It’s been known for years that burning fossil fuels releases black carbon particles into the air, commonly called soot. But for the first time, researchers – including several from Texas A&M University – have precisely pinpointed how much these particles impact air quality and climate in two very different cities: Beijing and Houston.
Renyi Zhang, Misti Levy Zamora and Don Collins, all with Texas A&M’s Department of Atmospheric Sciences, along with colleagues from the Jet Propulsion Laboratory, Peking University, the University of California-San Diego have had their work published in the current issue of PNAS (Proceedings of the National Academy of Sciences).
The team studied particulate matter over Houston and Beijing to learn how the properties of black carbon particles change over time.
They identified two distinct phases in black carbon evolution: an initial change that is mainly in shape, followed by a period of growth into denser particles that absorb more sunlight.
“We show that high levels of pollutants in Beijing rapidly coat black carbon particles and accelerate the particle growth, producing a larger ‘feedback’ that worsens outbreaks of severe haze,” Zhang explains.
“Since the air pollution in Beijing is some of the worst in the world, obviously this rapid change in black carbon particles tends to worsen the conditions. This means that the changes in air quality occur quicker in Beijing than in Houston. Our study also suggests that black carbon mitigation in Beijing improves air quality and climate conditions.”
Houston was selected, the authors say, because the “air there is also fairly polluted, but the main pollutant is ozone, not particulate matter. The many petro-chemical plants in the Houston area directly contribute to the ozone pollution.
“Beijing’s pollution, on the other hand, is mainly due to particulate matter that is typical of conditions in a rapidly developing country that has many industrial factories, power plants, along with congested traffic. Ozone is not a major problem there. The two cities make a strong contrast.”
Of the world’s 20 most polluted cities, 16 of them are in China, and Beijing’s air problems have been known for decades.
A recent study shows that the air in Beijing is so polluted that breathing it does as much damage to a person’s lungs as smoking 40 cigarettes a day, and that air pollution in China kills 4,000 people every day, which accounts for about 17 percent of all deaths in China.
Facemasks are a common site on Chinese citizens, so much so that companies that make them are among the most profitable in that country. Particulate matter levels over much of China are many times below acceptable levels set by the World Health Organization.
The researchers found a rapid change in black carbon particles are found in Beijing, which causes the particles to absorb more light and heat the air, and it directly affects meteorological conditions such as causing air stagnation.
“The whole process leads to a very stable atmosphere, which tends to prevent air movement,” Zhang adds.
“As a result, pollutants are mainly trapped near the surface, and this is responsible for severe pollution episodes in Beijing.”
The study was partially funded by the Houston Advanced Research Center and Robert A. Welch Foundation.