Los Angeles once suffered some of the worst smog on Earth

Pineapple research helped scientists solve Los Angeles' smog mystery

In the 1950s, chemist Arie Haagen-Smit applied methods he'd used studying pineapple plant chemistry to smog-filled air—discovering that sunlight reacting with car exhaust produced photochemical smog from hydrocarbons and nitrogen oxides, not factory smoke.

Photochemical smog forms when sunlight reacts with car and industrial emissions

The hazy phenomenon's name is a combination of "smoke" and "fog" and is composed of chemical pollutants that can cause eye irritation, lung damage and harm to crops. Smog buildup is more common in cities with sunny climates, minimal wind and surrounding mountains that trap these chemicals.

The Clean Air Act became the cornerstone of modern air pollution control

Passed in 1970 and strengthened through multiple amendments, the Clean Air Act authorizes the EPA to set national air quality standards, regulate industrial and vehicle emissions, and reduce pollutants such as ozone, sulfur dioxide, and lead.

How LA brought water to its booming population

By the turn of the 20th century, Los Angeles had grown from a dusty, crime-ridden pueblo into a thriving metropolis. The only problem was that it was growing too fast. Here's the story of how the booming town created a massive water infrastructure to redirect area rivers to its residents.

LA used to have one of the best mass transit systems in the country

A century ago, Los Angeles had one of the greatest urban transit networks in America. Today, driving in LA traffic can still be faster than taking the train. The city's rail design, which funnels traffic through a single point, fails to support a city with such a spread-out population.

Volatile chemical contamination can last in burn areas long after urban wildfires

Lead, arsenic, asbestos, and other chemicals have been found trapped in smoke-exposed rugs, couches, pillows, and other furniture that appeared otherwise undamaged from the 2025 LA wildfires. The gradual release of these substances has produced dangerous indoor air concentrations and contributed to increased emergency room visits and abnormal blood tests.

How Los Angeles got its palm trees

Los Angeles is known for its warm weather and palm trees, but the latter haven't always been part of the landscape. As Hollywood's movie industry grew, so did the number of palm trees. As this article points out, most of the city's palm trees were planted in the 1930s through an unemployment relief program.

In 1974, Los Angeles’s Community Analysis Bureau built a smart city

Los Angeles utilized aerial imaging and cluster analysis to gather and interpret civic data, leveraging surveillance technologies developed by the Department of Defense during the height of the Cold War. Instead of being used for military purposes, data insights helped direct social services to high-poverty neighborhoods.

The environmental crises of the late 1960s led to the founding of the EPA

Disasters such as the Cuyahoga River fire and the Santa Barbara oil spill prompted Congress and President Nixon to establish the Environmental Protection Agency in December 1970, with the goal of unifying federal efforts to control pollution.

The perplexing Battle of Los Angeles in 1942 generated swaths of UFO conspiracies

On Feb. 24-25, 1942, weeks after the Pearl Harbor attack, a US military radar warned of enemy aircraft. A citywide blackout went into effect, powerful searchlights were lit up, and US forces fired artillery at what they believed to be the enemy. However, no confirmed enemy planes were ever identified. Eyewitnesses reported seeing large objects flying overhead, and much of the public speculated about UFOs and extraterrestrial attacks.

Explore a real-time map of fine particle pollution from wildfires and other sources provided by the US Forest Service, which includes overlays for topography, street views, and satellite imagery.

Explore this real-time global air quality map with data reported from more than 10,000 stations around the world.

The Office of Air and Radiation oversees America's clean air and climate programs

The office develops and enforces national standards for air quality, vehicle emissions, and radiation protection. In 2025, the EPA announced the closure of two key divisions under the office responsible for regulating climate and air pollution: the Office of Atmospheric Protection and the Office of Air Quality Planning and Standards.

Hollywood's efficient response to the Spanish flu made it a filmmaking destination

In 1918, the Great Influenza epidemic killed more than 675,000 Americans. Los Angeles was one of the first cities to shut down movie theaters, most of which were independently owned and couldn’t afford the revenue loss. The results were twofold: the quick response meant that Hollywood could bounce back faster than other film hubs, and it also contributed to the rise of vertical integration as studios stepped in to purchase the flailing theaters.

Tornadoes can cause significant air pollution and diminish air quality

Asbestos, a hazardous material that can cause lung cancer, is commonly found in buildings constructed before 1980. Tornadoes that damage such buildings can release asbestos into the air, along with other toxic pollutants and dust as materials are lifted. Individuals, particularly those with asthma or other chronic lung diseases, are encouraged to wear masks after a tornado.

Air pollution in war-torn Iran unleashes invisible toxic threats

Burning oil depots and bombed buildings are endangering the health of millions of people during the 2026 attacks. Heavy metals from munitions and other damaged materials are going airborne, but the exact health implications depends on dose, wind currents, and other factors including preexisting health conditions.

Explore how close you live to some of the most contaminated places in the US

Known as Superfund sites, these toxic locations undergo long-term cleanup to remove hazardous waste, protect health, and restore land for safe reuse. As of 2025, the EPA lists around 1,300 active Superfund sites on its National Priorities List, with more than 450 cleaned and removed since 1980.

The toxic dust from 9/11 sites still claims lives decades later

In the years after 9/11, nearly 17,000 first responders enrolled in health programs have reported cancers and respiratory diseases linked to Ground Zero exposure. More have died from related illnesses than were killed on the day itself.

Hollywood, explained

It all began in 1887 when Hollywood was registered as a small town before merging with Los Angeles in 1910. Filmmakers moved west to avoid Thomas Edison’s patent lawsuits, and the sunny California climate provided the perfect setting for year-round production. By the 1910s, studios like Paramount and Warner Bros. established themselves, and Hollywood's global dominance was cemented during its golden age from the 1930s to the 1950s.

Environmental regulation had bipartisan support in the 1970s

During the 1970s, Democrats and Republicans alike backed landmark environmental laws. Congress passed the Clean Air, Clean Water, and Endangered Species Acts with overwhelming bipartisan majorities—reflecting broad public agreement on protecting the environment.

In the 1930s, New York banned buskers as part of an antinoise campaign

Mayor Fiorello LaGuardia was hoping to modernize the city and believed that street performers only crowded the streets and added to an annoying cacophony. Residents wrote to the mayor to protest the decision, arguing that buskers were appreciated by the public.

Watch a 1986 television special about the discovery of the ozone hole

The groundbreaking discovery of the Antarctic ozone hole in the mid-1980s marked a critical turning point, galvanizing international action to address the ozone-depleting properties of chlorofluorocarbons, which had been identified about a decade earlier. This environmental crisis was brought vividly to public attention through media pieces like this one.

Cleveland's Cuyahoga River caught fire over a dozen times

Between 1868 and 1969, the Cuyahoga River in Cleveland caught fire at least 13 times due to oil and industrial waste. The 1969 blaze garnered national attention, prompting federal action and contributing to the creation of the EPA, which ultimately led to a successful cleanup of the river.

The history of Earth's breathable atmosphere, made possible by photosynthetic bacteria

Between 3.2 billion and 2.8 billion years ago, threadlike microorganisms called cyanobacteria began consuming available water vapor, carbon dioxide, and sunlight to produce oxygen. However, molecules released from Earth's interior by volcanoes consumed this oxygen via chemical reactions, preventing it from accumulating until volcanism had sufficiently decreased about 2.4 billion years ago.

The 1969 Santa Barbara oil spill galvanized the modern environmental movement

In January 1969, an oil platform off the coast of Santa Barbara ruptured, releasing roughly 3 million gallons of crude into the Pacific. The spill killed over 10,000 seabirds, dolphins, and seals, coating 35 miles of coastline.

How the California wildfires are impacting wildlife

The deadly 2025 Eaton and Palisades Fires in California have devastated neighborhoods, forested canyons and chaparral—a type of shrubland. In addition to taking dozens of human lives and displacing thousands, the fires destroyed countless habitats and displaced many species. See the unfortunate effects of the flames on wildlife populations, including birds, snakes, wildcats, and fish.

Review the health effects of living near oil refineries, including increased respiratory risks

An analysis of 54 studies published between 1977 and 2024 in 15 international regions found evidence that proximity to refineries increased the risks of leukemia, asthma, bronchitis, and respiratory symptoms. Several studies also identified worse cardiovascular function in children and adults living near refineries, alongside other acute and chronic health impacts.

Large oil companies knew about the impact of carbon emissions since the ’70s

PBS Frontline’s The Power of Big Oil reveals how industry giants like Exxon and Shell were researching climate change in the 1970s but then funded denial campaigns—using internal science to sow public doubt for decades.

As of 2024, 13 states have plans to phase out gas-powered cars

In 2022, California adopted the Advanced Clean Cars II Act, which requires all new passenger cars, trucks, and SUVs sold to produce zero emissions by 2035. Other states adopted similar laws, joining more than 50 countries with phaseout plans.

The Clean Water Act became the national standard for protecting American waters

Enacted in 1972, the Clean Water Act grants the Environmental Protection Agency the authority to regulate pollutant discharges, establish water quality standards, and oversee water pollution controls. Its scope has narrowed due to recent Supreme Court rulings.

How Monet’s paintings changed the way we see London

Between 1899 and 1901, legendary French Impressionist painter Claude Monet produced over 100 paintings of London consistently shrouded in fog. Art historians claim this series left a permanent mark on how we perceive the capital city, inevitably layered in obscuring and dramatic mist. See some of the paintings and read more here.

The Love Canal disaster exposed the dangers of buried toxic waste

In the late 1970s, residents of Niagara Falls, New York, discovered their neighborhood was built atop 20,000 tons of chemical waste. Leaking toxins caused illness and birth defects, sparking nationwide outrage and leading to the creation of the EPA's Superfund cleanup program in 1980.

How amendments to the Montreal Protocol have expanded global ozone protections

Since 1990, five major amendments—London, Copenhagen, Montreal, Beijing, and Kigali—have accelerated chemical phase-outs, added new substances, such as hydrochlorofluorocarbons, and tightened enforcement.

Particles found in Martian air pose significant risks to human lungs

Ultrafine dust, just 3 micrometers wide, is small enough to bypass lung defenses and enter the bloodstream, where its highly reactive chemicals can cause thyroid disease. Silica in the dust can also cause silicosis, a chronic and incurable lung disease.

Rainfall and lush vegetation make the Great Smoky Mountains smoky

The national park is a rainforest that receives significant rainfall. When the vegetation on the mountains gets wet, it releases a gas that is smoky, and sometimes even appears blue, a phenomenon that gave the mountains (and the park) its name.

1970s U.S. energy crisis sparked waves of green innovation

Faced with the 1973 Arab oil embargo, the U.S. responded with bold innovation—enacting a 55 mph speed limit, pioneering daylight saving time, boosting solar research, expanding nuclear power, and pushing energy-efficient building designs and automotive technologies

Pollution from lead battery recycling has led to widespread contamination

Many small-scale operations worldwide remain unregulated, bypassing environmental regulations and causing increasing health threats, primarily to children. A 2020 report by UNICEF found that one-third of the world's children are being poisoned by lead from recycled batteries, among other sources.

The Hollywood sign originally said 'Hollywoodland'

The original sign, which was only intended to be up for 18 months and erected around 1903, advertised a new housing development in the Hollywood Hills. In 1949, the Hollywood Chamber of Commerce shortened it to "Hollywood."

Biologists believe over 5,000 coyotes inhabit LA as of 2025

Panic and fear of coyotes spread in the 1980s after the first recorded instance of a human killed by the animal in American history, but LA and Chicago residents today are learning to live alongside the animal. Research shows that coyotes can even benefit urban ecosystems by helping to control populations of geese and deer, and by improving songbird survival through preying on cats.

Before modern sanitation, New York City let pigs roam the streets to eat its garbage

In the early 1820s, an estimated 20,000 hogs roamed Manhattan's streets, feeding on trash that the city lacked a system to collect. Pigs were eventually banned at the urging of wealthy residents, who feared they would deter tourists and drive down property values.

A third of Americans now live in wildfire risk zones

Climate change and human development into fire-prone regions have extended the wildfire season, with some areas experiencing fire conditions year-round. Extreme conditions, poor compensation, and exposure to carcinogens have complicated firefighter recruitment, further exacerbating wildfire risks.

The resurgence of Black lung disease in coal miners

Black lung disease is a preventable condition long associated with coal miners who regularly breathe in toxic coal dust. Simple workplace safety procedures make the disease entirely preventable, but cases are rising. Due to lax enforcement of rules, miners in Central Appalachia are increasingly diagnosed with cases stemming from silica dust inhalation.

1970s New York was viewed by many as a city in decline

By 1975, the city owed $5B to $6B in short-term debt; over a million manufacturing jobs had left the city since the end of World War II. Meanwhile, the murder rate was more than double than 10 years earlier. Graffiti was seen as illegal vandalism perpetrated by unsupervised teenagers and was viewed by some as emblematic of the larger societal decline.

Louisiana's 'Cancer Alley,' an area with hundreds of industrial plants and petrochemical production, has cancer rates 50% above the national average.

How a polluted New York City waterway created extremophiles hungry for 'black mayonnaise'

In the 19th century, coal processing plants, oil refineries, a tannery, and other industries lining the Gowanus Canal contaminated its waters with coal tar, sewage, and other pollutants, forming the toxic sludge. Samples taken from the site before clean-up efforts revealed over 450 species of microbes with metabolisms adapted to break down these contaminants.

In the late 1800s, New York City streets were covered with millions of pounds of horse manure thanks to a widespread horse-driven transportation industry.

Watch a visualization of New York City's greenhouse gas emissions

About 1.72 tons of carbon dioxide-equivalent gases are released into the atmosphere every second in the Big Apple, enough to fill a balloon 33 feet across at standard pressure and 59 degrees Fahrenheit. After a day, the spheres would pile up into a pyramid whose base spans from the bottom of Manhattan to the south of Central Park.

Abandoned Detroit: the decline of America's car mecca

Detroit, Michigan, began as a fur trading post in the 1700s but would become the world epicenter of car manufacturing in the 1900s after Henry Ford developed his paradigm-shifting assembly line at a plant there. Racial tensions, a lack of economic diversification, and poor leadership would plunge the city into poverty and decay in the late 1900s, culminating in a 2014 bankruptcy. Browse the somber images of the city's abandoned spaces here.

Revelations that apples were sprayed with the chemical Alar led to its ban in the 1980s

Almost three decades after Rachel Carson’s “Silent Spring,” a “60 Minutes” segment on the use of Alar, a chemical sprayed on apples, drew national attention and inspired supermarkets and schools to remove apples from their shelves and cafeterias. That same year, the Environmental Protection Agency took action against the use of the chemical in food.

Hundreds of vulnerable Chicago residents died in 1995 during a long-lasting heat wave

Eric Klinenberg wrote a book diving into the specifics of the heat wave. His book, detailing the stories and context fueling more than 700 deaths during just one summer week, helps readers understand how social infrastructure lapses, power outages, and ineffective heat responses led to so many deaths.