Rapid single-particle mass spectrometry (RSMS): Inlet design and analysis

There is a growing body of research related to on-line, single particle characterization of airborne aerosols. Modern chemical characterization instruments employ an aerosol inlet that transmits atmospheric aerosols to the low pressure source region of a time-of-flight mass spectrometer, where particles are ablated and ionized using high energy irradiation. The analysis yields information about the composition of airborne particles.; Often, the rate at which particles are analyzed is limited by the transmission rate of the inlet. Particles, depending on their size, are lost during sampling due to either inertial effects or diffusion. Consequently, it is important that the inlet be designed carefully so as to efficiently transmit particles of interest. This thesis critically reviews various methods and mechanisms used for transmitting particles. Furthermore, it is also an attempt to document focusing mechanisms based on the fundamental behavior of high speed particle beams.; As a prelude to inlet design, particle growth due to vapor condensation is first estimated; due to the expansions involved in an inlet, vapor may condense or evaporate from particles and thus may bias measurements by altering their size and composition. Particle beams produced by simple fixed geometry inlets are studied next; mostly capillaries, conical nozzles or aerodynamic lenses are used as primary focusing elements. Mechanisms are identified through which these elements form high speed beams, and qualitative information is gathered about how the beam characteristics vary for different geometries and operating conditions.; Armed with a basic knowledge of particle beam characteristics, additional mechanisms are devised and explored that essentially extend the particle size range over which simpler inlets operate. These mechanisms are based on altering the size range dynamically by either continuously varying the inlet geometry or the flow conditions. Several implementations of these mechanisms, both for ultrafine and large particles, are presented and discussed along with their merits and drawbacks. In particular, an efficient design for focusing ultrafine particles is discussed in some detail--preliminary experimental results obtained from a prototype are also analyzed.