THE INFLUENCE OF RELATIVE-HUMIDITY ON THE SIZE OF ATMOSPHERIC AEROSOL

The relative humidity of ambient air is very often over 75% throughout the year in Taiwan. Thus, the influence of relative humidity on the g rowth of hygroscopic aerosols in the atmosphere is particularly import ant. In this study, a TDMA system (Tandem Differential Mobility Analyz er) equipped with newly developed a SMPS (Scanning Mobility Particle S izer) was used to observe the sizes of submicron ammonium sulfate aero sols, from 63.8nm to 224.7nm, at five controlled relative humidities, 50%, 75%, 81%, 85% and 89%. It is the first time that the hygroscopic growths and deliquescence points of submicron aerosols of ammonium sul fate have ever been closely observed by use of the SMPS. The experment al results showed that the abrupt size changes of aerosols at their de liquescence points can be more precisely observed than in previous stu dies. It was also shown that there was no apparent growth in an ammoni um sulfate aerosol until the relative humidities was over 75%. At rela tive humidities between 81% and 89%, the growth ratio of size was abou t a factor of 1.3 to 1.6 and the water content of ammonium sulfate aer osols by mass was about 47% to 66%.