China did have clearer skies during Olympics: Satellite imagery


Washington : China did have clearer skies and easier breathing when it shut down factories and banished many cars in a pre-Olympic sprint to clean up Beijing’s air.

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Taking advantage of the opportunity, researchers have since analysed data from NASA’s Aura and Terra satellites that show how key pollutants responded to the Olympic restrictions.

Emission restrictions had an unmistakable impact. During the two months when they were in place, the levels of nitrogen dioxide (NO2) — a noxious gas resulting from fossil fuel combustion (primarily in cars, trucks, and power plants) — plunged nearly 50 percent.

Likewise, levels of carbon monoxide (CO) fell about 20 percent, according to atmospheric scientist Jacquelyn Witte and colleagues from NASA’s Goddard Space Flight Center in Greenbelt.

Some scientists have questioned whether Beijing’s highly publicised air quality restrictions actually had an impact. This new data shows clearly that they did. “After the authorities lifted the traffic restrictions, the levels of these pollutants shot right back up,” Witte noted.

The steep decline in certain pollutants surprised the researchers. In a preliminary analysis of the data, the effect seemed to be minimal, explained Mark Schoeberl, project scientist for Aura mission.

The reductions only became noticeable when the investigators focused tightly on the Beijing area, according to a NASA release.

“If you take a wide view, you start to pick up long distance transport of pollutants,” Schoeberl said. That seemed to be the case with sulphur dioxide (SO2), which has a longer lifetime in the atmosphere,” said Schoeberl.

“Although satellites detected reductions in levels of SO2 — a major byproduct of coal-fired power plants and a key ingredient of acid rain — the decline was more widespread due to a larger effort to reduce SO2 emissions across China, explained Kenneth Pickering, another Goddard scientist involved in the research.

Witte and colleagues presume that winds carried SO2 in from the heavily industrialized provinces to the south of Beijing. However, she cautions that it is difficult to capture accurate SO2 readings from the satellites due to difficulties detecting the gas low to the ground, where it is most abundant. It’s best to consider the SO2 measurements a work in progress, emphasised Pickering.

China is currently in the midst of a sustained effort to reduce SO2, according to the Xinhua News Agency.

These findings were presented Tuesday at the American Geophysical Union in San Francisco.