Natural factors such as forest fires further affect air quality by emitting carbon monoxide and other gases that lead to the production of ozone.

CNN: Canadian forest fires add to U.S. pollution

The Montreal Protocol is the international agreement designed to protect the ozone layer by phasing out production of Cfc's and halons.

BBC: News | Sci/Tech | Ozone hole reaches record size

In fact, ozone levels have declined even as production has dramatically increased in the Barnett shale.

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He was instrumental in getting chlorofluorocarbon (CFC) refrigerant production banned because they accelerated the destruction of stratospheric ozone over and near Antarctica in early spring.

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In the Dallas-Fort Worth area, as total gas production in 2009 increased by 94 percent from 2000 levels, the levels of ground level ozone fell by nearly 15 percent.

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