China's smog has gotten so bad, it's almost impossible to see skyscrapers from the air

Some areas of China are experiencing some of the worst levels of pollution.

As of Wednesday, Beijing was under a "red alert" for smog - the highest of four levels - and a "yellow alert" for fog. Other areas, particularly in northern China were still under red alert as of Wednesday for both fog and smog.

This photo, by CNN chief national security correspondent Jim Sciutto, shows just how insane the smog has gotten, enveloping the capital so much that just the tops of the buildings can be seen.

The high pollution has been going on for a number of weeks, causing flight delays, and leading to traffic bans, as part of what Business Insider's Louise Liu called  "smog season" or "airpocalypse." Colder temperatures means more coal is burned to heat homes, which exacerbates China's air pollution problem. 

Coal, and things like soot and dust, contain a particulate matter called PM 2.5. The particulates are tiny, which makes it easy for them to get stuck in the lungs, leading to conditions like asthma and chronic lung disease.

Here's a video showing the smog roll in on Sunday.

The smog is expected to lift by the end of the week.