Two California scientists have been honored for their research into air pollution, outdoor and indoor. This year's winners of the $200,000 Tyler Prize for Environmental Achievement, John Seinfeld and Kirk Smith, have shown the far-reaching nature of the problem.
Nearly half of the world's people use biomass fuels such as wood or dried dung to cook their food, and many cook indoors.
Professor Kirk Smith of the University of California, Berkeley studies environmental impacts on human health, and wondered about the impact of smoke on the families. In the early 1980s he was studying energy use in rural Asia.
"And during that time, I noted the very smoky conditions in village households," said Smith. "I came back and I thought, well somebody must have looked at the health effects of this, and I could find nothing in the literature. My students and I looked. So we did some back-of-the-envelop calculations to figure roughly what kind of air pollution levels might exist, and we could not believe the results of our simple models."
Later measurements confirmed the estimates: household cooking produces as much smoke as 1,000 cigarettes burning per hour. His studies show that this leads to nearly two-million premature deaths a year, especially among women and children, and the emissions contribute to climate change.
Air pollution in one part of the world affects the air in another, says the other recipient of this year's Tyler Prize, John Seinfeld of the California Institute of Technology.
"Emissions from Asia will make it across the Pacific, will be in the air over the United States, and even in some cases be tracked out over the Atlantic heading to Europe," said Seinfeld. "And so you can think of the northern hemisphere as a big backyard."
He says the southern hemisphere has the same mixing, and there is long-term interaction between the hemispheres.
Seinfeld says natural and man-made substances interact.
"Every particle in the air anywhere on earth is a little kitchen sink of compounds that come from everywhere," he said. "So I got interested in understanding what this was, and it was very clear the atmosphere is just a big reactor."
He says the interactions are complicated. Human-produced greenhouse gases such as carbon dioxide are warming the atmosphere. Other man-made and natural substances can accelerate the process, or sometimes slow it. " The compounds they produce can be harmful to human health.
The scientists say environmental research requires careful measurement. In Guatemala, India, China, and other countries, Kirk Smith has overseen studies to measure household emissions and assess the long-term effects on those exposed to smoke from cooking.
Research teams are also assessing the effectiveness of low-pollution stoves, and Smith foresees widespread use of that technology when the results are in. He notes that many devices being distributed by non-profit organizations have not been fully tested.
"The motto of my research group is, you do not get what you expect, you get what you inspect," he said. "So it looks good, but we have to inspect before we can know what to expect."
He sees the financial burden being shared, as it is now in parts of China, where one third of the cost of a stove is paid by the family that uses it, one third by provincial authorities and one third with credits from the international carbon market.
He says stoves that are proven to be effective at reducing emissions will benefit families and communities and help to clear the air around the world.