Hygroscopicity of aerosol particles at low temperatures. 2. Theoretical and experimental hygroscopic properties of laboratory generated aerosols.
A Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) system has been used to measure hygroscopic growth curves and deliquescence relative humidities (DRH) of laboratory generated (NH4)2SO4, NaCl, and NaNO3 particles at temperatures T= 20 degrees C and -10 degrees C. Good agreement (better than 3.5%) between measured growth curves and Köhler theory was found using empirical temperature and concentration dependent values for water activity, solution density, and surface tension. The measured growth curves only experience a small temperature dependence in the observed temperature range. Therefore, to a first approximation, it is possible to neglect the temperature dependence of the water activity for theoretical calculations in the temperature range -10 degrees C < T < 25 degrees C. The small differences between experiment and theory, which were predominantly observed for NaCl particles, are probably caused by a small amount of water adsorbed on the "dry" crystals. It was also observed that these particles experience a significant restructuring at relative humidity RH < DRH, which was also taken into account for a comparison with theoretical curves. If salt particles are used for instrument calibration, precautions regarding the dry particle diameter have to be taken.
Gysel
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M
Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland.
Weingartner
E
E
Baltensperger
U
U
D000327:Adsorption; D000336:Aerosols / Q000032:analysis; D000393:Air Pollutants / Q000032:analysis*; D002138:Calibration; D003460:Crystallization; D004784:Environmental Monitoring / Q000295:instrumentation*; D010316:Particle Size; D013696:Temperature
D000336:Aerosols; D000393:Air Pollutants