Atmospheric particle counting

A method for particle detection, comprising:

• providing an atmospheric particle detector, comprising:
• an optical measurement cavity, a light baffle attached to 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;
• introducing an air sample into the optical measurement cavity through the light baffle, wherein the light baffle permits unobstructed airflow into the optical measurement cavity and blocks ambient light from entering the optical measurement cavity, and wherein the light baffle comprises a conduit attached to an opening of the optical measurement cavity that directs the air sample into the optical measurement cavity along semicircular pathways that converge at the opening of the optical measurement cavity;
• passing the light beam through the air sample in the optical measurement cavity between the photodetector and the retro reflector, wherein light from the light beam is scattered off of particles in the air sample to the photodetector or to the retro reflector which reflects the light back toward the photodetector;
• and
• detecting the light scattered off of the particles using the photodetector.