Many of us have heard about the terrible air quality in Beijing, China in a very abstract way. On January 10, 2012 the Earth Observatory, a NASA operated imaging satellite, captured images of a large cloud of smog that limited visibility to 200 meters. Smog clouds like this are more common in the winter, due to a phenomenon known as temperature inversion. (Essentially, during the shorter days of winter, the sun has less time to warm up the air, so the air does not rise and take the pollution with it.)
There are two sizes of particles that create this obscuring haze: 10 micrometers (about the diameter of a human cell) and 2.5 micrometers. The larger particles cause respiratory problems in the lungs, yet the smaller ones can actually enter the bloodstream through the lungs. While China currently monitors only 10-micrometer pollution, the U.S. Embassy in Beijing tweets hourly readings of the more hazardous 2.5-micrometer particulate. Below is a screen grab from the time of the Earth Observatory picture above:
Note that the concentrations are actually above the measurable index which only goes up to an Air Quality Index of 500! For a good comparison, at this writing the city of Chicago has an Air Quality Index of 72 (and that’s not great). This really makes me thankful that we have such relatively strict particulate pollution regulations.
A good resource for residents of the United States is the government-operated monitoring website Air Now.
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