A Timeline of New York City Air Quality After 9/11

by | Sep 11, 2026

The September 11, 2001 attacks changed the air over Lower Manhattan almost instantly.

The collapse of the World Trade Center towers pulverized enormous quantities of concrete, glass, insulation, metal, office materials, and other building components. Fires then burned within the debris for months, producing a constantly changing mixture of dust, smoke, gases, and combustion products.

Air conditions improved substantially as the fires were extinguished and debris was removed, but contamination inside buildings and concerns about long-term exposure continued for years.

September 11, 2001: The Dust Cloud

When the South and North Towers collapsed, enormous clouds of debris spread through Lower Manhattan and portions of Brooklyn.

The dust contained pulverized cement, glass fibers, gypsum, metals, asbestos-containing material, soot, paint, and other building debris. Chemical analyses later identified substances including lead, chromium, polycyclic aromatic hydrocarbons, PCBs, dioxins, and other combustion products.

The dust was also unusually alkaline because of the enormous quantity of pulverized concrete and other construction materials.

People caught directly in the cloud experienced the most intense short-term exposures.

Dust also entered apartments, offices, schools, ventilation systems, and other indoor spaces, creating contamination that would remain after outdoor concentrations declined.

September 12–18: Monitoring Begins

Federal, state, and city agencies quickly began collecting air and dust samples.

EPA and OSHA initially concentrated heavily on asbestos along with lead, volatile organic compounds, and other hazards.

On September 13, EPA announced that early measurements were generally reassuring. Five days later, EPA Administrator Christine Todd Whitman publicly stated that available monitoring indicated that New York’s air was safe to breathe.

That statement would later become one of the most controversial aspects of the environmental response.

Early monitoring did show that many outdoor samples away from the debris pile contained low concentrations of several contaminants. Conditions at Ground Zero, however, were substantially different, and the initial information did not fully characterize every contaminant, indoor environment, or population.

Late September–October: The Fires Become the Major Source

The collapse did not create only dust.

Thousands of tons of debris continued burning beneath Ground Zero.

Those fires produced particulate matter, volatile organic compounds, PAHs, metals, PCBs, and dioxins. EPA monitoring recorded some elevated VOC measurements in the smoke plume near the site.

Workers digging through the debris experienced particularly complicated exposures because excavation continually disturbed dust while fires and hot spots produced additional emissions.

EPA and OSHA increased monitoring, established worker washing stations, and recommended respiratory protection.

By early October, hundreds of air samples had been collected around Ground Zero, Lower Manhattan, Staten Island, Brooklyn, and nearby areas.

Fall 2001: Dust Becomes an Indoor Problem

Outdoor air gradually improved with distance from Ground Zero, but another problem remained.

World Trade Center dust had entered buildings.

Dust deposited on carpets, furniture, ventilation equipment, window ledges, and other surfaces could become airborne again during cleaning or normal activity.

Residents began raising concerns about whether apartments and workplaces had been adequately evaluated.

The distinction between ambient outdoor air and indoor residual contamination became increasingly important. A neighborhood monitor showing relatively low outdoor pollution did not necessarily establish that every nearby apartment was free of World Trade Center dust.

December 19, 2001: The Fires Are Declared Extinguished

After burning for more than three months, the major fires at Ground Zero were officially declared extinguished on December 19.

Small hot spots and flare-ups still occurred during debris removal.

The disappearance of the continuous fires produced a major improvement in air conditions.

EPA later concluded that concentrations of several pollutants declined noticeably by January 2002. Some benzene spikes were still detected during January and February when fires briefly flared during excavation.

The dominant air-quality problem was gradually shifting from an active burning disaster to debris removal and residual contamination.

January–May 2002: Excavating Ground Zero

Heavy equipment continued removing debris throughout the winter and spring.

Excavation itself could disturb particulate material, so air monitoring continued around Ground Zero, worker areas, debris transportation routes, and the barge system used to move material.

Between March and June, EPA reported relatively few elevated outdoor measurements, with several asbestos readings occurring around particular work areas.

On May 30, 2002, excavation at Ground Zero officially ended after approximately 1.8 million tons of material had been removed.

EPA said outdoor air in Lower Manhattan had, for most monitored pollutants, returned approximately to pre-September 11 conditions.

Summer 2002–2003: Attention Moves Indoors

As outdoor conditions stabilized, government attention increasingly turned toward buildings.

EPA launched a voluntary residential program for people living in Lower Manhattan. Residents could request professional cleaning followed by asbestos testing or request testing alone.

Cleaning involved methods such as HEPA-filtered vacuuming and wet wiping designed to remove residual World Trade Center dust without sending it back into the air.

More than 4,000 apartments in hundreds of buildings eventually participated in portions of the program.

EPA studies also evaluated whether recommended cleaning techniques effectively reduced contaminants such as lead, dioxins, PAHs, fiberglass, silica, and asbestos.

2003: The Early Reassurances Are Reexamined

In August 2003, EPA’s Office of Inspector General issued a major review of the government’s response.

The report concluded that EPA did not have sufficient information to make the broad September 18, 2001 assurance that the air was safe to breathe.

Investigators noted that EPA officials later described the statement as applying primarily to outdoor air, asbestos, healthy adults, and long-term risks rather than every possible exposure.

Those qualifications, however, were largely absent from the public message.

The report helped establish an important lesson from the disaster: reassuring environmental communication can be misleading when uncertainty and differences between exposure environments are not clearly explained.

2007–2008: Another Round of Testing

Concerns about residual contamination did not disappear.

EPA opened another Lower Manhattan Test and Clean Program in 2007 for residents and building owners still concerned about World Trade Center material.

Testing examined asbestos, fiberglass-type fibers, lead, and PAHs. Locations with elevated concentrations could receive additional cleaning.

That program concluded in 2008—nearly seven years after the attacks.

The Air Improved, but the Exposure Did Not Simply End

The most severe airborne conditions occurred during the initial collapse and the months of fires, excavation, and cleanup.

But the environmental consequences extended much further.

Research eventually connected World Trade Center exposures with respiratory diseases and numerous other health conditions among responders and survivors. Congress later established the World Trade Center Health Program to provide long-term monitoring and treatment.

The history of New York’s air after 9/11 therefore cannot be represented by a single measurement or a single statement that the air was either “safe” or “unsafe.”

Conditions changed by the hour, neighborhood, building, occupation, and stage of the cleanup.

What began as an enormous dust cloud on September 11 became a months-long combustion and construction exposure—and then a years-long effort to understand what remained behind.

References