Scenario 4 An extreme condition exists when the air temperature actually increases with altitude. This corresponds to a very stable condition where any polluted warm air released near the ground will be trapped and not vertically dispersed. This condition is known as a thermal inversion There are several causes for thermal inversions and their duration varies from a few hours to many days Their occurrence in cities such as Los Angeles, Denver, and Mexico City is a major contributor to the air pollution problems of those cities
Scenario 4 An extreme condition exists when the air temperature actually increases with altitude. This corresponds to a very stable condition where any polluted warm air released near the ground will be trapped and not vertically dispersed. This condition is known as a thermal inversion. There are several causes for thermal inversions, and their duration varies from a few hours to many days. Their occurrence in cities such as Los Angeles, Denver, and Mexico City is a major contributor to the air pollution problems of those cities
7000 6000 Prevailing temperature g5000 4000 Stable 3000 Unstable 2000 stable 1000 0 20 0 20 40 Air temperature('C Figure 9.2 Some possible temperature profiles in the lower atmosphere. The region to the left of the adiabatic lapse rate is unstable and will lead to appreciable vertical mixing of polluted air released near the ground. The region to the right represents stable conditions and air stagnation
Figure 9.2 Some possible temperature profiles in the lower atmosphere. The region to the left of the adiabatic lapse rate is unstable and will lead to appreciable vertical mixing of polluted air released near the ground. The region to the right represents stable conditions and air stagnation
All major air pollution incidents that have lead to documented elevated levels of human mortality have occurred during period of thermal inversions One of the most notable incidents of a thermal inversion occurred in London, England, on December 5, 1952. A thermal inversion developed enveloping the city in fog with essentially no vertical movement of air higher than 150 feet The sulfur dioxides and particulates from burning coal, in addition to the other pollutants of a large city, accumulated for four days During the four days, an estimated 4000 deaths occurred beyond those normally experienced for a four-day period Two similar episodes also occurred in 了oLER London in 1956 and 1962 This type of smog is now known as classic smog
One of the most notable incidents of a thermal inversion occurred in London, England, on December 5, 1952. A thermal inversion developed, enveloping the city in fog with essentially no vertical movement of air higher than 150 feet. The sulfur dioxides and particulates from burning coal, in addition to the other pollutants of a large city, accumulated for four days. During the four days, an estimated 4000 deaths occurred beyond those normally experienced for a four-day period. Two similar episodes also occurred in London in 1956 and 1962. This type of smog is now known as classic smog. All major air pollution incidents that have lead to documented elevated levels of human mortality have occurred during period of thermal inversions
Many courses of thermal inversions are now well understood, and their occurrence can usually be predicted by meteorologists One such cause is a high pressure subsidence When a high pressure region of the atmosphere subsides, or moves downward toward the earth where the pressure is greater, the air mass will be compressed and its temperature will rise This relatively dense warm air then will continue to move toward the earth until it meets the higher lemperature density air near the surface It was this kind of inversion that caused the A high pressure mass of air problems in London in 1952 subsides toward the earth and it compressed and heated in the process, causing a thermal inversion layer some distance above the ground
Many courses of thermal inversions are now well understood, and their occurrence can usually be predicted by meteorologists. One such cause is a high pressure subsidence. When a high pressure region of the atmosphere subsides, or moves downward toward the earth where the pressure is greater, the air mass will be compressed and its temperature will rise. This relatively dense warm air then will continue to move toward the earth until it meets the higher density air near the surface. It was this kind of inversion that caused the problems in London in 1952. A high pressure mass of air subsides toward the earth and it compressed and heated in the process, causing a thermal inversion layer some distance above the ground
Another type of inversion called a radiative thermal inversion is much more frequent but less troublesome On a clear night, the earth's surface radiates thermal energy into space, thus cooling both the surface and the air near the surface After a night of cooling the air near the surface will be cooler the next morning than the air above it. and a thermal inversion will result As the morning progressed, the sun will warm the surface of the ground and the lower atmosphere, and the thermal inversion will Because of radiative cooling during the night the air near the disappear by mid-afternoon ground surface is cooler than the Such radiative inversion are almost a daily air above occurrence in Denver and similarly situated cities
Another type of inversion called a radiative thermal inversion is much more frequent but less troublesome. On a clear night, the earth’s surface radiates thermal energy into space, thus cooling both the surface and the air near the surface. After a night of cooling, the air near the surface will be cooler the next morning than the air above it, and a thermal inversion will result. As the morning progressed, the sun will warm the surface of the ground and the lower atmosphere, and the thermal inversion will disappear by mid-afternoon. Such radiative inversion are almost a daily occurrence in Denver and similarly situated cities. Because of radiative cooling during the night, the air near the ground surface is cooler than the air above it