A serial dirty diaper dumper has struck again in Orange County, leaving about a dozen used diapers on streets in upscale Corona del Mar. A Newport Beach police still don’t know who is responsible for “disposing of the diapers in this manner,” according to spokeswoman Kathy Lowe. The diapers last appeared in May, prompting city code enforcement officers to try to find the person responsible. But unless the person is caught in the act, it may be difficult to cite them for littering, city officials said. In December 2011, there were at least three separate occasions where the diapers littered the roadway, causing cyclists to swerve to avoid them before city crews were able to remove them.