Sweltering temperatures and low winds over much of the Bay Area prompted the first Spare the Air day of the year today — but unlike previous poor air-quality days, free rides on most public transit systems will last only until 1 p.m.

Rides on all Bay Area buses will be free all day, but riders on the BART, Caltrain, ACE Train and all Bay Area ferries will have to pay after 1 p.m, according to the Bay Area Air District. Last year, free rides led to a spike in crime, as homeless people and bored teens spent most of the day riding aimlessly, according to transit officials.

National Weather Service forecaster Diana Henderson said Livermore will likely be the hottest place in the Bay Area today, at 103 degrees. Redwood City will see a high of 90 degrees, while temperatures at San Francisco International Airport will rise to 85 degrees, she said. The City’s high temperature is expected to be 78 degrees.

BART parking will also be free today, according to spokesman Linton Johnson. However, he encouraged people to avoid starting their vehicles and instead to walk, bike, carpool or take a bus to a BART station.