Twenty-five years after the Sept. 11 attacks, New York City has released a massive collection of records detailing its response to the terror attacks and the aftermath at ground zero.

The city launched a public portal Wednesday featuring 170,000 documents related to 9/11, including air quality tests, city responses, internal memos and other records.

The documents suggest city leaders were aware of concerns about toxic air quality following the attacks.

FDNY union leaders say they are frustrated that firefighters and other first responders were denied access to the records and that it took so long for the documents to become public.

Retired FDNY Lieutenant Michael O'Connell says the records could help first responders in their ongoing fight for expanded health care coverage and compensation for illnesses linked to their work at Ground Zero.

"Making sure something like autoimmune diseases get added. There are neurological conditions that people are suffering from. Dementia, we are seeing a high rate of that. It's not just cancer and lung ailments," O'Connell said.

O'Connell also shared the story of a close friend who died at 48 years old after suffering from encephalitis and repeated seizures.

More than 340 FDNY firefighters were killed while responding to the attacks.

In the years since, hundreds of other first responders have died from illnesses believed to be related to their exposure at Ground Zero.

City officials say additional 9/11 records will be released over the next year.