Imagine your are searching for articles about air pollution. What three keywords, besides "air pollution" would you have needed to search in order to find the following articles?

Keyword 1:
Keyword 2:
Keyword 3:

Effects of air pollutants on acute stroke mortality ; Environmental Health Perspectives v 110 no2 Feb 2002. p. 187-91

A tale of two cities: effects of air pollution on hospital admissions in Hong Kong and London compared ; Health Perspectives v 18 no1 Jan 2002. p. 67-77

Polluting your internal environment ; Environmental Health Perspectives v 110 no1 Jan 2002. p. A42-A43

Ontario launches controversial smog trading program ; Environmental Science and Technology v 36 no1 Jan 1 2002. p. 14A-15A