1fs. Smog in Southern CaliforniaLos Angeles has long had a
reputation for extremely bad air quality—and for good reason. Of all the
cities in the United States, Los Angeles is the only one classified by
the Environmental Protection Agency asan “extreme area” of noncompliance
with ozone standards. A number of factors work together to make the air
quality bad enough to earn this dubious distinction. As shown in Figure
14-2-1.Los Angeles occupies part of a basin bounded by mountains to the
north and east that block the free movement of pollutants by the sea
breeze, while the presence of a subsidence inversion during the warmer
months restricts vertical dispersion. Add to that the typically
cloud-free conditions during the midday period that trigger
photochemical reactions. And finally there is the city's well-known love
affair with the automobile, which contributes much of the estimated 2
million kilograms (2200 tons) of hydrocarbons and 1 million kilograms
(1200 tons) of NOx released each day into the four-county South Coast
Air Basin.During the summer, daily concentrations of photochemical smog
vary on a regular basis in the course of a day. Prior to the morning
rush hour, residual primary and secondary pollutants from the previous
day leave a background level of air pollution. As traffic increases
during the morning, emissions increase substantially.Early morning winds
are usually weak, which leads to little movement of pollutants. At the
same time, the low Sun angle and common presence of early morning fog
and low clouds inhibit photochemical activity. The situation normally
changes by late morning. A sea breeze usually develops along the coast
and moves pollutants inland, while clearing skies and increasing Sun
angles increase photochemical conversions.As the sea breeze develops, a
boundary called a sea breeze front separates the relatively clean marine
air from the more polluted, drier air ahead. As the sea breeze front
moves inland, it pushes the emissions eastward or northeastward. This
often creates a strong gradient in ozone concentrations near the sea
breeze front, with relatively clean air behind it and increasing
concentrations to the east or northeast (Figure 14-2-2). By late
afternoon, the cities in the eastern portion of the basin get the full
onslaught of the ad-vected pollutants, while local commuters add their
own contribution to the photochemical smog. As a result, pollution
levels can become extraordinarily high in the areas downwind of Los
Angeles.The area to the south of Los Angeles—including Orange and San
Diego counties—also has a significant air pollution problem. Usually the
air pollution in San Diego, some 150 km (100 mi) to the south, is of
local origin. During severe episodes, however, most of the pollution
originates over Los Angeles and Orange counties and gets carried into
San Diego by the wind. These episodes often occur as Santa Ana winds die
out. During the Santa Ana, the easterly winds force the basin's
pollutants offshore. As the Santa Ana begins to weaken, a thermally
induced low-pressure system over the eastern desert stretches into the
San Diego area. This creates a northwesterly flow that transports
pollution originating over Los Angeles and Orange counties. A number of
state-mandated rules have had a remarkable effect on air quality, such
as biannual smog checks on vehicles, special pollution-reducing gasoline
blends during the summer period, and rubber sleeves on gas pump nozzles
that capture escaping fumes. Figure 14-2-3 illustrates the dramatic and
consistent improvement in air quality in the Los Angeles area, showing
both the number of days that ozone exceeded federal guidelines and the
maximum eight-hour average of ozone. Though ozone pollution is still a
serious problem, the number of days with excessive concentrations is
about half of what it was during the late 1970s....FIGURE 14-2-2 Smog
Pattern. The map shows a typical pattern of smog on a summer afternoon
in the Los Angeles basin. Highest ozone concentrations (shown by dashed
lines with units of parts per hundred million) occur in the northeast,
ahead of the sea breeze front. Solid lines show the wind
direction....Describe some of the reasons why Los Angeles is so prone to
heavy air pollution. Get solution
2fs. Smog in Southern CaliforniaLos Angeles has long had a reputation for extremely bad air quality—and for good reason. Of all the cities in the United States, Los Angeles is the only one classified by the Environmental Protection Agency asan “extreme area” of noncompliance with ozone standards. A number of factors work together to make the air quality bad enough to earn this dubious distinction. As shown in Figure 14-2-1.Los Angeles occupies part of a basin bounded by mountains to the north and east that block the free movement of pollutants by the sea breeze, while the presence of a subsidence inversion during the warmer months restricts vertical dispersion. Add to that the typically cloud-free conditions during the midday period that trigger photochemical reactions. And finally there is the city's well-known love affair with the automobile, which contributes much of the estimated 2 million kilograms (2200 tons) of hydrocarbons and 1 million kilograms (1200 tons) of NOx released each day into the four-county South Coast Air Basin.During the summer, daily concentrations of photochemical smog vary on a regular basis in the course of a day. Prior to the morning rush hour, residual primary and secondary pollutants from the previous day leave a background level of air pollution. As traffic increases during the morning, emissions increase substantially.Early morning winds are usually weak, which leads to little movement of pollutants. At the same time, the low Sun angle and common presence of early morning fog and low clouds inhibit photochemical activity. The situation normally changes by late morning. A sea breeze usually develops along the coast and moves pollutants inland, while clearing skies and increasing Sun angles increase photochemical conversions.As the sea breeze develops, a boundary called a sea breeze front separates the relatively clean marine air from the more polluted, drier air ahead. As the sea breeze front moves inland, it pushes the emissions eastward or northeastward. This often creates a strong gradient in ozone concentrations near the sea breeze front, with relatively clean air behind it and increasing concentrations to the east or northeast (Figure 14-2-2). By late afternoon, the cities in the eastern portion of the basin get the full onslaught of the ad-vected pollutants, while local commuters add their own contribution to the photochemical smog. As a result, pollution levels can become extraordinarily high in the areas downwind of Los Angeles.The area to the south of Los Angeles—including Orange and San Diego counties—also has a significant air pollution problem. Usually the air pollution in San Diego, some 150 km (100 mi) to the south, is of local origin. During severe episodes, however, most of the pollution originates over Los Angeles and Orange counties and gets carried into San Diego by the wind. These episodes often occur as Santa Ana winds die out. During the Santa Ana, the easterly winds force the basin's pollutants offshore. As the Santa Ana begins to weaken, a thermally induced low-pressure system over the eastern desert stretches into the San Diego area. This creates a northwesterly flow that transports pollution originating over Los Angeles and Orange counties. A number of state-mandated rules have had a remarkable effect on air quality, such as biannual smog checks on vehicles, special pollution-reducing gasoline blends during the summer period, and rubber sleeves on gas pump nozzles that capture escaping fumes. Figure 14-2-3 illustrates the dramatic and consistent improvement in air quality in the Los Angeles area, showing both the number of days that ozone exceeded federal guidelines and the maximum eight-hour average of ozone. Though ozone pollution is still a serious problem, the number of days with excessive concentrations is about half of what it was during the late 1970s....FIGURE 14-2-2 Smog Pattern. The map shows a typical pattern of smog on a summer afternoon in the Los Angeles basin. Highest ozone concentrations (shown by dashed lines with units of parts per hundred million) occur in the northeast, ahead of the sea breeze front. Solid lines show the wind direction....How does the sea breeze front influence Los Angeles air quality? Get solution
2fs. Smog in Southern CaliforniaLos Angeles has long had a reputation for extremely bad air quality—and for good reason. Of all the cities in the United States, Los Angeles is the only one classified by the Environmental Protection Agency asan “extreme area” of noncompliance with ozone standards. A number of factors work together to make the air quality bad enough to earn this dubious distinction. As shown in Figure 14-2-1.Los Angeles occupies part of a basin bounded by mountains to the north and east that block the free movement of pollutants by the sea breeze, while the presence of a subsidence inversion during the warmer months restricts vertical dispersion. Add to that the typically cloud-free conditions during the midday period that trigger photochemical reactions. And finally there is the city's well-known love affair with the automobile, which contributes much of the estimated 2 million kilograms (2200 tons) of hydrocarbons and 1 million kilograms (1200 tons) of NOx released each day into the four-county South Coast Air Basin.During the summer, daily concentrations of photochemical smog vary on a regular basis in the course of a day. Prior to the morning rush hour, residual primary and secondary pollutants from the previous day leave a background level of air pollution. As traffic increases during the morning, emissions increase substantially.Early morning winds are usually weak, which leads to little movement of pollutants. At the same time, the low Sun angle and common presence of early morning fog and low clouds inhibit photochemical activity. The situation normally changes by late morning. A sea breeze usually develops along the coast and moves pollutants inland, while clearing skies and increasing Sun angles increase photochemical conversions.As the sea breeze develops, a boundary called a sea breeze front separates the relatively clean marine air from the more polluted, drier air ahead. As the sea breeze front moves inland, it pushes the emissions eastward or northeastward. This often creates a strong gradient in ozone concentrations near the sea breeze front, with relatively clean air behind it and increasing concentrations to the east or northeast (Figure 14-2-2). By late afternoon, the cities in the eastern portion of the basin get the full onslaught of the ad-vected pollutants, while local commuters add their own contribution to the photochemical smog. As a result, pollution levels can become extraordinarily high in the areas downwind of Los Angeles.The area to the south of Los Angeles—including Orange and San Diego counties—also has a significant air pollution problem. Usually the air pollution in San Diego, some 150 km (100 mi) to the south, is of local origin. During severe episodes, however, most of the pollution originates over Los Angeles and Orange counties and gets carried into San Diego by the wind. These episodes often occur as Santa Ana winds die out. During the Santa Ana, the easterly winds force the basin's pollutants offshore. As the Santa Ana begins to weaken, a thermally induced low-pressure system over the eastern desert stretches into the San Diego area. This creates a northwesterly flow that transports pollution originating over Los Angeles and Orange counties. A number of state-mandated rules have had a remarkable effect on air quality, such as biannual smog checks on vehicles, special pollution-reducing gasoline blends during the summer period, and rubber sleeves on gas pump nozzles that capture escaping fumes. Figure 14-2-3 illustrates the dramatic and consistent improvement in air quality in the Los Angeles area, showing both the number of days that ozone exceeded federal guidelines and the maximum eight-hour average of ozone. Though ozone pollution is still a serious problem, the number of days with excessive concentrations is about half of what it was during the late 1970s....FIGURE 14-2-2 Smog Pattern. The map shows a typical pattern of smog on a summer afternoon in the Los Angeles basin. Highest ozone concentrations (shown by dashed lines with units of parts per hundred million) occur in the northeast, ahead of the sea breeze front. Solid lines show the wind direction....How does the sea breeze front influence Los Angeles air quality? Get solution
