Image: NASA’s satellite-derived map of air pollution, throughout planet earth, between 2001-2006. Specifically, the “warmer” areas of the color map (yellow, orange, red) indicate higher densities of problematic particles known as fine particulate matter, or PM2.5. These are 2.5 micrometers or less in diameter, roughly 1/10 the width of a strand of human hair. They’re small enough to sneak past your body’s defenses, and lodge inside your lungs.
Sure makes China look like a place to stay away from. Now, you have to be careful with rainbow maps like this because we react very strongly to red but not much at all to blues. Also, did you notice that the scale is non-linear.
There are 20 different shades of color for 0-20 but only 12 for 20-80. So the map is really designed to help differentiate the lower levels from each other while screaming out the higher levels. This is actually a much better way to display a rainbow color scheme. Provide less differentiation between each shade of red since we really see all of the as hot, while providing a ot of different shades of blue for the lower scale, since most of the world is lower and it allows greater differentiation.
So, the scale, while non-linear is effective in allowing us to rapidly see what parts of the world are doing poorly while getting a good idea of how to differentiate the large part of the world that is doing much better. So the ‘brightest’ region in the US has 1/5th the level of particulates as China.