EFFECT OF RELATIVE HUMIDITY ON MIXED AEROSOLS IN ATMOSPHERE

Abstract

In this study, the effects of relative humidity on the deliquescent point and size of internally mixed aerosols diameter, NH₄NO₃ and (NH₄)₂SO₄ were investigated using a Tandem Differential Mobility Analyzer (TDMA) with a relative humidity conditioner. The growth of mixed aerosols appears to have two deliquescent steps. The first one was at about 61.2 ∼ 61.3%, but the second one was at around 77 ∼ 78%. At the first deliquescence point, growth ratio at phase change was 7.5%, which agrees with the growth ratio of ammonium nitrate aerosol. Growth ratio of phase change at the second deliquescence point was about 20%, lower than the growth ratio of ammonium sulfate aerosol. In the relative humidity range of 80 ∼ 85%, the growth ratio of the mixed aerosols reached 60%. In other words, it appears that growth ratio increases with the size of aerosol. Furthermore, a theoretical growth model of mixed aerosols was developed and applied to estimate the amount of composition of the mixed aerosols dissolved at each deliquescence point. The results also show that some of ammonium sulfate already dissolved at the first deliquescence point according to the theoretical growth model.

Keywords:

• Ammonium sulfate
• Ammonium nitrate
• Mixed aerosol
• Relative humidity
• Hygroscopic aerosols
• Atmospheric aerosols

ACKNOWLEDGMENTS

This study was funded by National Science Council, R.O.C., through grant NSC 82-0410-E-002-116.