The word "smog" (a portmanteau of "smoke" and "fog") is used to describe several forms of air pollution commonly found in urban and industrialized areas.

"[16] The air "over much of the eastern half of the country [was] chronically polluted", and the nation's most-polluted population centers were New York City, Chicago, Los Angeles, St. Louis, and Philadelphia.

[26] At the time of the 1966 smog, air quality measurements were recorded from only a single station, the Harlem Courthouse building on East 121st Street,[25] run by Braverman and his staff of 15.

[26] Taking measurements from a single station meant that the index reflected conditions in the immediately surrounding area, but served as a crude, unrepresentative gauge of overall air quality across the entire city.

[24] The Interstate Sanitation Commission, a regional agency run by New York, New Jersey, and Connecticut and headquartered at Columbus Circle, also relied on the Harlem Courthouse laboratory.

[1] AQI measurements in the United States are now standardized and overseen by the EPA, but in the 1960s, local governments in different regions used "a confusing and scientifically inconsistent array of air quality reporting methods".

Critics pointed out that the index could have potentially allowed the city to reach lethal concentrations of carbon monoxide without triggering any alert at all, so long as the levels of other pollutants remained low.

"[37] The same year, the New York mayor's office established a 10-member task force headed by Norman Cousins (known as the editor of the weekly magazine Saturday Review) to study the problem of air pollution.

[2] Health officials cautioned those with chronic lung diseases to stay indoors and advised patients that symptoms of pollution-related illness usually lagged 24 hours after exposure.

[51] The city told 18 inspectors "to forget their turkey dinners and start looking for dirty air," and they issued an "unusually high" number of citations for emissions violations, including two for Con Ed plants.

But no deaths were attributed to the smog ... By Friday November 25, a first-stage alert for the New York metropolitan area, including parts of New Jersey and Connecticut, was declared through newspaper, radio, and television announcements.

[53] Although not part of the area covered by the alert, unusually high smog was reported as far as Philadelphia, Pennsylvania and Boston, Massachusetts,[note 6] whose mayor issued a similar health warning.

[51] An official at the city Department of Health noted that some hospitals were receiving fewer asthma patients, and attributed the reported increases to ordinary random fluctuations.

After the 1966 smog, the task of reducing air pollution became an essential part of the municipal government's goal to make "the city attractive again to the middle class and acceptable to all its residents.

[50] Residents who remained in the city often lacked the financial resources that would have enabled them to move somewhere else, even if they had wanted to flee the unpleasant environment and health hazards caused by pollution.

[50] The smog is commonly cited as one of the most-visible and most-discussed environmental disasters of the 1960s in the United States, alongside the 1969 Santa Barbara oil spill and the 1969 Cuyahoga River fire.

[64] National public awareness of the smog and its health effects spurred the nascent environmental movement in the United States and galvanized support for legislation to regulate air pollution.

[65] Vernon McKenzie, chief of the air pollution division of the federal Public Health Service, called the smog "a warning of what can happen—and will happen—with increasing frequency and in wider areas unless something is done to prevent it.

"[58] The mayor's office prepared a report in the aftermath of the smog, singling out the coal-burning Consolidated Edison company, city buses, and apartment building incinerators as significant contributors to air pollution.

[33] The new index system was similar in that it used weather forecasts and measurements of pollutants in the air and had three progressive stages of severity ("alert," "warning," and "emergency") requiring stronger actions by city, industry, and citizens.

[80] For example, federal law provided resources like research, training, grants to improve state and local programs, and a conference procedure to convene agencies and polluters under the guidance of the Department of Health, Education and Welfare.

[80] The governors of New York (Rockefeller), New Jersey (Hughes), Delaware (Charles L. Terry Jr.), and Pennsylvania (Raymond P. Shafer) met in December 1966 to address air pollution in their region.

[69] Edward Teller—the physicist known for his role in developing the hydrogen bomb and an advisor to Mayor Lindsay on pollution and energy issues—advocated for New York state to adopt stricter sulfur fuel standards than the city.

[93] Johnson cited the experiences of specific American cities and towns in the message, and highlighted the 1966 smog at length: Two months ago, a mass of heavily polluted air—filled with poisons from incinerators, industrial furnaces, power plants, car, bus and truck engines—settled down upon the sixteen million people of Greater New York.

In Train v. Natural Resources Defense Council, Inc., a 1975 decision by the Supreme Court of the United States, Justice William Rehnquist summarized the law's effect as follows: The focus shifted somewhat in the Air Quality Act of 1967, 81 Stat.

[100]Among contemporaneous critics, John C. Esposito—an environmentalist and affiliate of Ralph Nader—wrote the 1970 book Vanishing Air to accuse Muskie of watering down the bill and adding needless complications to satisfy industry.

[103] The most widely recognized legacy of the 1966 smog was the political reaction to it, which galvanized the nascent environmental movement in the United States and prompted demand for sweeping air-pollution control laws.

Elizabeth M. Lynch, a New York–based legal scholar, said that images of visible air pollution in Beijing from 2012 were "gross" but not "that much different from pictures of New York City in the 1950s and 1960s", specifically referring to the 1952, 1962,[note 1] and 1966 smog events.

Club interpreted the writers' use of the smog as a symbolic representation of the character Betty, who spends the episode "longing to enter [Don Draper's] apartment and tear some shit up"—"hover[ing]" and "waiting to poison it from within".

Articles published by The New York Times,[113] Vice Media's tech-news site Motherboard,[114] public radio station WNYC,[115] real-estate news site 6sqft,[116] and the Natural Resources Defense Council (NRDC) environmental advocacy group[117] connected Trump's declared policy agenda to a risk of returning to a more polluted environment, with each publication evoking the 1966 smog as an example of the potential dangers of defunding and deregulation.