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Climate change

China launches satellite to monitor nation’s greenhouse gas emissions

Experts, however, have questioned how accurate its figures will be if it tries to take readings through the smog that frequently envelops the mainland

PUBLISHED : Thursday, 22 December, 2016, 9:34am
UPDATED : Monday, 12 June, 2017, 12:53pm

China launched a satellite to monitor its greenhouse gas emissions early on Thursday, but experts have questioned how accurate its figures will be if it has to take readings during thick smog.

The satellite was launched via a Long March-2D rocket from the Jiuquan Satellite Launch Centre in the northwestern Gobi Desert, the state-run news agency Xinhua said.

The initiative from the world’s biggest greenhouse gas emitter comes as large sections of northern China have been shrouded in near record levels of air pollution for most of the past week, disrupting flights, closing factories and schools, and forcing the authorities to issue red alerts.

The 620 kg satellite TanSat was sent into orbit about 700 km above the Earth and will monitor the concentration, distribution and flow of carbon dioxide in the atmosphere.

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The mission aims to precisely identify the source of carbon dioxide emissions and can even target areas as small as one factory.

The information will help the government make or implement policies such as a tax on carbon emissions. The satellite will also generate new data for continuing international negotiations on greenhouse gas reductions.

The satellite measures carbon dioxide by analysing sunlight that hits the ground and bounces back to space.

Carbon dioxide in the atmosphere absorbs light at certain wavelengths and leaves dark lines in the spectrum of light.

Sensitive detectors in the satellite can analyse these lines to estimate the concentration of carbon dioxide in a given area.

However, the technology called absorption spectroscopy works best on a clear day, according to an environmental scientist at Peking University.

Naturally occurring cloud and dust can create distortions in the measurements, which have to be carefully calibrated.

But if light is bounced back by sulphates in smog before reaching the ground, the results will be even more inaccurate said the researcher, who asked not to be named.

A recent study by scientists from China, Germany and the United States found smog in Beijing can produce almost as much sulphates as a volcano’s eruption near its surface.

In cases of severe smog, such as the air pollution which has blanketed much of northern China this month, the satellite may have difficulty measuring the amount of carbon dioxide close to the ground, leading to relatively low estimates, the researcher said.

It is premature, however, to judge the accuracy of TanSat’s results before the first batch of data is received, according to a researcher at the Chinese Academy of Sciences who is familiar with the project.

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The project team have considered some of the difficulties in measuring carbon dioxide through smog in their designs, the researcher said.

Unlike other carbon satellites, TanSat carries special equipment called a cloud and aerosol polarimetry imager, which can help correct errors caused by small water droplets and air pollutants.

The probe also measured light near the infrared range, which had a better capability to penetrate smog.

The satellite will also work with numerous ground carbon dioxide monitoring stations to further improve its accuracy.

However the researcher warned that monitoring carbon dioxide emissions from space was a relatively new technology with many problems unsolved, including smog potentially distorting results.

The United States and Japan have also launched a carbon satellite and they “cannot not deal with smog, either”, he said.