2010 Feb. 5: CA San Diego: Ramanathan: Set the Sun on Black Carbon:

Set the Sun on Black Carbon – Feb. 5, 2010
By V. Ramanathan
Monday, Jan 25, 2010
Over a four-day period in December 1952, a thick still fog settled on London. By the time it dissipated, an estimated 5,000 people had been killed. The culprit was the smoke and sulphur particles belching forth from thousands of chimneys throughout the city. Soot or black carbon is a major component of smoke. In addition to the health hazards, recent research has revealed that the black carbon traps significant amount of sunlight in the air, thus linking air pollution with climate change.

Fog forms when water vapour condenses on tiny particles in the air. The sources of those particles are both natural and manmade. In cities like London and Los Angeles, man-made particles from industrial smoke can outnumber natural particles by factors of two to 10 while in cities like Delhi, Beijing or Mexico City, smoke particles can be 10 to 100 times more. During winter, sudden drops in temperature trigger condensation of moisture on the haze particles, leading to persistent fog events. This smoke-filled fog or smog blocks sunlight from reaching the ground causing dimming and visibility reduction — which in turn cools the ground.

The 1952 London fog made the city colder, so people threw more coal on their home fires and fed the toxic haze, what we would now refer to as a brown cloud. There is also a feedback of sorts that develops when fog and smoke mix. The intense solar heating of air and dimming at the ground by the soot can make things worse; eventually, the pollution will be concentrated at ground level. In London, the elderly and other vulnerable residents literally suffocated to death as they walked the streets.

Smoke from one kitchen fire or one lorry may seem innocuous enough but when burning in their millions, and combined with episodes like the recent heavy fog that blanketed Delhi, the historical precedents should alarm us. The particles remain aloft for as much as two weeks, enough time for the pollution to become widespread and blanket all of the Indo-Gangetic plains with a 3 km thick “brown cloud” — and even coat Himalayan glaciers with a layer of black carbon, as seen routinely in satellite images. The estimated regional impacts include large-scale dimming, disruption of monsoon rainfall, melting of Himalayan snowpacks and glaciers, decrease in rice yields and a contribution to nearly one million deaths annually.

Black carbon is sometimes thought of as “poor man’s pollution”. This is not the case; it is a worldwide problem, a major source of global climate change. Indeed, per capita emissions of black carbon in the United States and China are larger than India’s. In developed nations, diesel is the major source whereas, in India, rural cooking with wood and dung as well as diesel are major sources. Villagers can’t afford fuels any cleaner than the free wood and dung they use in their mud-stoves.

But as climate change problems go, this is a situation in which there is good news. In the wake of last month’s largely failed climate talks in Copenhagen, nations have a chance to take action that I believe will produce nearly instantaneous benefits: reducing their black carbon emissions. Pilot programmes to replace homemade stoves with cleaner-burning alternatives are already gaining a foothold. India, in particular, is a pioneer in clean cookstove initiatives. One project in which I am involved, Project Surya, is an experiment, based out of the village of Khairatpur in UP, to measure the atmospheric effects that use of clean cookers can make. Deploying stoves that burn wood much more cleanly than the mud-stoves, we anticipate measurements revealing an island of clean air.

I estimate that with a Rs 40,000-crore one-time investment, several problems can be significantly mitigated. That sum would buy clean stoves for 150 million households as well as replace polluting kerosene lamps with solar lamps across rural India. Unlike the greenhouse gas carbon dioxide, which lingers in the atmosphere for more than a century, black carbon is washed from the sky in two weeks and hence elimination of its source will have immediate impacts. The act would make India a global leader in air pollution and climate change response. In addition to safeguarding the health of its people and water supply, the direct economic benefit to India’s poor will be immediate, as the new stoves and lamps earn credits in carbon-equivalent markets.

The deadly London fog of 1952 was thankfully never repeated. England took immediate measures to safeguard the health of its citizenry. It reduced a contributor to global warming long before anyone cared about such matters. India has a similar opportunity; only this time it has a far greater understanding of what’s at stake.
The writer is distinguished professor of climate and atmospheric sciences at Scripps Institution of Oceanography at the University of California, San Diego


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