Mixing state of carbonaceous aerosol in an urban environment: single particle characterization using the soot particle aerosol mass spectrometer (SP-AMS)

摘要

Understanding the impact of atmospheric black carbon (BC)-containingparticles on human health and radiative forcing requires knowledge of themixing state of BC, including the characteristics of the materials withwhich it is internally mixed. In this study, we examine the mixing state ofrefractory BC (rBC) and other aerosol components in an urban environment(downtown Toronto) utilizing the Aerodyne soot particle aerosol massspectrometer equipped with a light scattering module (LS-SP-AMS). -meanscluster analysis was used to classify single particle mass spectra intochemically distinct groups. One resultant particle class is dominated by rBCmass spectral signals (C to C) while the organicsignals fall into a few major particle classes identified ashydrocarbon-like organic aerosol (HOA), oxygenated organic aerosol (OOA),and cooking emission organic aerosol (COA). A gradual mixing is observedwith small rBC particles only thinly coated by HOA (~ 28%by mass on average), while over 90% of the HOA-rich particles did notcontain detectable amounts of rBC. Most of the particles classified intoother inorganic and organic particle classes were not significantlyassociated with rBC. The single particle results also suggest that HOA andCOA emitted from anthropogenic sources were likely major contributors toorganic-rich particles with vacuum aerodynamic diameter () rangingfrom ~ 200 to 400 nm. The similar temporal profiles and massspectral features of the organic classes identified by cluster analysis andthe factors from a positive matrix factorization (PMF) analysis of theensemble aerosol data set validate the interpretation of the PMF results.