Aldona Wiacek

Water uptake of clay and desert dust aerosol particles at sub- and supersaturated water vapor conditions

Airborne mineral dust particles serve as cloud condensation nuclei (CCN), thereby influencing the formation and properties of warm clouds. It is therefore of atmospheric interest how dust aerosols with different mineralogy behave when exposed to high relative humidity (RH) or supersaturation (SS) with respect to liquid water. In this study the subsaturated hygroscopic growth and the supersaturated cloud condensation nucleus activity of pure clays and real desert dust aerosols were determined using a hygroscopicity tandem differential mobility analyzer (HTDMA) and a cloud condensation nuclei counter (CCNC), respectively. Five different illite, montmorillonite and kaolinite clay samples as well as three desert dust samples (Saharan dust (SD), Chinese dust (CD) and Arizona test dust (ATD)) were investigated. Aerosols were generated both with a wet and a dry disperser. The water uptake was parameterized via the hygroscopicity parameter kappa. The hygroscopicity of dry generated dust aerosols was found to be negligible when compared to processed atmospheric aerosols, with CCNC derived kappa values between 0.00 and 0.02 (the latter corresponds to a particle consisting of 96.7% by volume insoluble material and approximately 3.3% ammonium sulfate). Pure clay aerosols were generally found to be less hygroscopic than natural desert dust particles. The illite and montmorillonite samples had kappa approximately 0.003. The kaolinite samples were less hygroscopic and had kappa=0.001. SD (kappa=0.023) was found to be the most hygroscopic dry-generated desert dust followed by CD (kappa=0.007) and ATD (kappa=0.003). Wet-generated dust showed an increased water uptake when compared to dry-generated samples. This is considered to be an artifact introduced by redistribution of soluble material between the particles. Thus, the generation method is critically important when presenting such data. These results indicate any atmospheric processing of a fresh mineral dust particle which leads to the addition of more than approximately 3% soluble material will significantly enhance its hygroscopicity and CCN activity.

Scanning the Earth's limb from a high-altitude balloon: The development and flight of a new balloon-based pointing system

Abstract The development and first flight of a new balloon-borne pointing system is discussed. The system is capable of pointing a platform of optical instruments at an inertial target from a pendulating platform suspended below a high-altitude balloon. It operates in both a traditional occultation-scan mode, to observe solar absorption, and a limb-scan mode, to make measurements of Earths limb. The system employs integrated sensors and high-level icon-based software (Labview). A microprocessor controller derives real-time estimates of gondola attitude, employing an extended Kalman filter to combine gyro, magnetometer, tilt-sensor, and shaft-encoder information. These estimates are used to develop control demands that point a platform of instruments in elevation and azimuth. The systems first flight was from Vanscoy, Saskatchewan, Canada, on 29 August 2000. Results of the systems performance during this mission are presented. In flight, the system demonstrated a pointing accuracy better than 0.1° (1σ) ...

A New High-Resolution Fourier Transform Infrared Spectrometer for Atmospheric Remote Sensing in Toronto

Atmospheric remote sensing is performed with a new Bomem DA8 FTIR spectrometer at the University of Toronto Atmospheric Observatory. The abilities of the instrument and the first retrieved vertical profiles of atmospheric constituents are presented.

A new high-resolution Fourier transform infrared spectrometer for ground-based atmospheric measurements in Toronto

The optical design of a new high-resolution Fourier Transform infrared Spectrometer (FTS) is described. The FTS is dedicated to ground-based atmospheric measurements from Toronto, Canada. The solar absorption observation geometry and measurement parameters are presented. Finally, instrument performance is discussed in terms of instrumental line shape (ILS) and baseline stability.

Ground-based Fourier-transform infrared measurements of atmospheric trace gases over Toronto, Canada

Continuous measurements of solar absorption spectra with a ground-based high-resolution Bomem DA8 Fourier-Transform InfraRed (FTIR) spectrometer were started in Toronto, Canada, in October 2001. These measurements aim to cover the gap in ground-based FTIR data in southern Canada. Column amounts of atmospheric tracers derived from spectra measured during fall 2001 are presented.