A simple solution to air pollution from wood-burning cookstoves

Up to now, most interventions have focused on improving the cookstove to lower emissions. And that would be fine, if there were enough improved cookstoves to go around. But there aren't. In 2012, only 2.5 million improved cookstoves were distributed, improving the household air pollution situation for exactly one-half of 1 percent of the world's biomass burners.

So an interdisciplinary team of Michigan Technological University students took a different tack. They decided to look for ways to improve the cooking environment, not just the stove. And they found a low-cost, highly effective way to reduce the impact of cooking over biomass fires without designing and installing high-tech, costly stoves.

Better ventilation.

The cookstove project was born in small town on the Guatemalan border with Mexico, where Michigan Tech environmental engineering graduate student Kelli Whelan was working on an Engineers Without Borders project. She noticed that the kitchen of a family who had built an attic to insulate their house from a hot aluminum roof was much cooler than others she had visited, although they all used the same kind of wood-burning cookstove.

"That made me wonder if the temperature difference helped clear the smoke out, either by a draft or the greater temperature differential between the fire and the surrounding space," she explains.

When she returned to Michigan Tech, Whelan and several fellow environmental engineering graduate students started work on a project to explore the situation. They built both a working model of a biomass cookstove and a computer model to test different kitchen and cooking conditions.

After receiving the EPA P3 grant, they surveyed Peace Corps Master's International and Pavlis Global Technological Leadership Institute students at Tech who had worked in countries where biomass-burning cookstoves are used. They also conducted more physical and computational model tests, 57 of them, testing for the presence and transport of particulate matter, carbon monoxide and carbon, as well as comparing wind speed, temperature, humidity, roofing materials, wall height, cookstove placement and windows and doors open or closed.

"Our focus was not on ventilation, but on trying to determine which factors really influence the air quality in a kitchen and which do not," said Whelan.

They discovered that ventilation is very important. "The improved cookstoves, which are supposed to reduce emissions, actually made the air quality worse under completely enclosed conditions," she said. "In contrast, we saw the greatest reduction in ambient particulate matter and carbon monoxide with an improved cookstove and with windows and doors open."

They also learned that not all ventilation helps. "Having two windows open on opposite ends of the kitchen was best, whereas having all the windows and doors open was worse," Whelan said. "This is because having all outlets open creates turbulence inside the kitchen, and the smoke is not forced out."

The Michigan Tech students took the results of their field and computer modeling analysis of cookstove air pollution to the EPA Sustainable Design Expo in Washington, DC, last week.