1966 New York City smog has immediate cause inversion
November 19–23: stagnant air traps pollutants
In November 1966, New York City was experiencing an unseasonably warm "Indian summer". A cold front from Canada brought clean air to the city on November 19, but the cold front was held in place by pressure from the higher atmosphere. An anticyclonic temperature inversion—in other words, a warm, mostly stationary air mass located atop a cooler air mass—formed over the East Coast on November 20.Unlike atmospheric convection—the ordinary process of lower, warm air rising—inversions leave cooler air suspended below warm air, preventing the lower air from rising and trapping airborne pollutants that would ordinarily disperse in the atmosphere. Such weather events are common, but they are usually followed by a strong cold front that brings an influx of clean air and disperses pollutants before they have enough time to become highly concentrated; in this case, a cold front approaching west through southern Canada was delayed. When explained in less formal terms, the process of an inversion causing a smog event has been compared to a lid that holds in pollutants or a balloon that fills with pollutants. In general, smog events occur not because of a sudden increase in a region's output of pollution, but rather because weather conditions like stagnant air prevent the dispersal of pollutants that were already present.The inversion prevented air pollutants from rising, thereby trapping them within the city. The smog event itself started on Wednesday November 23, coinciding with the beginning of the long Thanksgiving weekend. The material sources of the smog were particulates and chemicals from factories, chimneys, and vehicles. Sulfur dioxide levels rose and smoke shade—a measure of visibility interference in the atmosphere—was two to three times higher than usual.
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