1.   Air pollution has become one of the most significant health problems of our time.

2.   But on the West Coast, pollution has become an irritant between Canada and the United States, with Americans doing much of the complaining.

3.   In the last few years, urban air pollution has become noticeable for the first time in this pristine Himalayan outpost.

4.   Dioxin pollution has increasingly become a concern in this country, and levels here are believed to be among the highest in the world.

5.   What is missing in urban centres where air pollution has become critical, is an integrated public transport system.