NEW YORK (CBSNewYork) – Like many others who were in the city on Sept. 11, 2001, Lady Gaga has emotional memories of that day.

Gaga was 15-years-old when she stood on the roof of her Upper East Side high school watching the World Trade Center towers fall.

“I remember where I was and what I did, exactly every moment and the smell of everything about it,” Lady Gaga told ABC News.

She said this Sunday she will be marking the 10th anniversary like every New Yorker, by mourning the lives lost that day.

Lady Gaga, along with other celebrities including NAS, Pauly D, Fran Drescher, Drake Bell and Julianne Hough, filmed a public service announcement for the 9/11 Tribute Movement which asks, “10 years later, what do you remember?”

“We were in disbelief,” Gaga says in the video.

“No one was ready for 9/11. For what happened,” Nas says.

In the video, the celebrities reach out to their fans and ask them to find ways to give back to their communities.

On the 9/11 Tribute Movement website, people can upload their own tribute videos and write about what they’ll do to honor the victims.

What do you remember about 9/11? Let us know below…