This question isn’t a common thought but refers to ‘smog’ which is air pollution produced by burning fossil fuels. This air pollution contributes to the greenhouse gases that are caught in our atmosphere, aiding an increase in the earth’s temperature.
The image above, taken over the east coast of Australia, shows a slight browning surrounding the horizon in the image. This browning is the physical form of smog that can only be seen when in relatively high concentrations. Think of it like colouring in a drawing; the lighter the pressure the lighter the colour, whereas the heavier the pressure the darker the colour. The pressure is the concentration.
In the past this browning wasn’t visible. But with the higher use of vehicles and energy sources which require fossil fuels, it has now started to show. This however can be rectified through innovation bringing nature back into balance. Help us reduce the brown and make the sky more blue.