Characterization of Single Particles in Urban Atmospheric Aerosols Over Nagoya Based on Mass Spectral Analysis

Mass spectral analysis of single aerosol particles was performed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) in the urban area of Nagoya, Japan, for five days in the autumn of 2010. An ion-series analysis was applied to the single-particle mass spectra; the sum of the masses at Δ of 1, 3, 4, and 5 divided by the total mass of organics (f_Δ1,3-5) was used as an indicator of the degree of oxygenation of the organics. The organic mass fraction (F_org) and f_Δ1,3-5 of single particles varied substantially, and the results for the entire period indicate that two groups of particles with high and low f_Δ1,3-5 were present. The organics in particles with high F_org were less oxygenated, whereas those with low F_org were more oxygenated; these different particles were associated with hydrocarbon-like organic aerosols (HOA) and low-volatility oxygenated organic aerosols (LV-OOA), respectively, based on the PMF analysis of the MS mode data. The size distributions of the two types of particles overlapped substantially. The degree of the overlap depends on the equivalent particle diameter used, indicating the importance of single-particle analysis in understanding the size-composition relationship in detail. Alteration of the aerosol mixing state was clearly indicated by the changes in f_Δ1,3-5 and F_org; the homogeneous conditions changed to externally mixed conditions from the evening until noon of the next day. Possible causes of this alteration include the condensation of oxygenated organics and ammonium nitrate onto pre-existing particles. This study demonstrated the usefulness of single-particle analysis based on electron-ionization aerosol mass spectrometry.

Copyright 2015 American Association for Aerosol Research