Air Quality and Climate Change: A Delicate Balance
Ground-level ozone (O3) is one of the major air pollutants discussed in terms of climate change. Some refer to O3 in terms of "the good, the bad, and the ugly," says Megan L. Melamed, executive officer of the International Global Atmospheric Chemistry Project. The ozone layer located in the stratosphere, which protects human life from harmful ultraviolet radiation, is the "good." Ground-level O3, with its myriad adverse health effects, is the "bad." O3 also acts a short-lived climate pollutant, contributing to the greenhouse effect—the "ugly."
Although higher temperatures are associated with elevated ground-level O3, ozone events require sunlight. Overall, the Intergovernmental Panel on Climate Change predicts, warmer temperatures and increased water vapor abundance will reduce baseline concentrations of ground-level O3—a positive development, given the health harm this pollutant can do. But other factors are likely to intensify O3 production in polluted areas, especially during heat waves and drought.
O3 is created by chemical reactions between ultraviolet radiation and precursor air pollutants, including oxides of nitrogen (NOx), carbon monoxide, and volatile organic compounds (VOCs). These precursors come from anthropogenic sources such as automobile emissions, gasoline vapors, and power plants. They also come from natural sources, including vegetation (in the case of VOCs) and lightning (in the case of NOx).
The smell of O3 is familiar to many city dwellers during the dog days of summer. The summer air seems to thicken when a high-pressure weather system stalls over a city, baking streets in blazing temperatures under cloudless skies. Winds die down, and hot city air is trapped under a dome of high pressure (or "heat dome"), concentrating pollutants near the ground in what's called a stagnation event. These conditions are ideal for producing ground-level O3.
Ground-level O3 can be formed anywhere in the troposphere, the lowest layer of the atmosphere, which ranges from the surface up to elevations around 10–15 km, depending on latitude and season. O3 is also formed in the lower stratosphere, the next higher level of the atmosphere, up to elevations around 50 km.
Cities can have lower levels of O3 than one might expect, based on the amount of precursors produced by urban sources. Interaction with traffic-related NOx emissions transforms a portion of urban O3 to O2, the most stable form of oxygen. Furthermore, once a stagnation event ends and winds resume, large concentrations of urban O3 and precursor pollutants can be transported into surrounding rural areas hundreds of miles downwind. O3 concentrations therefore tend to peak downwind of major cities, not in them.
Ozone: The Good, the Bad, and the Ugly
Ground-level ozone (O3) is one of the major air pollutants discussed in terms of climate change. Some refer to O3 in terms of "the good, the bad, and the ugly," says Megan L. Melamed, executive officer of the International Global Atmospheric Chemistry Project. The ozone layer located in the stratosphere, which protects human life from harmful ultraviolet radiation, is the "good." Ground-level O3, with its myriad adverse health effects, is the "bad." O3 also acts a short-lived climate pollutant, contributing to the greenhouse effect—the "ugly."
Although higher temperatures are associated with elevated ground-level O3, ozone events require sunlight. Overall, the Intergovernmental Panel on Climate Change predicts, warmer temperatures and increased water vapor abundance will reduce baseline concentrations of ground-level O3—a positive development, given the health harm this pollutant can do. But other factors are likely to intensify O3 production in polluted areas, especially during heat waves and drought.
O3 is created by chemical reactions between ultraviolet radiation and precursor air pollutants, including oxides of nitrogen (NOx), carbon monoxide, and volatile organic compounds (VOCs). These precursors come from anthropogenic sources such as automobile emissions, gasoline vapors, and power plants. They also come from natural sources, including vegetation (in the case of VOCs) and lightning (in the case of NOx).
The smell of O3 is familiar to many city dwellers during the dog days of summer. The summer air seems to thicken when a high-pressure weather system stalls over a city, baking streets in blazing temperatures under cloudless skies. Winds die down, and hot city air is trapped under a dome of high pressure (or "heat dome"), concentrating pollutants near the ground in what's called a stagnation event. These conditions are ideal for producing ground-level O3.
Ground-level O3 can be formed anywhere in the troposphere, the lowest layer of the atmosphere, which ranges from the surface up to elevations around 10–15 km, depending on latitude and season. O3 is also formed in the lower stratosphere, the next higher level of the atmosphere, up to elevations around 50 km.
Cities can have lower levels of O3 than one might expect, based on the amount of precursors produced by urban sources. Interaction with traffic-related NOx emissions transforms a portion of urban O3 to O2, the most stable form of oxygen. Furthermore, once a stagnation event ends and winds resume, large concentrations of urban O3 and precursor pollutants can be transported into surrounding rural areas hundreds of miles downwind. O3 concentrations therefore tend to peak downwind of major cities, not in them.
Source...