He talked about keeping the building open as a civic obligation.

“I drive over the Long Island bridge, and it always amazes me the beauty of the city skyline, and I see this place equal to that,” Mr. Katsarelis said. “I want to keep it open, and I want to keep it clean, and I want to keep us healthy so I can do it for a little bit longer.”

The disinfection crew sprayed just about everything but the opening bell.

They finished early Saturday morning, funneling out in civilian clothes before the sun rose over Wall Street, quiet on a weekend.

On Monday morning, as New York schools, restaurants and shops stayed dark and with subways eerily quiet, the stock exchange lit up like normal. On Sunday, the Federal Reserve had cut interest rates to near zero to help stimulate the economy.

The CNBC lights came back on. The stock prices flashed. Traders returned, not quite elbow to elbow anymore.

“This is one of four buildings that defines America: the White House, the Capitol, the Supreme Court and the New York Stock Exchange. All three branches of government and then the economy,” Mr. Tuttle said. “We can’t close.”