in Mississippi

EPA must designate areas as meeting (attainment) or failing to meet (nonattainment) the required
standards. The CAA requires states to develop a general plan to attain and maintain the NAAQS
in all areas of the country and a specific plan to attain the standards for each area designated
nonattainment for a NAAQS. State and local air quality management agencies develop these
plans, known as State Implementation Plans (SIPs), and submit those plans to the EPA for
approval. If a SIP is not acceptable, EPA can take over enforcing the CAA in that state.
Nitrogen Dioxide
NO 2 forms when fuel is burned at high temperatures. The primary manmade sources of NO 2 are
motor vehicles (49%) and electric utilities (27%).
In 1971, EPA established the first primary and secondary NO 2 standard at 53 parts per billion
(ppb) averaged annually. (40 C.F.R. § 50.11) In 2010, EPA established the first hourly NO 2
standard. This new 1-hr standard is set at 100 ppb. (75 Fed. Reg. 6474)
Ozone
Ozone is primarily formed when nitrogen oxides and volatile organic compounds (VOCs) react
in the presence of sunlight. Primary VOC contributors are automobile and industrial exhaust.
Since the 1970’s, EPA has periodically revised the ozone NAAQS. In 1971, EPA set the first
primary and secondary NAAQS at 0.08 parts per million (ppm) over a 1-hr averaging period. In
1979, the EPA revised the primary and secondary standards upward to 0.12 ppm. (40 C.F.R. §
50.9) In 1997, EPA revised the primary and secondary standards back to 0.08 ppm, but changed
the averaging period to an 8-hr average concentration. (40 C.F.R. § 50.10) In 2008, EPA again
lowered primary and secondary standards to 0.075 ppm. (40 C.F.R. § 50.15)
Sulfur Dioxide
Sulfur dioxide primarily emitted from stationary sources such as coal-fired power plants, steel
mills, refineries, and pulp and paper mills. Electric utilities produce about 70% of all sulfur
dioxide.
In 1971, EPA created two sulfur dioxide standards: (1) an annual average and (2) a maximum
24-hour concentration. The annual average standard was set at 30 ppb. (40 C.F.R. § 50.4) The
24-hour standard was set at 140 ppb. (40 C.F.R. § 50.4)
In 2009, EPA proposed to establish a new 1-hr primary standard within the range of 50 to 100
ppb. In 2010, EPA established a new 1-hr standard at a level of 75 ppb. The EPA also revoked
both existing 24-hr and annual primary standards. (75 Fed. Reg. 35520)
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