Encyclopedia of Environmental Science and Engineering, Volume I and II

748 NITROGEN OXIDES REDUCTION

United States Environmental Protection Agency

(USEPA). The National Emissions Standards for

Hazardous Air Pollutants (NESHAP’s) set in ear-

lier versions of the CAA will remain intact, but the

USEPA will now be required to use the best dem-

onstrated emissions control practices in a particu-

lar industry to regulate sources for that industry.

Under standards set by the USEPA, major sources

will be required to apply Maximum Available

Control Technology (MACT). A major source is

defined as one that emits 10 tons/year of a HAP or

25 tons/year of any combination of HAPs.

• Title IV —Under Title IV, the USEPA is required
  to establish a program to reduce the occurrence of
  acid rain. Because SO 2 and NO x are the two main
  contributors to acid rain, facilities that fall under
  control of Title IV will be forced to meet certain
  standards and will be required to obtain an acid
  rain permit.


• Title V —A comprehensive operating permit pro-
  gram was established for all significant air emission
  sources.


• Title VI —Under this Title, a new national program
  was developed to phase out the use of chlorofluoro-
  carbons (CFCs) and similar compounds to protect
  the stratospheric ozone layer.


• Title VII —The USEPA’s enforcement ability was
  greatly enhanced with more criminal and civil
  powers.

Included in the Title I requirements are the National Ambient

Air Quality Standards (NAAQS), which specify the maximum

allowable concentrations for six criteria pollutants. These

pollutants are: (1) carbon monoxide; (2) lead; (3) nitrogen

oxides; (4) ozone; (5) particulates ( 10 microns diameter);

and (6) sulfur oxides. There are two types of NAAQS, which

are defined in the USEPA 40 CFR Part 50 Regulations:

• primary—standards are designed to protect the
  public health.


• secondary—standards are designed to protect the
  public from a pollutant’s effects on visibility, per-
  sonal comfort, properly, etc.

If an airshed area exceeds the ambient air concentrations of

one of these pollutants, then that area is considered to be

in nonattainment. For nitrogen oxides, the primary and sec-

ondary National Ambient Air Quality Standards expressed

as annual arithmetic mean concentration are 0.053 parts per

million (100 m g/m^3 ).^8 This limit should not be exceeded,

during any 12 consecutive month period, for the annual aver-

age of the 24-hour concentrations. Figure 1^9 shows the con-

trol technologies required by facilities to meet the NAAQS.

The three main categories are BACT, LAER, and RACT.

BACT or Best Available Control Technology, is defined by

the CAA as “ ... an emission limitation based on the maxi-

mum degree of reduction of each pollutant ... which the per-

mitting authority ... ”^9 considers appropriate. BACT applies

to new or modified sources of emissions in attainment areas.

LAER or Lowest Achievable Emission Rate applies to new

or modified sources in nonattainment areas. It refers to the

most stringent emission limitation achieved by a similar

facility or a particular source category.^9 RACT or Reasonably

NAAQS

Sources in

attainment areas

New or

modified sources

Best Available

Control Technology

Lowest Achievable

Emission Rate

Reasonably Available

Control Technology

Maximum Achievable

Control Technology

Generally Available

Control Technology

New or

modified sources

Areas sources

NESHAP

Major sources

Sources in non-

attainment areas

New or

modified sources

Existing sources

Case by case

Fewer than

30 sources

More than or equal

to 30 sources

FIGURE 1 Relationships between control technologies and standards.^9

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