A portable pulsed cavity ring-down transmissometer for measurement of the optical extinction of the atmospheric aerosol

A small portable system is described which is used to directly determine th e optical extinction of the atmospheric aerosol. The requisite highly sensi tive measurement of the optical extinction is accomplished simultaneously a t two wavelengths in the near-infrared (1064 nm) and visible (532 nm), usin g the pulsed cavity ring-down (CRD) approach. The measurement at the two wa velengths can aid in separating the scattering and absorption components of the optical extinction. Rayleigh equivalent optical extinction of similar to 10 x 10(-6) m(-1) from particulate matter in the atmospherically importa nt 0.1-2.5 mum diameter size range (fine particle accumulation mode) can be readily observed with short ( <5 s) integration times. Optical extinction is inversely related to the visual range, and so the instrument provides a direct measurement of this particulate-related air quality indicator. The i nstrument can also provide particle size range-selected multiwavelength opt ical property measurements. which can be inverted to provide valuable infor mation about the extant airborne particulate distribution.