A system for determining visibility comprises a particle sensor unit mounted onboard a vehicle, and a processor unit in communication with the particle sensor unit. The particle sensor unit comprises a light source configured to transmit a light beam into an external air region; a set of receive optics configured to collect a scattered portion of the light beam from particles in the air region; and an optical detector configured to receive the collected scattered portion and measure a signal intensity. The processor unit is operative to perform a method for determining visibility that comprises analyzing data received from the particle sensor unit to determine particle distribution in a volume of the air region; performing particle differentiation to determine sizes and types of particles in the distribution; calculating visibility data based on the sizes and types of the particles; and outputting the visibility data to one or more onboard systems.