Relaxed Eddy Accumulator for Flux Measurement of Nanometer-Size Particles

ABSTRACT An investigation of the relaxed eddy accumulation (REA) technique to measure the flux of ultrafine (∼1 nm in diameter) aerosol particles using unattached radon progeny as a tracer and the construction of a prototype system based on the REA principle is reported. The system consisted of a sonic anemometer with a response frequency of 21 Hz, three screen/filter holders, a custom-built electronic circuit to control three electromagnetic inlet valves for sampling the up-, down- and neutral vertical winds, a high-capacity air blower and a portable PC. A 635-wire mesh screen/fiberglass filter combination was used in each intake to provide a separate measure of the unattached-to-aerosol and attached-to-aerosol radon progeny. The 9 cm-diameter 635 mesh screen, combined with an air flow rate of 230 L min−1, resulted in 50% penetration for 2.7 nm-diameter particles. Corrections for a system response delay of 125 ms and the screen collection and alpha counting efficiencies were incorporated into the flux ca...