Satellite images depicting the extent of dangerous smog blanketing eastern China last month have been released by a Chinese government science agency.

Colorized composites of flyby images snapped Jan. 29 and 30 by China’s polar-orbiting Feng Yun 3A weather satellite were posted Feb. 6 on the website of the Chinese Academy of Science’s Center for Space Science and Applied Research.

Releasing the imagery was the latest sign of the Chinese government’s interest in making official pollution data more accessible to the public.

Feng Yun 3A Imagery

The kidney-shaped red swath on a Jan. 29 composite image prepared by the Space Environment Exploration Laboratory for the China Meteorological Administration marks a huge area of the sky with heavy concentrations of aerosols, mainly smoke and dust.

The red area depicts high Absorbing Aerosol Index (AAI) readings and stretches about 1,200 kilometers from the Bohai Sea in the north to Jiangxi Province in the south.

The image puts China’s capital Beijing, where heavy smog that day drew international media attention, in a yellow region with lower aerosol readings than in many other parts of the country.

The follow-up image taken the morning of Jan. 30 shows only the easternmost tip of Shandong Province still in the red with high AAI readings. Most of the aerosol cloud by that time had blown off the mainland into the sea.

Neither actual AAI readings nor any other statistics from the satellite’s monitors were included in a press release that accompanied the images. No one was available for comment at the science center, which was closed Feb. 6 for China’s Spring Festival holidays.

Environmental officials last year in the cities of Beijing and Shanghai, under public pressure following a December 2011 smog emergency, widened air quality index reports to include the concentrations of particulates smaller than 2.5 micrometers in diameter. These fine particles, known as PM 2.5, are believed to pose the greatest health risk because their small size — less than one-seventh the width of a human hair — allows them to lodge deeply in the lungs.

Prior to the change, the U.S. Embassy in Beijing had been tracking and releasing PM 2.5 data on Twitter, which is blocked in China. Starting in January, the science center’s press release said, instruments aboard Feng Yun 3A that measure ultraviolet radiation and ozone would be used by the meteorological administration to calculate AAI readings during events of “fog and haze” — government euphemisms for urban and factory smog.

“Persistent fog and haze” affected China’s “central and eastern districts from Jan. 7 to 16, and from Jan. 28 to 31,” the press release said. The images depict “haze monitoring” from Jan. 29 to 30.

The Feng Yun 3A satellite was launched in May 2008.