Aerosol Mass Spectrometry via Laser-Induced Incandescence Particle Vaporization Final Report

Abstract. An air-to-air ultrafine particle concentrator (Aerosol Dynamics Inc. concentrator; ADIc) has been designed to enhance on-line chemical characterization of ambient aerosols by aerosol mass spectrometry. The ADIc employs a three-stage, moderated water-based condensation growth tube coupled to an aerodynamic focusing nozzle to concentrate ultrafine particles into a portion of the flow. The system can be configured to sample between 1.0–1.7 L min−1 with an output concentrated flow between 0.08–0.12 L min−1, resulting in a theoretical concentration factor (sample flow/output flow) ranging from 8 to 21. Laboratory tests with monodisperse particles show that the ADIc is effective for particles as small as 10 nm. Laboratory experiments conducted with the Aerosol Mass Spectrometer (AMS) showed no shift in the particle size after the ADIc, as measured by the AMS particle time-of-flight. The ADIc-AMS system was operated unattended over a one-month period near Boston, Massachusetts. Comparison to a parallel AMS without the concentrator showed concentration factors of 9.7 ± 0.15 and 9.1 ± 0.1 for sulfate and nitrate, respectively, when operated with a theoretical concentration factor of 10.5 ± 0.3. Concentration factor of organics was lower, possibly due to the presence of large particles from nearby road-paving operations, and a difference in aerodynamic lens cutoff between the two AMS instruments. Another field deployment was carried out in Helsinki, Finland. Two ~ 10-day measurement periods showed good correlation for the concentrations of organics, sulfate, nitrate and ammonium measured with an Aerosol Chemical Speciation Monitor (ACSM) after the ADIc, and a parallel AMS without the concentrator. Additional experiments with an AMS alternating between the ADIc and a bypass line demonstrated that the concentrator did not change the size distribution or the chemistry of the ambient aerosol particles.

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Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-12741-2005 ◽

2005 ◽

Vol 5 (6) ◽

pp. 12741-12773 ◽

Cited By ~ 9

Author(s):

L. C. Marr ◽

K. Dzepina ◽

J. L. Jimenez ◽

F. Reisen ◽

H. L. Bethel ◽

...

Keyword(s):

Mass Spectrometry ◽

Polycyclic Aromatic Hydrocarbons ◽

Mexico City ◽

Aromatic Hydrocarbons ◽

Heterogeneous Reactions ◽

Field Campaign ◽

Aerosol Mass ◽

Aerosol Mass Spectrometry ◽

Polycyclic Aromatic ◽

First Time

Abstract. Understanding sources, concentrations, and transformation of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere is important because of their potent mutagenicity and carcinogenicity. The measurement of particle-bound PAHs by three different methods during the Mexico City Metropolitan Area field campaign in April 2003 presents a unique opportunity for characterization of these compounds and assessment of the methods. The three methods are (1) collection and analysis of bulk samples for time-integrated gas- and particle-phase speciation by gas chromatography/mass spectrometry; (2) aerosol photoionization for fast detection of PAHs on particles' surfaces; and (3) aerosol mass spectrometry for fast analysis of size and chemical composition. This research represents the first time aerosol mass spectrometry has been used to measure ambient PAH concentrations and the first time that fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH measurements suggest that motor vehicles and garbage and wood burning are important sources in Mexico City. The diurnal concentration patterns captured by aerosol photoionization and aerosol mass spectrometry are generally consistent. Ambient concentrations typically peak at ~110 ng m−3 during the morning rush hour and rapidly decay due to changes in source activity patterns and dilution as the boundary layer rises, although surface-bound PAH concentrations decay faster. The more rapid decrease in surface versus bulk PAH concentrations during the late morning suggests that freshly emitted combustion-related particles are quickly coated by secondary aerosol material in Mexico City's atmosphere and may also be transformed by heterogeneous reactions.

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