The first electrostatic air filter was invented in Pittsburgh by a fellow named Gaylord W. Penney. According to a 1942 Time article,
The Precipitron came out of “a successful failure” in research, and a hopeful house-cleaning experiment in Pittsburgh. Some six years ago a young research engineer, Gaylord W. Penney (now manager of the electrophysics laboratories), sought a conclusion to German experiments with ionized air, found a clue to cleaner air. With a wire, a couple of aluminum plates and a burning oily rag, he rigged his first crude electrostatic dirt trap.