Laboratory Evaluation of a Condensation Particle Counter Under Airborne Measurement Conditions

NOBUYUKI TAKEGAWA (1), Hiromu Sakurai (2)

(1) RCAST, University of Tokyo, Japan, (2) NMIJ, AIST, Japan

     Abstract Number: 197
     Last modified: April 29, 2010

Abstract
Performance of a condensation particle counter (CPC, Model 3771, TSI Inc.), which has the nominal cutoff diameter (d50) of 10 nm, has been tested in the laboratory for the purpose of airborne measurements. First, effects of particle coincidence at concentrations above the upper limit specified by the manufacturer (> 10^4 cm-3) were evaluated. The default live-time counting was not sufficient to account for the coincidence effect even below the upper limit. By applying a correction factor derived from experimental results, the CPC can quantify particle concentrations of as high as 5 x 10^4 cm-3. Second, effects of inlet pressures (p) on the size dependence of the detection efficiency were investigated (particle diameter (d) = 8-100 nm, p = 1010-300 hPa). We found that the cutoff diameter increased and the maximum (asymptotic) detection efficiencies decreased with decreasing the pressure. The pulse height analysis indicated that the decrease in the asymptotic detection efficiency observed for our CPC was mainly due to reduction of the saturation ratio that caused insufficient condensational growth. Finally, temporal variation of the detection efficiency during continuous operation of the CPC without supply of 1-butanol was investigated (d = 10 and 100 nm, p = 1010 and 600 hPa). The detection efficiencies did not show significant change at least over 6 h without supply of 1-butanol, which ensures stable performance of the CPC for flight durations of 4-5 h. Based on our laboratory evaluations, possible errors in airborne measurements were estimated assuming typical particle number size distributions of ambient aerosols.