[paulsutter]

Anyone know why is pollution is worst in winter? heating?

We were in India in the winter, and the smell everywhere was like smoke from burning.

[snarfy]

It's because colder air is more dense, making it more heavy and stay closer to the ground.

[robjan]

Think there is a different explanation depending on the country. In China, for instance, production is usually ramped up in the months leading up to Lunar New Year which occurs in Jan/Feb.