REAL-TIME ANALYSIS OF AQUEOUS AEROSOLS USING AEROSOL TSME-OF-FLIGHT MASS SPECTROMETRY

摘要

Atmospheric aerosols are receiving increased attention by governmental, industrial, and scientific communities due to recent studies that report a correlation between high levels of particulate pollution and adverse health effects. Real-time on-line laser desorption ionization mass spectrometry has developed into a widely used method for chemical characterization of individual aerosol particles. In the present study, the spectra of laboratory-generated particles were obtained as function of relative humidity to elucidate potential artifacts associated with ambient measurements and the effects of water on the laser desorption ionization mass spectra of single aerosol particles are explored. Laser desorption ionization is performed at 248nm. Particles were conditioned at humidities both above and below the respective deliquescence-relative humidities (DRH) and they undergo deliquescent growth. Water affects the mass spectra and ionization characteristics of the particles in several ways. It affects the mass spectra of aerosol particles by altering the distribution of ions formed, decreasing the total ion current, and increasing the threshold laser fluence. Peaks derived from water appear and the number of cluser ions resulting from the solute decreases. In addition, aqueous particles exhibit a two- to four-fold higher threshold laser fluences, a lower total ion current at a comparable laser fluence, and less peak broadening at high laser fluences than their dry particle counterparts.