What factors have reduced air pollution in western europe

Policies that favours public transport and cycling to personal transport.s
Sustainable energy use practices.
Focus on renewable energies,
focus on recycling and reuse.

Policies that favour public transport and cycling to personal transport.s
Sustainable energy use practices.
Focus on renewable energies,
focus on recycling and reuse.

Explanation:
catalytic converters, fuel potency, and improved engines. The third stage of conversion may be a system that monitors the exhaust stream and uses this data to regulate the fuel injection system. there's associate degree chemical element device mounted upstream of the converter, which means it's nearer to the engine than the device. This device tells the engine pc what quantity chemical element is within the exhaust.

Physical systems is the answer