Paris’ present smog crisis is an example of how weather patterns affect air pollution levels. Changes in weather and temperature fluctuations have been known to cause variations in pollution levels ever since the industrial age.
Right now, in Paris, smog levels are at an atypical high and the city is doing everything it can to discourage the use of automobiles, with tailpipe emissions being the main source of the pollution. Interventions include providing free public transportation for tourists as well as gratis bicycles and electric cars. Other measures include lowering the speed limits, appealing to trucks carrying heavy loads to refrain from driving, and asking factories to reduce work hours.
Residents with chronic lung and airway diseases such as emphysema and asthma are finding it more difficult to breathe and joggers are having trouble running their usual distances without feeling short of breath. Air pollen, also on the rise, has been a contributing factor.
These unusually high levels of smog have been the result of a high pressure system, lack of wind, and temperature inversion, all combining into a weather pattern that affects air pollution concentrations. Under normal conditions temperatures nearer to the ground are warmer and decrease with altitude by about 3.5 degrees fahrenheit for every 1000 feet. This type of pressure gradient, known as an unstable air mass, allows air to circulate freely and disperse pollutants. Temperature inversions occur when a warm air mass moves over a cold air mass. These are called inversion layers, whereby the higher, less dense warm air mass traps the cooler, less dense mass below, and the air pollution and pollen contained within.
It seems likely that, in Paris, a spate of warm days and cool nights, combined with a lack of sufficient wind, acted together to trap air pollution beneath a warm inversion level. A recent high pressure system in Paris made for clear skies that facilitated ground cooling at night while the air above retained the heat released from paved surfaces, heat that was stored during the sunny days.
The problem, for Paris, might be temporary, but many cities throughout the world are routinely subjected to highly concentrated levels of pollution due to weather, such as Mumbai, Mexico City, and Tehran. The Great Smog of 1952 occurred in when an unusual cold spell gripped London in December, prompting inhabitants to burn more coal to keep warm. An inversion system resulted in trapped smoke so thick that it made it impossible to see for more than a few feet ahead. Initially Londoners, accustomed to thick fog, were not alarmed. But over 12,000 dwellers died over the following weeks.
Many cities have regular smog alerts when air quality becomes hazardous. These alerts caution citizens to reduce activity levels and to stay indoors to avoid exposure. People with chronic heart and lung conditions are especially sensitive to the fluctuations in air quality.
Aside from the usual suspects such as tailpipe emissions and exhaust from industrial sites, air pollution levels are affected by weather patterns such as high pressure systems, combined with lack of wind and inversion temperatures that trap air. The recent spike in pollution in Paris seems to fit the criteria, and city officials are doing what they can to mitigate the problem.
By Robert Wisnewski
The Clean Air Campaign