Business Notes TRANSPORTATION

According to federal air-quality standards, the stuff that floats above Los Angeles is unfit for humans to breathe for more than half the year. As a / result, the second most populous city in the U.S. last year implemented the nation's toughest antismog regulations. United Parcel Services said last week it will comply with the new rules by converting its 2,700 delivery trucks in Los Angeles to cleaner-burning natural gas. By the year 2007, the city expects all its cars and trucks to run on cleaner fuel.

United Parcel, with headquarters in Greenwich, Conn., has spent a year testing 10 natural gas-fuel trucks in Brooklyn, N.Y. Reduction of smog-causing gases has been so effective in those vehicles that the company is preparing to make sample conversions by early 1991 in its 600-vehicle fleet in Manhattan. They will come none too soon; New York City has the second worst air in the U.S., after Los Angeles.