Laboratory Evaluation of a TSI Condensation Particle Counter (Model 3771) Under Airborne Measurement Conditions

The performance of a condensation particle counter (CPC, Model 3771, TSI Inc.), which has a nominal minimum detectable particle size (d 50) of 10 nm, has been tested in the laboratory for the purpose of airborne measurements. First, the effects of particle coincidence at concentrations above the upper limit specified by the manufacturer (>104 cm-3 were evaluated. By applying a correction factor derived from experimental results, the CPC can quantify particle concentrations of as high as 5 × 104 cm– 3. Second, the effects of inlet pressure (p) on the size dependence of the detection efficiency were investigated (particle diameter (d)= 8–100 nm, p= 1010–300 hPa). The asymptotic detection efficiency and d 50 showed decreasing and increasing trends with decreasing pressure, respectively, especially at p < 600 hPa. It is likely reduction of the 1-butanol saturation ratio in the condenser at decreased pressures can explain the observed pressure dependence. Finally, the temporal variation of the detection efficiency during continuous operation of the CPC without the 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 the 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.