New York City officials have released thousands of previously unseen documents questioning the air quality at Ground Zero following the 9/11 attacks.

The city launched its public online portal on Tuesday with more than 170,000 pages of documents from across government agencies dealing with post-9/11 air quality and health risks. 

The documents provide more evidence that concerns about toxic air persisted for months after the attacks. Meanwhile, officials at the time assured the public the air was safe. 

The files released Tuesday include 68 boxes of documents that were found last year, the Harding Memo, and records concerning World Trade Center 7.

"These are documents that show what the city knew about the toxic air around Ground Zero, when they knew it, and how they acted to limit liability," Mayor Zohran Mamdani said. 

Mamdani launched the release at a news conference with other city officials and 9/11 health advocates, including comedian and advocate Jon Stewart. 

"The very least our city owes the families, survivors and first responders whose lives were forever changed by the September 11th attacks is transparency and accountability," Mamdani said. "For too long, New Yorkers have had to fight for access to records that should have been available to them in the first place. This portal is part of our administration's enduring commitment to honor those we lost, care for those living with lasting health consequences, and give thousands of New Yorkers the answer they've been asking for." 

The air quality reports, contamination records and correspondence among city staff show health officials were still finding evidence of asbestos at least 10 months later. That's long after officials repeatedly assured New Yorkers that the air around Ground Zero was safe to breathe.

"There was poison in the air and on the ground and in the window sills and in your air conditioners and covering your pets and your clothes, and it stayed there for months. Everyone knew. And now it's very clear that the city knew as well," Stewart said, adding, "Rather than take the steps to ameliorate the damage that that would cause to its citizens and to the people that were down there, they instead covered it up to get back to business as usual."

A spokesman for former Mayor Eric Adams said, in part, "Any documents related to post-9/11 air quality must be released and scrutinized, but Mayor Adams did not create, conceal or control records from prior administrations."

CBS News New York has also reached out to former Mayors Rudy Giuliani, Michael Bloomberg and Bill de Blasio for comment and have not heard back.

Mamdani also announced the settlement of two lawsuits brought by 9/11 Health Watch, ending a multiyear legal battle over the records.

The Harding Memo is a notable document released after it surfaced earlier this year. The document was written just weeks after the attacks and discussed the possibility of lawsuits from people who could claim they were exposed to toxic air. 

New York Rep. Jerry Nadler said government officials under former Mayor Giuliani predicted thousands of New Yorkers would face devastating health effects, according to the memo.

"The failure of government officials to share this information with the public and adequately respond to the dangers has had devastating and, in too many cases, fatal consequences," he said.

The records also include multiple reports documenting asbestos around the area. Some of them appear to show levels below limits set by environmental and worker protection agencies. Others indicate higher levels, but many don't include a written analysis explaining the results.

More documents are expected to be added on a rolling basis.

Mamdani said City Hall will appoint people to help eligible New Yorkers use the documents as proof of their presence in the exposure zone in order to access federal health programs.

"Those people who lived there are already eligible because they meet the criteria -- people who worked downtown, got caught in the dust cloud, [and] people who didn't know about it," attorney Matthew McCauley said.

In:

• New York City
• 9/11
• Zohran Mamdani