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“30 percent in patients complaining of respiratory issues, according to news reports.
NASA's Terra satellite acquired these natural-color images of northeastern China on Jan. 14 and Jan. 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 Jan. 3 image.)
At the time the Jan. 14 image was taken by satellite, ground-based sensors at the U.S. Embassy in Beijing reported PM2.5 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's small enough to enter the passages of the human lungs. Most PM2.5 aerosol particles come from the burning of fossil fuels and biomass (wood fires and agricultural burning). The World Health Organization considers PM2.5 to be safe when it's below 25.
Image courtesy of NASA.