Abstract
A new parameterization for quantifying the mixing state of aerosol populations has been applied for the first time to samples of ambient particles analyzed using spectro-microscopy techniques. Scanning transmission X-ray microscopy/near edge X-ray absorption fine structure (STXM/NEXAFS) and computer-controlled scanning electron microscopy/energy dispersive X-ray spectroscopy (CCSEM/EDX) were used to probe the composition of the organic and inorganic fraction of individual particles collected on 27 and 28 June during the 2010 Carbonaceous Aerosols and Radiative Effects study in the Central Valley, California. The first field site, T0, was located in downtown Sacramento, while T1 was located near the Sierra Nevada Mountains. Mass estimates of the aerosol particle components were used to calculate mixing state metrics, such as the particle-specific diversity, bulk population diversity, and mixing state index, for each sample. The STXM data showed evidence of changes in the mixing state associated with a buildup of organic matter confirmed by collocated measurements, and the largest impact on the mixing state was due to an increase in soot dominant particles during this buildup. The mixing state from STXM was similar between T0 and T1, indicating that the increased organic fraction at T1 had a small effect on the mixing state of the population. The CCSEM/EDX analysis showed the presence of two types of particle populations: the first was dominated by aged sea-salt particles and had a higher mixing state index (indicating a more homogeneous population); the second was dominated by carbonaceous particles and had a lower mixing state index.
| Original language | English |
|---|---|
| Pages (from-to) | 9591-9605 |
| Number of pages | 15 |
| Journal | Journal of Geophysical Research: Biogeosciences |
| Volume | 120 |
| Issue number | 18 |
| DOIs | |
| State | Published - 2015 |
| Externally published | Yes |
Funding
Data supporting all figures are available in Tables S1–S8. Raw image files and codes to process the data are available on request from the corresponding author. This work was supported by the U.S. Department of Energy’s Atmospheric System Research, an Office of Science, Office of Biological and Environmental Research program. STXM/NEXAFS was done at beamlines 5.3.2.2 and 11.0.2 at The Advanced Light Source at Lawrence Berkeley National Laboratory, which are supported by the Director, Office of Science, Office of Basic Energy Sciences, (beamline 11.0.2 is also supported by the Division of Chemical Sciences, Geosciences, and Biosciences) of the U.S. Department of Energy under contract DE-AC02-05CH11231. CCSEM/EDX analysis of particles was performed at Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by OBER at Pacific Northwest National Laboratory. PNNL is operated by the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RL0. Q.Z. and Y.S. would like to acknowledge funding from DE-FG02-11ER65293. We wish to acknowledge the continued support of A.L.D Kilcoyne and T. Tyliszczak for their support on the STXM instruments. We also wish to acknowledge the support of Nels Laulainen for assistance with the collection of Sunset ECOC data and Celine Kluzek for assistance with the collection of PILS data.