. However, unlike CO2, BC does not accumulate in the atmosphere; it stays in the atmosphere for a few weeks. Thus impacts are more concentrated in the areas where BC are produced, and reducing BC emissions would have near-term benefits in those areas.

BC is produced by both natural processes and human activity from the incomplete combustion of fossil fuels, biofuels, and biomass. According to Ramanthan, the regional effects of BC are particularly large over the Arctic, Africa, and Asia. BC leads to increased melting of snow and ice in the Arctic, Sahelian drought, and decreased monsoon rainfall. Primary sources include diesel engines, small industrial sources, residential coal and solid biofuels for cooking and heating, and agricultural and forest fires.

Since BC impacts are regional, there are significant local environment, public health, and economic benefits of reducing BC emissions. Reducing BC emissions in India for example, would not only produce environmental benefits of cleaner air and negate rainfall loss, but would also save lives. Ramanathan’s calculations indicate that replacing cook stoves in India with advanced biomass stoves could prevent 2 million deaths from the reduction of particulate matter produced by traditional stoves. Mitigating BC emissions would also prevent reduced rainfall and reduced agriculture yields.

According to another panelist, Conrad Schneider, reducing BC emissions can create clean jobs even in the US. Even though BC isn’t much of a climate forcing in the US and a potentially expensive source of reductions, there is a billion dollars worth of work to reduce diesel’s BC emissions. For example, retrofitting 11 million diesel engines in the US today could achieve the same environmental benefit as removing 21 million cars from the road, would save approximately 7,500 lives through reduced particulate matter pollution, and create tens of thousands of domestic jobs.

China: I am currently studying Chinese environmental issues.  This is one of the most intensely particle-polluted areas on earth – mainly due to fossil fuel burning rather than biomass combustion – the introduction of improved wood stoves in rural areas.  Over recent decades China has experienced heavy rains and flooding in the south and increased drought and dust storms in the north.  Modeling suggests an influence of BC on the drying in the north and a possible role in the south.

Soot also impacts on the retreat of the Himalayan glaciers. Apart from increasing temperatures soot deposition darkens snow and ice increasing sunlight absorption.

Of course the soot particulates are implicated in the deaths of 450,000 Chinese (infamous WHO estimates) from sulphates, BC and organic particles.  It is difficult to attribute soot alone as a particular source of mortality.

6 comments to Soot

  • conrad

    “increased drought and dust storms in the north”

    I was under the impression there is a terrible drought in the south now also (the worst in decades apparently), although I’m not sure if this is a one-off.

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