International Regulation of Urban Smog Since the 1940s - Air Pollution and Global Warming: History, Science, and Solutions - page 185

oxides of nitrogen [NO x (g)]. Such emissions were sus-
pected of exacerbating ozone in the petitioning states.
In September 1998, the U.S. EPA implemented a rule
(known as the Nitrogen Oxide SIP Call )that required
these twenty-two states and the District of Columbia
to submit SIPs that addressed the regional transport of
ozone. The rule required reductions of NO x (g), but not
nonmethane organic gases (NMOGs), in these states by
2003.
In 2005, the U.S. EPA established the Clean Air
Interstate Rule (CAIR) ,which mandated reductions
in power plant SO 2 (g) emissions by 70 percent and
NO x (g) emissions by 60 percent relative to 2003 lev-
els in twenty-eight eastern states and the District of
Columbia. The emission reductions would be obtained
by a cap-and-trade system by which overall emis-
sion limits and pollution allowances were set each
year, and industries could trade among each other
for the pollution allowances. Enforcement of the reg-
ulation was based on monitoring of emissions and
penalties for exceeding emission allowances. On July
6, 2010, the U.S. EPA proposed a modification to
CAIR, expanding it to thirty-one states and reduc-
ing power plant SO 2 (g) emissions by 71 percent and
NO x (g) emissions by 52 percent relative to 2005 levels
by 2014.
Transboundary pollution between Canada and the
United States is formally recognized through the
Canada-U.S. Air Quality Agreement. Article V of
the agreement states that Canada and the United States
must notify each other of any proposed projects within
100 km of the border that would be likely to emit more
than 82 tonnes/yr of SO 2 (g), NO x (g), CO(g), TSPs, or
ROGs. Between 1998 and 2010, the United States noti-
fied Canada of sixty-nine new facilities.

On a smaller scale, the United States and Mex-
ico implemented a cooperative study, the Big Bend
Regional Preliminary Visibility Study, to examine
causes of visibility reduction in Big Bend National Park.
In 1998, this preliminary study concluded that sources
in both the United States and Mexico degraded visibil-
ity in the park, depending on the wind conditions. In
September 2002, a joint U.S.-Mexico program called
Border 2012 wasproposed with the goal of reducing
air pollution and other environmental problems within
100 km on each side of the border in ten U.S. and Mex-
ican border states. This program is administered by the
U.S. EPA and the Mexican Ministry of the Environ-
ment and Natural Resources and provides funding for
projects in local communities to study and reduce air
pollution.

8.1.14. Smog Alerts
Because ozone is a criteria pollutant and its mixing
ratios exceed federal and state standards more than do
those of any other pollutant and because high levels of
ozone are often good indicators of the severity of pho-
tochemical smog problems, many cities in the United
States and worldwide issue smog alerts when ozone
levels reach certain plateaus. Smog alert levels exist for
pollutants aside from ozone as well. Table 8.3 identi-
fies the mixing ratios of ozone, carbon monoxide, and
nitrogen dioxide required to trigger a California stan-
dard violation; a federal standard violation; a California
health advisory; and a California Stage 1, 2, and 3 smog
alert.
Smog alerts in Los Angeles have been in place since
the 1950s. Ozone levels required for a Stage 1, 2, or 3
alert are based on the relative health risk associated

Table 8.3. Mixing ratios required before the given 1-hour standard is exceeded

Ozone Carbon monoxide Nitrogen dioxide

1-hour average 1-hour average 1-hour average

Health standard level mixing ratio (ppbv) mixing ratio (ppmv) mixing ratio (ppbv)

California standard 90 20 180

National Ambient Air Quality Standards (NAAQS) 120 a 35 100

Health advisory 150 b - -

Stage 1 smog alert b 200 40 600

Stage 2 smog alert b 350 75 1,200

Stage 3 smog alert b 500 100 1,600

a Prior to 1997.
b Applies to California.