Simple answer: Burning of fossil fuels is by far the biggest source of air pollution. This produces nitrogen oxides and sulphur oxide which can lead to acid rain, particles and unburnt hydrocarbons which lead to smog, Carbon dioxide which leads to the enhanced greenhouse effect and climate change. so the best thing we can do is to stop burning fossil fuels or at least reduce our reliance on them.
Detailed answer: As always things are more complicated than they seem! As you know there are many different things that involve burning of fuel – petrol cars, diesel-powered trucks and buses, ships, coal-fired power stations, solid fuel burning in the home (coal/peat and wood). A major part of my research is to work out how much each of these different sources contribute to air pollution. we have mad measurements in a variety of places. Our most detailed study was in Cork City and we worked out that during summer months traffic is the major source while in winter months solid fuel burning takes over and contributes more than 50% of air pollution. So even though there is a smoky coal ban in Cork city, fuel burning is still the major contributor! Clearly we still need to make improvements!