Development and Characterization of an Aerosol Time-of-Flight Mass Spectrometer with Increased Detection Efficiency

Abstract

This paper describes the development and characterization studies of a more efficient aerosol time-of-flight mass spectrometer (ATOFMS), showing results for the on-line detection and determination of the size and chemical composition of single fine (100-300 nm) and ultrafine (<100 nm) particles. An aerodynamic lens inlet was implemented, replacing the converging nozzle inlet used on conventional ATOFMS instruments. In addition, the light scattering region was modified to enhance the scattering signals for smaller particles. Polystyrene latex spheres (PSL) with aerodynamic diameters ranging from 95 to 290 nm were used to characterize the particle sizing efficiency (product of particle transmission efficiency and particle scattering efficiency), particle detection efficiency (product of particle sizing efficiency and particle hit rate), and particle beam profile and perform instrument calibration. At number concentrations of <20 particles/cm(3), the particle sizing efficiencies were determined to be approximately 0.5% for 95 nm and approximately 47% for 290-nm PSL particles, while the particle detection efficiencies were measured to be approximately 0.3% for 95 nm and 44% for 290-nm PSL particles. This represents a significant increase (i.e., at least 3 orders of magnitude) in detection efficiencies for smaller particles over the conventional ATOFMS. In addition, the beam profiles for PSL particles of various sizes were measured in the ion source of the mass spectrometer and follow a Gaussian distribution with a full width at half-maximum of approximately 0.35 mm. The resulting higher detection efficiencies allow ATOFMS to obtain higher temporal resolution measurements of the composition of fine and ultrafine individual particles as demonstrated in initial ambient measurements in La Jolla, CA. At typical ambient particle number concentrations of 10(2)-10(3) particles/cm(3), approximately 30 000 particles with aerodynamic diameters of <300 nm were detected with average 24-h hit rates of 30% for particles between 50 and 300 nm. This advancement, allowing for high temporal resolution measurements of the composition of smaller particles with higher efficiency, adds to a growing number of instruments that can chemically characterize individual fine and ultrafine particles, with the goal of providing new insights into a number of areas including environmental and material sciences, health effects studies, industrial hygiene, and national security.

Enhanced trimethylamine-containing particles during fog events detected by single particle aerosol mass spectrometry in urban Guangzhou, China

“…The energy of desorption/ionization laser in this study was kept relatively low, with power density at about 1.06E þ 08 W cm À2 . To minimize the effects of size dependent detection efficiency for SPAMS (Allen et al, 2000;Su et al, 2004), the particle counts in small size bins (100 nm in width) were examined and merged if they were of similar temporal trends.…”

Sources and mixing state of summertime background aerosol in the north-western Mediterranean basin

“…A detailed description of the ATOFMS can be found elsewhere (Gard et al, 1997). Briefly, it consists of (i) an aerodynamic focusing lens (TSI AFL100) (Su et al, 2004) that transmits particles in the aerodynamic diameter (D a ) range 100-3000, (ii) a particle sizing region, and (iii) a bipolar reflectron time-of-flight mass spectrometer. Single particles are desorbed/ionised using a pulsed Nd:YAG laser (λ = 266 nm, ∼ 1 mJ pulse −1 ).…”

Mixing state of biomass burning particles by single particle aerosol mass spectrometer in the urban area of PRD, China

“…yaada.org) was utilized to search and analyze the imported information for individual particles. Because the particle-detection efficiency of the SPAMS exhibits strong dependent on particle size Su et al, 2004), each size range represents the relative counts of different particle types and not the actual atmospheric concentration, but the size distributions remain useful for comparing particle types.…”