International Regulation of Urban Smog Since the 1940s - Air Pollution and Global Warming: History, Science, and Solutions - page 189

at a wavelength of 0.55 m not be less than 10 miles

(16.09 km) outside Lake Tahoe and 30 miles (48.3 km)
in Lake Tahoe when the relative humidity was less than
70 percent. In 1990 and 1994, visibility in the eastern
Los Angeles Basin was less than the state standard on
50 percent or more of the days of each year. Such visi-
bility degradation was due primarily to aerosol particle
buildup in the eastern basin.
At the federal level, prevailing visibility data have
been collected at 280 monitoring stations at airports in
the United States since 1960. These data have been used
primarily by air traffic controllers. From an analysis of
the data, the U.S. EPA Office of Air and Radiation found
that visibility deteriorated in the eastern United States
between 1970 and 1980, but improved slightly between
1980 and 1990. Schichtel et al. (2001) similarly found
that, between 1980 and 1995, visibility improved by
about 10 percent in the eastern United States and in hazy
parts of California. According to both studies, visibility
improvements in the eastern United States coincided
with decreases in sulfur dioxide emissions .Figure 7.24
compares summer versus winter visibility in the United
States for 1991 to 1995, from the second study.
In July 1999, the U.S. EPA set regional haze rules
designed to improve visibility in 156 Class I pristine
areas (Section 8.1.9), primarily large national parks,
wilderness areas, memorial parks, and international
parks in existence as of August 1977, the month that
CAAA77 was passed. The regulations required states
to make short- and long-term efforts to reduce emis-
sions affecting haze in these areas down to natural lev-
els within 60 years. Part of these efforts required the
use of a best available retrofit technology (BART) for
industrial facilities that emit visibility-reducing air pol-
lutants. State plans were required to be submitted to the
U.S. EPA for approval. In 2006, the U.S. EPA finalized
arulethat allowed states to use emission trading to sat-
isfy the visibility improvement requirements. In 2009,
the U.S. EPA found that thirty-seven states had missed
deadlines for submitting regional haze rule plans.
Figure 8.5 shows the change in visibility in national
parks and wilderness areas in the western and east-
ern United States between 1992 and 2008. Visibility
increased in both regions during this period not only on
good visibility days, but also on midrange and poor vis-
ibility days. Visibility was uniformly lower in the east
than in the west because the relative humidity is gener-
ally higher in the east, so aerosol particles have greater
liquid water contents and larger sizes in the east than in
the west. The largest contributor to visibility reduction
in both the east and west is sulfate, which causes more

300

Best days-west

250

200

Mid-range days-west

150

Best d ays-east

100

Worst days-west

50

Mid- r ange days-east

Worst d ays-east

0

1992 1996 2000 2004 2008

Year

Figure 8.5. Visibility (visual range) in thirty national
parks and wilderness areas in the western United
States and eleven in the eastern United States,
1992-2008, on best, midrange, and worst visibility
days. From Debell et al. (2006); IMPROVE (n.d.).

than 60 percent of the visibility loss in the east and 25
to 65 percent of the loss in the west. Organic matter,
nitrates, black carbon, and soil dust cause most of the
remaining visibility loss in both regions.

8.2. Pollution Trends and Regulations
outside the United States
The United States began to consider urban air pollu-
tion reduction formally beginning in 1955, and the UK
enacted legislation in 1956 (Section 8.2.2). However,
national air pollution regulation and/or enforcement in
most other countries of the world lagged until the 1970s
through the 1990s. In the 1950s, Los Angeles, Califor-
nia, was the most polluted city in the world in terms of
ozone, and London may have been the most polluted
in terms of particulate matter. In 2011, Linfen, Beijing,
Calcutta, Mexico City, New Delhi, Cairo, Sao Paulo,
Shanghai, Jakarta, Bangkok, and Tehran were among
the most polluted.
Worldwide, 2.5 to 3 million people die each year
prematurely, and tens of millions of others suffer ill-
ness from air pollution. Of the fatalities, 1.6 million
deaths/yr are from indoor air pollution (World Health
Organization (WHO), 2005), with the rest being from
outdoor air pollution (WHO, 2002; Jacobson, 2010b).
More than half the air pollution health problems world-
wide are in developing countries. In many of the world's
cities, annual averaged outdoor PM 10 concentrations
exceed 70 gm − 3 ,much higher than the recommended

gm − 3 .Inthis section, air quality trends levels of 20