By Keith Randall

Attention residents of Houston, Los Angeles, Mexico City and anywhere else that has ongoing air pollution troubles: you could also be facing soot problems that could affect everything from your weather to your health, and the situation may get worse, according to a study from a Texas A&M University group published in the Proceedings of the National Academy of Sciences.

Renyi Zhang, professor of atmospheric sciences at Texas A&M and leader of the study, says there is no doubt that soot particles may not only affect cloud formation, rainfall amounts, and ultimately climate change but also could present significant human health problems in the form of respiratory ailments. The team’s work was funded by the Department of Energy, the National Science Foundation and the Welch Foundation.

Zhang and the team members studied soot particles and how they react with other pollutants in the atmosphere. Soot is found high in the atmosphere throughout the world but is especially prevalent near cities that have power plants, factories, refineries and significant amounts of diesel truck emissions. It can also be created from large areas of biomass burning, such as forest fires.

Most aerosols tend to scatter light, meaning they generally have a cooling effect on climate. Because soot is black, it absorbs light in contrast to other aerosols, meaning it tends to have a warming effect.

“Because of the way it collects other pollutants, particularly sulfate that is originated from power plants, soot can have much larger effects on visibility and cloud formation,” Zhang explains.

“We found fresh soot directly from sources have rather limited properties, but transformation of soot in the atmosphere drastically enhances their atmospheric effects. This can actually inhibit cloud formations, which can directly affect rainfall amounts, which potentially could impact drought conditions. In the Houston area, for example, we found that soot can reduce cloud coverage up to 20 percent.”

Because Houston and other cities have large numbers of factories and refineries, a process called “photochemical pollution” occurs, Zhang says. This can result in significant breathing problems for people because particles can be deposited on human lungs.

Soot can also diminish the amounts of sunlight some regions receive, which directly affects surface ozone levels from 5 to 20 percent, Zhang adds.

Making the problem worse is that soot can last for several days in the atmosphere. Emerging development from countries such as China and India , which have large numbers of factories and power plants in recent years that produce soot, could add to the problem, Zhang says.

Soot, in the form of black carbon, could also have the potential to collect on ice packs and attract more heat from the sun, even potentially accelerating the melting of the polar ice caps.

“Presently, our knowledge about soot is very limited because of its complex transformation in air and this work will help to reduce uncertainty in our effort to assess its atmospheric effects,” Zhang notes.

“Soot can affect the tiny droplets in the clouds themselves or even prevent clouds from forming at all. In that sense, soot can have a direct impact on the world’s weather, and also a direct impact on health issues. It’s a problem that faces virtually every region of the Earth.”

For more information contact Dr. Renyi Zhang by phone at 979.845.7656 or email him at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .