Wu Da! (雾大 !) translated from Chinese means 'Heavy Fog'. It is also the answer you get from most people in the Chinese capital if you ask them what's wrong with the sky. But this 'fog' has hardly anything to do with water droplets in the air. The AQI is a scale from 0-500 measuring the pollution particles in the air. A good example would be an average day in my hometown Basel which reaches around AQI 10/500 compared to a very polluted day in Los Angeles which will reach as high as 120/500. From a visual perspective, there is a strange beauty within the smog. An intriguing soft light that covers things almost like in a magical winter storm. The famous PM 2.5 particles make for quite amazing photography.