A novel tandem differential mobility analyzer with organic vapor treatment of aerosol particles

[摘要] A novel method to characterize the organic composition of aerosolparticles has been developed. The method is based on organic vapor interaction with aerosol particles and it has been named anOrganic Tandem Differential Mobility Analyzer (OTDMA). The OTDMA method has been tested for inorganic (sodium chloride and ammoniumsulfate) and organic (citric acid and adipic acid) particles. Growth curves of the particles have been measured in ethanol vaporand as a comparison in water vapor as a function of saturation ratio.

Measurements in water vapor show that sodium chloride and ammonium sulfate as well as citric acid particles grow at water saturationratios (S) of 0.8 and above, whereas adipic acid particles do not grow atS<0.96. For sodium chloride and ammonium sulfate particles, a deliquescence point is observed atS= 0.75 and S= 0.79, respectively. Citric acid particles grow monotonouslywith increasing saturation ratios already at low saturation ratios and no clear deliquescence point is found.

Forsodium chloride and ammonium sulfate particles, no growth can be seen in ethanol vapor at saturation ratios below0.93. In contrast, foradipic acid particles, the deliquescence takes place at aroundS= 0.95 in the ethanol vapor. The recrystallization of adipic acid takes placeat S< 0.4. Citric acid particles grow in ethanol vapor similarly as inwater vapor; the particles grow monotonously with increasing saturation ratios and no stepwise deliquescence is observed.

The results show that the working principles of the OTDMA are operational for single-component aerosols.Furthermore, the results indicate that the OTDMA method may prove useful in determining whetheraerosol particles contain organic substances, especially if the OTDMA is operated in parallel with ahygroscopicity TDMA, as the growth of many substances is different in ethanoland water vapors.

[学科分类] 大气科学