The smog of 1966 was preceded by two other major smog episodes in New York City: one in November 1953, and one in January–February 1963. Using statistical analysis that compares the number of deaths during periods of smogs with the number of deaths during the same time in other years, medical scientists led by Leonard Greenburg were able to determine that a statistically significant number of excess deaths occurred during those smogs, implying that the smog caused or contributed to those deaths. An estimated 220–240 people died during the six-day 1953 smog, and an estimated 300–405 people died during the two-week 1963 fog. Other episodes of smog occurred in the city, but these were not accompanied by significant excess deaths.
Starting in 1953, the city started a laboratory to monitor pollution that would become its Department of Air Pollution Control. The department quantified pollution with an air quality index, a single digit based on combined measurements of sulfur dioxide, carbon monoxide, and haze or smoke levels in the air. The index average was 12, with an "emergency" level if the index was higher than 50 for a 24-hour period. Using the index, the city developed a corresponding air-pollution alert system with three stages of severity.
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, run by department co-founder Moe Mordecai Braverman and his staff of 15. Taking measurements from a single station meant that the index reflected conditions in that area, but served as a poor gauge of the air across all of New York City. The Interstate Sanitation Commission, a regional agency run by New York, New Jersey, and Connecticut and headquartered in Columbus Circle, also relied on the Harlem Courthouse laboratory. Formed in 1936, the advisory agency was authorized in 1962 by New York and New Jersey to oversee air pollution issues.
The public knew that New York City had an air pollution problem prior to the smog episode; although the photochemical smog of Los Angeles was more visible and famous, New York City had more emissions proportional to its area. A scientist with the Weather Bureau predicted in 1963 that the Northeastern and Great Lakes regions could anticipate a major smog event every three years due to the confluence of weather events and trends like growing population, industrialization, and increased emissions from cars and central heating. A report from the New York City mayor's office in spring 1966 warned that the city "could become a gas chamber" in the wrong weather conditions.
In November 1966, New York City was experiencing unseasonably warm "Indian summer" weather. An anticyclonic thermal inversion — in other words, a stationary, warm mass of air — formed over the East Coast on November 20. Inversions can act like a lid, preventing the usual process of lower, warm air rising. Such weather events are common, and they are usually followed by a cold front that blows them away; in this case, the cold front approaching west through southern Canada was delayed.
The inversion prevented air pollutants from rising and trapped them within the city. The smog itself started on Wednesday November 23, coinciding with the beginning of Thanksgiving weekend. The sources of the resulting smog were particulate and chemical matter from factories, chimneys, and vehicles. Sulfur dioxide levels rose. Smoke shade, a measure of visibility interference in the atmosphere, was two to three times higher than usual.
Austin Heller, the city's commissioner of air pollution control, said he nearly declared a first-stage alert between 6 a.m. and 10 a.m. on November 24. Heller also said the index had reached a high of 60.6, 10 points higher than the "emergency" mark, between 8 and 9 p.m. Heller said at the time that the 60.6 reading was possibly the highest in the city's history. After a nighttime lull, Heller cautioned, the smog would likely spike again in the morning.
The unusually heavy smog was evident to a crowd of one million onlookers at the Macy's Thanksgiving Day Parade on November 24. Tabloids and newspapers that ordinarily ran front-page stories about the Macy's Thanksgiving Day Parade instead carried stories on the smog.
On November 24, the city closed all 11 of its municipal garbage incinerators. Energy companies Consolidated Edison and Long Island Lighting Company were asked to burn natural gas rather than fuel oil to minimize the release of sulfur dioxide; both companies voluntarily cut back emissions, with Consolidated Edison reducing its emissions by 50 percent. 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. Representative William Fitts Ryan of Manhattan sent a telegram to Secretary of Health and Human Services John W. Gardner requesting an emergency meeting with New York Governor Nelson Rockefeller, New Jersey Governor Richard J. Hughes, and other regional leaders.
By Friday November 25, a first-stage alert for the New York metropolitan area, including areas in New Jersey and Connecticut, was declared through newspaper, radio, and television announcements. Governors Rockefeller and Heller attended a press conference; Deputy Mayor Robert Price stood in for Mayor Lindsay, who was on vacation in Bermuda. The announcement "was believed to be the first appeal ever made to New York's citizens in connection with a smog problem." Conrad Simon, who acted as a liaison between the scientific and political communities during the crisis, later said "We came close to closing the city down."
The alert was declared upon the advice of the Interstate Sanitation Commission. Members of the commission had been monitoring the smog situation in shifts for three days, nonstop. Thomas R. Glenn Jr., the commission's director and chief engineer, recommended the alert at 11:25 a.m. after seeing instruments in New York and New Jersey that showed carbon monoxide greater than 10 ppm and smoke greater than 7.5 ppm, both for more than four consecutive hours.
In New York, the city asked commuters to voluntarily stop driving unless necessary, apartment buildings to stop incinerating their residents' garbage, and apartment buildings to reduce their heating to 60 °F. New Jersey and Connecticut asked their residents to voluntarily reduce consumption of heating, electricity, and transportation. Although it was a workday, traffic was light in New York City. A check on 303 buildings of the New York City Housing Authority later found near-total cooperation with the city's requests. Private residences were also believed to have a high rate of voluntary cooperation with the city's plea to cut energy consumption.
The weather forecast called for the heat inversion to end that day, followed by a cold wind that would disperse the smog. Nevertheless, Heller said that if the wind did not come, a first-stage alert would likely remain in effect and it may become necessary to declare a second-stage alert if conditions worsened.
Some hospitals reported increased admissions of patients with asthma. However, an official at the city Department of Health also reported that some hospitals were receiving fewer asthma patients, chocking up hospitals with increases to random fluctuation, and told The New York Times that "In not one [hospital] is a pattern emerging which would suggest we are dealing with an important health hazard as of this moment." By this time, the inability to incinerate had generated an excess garbage. Hundreds of sanitation workers worked overtime to transport garbage to landfills in the Bronx, Brooklyn, and Staten Island, with the bulk going to Fresh Kills Landfill in Staten Island.
Rain came in the night. The cold front that would blow away the smog was forecasted to arrive between 5 a.m. and 9 a.m. Shortly after 9 a.m. the wind arrived, moving mostly from the northeast between 5–6 miles per hour and bringing cooler temperatures in the 50s °F. Glenn at the Interstate Sanitation Commission sent a message advising the alert to end at 9:40 a.m., based on weather and air readings. Shortly after noon, Governor Rockefeller declared the end of the alert; New Jersey and Connecticut also ended their alerts that day.
It was not initially clear how many casualties and illnesses had been caused by the smog — or indeed, whether the smog had caused any casualties at all. The population of the area affected by the smog has been estimated at 16 million. After studying admissions to municipal hospitals for cardiac and respiratory complications, the city commissioner of hospitals, Joseph V. Terenzio, told the press "I can report almost with certainty that there was no detectable immediate effect on morbidity and mortality because of the smog. ... It now seems unlikely that final statistical analysis will reveal any significant impact on the health of New York City’s population."
A study conducted by a nonprofit health research group found that 10 percent of the population suffered some health effects from the smog, including stinging eyes, coughing, wheezing, coughing up phlegm, or difficulty breathing. The director of the research group said anything that could adversely affect 10 percent of the population indicated a serious public health problem.
President Lyndon B. Johnson said 80 people died in the smog in a message delivered to Congress on January 30, 1967.
Leonard Greenburg — the same medical researcher who had previously published findings on the death count of the 1953 and 1963 smogs — published a paper in October 1967 showing that the previous year's smog had likely killed 168 people. The paper used the same statistical method that Greenburg used to analyze past smog casualties: comparing the expected number of deaths for that time of year and finding excess deaths. Greenburg showed that there were 24 deaths a day over seven days in excess of how many would normally be expected at that time of year — a period lasting four days longer than the smog, because of the delay between smog exposure and health effects. Although not a completely certain figure, it is likely that these 168 excess deaths were caused by the smog. Greenburg said that his analysis could not account for damage during the smog that would remain latent and continue to cause disease and death for years. A 1978 medical paper estimated that the smog shortened the lives of 366 people.
The smog was compared to the 1948 smog in Donora, Pennsylvania and the Great Smog of London of 1952, both of which lasted five days. The London smog's death toll of 4,000 was far higher than Donora, but the smog in Donora was far more severe; at the time of its smog, Donora was a small industrial town with a population of only 13,000, and its population was proportionally hit much harder with 20 deaths and smog-related illnesses among 43 percent of the population. Pollution experts estimated that if a smog as strong as the Donora smog occurred in the much more populous New York City, the death toll could have been as high as 11,000 with four million ill.
Several factors offset the smog's potential strength and health damage. The event began during Thanksgiving weekend, not during workdays, meaning that many factories were closed and far fewer people were in traffic than normally would be. The warm weather meant the demand for central heating was also lower than usual; the November 25 high of 64 °F broke the previous record high for that date, leading the reporter Homer Bigart to describe the apartment heating restrictions as "no problem." Because of these factors, pollution — and the death toll — were likely lower than they could have been otherwise.
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. 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. 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." In the 1968 book Killer Smog, William Wise warned that the 1966 smog and the 1952 London smog represented a vulnerability to air pollution disasters among American cities:
Perhaps, as in Great Britain, change will begin to come only after a large-scale tragedy. The conditions are favorable for one in any of a dozen of the nation's most populous cities. A mass of still air drifting slowly eastward, an intense thermal inversion, and then five, six, seven days of increasingly poisonous smog. The air will look bronze, almost copper-colored, as it did during New York's 1966 Thanksgiving smog. … From every appearance, a similar tragedy is now being prepared in America—and there is very little time left in which to prevent it.
At the time of the smog event, only half of the urban population of the United States lived with local protections on air quality; the smog event catalyzed the call for federal regulation on the issue. According to Spencer R. Weart of the American Institute of Physics, the American public "did not take the problem [of air pollution] seriously" until the 1966 smog. Weart also wrote that because the smog took place in New York City, it had a "disproportionate influence on the media headquartered there."
At the city level, the smog impelled an immediate response. Lindsay, then a liberal Rockefeller Republican, had run as a supporter of stronger air pollution control in his 1965 mayoral campaign, and the 1966 smog reinforced Lindsay's position on the issue.
City Council member Robert A. Low, a Manhattan Democrat and chairman of the city subcomittee on air pollution, criticized Lindsay for failing to enforce an air-pollution bill that had been passed in May. The bill, authored by Low, would update city incinerators and require apartment buildings to replace their incinerators with other garbage disposal methods. Low accused Lindsay's administration of "dragging its feet" on the problem of air pollution, which Lindsay called a "political attack."
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. The report noted that the change in weather that dispersed the smog "spared the city an unspeakable tragedy," and that if New York City had stagnant smog at the high levels commonly found in Los Angeles, "everyone in the city would have long since perished from the poisons in the air."
In December 1966, the New York City Administrative Code section on pollutant levels in the air was strengthened by a bill that was later described as the "toughest air pollution control bill in the country" at that time. The city called minor smog alerts in 1967 and 1970; conversely, a four-day inversion similar to Thanksgiving weekend 1966 occurred in September 1969, but it passed without incident — neither smog nor deaths resulted. Norman Cousins, chairman of the mayor's task force on air pollution, credited the regulations enacted since the 1966 smog for the prevention of a comparable September 1969 event. Cousins wrote in a message to Lindsay:
New York City's air is cleaner and more breathable today than it was in 1966. ... It is important to ask what would have happened on those days [in September 1969] if the pollution levels had continued to worsen at the same rate of deterioration that occurred from 1964 to 1966. The answer is that there could have been a substantial number of casualties. The fact that an episode did not occur attests to the capability of the City's programs to protect its air resources.
Lindsay announced a plan to install 36 new stations for the Department of Air Pollution Control to measure air pollution levels throughout the city — an upgrade from the sole station in the Harlem Courthouse building. The stations would send data to a central computer using telemetry to create a profile of the city atmosphere. Five of those stations would also send data to the Interstate Sanitation Commission. The city purchased a computer system and equipment from the Packard Bell Company for $181,000 (about $1,300,057 in 2017 dollars). In November 1968, the city opened 38 monitoring stations, 10 outfitted with computer equipment. The 10 computerized stations were designed to send data every hour to the central computer, while the other 28 operated manually as back-up. The index used during the 1966 smog, which produced a single number from multiple measurements, was abandoned as too simplistic.
After the passage of strict new state and federal air regulations, the city passed its updated Air Pollution Control Code in 1971, designed in part to address concerns that nitrogen oxides and unburned hydrocarbons had been left insufficiently controlled by the previous changes. By 1972, New York City had cut levels of sulfur dioxide and particulates by half from their peak. According to the EPA, those "improvements are the legacy of concern that emerged after the 1966 Thanksgiving Day smog disaster."
The smog brought into focus the complexity and interdependency of environmental problems and other urban issues. Lindsay reflected in his 1969 book The City that "Every time you shut down an incinerator, you increase the amount of garbage on city streets." Environmental harms — especially those that created obvious and unpleasant effects like smog — exacerbated the flight of middle-class residents from the city, resulting in a loss of financial and human resources. Residents who remained in the city, often poorer than those who could afford to flee, were left acutely impacted by problems that stemmed from city reactions to pollution or lack of municipal resources, for example, uncollected garbage in the streets.
The governors of New York (Rockefeller), New Jersey (Hughes), Delaware (Charles L. Terry Jr.), and Pennsylvania (Raymond P. Shafer), all member states of the Delaware River Basin Commission, met in December 1966 to address air pollution in their region. Each governor pledged to enforce their state's pollution abatement laws and to prevent their own state from becoming a "pollution haven" with lax regulations to attract industry. They also discussed the possibility of new tax incentives to motivate industry to reduce pollution and the creation of a new interstate compact to set industry standards, which would require adoption by all member states and approval by Congress. New York, New Jersey, and Connecticut adopted the Mid-Atlantic States Air Pollution Control Compact, and its approval by Congress became a policy goals in Rockefeller's failed bid for the 1968 Republican nomination for president. The compact was never approved by Congress and thus never took effect.
Air pollution control, already a priority of President Lyndon B. Johnson's administration, became a greater concern after the smog. By early 1967, his statements on air pollution became more rhetorically urgent. In January 1967, Johnson sent a message to Congress entitled "Protecting Our National Heritage," the first section of which was entitled "The Pollution of Our Air" and focused on the problems posed by air pollution. The message was prompted by wide public discussion of the problem following the 1966 smog. 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.
For four days, anyone going out on the streets inhaled chemical compounds that threatened his health. Those who remained inside had little protection from the noxious gases that passed freely through cooling and heating systems.
An estimated 80 persons died. Thousands of men and women already suffering from respiratory diseases lived out the four days in fear and pain.
Finally, the winds came, freeing the mass of air from the weather-trap that had held it so dangerously. The immediate crisis was ended. New Yorkers began to breathe "ordinary" air again.
"Ordinary" air in New York, as in most large cities, is filled with tons of pollutants: carbon monoxide from gasoline, diesel and jet engines, sulfur oxides from factories, apartment houses, and power plants; nitrogen oxides, hydrocarbons and a broad variety of other compounds. These poisons are not so dramatically dangerous most days of the year, as they were last Thanksgiving in New York. But steadily, insidiously, they damage virtually everything that exists.
Johnson called for a bill regulating toxins in the air and increasing funding for pollution programs. Edmund Muskie, a Senator from Maine and political environmentalist, praised Johnson's words, pledged to hold hearings on the proposals, and would soon sponsor the Johnson administration's bill, which became the Air Quality Act. Muskie also co-sponsored bills in 1967 for research on non-polluting automobiles using either electric or fuel cell technology. While discussing the research bills on the Senate floor, Muskie said "the serious air pollution situation in New York City [in November of 1966] dramatically illustrated what our cities may be facing in the future if an alternative to the [internal] combustion engine is not developed."
Congressional interest and public pressure for greater air pollution regulation had existed since the signing of the 1963 Clean Air Act, the first federal legislation on the issue, but further action was opposed by members of congress who believed responsibility for air regulation properly lay with the states, not the federal government. Partly in response to the added public pressure spurred by the smog event, Congress passed and Johnson signed the 1967 Air Quality Act, which amended the 1963 Clean Air Act to provide for study of air quality and control methods. The Air Quality Act was not without criticism for its ineffectiveness: a 2011 encyclopedia of environmental law judged that the act "was a failure but it was the first step in federal air pollution control." Among contemporaneous critics, Ralph Nader affiliate and environmentalist John C. Esposito wrote the book Vanishing Air to accuse Muskie of watering down the bill and adding needless complications in order to satisfy industry. Calls for greater air pollution regulation in this era culminated with the passage under President Richard Nixon of the 1970 Clean Air Act, which supplanted the Air Quality Act and has been described as the most significant environmental legislation in American history.
The full range of negative health effects arising from the September 11 attacks came to light in the years following the attacks. The 1966 smog serves, along with the earlier major New York City smog events in 1953 and 1963, as a precedent used for comparison with the air effects of September 11. However, unlike the air impact of the September 11 attacks, the New York City smog events were chronic and cumulative rather than acute, sudden, and short-lasting and had thousands of small sources rather than a single culpable source. The absence of prior events similar to the September 11 attacks left "a hole in the medical library."
Other major air pollution, particularly in China, has been compared to the 1966 smog. Elizabeth M. Lynch, a New York City 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, and 1966 smog events. Lynch wrote that the Chinese government's increased transparency on the issue was an encouraging sign that pollution in China could be regulated and abated just as it had in the United States. Similar comparisons between the 1966 smog and Chinese pollution in late 2012 appeared in Business Insider and Slate. USA Today cited the 1966 smog when China issued its first "red alert" air quality warning in December 2015.
The smog event has been referenced in pop culture. Smog figures into the plot of the 2012 Mad Men episode "Dark Shadows", which is set in New York City during the same Thanksgiving weekend in 1966. A reviewer in The A.V. 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." The New York City-based indie pop band Vampire Weekend used a photograph of the smog over the city skyline, taken by Neal Boenzi and originally published in The New York Times, for the cover of their 2013 album Modern Vampires of the City.