abundant sunlight
high relative humidity (RH)
and reduced vertical mixing
produce conditions favorable for regional haze production. Such haze is visible from orbiting Earth satellites. The decline in visibility observed during summer months in the Northeast
Midwest
and Southeast is strongly correlated with increased use of coal to produce electrical power to serve air conditioning needs in residential and nonresidential buildings. 4.7.2.3 Pristine Air Visibility impairment has historically been a problem in U.S. urban centers; it is increasingly a problem on a broad regional scale in many areas east of the Mississippi River. In the regulatory sense
however
it has been pristine areas of the western U.S. that have received the most attention. The scenic beauty associated with our national parks
monuments
and wilderness areas is due in great measure to the high air quality
high visibility (visual ranges of 100 to 164 km (62 to 102 mi) are not uncommon)
and contrast characteristics of these regions. Major concerns include visibility-reducing and aesthetics-degrading power plant plumes and regional hazes produced by photochemical conversion of SO2. The former is commonly described as plume blight. In pristine areas
power plant plumes may maintain their distinct character for tens of kilometers downwind. The plume
and haze it will eventually produce
causes blighted vistas
destroying the unique character of some of Americaâs most beautiful landforms and environments. The problems of visibility degradation of pristine air and protection of areas of high air quality have been addressed in clean air legislation and subsequent regulatory actions by the U.S. Environmental Protection Agency (USEPA) (see Chapter 8). 4.7.2.4 Arctic Haze The phenomenon of Arctic haze was first reported by weather reconnaissance crews flying over the Arctic in the 1950s. Significant springtime visibility reduction was observed over areas such as Barrow
AK
where the environment was considered to be relatively pristine. The Arctic haze phenomenon has intensified over the past half century. It now covers a linear expanse of 800 to 1300 km (496 to 806 mi). It occurs at altitudes below 9 km (5.8 mi)
with a maximum intensity at ~4 to 5 km (2.5 to 3.1 mi). The primary cause of Arctic haze is industrial emissions of SO2
elemental carbon (EC)
HCs
metals
and other gases and particles from northern European and Eurasian sources. These pollutants are transported northward into an environment where removal processes are less efficient. A steep inversion layer (up to 30 to 40°C (86 to 104°F) differential between cooler surface and warmer air layers several hundred meters above) further contributes to the phenomenon. Sulfates
at concentrations of 2 µg/m3
are on the order of 10 to 20 times greater than would be expected from sources in the affected region. Atmospheric effects 103
Menu
