Over the last few months, you may have heard about China’s growing smog problem. In Beijing, Shanghai, and many other areas of China, the smog is so bad that the air quality index (AQI) has started spiking over 400, and sometimes reaching 500 — the top of the AQI scale. Just for some context, an AQI above 100 is generally considered unhealthy — over 300, and we’re talking about a serious hazard to health (i.e. it can be lethal). To better illustrate the scale of China’s smog problem, NASA has captured an image of China’s northeastern seaboard — in the image above (a larger version is embedded below), the telltale gray haze of hazardous airborne pollution spans the 750 miles (1200 km) between Beijing and Shanghai.

It is not unusual for regions of China to be blanketed in smog. Smog can be created by natural causes (such as volcanoes), but by far the most common cause is the burning of coal, which releases large amounts of soot particles (particulate matter, PM) and toxic gases (primarily sulfur dioxide). Combine these airborne pollutants with unfavorable weather (heat, lack of wind) and you get smog. If you continue to burn lots of coal, and you still don’t get the necessary winds to disperse the pollution, the smog gets worse. Coal is particularly dangerous because it produces a lot of PM2.5 — particles that are 2.5 microns or less, which can really irritate your respiratory system.

China, as you probably know, burns a lot of coal. China is the largest consumer of coal in the world, currently mining and consuming around three billion tons of of coal per year (about 50% more than the US, which is the world’s second largest consumer of coal). Most of China’s coal is burned to produce electricity, and for industrial uses such as making steel. As China’s economy continues to grow at a truly insane rate, as does its consumption of coal — and its production of smog. Just recently, faced with chronic delays due to smog — only 18% of flights depart on time from Beijing — China’s aviation authority ordered pilots to train specifically for heavy-smog landings.

The satellite image (below) of China’s northeastern seaboard was captured by NASA’s Terra, an Earth Observing System (EOS) satellite that’s tasked with climate research. On the day the image was captured (December 7 2013), the US embassies in Bejing and Shanghai were reporting an AQI of 487 and 404. An AQI of below 50 is desirable, while most industrial areas are generally around 100-200. At an AQI of 100, sensitive groups (the elderly and those with weak lungs) start to feel the effects of the pollution; at 200-300, you should wear a mask and preferably stay indoors. An AQI of 300 to 500 is hazardous to everyone, and may result in immediate sickness, reduced lifespan, etc.

In the image, which is natural-color (how your own eyes would see it from space), the gray haze is smog. The flat gray-white area is also smog (but foggier). The whiter, more-defined features are clouds (not smog). You can click the image above to zoom in.

For a real-time map of air pollution in Asia, and the rest of the world, hit up the AQICN website. AQICN (air quality index China) collates real-time information from AQI sensors throughout China and the rest of the world, so that you can see at a glance just how bad the air pollution is in China (no other country comes close). China, for its part, is investing heavily in renewable and other non-coal-based sources of energy — but given the sheer speed at which the Chinese economy is expanding, the smog problem is definitely going to get a lot worse before it starts to get better.

Now read: A portrait of Earth’s dirty atmosphere, captured by NASA’s satellites