Stack effect? I'm not totally sure about this...
Explanation:
Large amount of tiny particles of water droplets, dust and smoke are present on a misty day. These tiny particles in the air scatter blue colour of white light passing through it. When this scattered light reaches our eyes, the smoke appears blue.
3 sig figs= 27.6
N2 + 3 H2 = 2 NH3
Reaction type: synthesis