The Improvement Of Single Particle Aerosol Mass Spectrometer And Environmental Application

Aerosols are becoming more widely recognized throughout the world due totheir significant local, regional, and global impacts. With high complexity for theatmospheric aerosols, it is a considerable challenge to makes in-depth study of thephysical and chemical properties, source characteristics and evolution mechanism ofatmospheric aerosols. Single particle aerosol mass spectrometry, as a new-styledaerosol analytical tool, has high time and spatial resolution, which can detect theaerosol particles on the single particle level. Compared with traditional analysismethods, single particle aerosol mass spectrometry has the advantages including:online sample inlet, no need for sample dispose, size and chemical compositionanalysis at the same time, which play important roles to study the different types ofatmospheric particles and their mixing state, evolution and source apportionment.During my master degree time，I participated in the design, performance,characterization and basic application of the instrument. In my doctoral study, theauthor improved of the prototype of the single particle mass spectrometer and carriedout the source characterization applications of vehicle exhaust and ambient sourcecharacterization in Beijing.(1) Aerosol and applications of single particle mass spectrometers in variousfields. The characters, effect and measurement methods of aerosols are introducedbriefly. The applications of single particle mass spectrometry in environmentalmonitoring, atmospheric chemistry, materials science, biomedicine, defense, securityand other fields have been reviewed.(2) Principle of online single particle mass spectrometers. In this chapter,The detailed technical principles, main constitutes, and the advantages anddisadvantages of aerosol mass spectrometry technology are discussed. In addition,the instrument advantages are introduced in detail.(3) Performance improvements for the inlet and sizing system. In order to meet the analysis demand of PM2.5, the instrument inlet, relaxation chamber andaerodynamic lens were improved and the transmission efficiency of largeparticulates has been increased effectively. The optical structure of the sizing systemwas improved as well, and a filter system was designed to reduce the backgroundnoise of the instrument greatly, making a7fold increase in signal to noise ratio for100nm particles.(4) Dynamic range and sensitivity improvements for a single-particleaerosol mass spectrometer. Because the tremendous kinetic dispersion of ionsgenerated during initial ionization reduced the sensitivity and resolution of TOFMS,a lens focusing system was simulated and applied in the instrument. As a result, thesensitivity of the instrument was increased nearly2-fold. In order to acquire thelarger and smaller signal simultaneously, the data acquisition system was improvedby collecting the single signal using dual-channel superimposed to achieve40timeshigher dynamic range than previous type.(5) Source characterization of diesel vehicles with a single particle aerosolmass spectrometer. The single particle aerosol mass spectrometer was used toanalyze the sources of diesel exhaust emissions. Particles from real-time emissionsand aged particles were characterized to clarify the main mass spectral signaturesand the mixing state of particulate matter from diesel exhaust emissions.(6) Application of a single particle aerosol mass spectrometer in Beijingurban areas. A single-particle aerosol mass spectrometer was used to detect theaerosols in Beijing urban areas during spring time. During this period, there are threetypical weather conditions, clean and sunny, heavily polluted haze and sandstormdays. During clear days, OC and biomass-K are associated with biomass burningactivities. During the two haze periods, K-nitrate, ECK, rich-Fe and rich-Pb particlesdominated, associated with industrial emissions from regional transport, suggestingthat industrial emissions have a greater impact on haze formation. Four main typesof dust particles were identified as dust-Si, dust-Ca, dust-Al, and dust-Ti, respectively. NaK-EC particles showed a similar diurnal trend to NOx, reflecting apossible local traffic source. The secondary species (sulfate and nitrate) showed adifferent mixing state in different type of particles.