Where does haze-forming pollution come from?

This is a complex question to answer because only some of the
haze-causing particles are directly released into the air. Many haze-causing
particles are actually formed in the air when pollutant "precursor" gases
undergo a chemical reaction in the sky.  Haze-causing particles and their
precursor gases come from both nature and man-made sources.  Natural
sources can include windblown dust, wildfires, "biogenic" emissions from
trees and coastal emissions from the ocean.  Man-made sources can
include motor vehicles, electric utility and industrial fuel burning, and
manufacturing operations.  In addition, the formation of haze is greatly
impacted by factors such as humidity and weather.  

What is Haze?

Where does haze-forming pollution come from?

What is being done about haze?

What can you do?

What is a Regional Planning Organization (RPO)?