Atmospheric particle detectors having a hybrid measurement cavity and light baffle are provided. In one aspect, an atmospheric particle detector includes: an optical measurement cavity; a light baffle attached to the optical measurement cavity, wherein the light baffle is configured to i) permit unobstructed airflow into the optical measurement cavity and ii) block ambient light from entering the optical measurement cavity; a photodetector on a first side of the optical measurement cavity; a retro reflector on a second side of the optical measurement cavity opposite the photodetector, and a light source configured to produce a light beam that passes through the optical measurement cavity without illuminating the photodetector. A method for particle detection using the atmospheric particle detector is also provided.