Beijing Residents Warned To Stay Indoors

Residents of Beijing and many other cities in China were warned to stay inside in mid-January 2013 as the nation faced one of the worst periods of air quality in recent history. The Chinese government ordered factories to scale back emissions, while hospitals saw spikes of more than 20 to 30 percent in patients complaining of respiratory issues, according to news reports.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired these natural-color images of northeastern China on January 14 (top) and January 3, 2013. The top image shows extensive haze, low clouds, and fog over the region. The brightest areas tend to be clouds or fog, which have a tinge of gray or yellow from the air pollution. Other cloud-free areas have a pall of gray and brown smog that mostly blots out the cities below. In areas where the ground is visible, some of the landscape is covered with lingering snow from storms in recent weeks. (Snow is more prominent in the January 3 image.)

At the time that the January 14 image was taken by satellite, ground-based sensors at the U.S. Embassy in Beijing reported PM_2.5 measurements of 291 micrograms per cubic meter of air. Fine, airborne particulate matter (PM) that is smaller than 2.5 microns (about one thirtieth the width of a human hair) is considered dangerous because it is small enough to enter the passages of the human lungs. Most PM_2.5 aerosol particles come from the burning of fossil fuels and biomass (wood fires and agricultural burning). The World Health Organization considers PM_2.5 to be safe when it is below 25.

Also at the time of the image, the air quality index (AQI) in Beijing was 341. An AQI above 300 is considered hazardous to all humans, not just those with heart or lung ailments. AQI below 50 is considered good. On January 12, the peak of the current air crisis, AQI was 775 the U.S Embassy Beijing Air Quality Monitor—off the U.S. Environmental Protection Agency scale—and PM_2.5 was 886 micrograms per cubic meter.

NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response. Caption by Mike Carlowicz.

Instrument: Terra - MODIS

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Thick Haze Blankets China

Thick haze blanketed eastern China in early November 2011. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image on November 10. The haze extends southward from Beijing along the coastal plain bordering Bo Hai and the Yellow Sea.

Intermittent haze had clogged the skies over eastern China for at least a month by the time MODIS acquired this image. In early November 2011, The New York Times reported that Beijing had suffered from heavy air pollution for weeks, and the United States Embassy in Beijing had repeatedly registered unsafe levels of particulate matter.

Airborne particles come in different sizes, often measured in microns (also micrometers): one-millionth of a meter. Whereas Beijing’s air-monitoring center has traced particles at 10 microns or larger, the U.S. Embassy in Beijing has measured smaller particles, down to a size of 2.5 microns, known as PM2.5, according to news reports. This has caused a discrepancy in air-quality assessments, with the U.S. Embassy classifying pollution levels as hazardous on days when the local government classifies pollution levels as moderate or slight, said The New York Times. Particles with diameters of 2.5 microns or smaller are believed to pose the greatest health risks because they can lodge deeply in the lungs, according to the U.S. Environmental Protection Agency.

On November 11, 2011, People’s Daily reported that China’s vice-minister of environmental protection described the country’s air pollution standards as “rather lax.” People’s Daily further reported that the government was discussing implementing PM2.5 readings, and hoped to lower fine-particle pollution by about 10 percent by 2015.

NASA image courtesy LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Michon Scott. Instrument: Terra - MODIS

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