Calibration of LACIS as a CCN detector and its use in measuring activation and hygroscopic growth of atmospheric aerosol particles

Abstract

Abstract. A calibration for LACIS (Leipzig Aerosol CloudInteraction Simulator) for its use as a CCN (cloud condensation nuclei) detector has been developed. For this purpose, sodium chloride and ammonium sulfate particles of known sizes were generated and their grown sizes were detected at the LACIS outlet. From these signals, the effective critical super-saturation was derived as a function of the LACIS wall temperature. With this, LACIS is calibrated for its use as a CCN detector. The applicability of LACIS for measurements of the droplet activation, and also of the hygroscopic growth of atmospheric aerosol particles was tested. The activation of the urban aerosol particles used in the measurements was found to occur at a critical super-saturation of 0.46% for particles with a dry diameter of 75 nm, and at 0.42% for 85 nm, respectively. Hygroscopic growth was measured for atmospheric aerosol particles with dry diameters of 150, 300 and 350 nm at relative humidities of 98 and 99%, and it was found that the larger dry particles contained a larger soluble volume fraction of about 0.85, compared to about 0.6 for the 150 nm particles.

Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies

“…These are the water sub-and supersaturated modes for the temperature range above T 0 = 273.15 K, the water sub-, ice supersaturated, and the water super-and ice supersaturated modes below T 0 = 273.15 K. If the inlet dew point temperature is lower than the wall temperature, the inner tube walls are in equilibrium with the water vapor of the flow and the dew point temperature remains constant (water subsaturated mode). Applying this water sub-saturated mode for T > 273.15 K with inlet and wall temperature being identical, deliquescence and hygroscopic growth of aerosol particles can be investigated (Wex et al, 2006Voigtländer et al, 2008;Ziese et al, 2008;Niedermeier et al, 2008). With higher inlet dew point temperature compared to the wall temperature, supersaturation can be achieved as a result of the simultaneous heat and vapor diffusion, which occur at slightly different rates, because of the non-linearity of the water vapor pressure curve.…”

“…As a result a thin water film accumulates on the tube walls and the dew point temperature of the flow converges to the wall-temperature set point. With this method, critical supersaturations for cloud droplet activation and growth, including kinetic effects, can be studied (Wex et al, 2006Voigtländer et al, 2008;Niedermeier et al, 2008;Ziese et al, 2008).…”

LACIS-measurements and parameterization of sea-salt particle hygroscopic growth and activation

“…The larger particles for which the present saturation in LACIS is adequate for activation grow dynamically. Earlier activation measurements (Wex et al, 2006) showed that the results for hygroscopically grown particles could be linked through a straight line. The results for dynamically grown particles, however, could be reproduced by a polynomial curve.…”

“…The calibration of LACIS with respect to the supersaturation was done with ammonium sulfate particles (Wex et al, 2006). At each supersaturation the diameter of the investigated dry salt particles was varied until the critical diameter D crit was found.…”

Hygroscopic growth and activation of HULIS particles: experimental data and a new iterative parameterization scheme for complex aerosol particles

“…The supersaturated mode of operation was applied for the activation measurements (Wex et al, 2006). In contrast to the sub-saturated mode, the wall temperature (here varied between 5.51 • C and 5.82 • C) is below the dewpoint temperature (22.0 • C) of the aerosol and the sheath air.…”