But the smog is temporary. Skies in the region are expected to clear up in the coming days as winds carry the wildfire smoke out over the Atlantic.
That’s not the case in some places around the world. Many people in other countries breathe air of comparably low quality every day.
The burning of fossil fuels, along with wildfires exacerbated by climate change, have created what some experts describe as the biggest danger to global public health. One study last year found air pollution shaves more than two years off of global average life expectancy — more than do cigarettes, alcohol or war. And roughly 97 percent of the world’s population lives in places where air pollution exceeds the level recommended by the World Health Organization.
Outside of the United States, the most polluted cities this week included Tel Aviv; Hanoi; Kolkata, India; Lima, Peru; and Lahore, Pakistan, according to a ranking by the air-quality monitoring site IQAir.
“Today on the East Coast, people are experiencing air pollution concentrations that hundreds of millions of people around the planet deal with on an average day,” said Michael Greenstone, director of the Energy Policy Institute at the University of Chicago and an author of the study. “We’re getting a taste of what I think is the greatest public health risk on the planet.”
Here are three cities that have contended with significant air pollution — and in some cases cleaned up the air.
In the Delhi area, where nearly 33 million people live, “pollution season” begins in October and lasts for several months. It’s caused by vehicle exhaust, construction dust, industrial emissions and crop burning in nearby states, and is made worse by geographic factors.
The smog gets so bad that some of the population’s elites have fled the city, taking refuge in places with clearer skies. Others buy air purifiers and face masks.
Air pollution measurements often focus on fine particulates, known as PM2.5, that can be inhaled through a person’s lungs and enter the bloodstream. Exposure can trigger short-term respiratory problems, such as coughing and wheezing, and exacerbate asthma. Long-term exposure has been linked to heart attacks, stroke and damage to cognitive functions.
Delhi had an annual average of 107.6 micrograms of PM2.5 per cubic meter in 2020, according to the University of Chicago’s Air Quality Life Index. By contrast, New York City recorded an annual average of 7.43 micrograms per cubic meter that year. The global standard set by the WHO, revised downward in 2021, is 5.
If Delhi met the WHO guideline for air quality, Greenstone and his research team estimate the area’s life expectancy could increase by about 10 years.
“India has announced a program to reduce air pollution, and at this point, the jury is out on its success,” Greenstone said. “It is one of the very most polluted countries in the world, and it is a place where reductions [in pollution] offer very large potential benefits.”
Beijing used to be known as the air pollution capital of the world. Rapid growth and urbanization, along with an explosion of car ownership, drove a huge uptick in polluting emissions. In 2005, Beijing and surrounding regions had the world’s worst levels of nitrogen dioxide, which can fatally damage the lungs, and air pollution was blamed for more than 400,000 premature deaths per year, the Guardian reported. Satellite imagery in 2006 showed pollution forming a brownish-gray curtain over Beijing, virtually obscuring the city.
China’s obsession with the smog began in earnest in the run-up to the 2008 Summer Olympic Games in Beijing, when athletes expressed concerns about competing in the haze. China launched a grand, but temporary, cleanup campaign to shut down or move factories and limit traffic.
The games would prove a turning point for public awareness of poor air quality in Beijing, as more residents began asking for the blue skies to stay.
Building on work by Chinese environmental activists, the U.S. Embassy in 2008 installed monitors and began sending hourly tweets of its in-house air quality readings. Those data often contradicted official figures and became a go-to resource for the city’s elites, intensifying pressure on authorities to tackle the issue. In November 2010, when the city pollution levels exceeded the Environmental Protection Agency’s index, the U.S. Embassy simply ruled the situation “crazy bad.”
Dealing with air pollution soon became part of daily life in Beijing. Residents checked air quality apps as regularly as the weather, often limiting time outdoors on polluted days. Air purifiers, ranging from expensive imported brands to more cost-effective HEPA-filters velcroed to a fan, became must-have home appliances. Terms like PM2.5 entered common parlance. One microbrewery launched an “airpocalypse” IPA and handed it out free when the AQI — the U.S. government’s air quality index — reached over 500, meaning the air was considered hazardous for everyone.
In 2013, average PM2.5 levels in the city hit 17 times the WHO’s limit. Environmental economists began gathering evidence of dramatic air pollution-linked declines in life expectancy in northern China. In 2015, an online documentary raised concerns about the impact of smog on health and criticized state-run fossil fuel giants. It went viral — and was quickly censored.
Top leaders responded with a “war” on pollution to clean up the skies in the country’s most populous regions, including Beijing. The nearly $280 trillion effort mostly relied on top-down incentives for polluting industries to adopt cleaner technologies, combined with punishments for companies or localities that failed to hit targets. According to official data, concentrations of PM2.5 dropped by 58 percent nationwide from 2013 to 2021.
Despite dramatic progress, occasional bouts of bad air still afflict Beijing. When smog threatened to undermine the 2022 Beijing Winter Olympics, the Chinese authorities reverted to a favorite temporary fix: cloud-seeding to induce rain and wash particulate matter from the skies.
These days, Beijing ranks much further down on the list of most-polluted cities. But Shanghai, China’s biggest city, stands at number 13, with a concentration of 36 micrograms of PM2.5 per cubic meter of air Thursday — about a quarter of the concentration recorded in smog-hit New York City, according to IQAir.
Mexico City is also known for its high pollution levels, even though the country has made important strides in the past three decades to clean up its air. According to the air-quality monitoring site IQAir, the city’s average annual level of PM 2.5 in 2022 was more than four times the limits set by the World Health Organization.
The city is part of a sprawling metropolitan region of around 20 million people. While Mexico has taken steps to remove lead from gasoline, expand public transit and bike paths and get older cars off the road, Mexicans are still automobile fans. According to the newspaper El Economista, in December 2022 there were 6.2 million motor vehicles registered in Mexico City, which has a population of 9.2 million.
When pollution reaches dangerous levels, local governments declare “environmental contingencies,” which reduces the number of cars allowed on the roads. (The city already has a program called “Hoy No Circula,” in which certain cars must stay off the roads at least one day a week, even in normal conditions.)
When those contingencies are declared, buses and metro trains are typically jammed, and many taxis increase their rates. The disruption causes a significant number of residents to miss work. Contingencies can force school closures and the cancellations of outdoor activities, including soccer matches.
Mexico City, while at high altitude, is set in a kind of bowl surrounded by mountains. The worst time of the year is winter, which brings “thermal inversions” — a phenomenon in which a layer of cold air traps pollutants in the city below. As climate change intensifies, the city has also been affected by a growing number of wildfires in nearby areas at other times of the year. There was a particularly dire pollution emergency in Mexico City caused by forest fires in May 2019, somewhat similar to what northeastern U.S. cities are experiencing now.
The phenomena driving air pollution are related, Greenstone said. “It is the planet’s warming that is increasing the odds of wildfires, and that warming is being caused by the continued heavy reliance on fossil fuels,” he said.
Amudalat Ajasa, Niha Masih and Joanna Slater contributed to this report.
Claire Parker, Christian Shepherd, Gabriela Martinez
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