A chemical analyzer for charged ultrafine particles

[摘要] New particle formation is a frequent phenomenon in the atmosphere and ofmajor significance for the Earth's climate and human health. To date themechanisms leading to the nucleation of particles as well as to aerosolgrowth are not completely understood. A lack of appropriate measurementequipment for online analysis of the chemical composition of freshlynucleated particles is one major limitation. We have developed a ChemicalAnalyzer for Charged Ultrafine Particles (CAChUP) capable of analyzingparticles with diameters below 30 nm. A bulk of size-separated particles iscollected electrostatically on a metal filament, resistively desorbed andsubsequently analyzed for its molecular composition in a time of flight massspectrometer. We report on technical details as well as characterizationexperiments performed with the CAChUP. Our instrument was tested in thelaboratory for its detection performance as well as for its collection anddesorption capabilities. The manual application of defined masses of camphene(C₁₀H₁₆) to the desorption filament resulted in a detection limitbetween 0.5 and 5 ng, and showed a linear response of the mass spectrometer.Flow tube experiments of 25 nm diameter secondary organic aerosol fromozonolysis of alpha-pinene also showed a linear relation between collectiontime and the mass spectrometer's signal intensity. The resulting mass spectrafrom the collection experiments are in good agreement with published work onparticles generated by the ozonolysis of alpha-pinene. A sensitivity studyshows that the current setup of CAChUP is ready for laboratory measurementsand for the observation of new particle formation events in the field.

[学科分类] 几何与拓扑