Two ways in which human activities pollute the air:

1. Burning of fossil fuels in vehicles: When petrol and diesel are burnt in vehicles, smoke and carbon dioxide gas are produced which pollute the air. Over-dependence on fossil fuels for transportation has resulted in large-scale air pollution.

2. Industrial activities and burning of fuels: Industries release harmful gases and smoke into the air. Earlier, coal, wood, and dung cakes were used as fuels for cooking, which also caused air pollution.

Action to reduce air pollution: Use public transport instead of personal vehicles to reduce the number of vehicles on the road, thereby reducing smoke and emissions. Alternatively, walking or cycling for nearby places, using electric vehicles that do not release smoke, or planting more trees can help reduce air pollution.