Local air regulators are investigating a mysterious rotten-egg odor that prompted dozens of complaints from people throughout San Francisco Wednesday morning.
More than a half-dozen city and federal agencies, Pacific Gas and Electric and the city's garbage collector say they don't know what caused it.
Inspectors from the Bay Area Air Quality Management District began investigating the smell shortly after 9 a.m., said district spokesman Walter Wallace.
But, by that time people had stopped reporting the odor.
PG&E and the city's Fire Department say that shortly after 2 a.m. people began calling the utility and dispatchers, complaining of a sulfurlike smell.