The isothermal haze chamber with discontinuous flow: a new experimental device for CCN measurements at low supersaturation

An isothermal haze chamber (IHC) has been designed, incorporating results f rom the tests of earlier instruments held at the 1981 Reno (NV) workshop. T his instrument, named isothermal haze chamber with discontinuous flow (IHCD F), periodically discontinues the flow through the haze chamber in order to form a well-defined region of 100% RH in the center of the chamber. Indeed , tests performed with our conventional continuous flow IHC showed a poorly defined 100% RH field in the chamber, mainly due to an unsteady laminar ai r flow through the chamber during measurement. Experiments with polydispersed NaCl aerosol showed that a supersaturation s pectrum could be obtained within a growth time of 300 s, over a supersatura tion range of 0.01-0.1%. The instrument is suitable for field use. It is contained in a package 1.4 m high and weighs 5 kg. Three minutes is required to collect the air sample and 5 min for drop growth, thus permitting the analysis of seven samples p er hour. (C) 2000 EIsevier Science B.V. All rights reserved.