NEW ORLEANS — No one goes to a bar here, particularly one that advertises its hours as “2 p.m. till,” and expects precision about the time of day. But it was right on the stroke of midnight that Frankie Mazzanti, 56, one of the owners of the low-ceilinged neighborhood joint called 45 Tchoup, went along the bar picking up ashtrays and tossing them in a plastic bag.

“All right guys, put ’em out,” he said. “Sorry, it’s over.”

Just after midnight, it became illegal to smoke in bars in New Orleans. Last call for cigarettes went out across the city: at the hazy Bud Rip’s bar in the Bywater; among the cigar-smoking crowd in the leopard print chairs at the French 75 bar in the French Quarter; at the Kingpin, where the bartenders handed out Nicorette gum; and at 45 Tchoup, where smoke had settled in so heavily that it began to form something like an Alpine cloud bank.

“This is one of the smokiest bars in town,” said Steve Zweibaum, 57, the owner of a jazz venue nearby who, while smoking a cigarette, spoke of how he had quit smoking long ago. “I know a bunch of people who don’t come in here because of the smoke,” he said, listing names. “Maybe they’ll come back.”