An evaluation of optical particle counter measurements of the dry deposition of atmospheric aerosol particles

Abstract

Eddy correlation flux measurements of total atmospheric aerosol particulates were collected over a grass surface at Champaign, Illinois, in June 1982. PMS ASAS‐300A and Royco 225 optical particle counters were used as sensors to measure fluxes in four size ranges from 0.15 to 2.5 μm. The fluxes were quite variable, both in time and between sensors. The sensor signals are also quite noisy, but we demonstrate that, with certain limitations, the sensor systems are suitable for making flux measurements. This variability in the flux measurements is, in part, a result of the sensor noise and is also at times possibly the result of the transport through vertical moisture gradients, flux divergence, and changes in particulate concentration. However, frequent occurrences of upfluxes indicate it is also possibly the result of organic emissions from the surface. Ensemble average deposition velocities for each sensor were negative and quite small and, in most cases, not statistically significant. However, daily average values were often quite large and negative and showed good agreement between sensors.