The measurement of liquid water mass associated with collected hygroscopic particles

This work presents the measurements of aerosol liquid water (LW) mass of NH4NO3, NaNO3, NH4HSO4, and NaCl using a newly developed method (Lee and Hsu (1998) J.Aerosol. Sci. 29, 827-837) for the changing relative humidity (RH) at a stable room temperature. The target aerosol was generated by atomizing the 1.5% (wt/wt) solution Of a known chemical and was subsequently collected on a Teflon filter. The four inorganic salts selected in this work were ail hygroscopic, but their humidographs showed either with or without a hysteresis phenomenon. The NH4NO3 particles deliquesce at around 62% RH and re-crystallize at 32% RH with a gradual decline of LW mass. In contrast, the NaCl particles show a distinctive re-crystallization point at 47% RH and a deliquescent relative humidity (DRH) at around 76%. For NaNO3 and NH4HSO4 particles, no hysteresis effect was observed during the hydration and dehydration processes. A check on the evaporative loss of NH4NO3 particles showed no significant variation in the measurement of LW mass in 24 h. The comparison of the humidographs between sea salt and NaCl particles reveals that the amount of water uptake From sea salt is higher than that of the NaCI on a mol basis. The measured data and two humidographs from previous work were compared with a model calculation. A good agreement was found for most salts except for (NH4)(2)SO4 in the descending RH mode and NaCl in the ascending and descending RH modes. Finally, the effects of filler substrate on particles are discussed on the contact angle, particle agglomeration, and mass loading. (C) 1999 Elsevier Science Ltd. All rights reserved.