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Arizona’s Valley of the Sun “Brown Cloud”
Pollution over Phoenix
•  Observed since early 1990’s; contains C Particles and NO2 (brown) gas
•  From burning fossil fuels: cars, construction equipment, power plants, lawn mowers, leaf blowers contribute to this brown cloud
•  Weather also a key factor
Phoenix photo from http://phoenix.about.com/library/weekly/uc051601a.htm, accessed Mar 2004