Single-particle measurements of phase partitioning between primary and secondary organic aerosols.
Organic aerosols provide a measure of complexity in the urban atmosphere. This is because the aerosols start as an external mixture, with many populations from varied local sources, that all interact with each other, with background aerosols, and with condensing vapors from secondary organic aerosol formation. The externally mixed particle populations start to evolve immediately after emission because the organic molecules constituting the particles also form thermodynamic mixtures - solutions - in which a large fraction of the constituents are semi-volatile. The external mixtures are thus well out of thermodynamic equilibrium, with very different activities for many constituents, and yet also have the capacity to relax toward equilibrium via gas-phase exchange of semi-volatile vapors. Here we describe experiments employing quantitative single-particle mass spectrometry designed to explore the extent to which various primary organic aerosol particle populations can interact with each other or with secondary organic aerosols representative of background aerosol populations. These methods allow us to determine when these populations will and when they will not mix with each other, and then to constrain the timescales for that mixing.
Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA. nmd@cmu.edu and Earth System Research Laboratory, National Oceanographic and Atmospheric Administration, 325 Broadway, Boulder, Colorado 80305-3337, USA.
Ellis Shipley
ES
Robinson
Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA. nmd@cmu.edu.
Neil M
NM
Donahue
Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA. nmd@cmu.edu.
Adam T
AT
Ahern
Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA. nmd@cmu.edu.
Qing
Q
Ye
Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA. nmd@cmu.edu and Penn State Greater Allegheny, 4000 University Drive, McKeesport, Pennsylvania 15132, USA.
Eric
E
Lipsky
D000336:Aerosols / Q000032:analysis / Q000737:chemistry*; D000397:Air Pollution / Q000032:analysis; D005740:Gases / Q000737:chemistry; D013058:Mass Spectrometry; D009608:Nitrous Acid / Q000737:chemistry; D009930:Organic Chemicals / Q000032:analysis / Q000737:chemistry*; D013816:Thermodynamics
D000336:Aerosols; D005740:Gases; D009930:Organic Chemicals; D009608:Nitrous Acid