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IEPOX-SOA as observed by the AMS 3 Hu et al, 2015, Isaacman et al, in prep SOAS Quite a few ground studies in the literature since 2011 IEPOX-SOA PMF Factor correlates well with molecular tracers SEAC 4 RS dataset unique in breadth and scope, ideally suited for testing the robustness of the assignment
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SOA derived from isoprene epoxydiols: Insights into formation, aging and
distribution over the continental US from the DC3 and SEAC4RS campaigns
Pedro Campuzano-Jost, Weiwei Hu, Brett B. Palm, Douglas A. Day, Amber M. Ortega, Jose-Luis Jimenez, Jin Liao, Karl D. Froyd,
Fabien Paulot, Gabriel Isaacman, Allen Goldstein, Jason M. St. Clair, John D. Crounse, Paul O. Wennberg, Luke D Ziemba, Bruce
E Anderson, Simone Meinardi, Barbara Barletta, Don Blake
CU Boulder, NOAA ESRL, UC Berkeley, Princeton U, Caltech, NASA LarC, UC Irvine
2
What is “IEPOX-SOA”?
Paulot et al, 2009, Surrat et al, 2010, Robinson et al., 2011; Budisulistiorini et al., 2013
IEPOX (Isoprene epoxidiol) formed from oxidation of isoprene under low NO conditions
IEPOX uptake on acidic sulfate particles produces a variety of polyols, organosulfates and oligomers
The sum of all these is IEPOX-SOA Despite the complexity of the
chemistry, AMS spectra retrieved by PMF show a very specific and reproducible, yet slightly variable pattern
IEPOX-SOAC4H5 C5H6OC3H7O2
3
IEPOX-SOA as observed by the AMS
Hu et al, 2015, Isaacman et al, in prep
SOAS
• Quite a few ground studies in the literature since 2011
• IEPOX-SOA PMF Factor correlates well with molecular tracers
• SEAC4RS dataset unique in breadth and scope, ideally suited for testing the robustness of the assignment
4
Geographical distribution: SEAC4RS
IEPOX IEPOX-SOA
• SE US clearly stands out as a main source region, some in OR/CA as well• There are however quite a few hotspots in the W US for both (and sometimes IEPOX-OS)
2013 global IEPOX model from Fabien Paulot
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Vertical Distribution: SEAC4RS
EAST
WEST
• Contribution varies between 20%-50%
• Lower values at the beginning and end of the campaign (colder periods)
• This is almost twice as much as observed during SOAS
• Not an “isoprene volcano” artifact
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Geographical distribution: DC3
IEPOX IEPOX-SOA
• Limited sampling, but SE IEPOX chemistry was still robust • There is IEPOX in OK/CO/TX. Some IEPOX-SOA was found as well, might be anomaly
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Vertical Distribution: DC3
EAST
WEST• IEPOX was higher than SEAC4RS,
so substantial IEPOX-SOA production despite lower temps and less acidic aerosol not surprising.
• Some layering apparent, not only due to lower statistics.
8
IEPOX-SOA Formation:What can we learn from the field data?
Main factors affecting IEPOX-SOA formation according to our current understanding:- IEPOX- Acidity/Liquid water
content- Sulfate availability
Organosulfates are formed during IEPOX uptake. IEPOX-OS can be quantified by the PALMS instrument, and should hence be a good marker of fresh IEPOX-SOA
Surrat et al, 2010, Froyd et al 2010, Nguyen et al 2015, Liao et al 2015
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DC3: Close to sources, plenty of waterLook Rock 10:1
“1:1”
• More IEPOX-SOA formed at high RH/high liquid water/high sulfate• This means mostly at higher altitudes/in the residual layer• Little pH dependence, otherwise trends as expected
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SEAC4RS:Many sources, different regimes
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Variability of IEPOX-SOA Composition
• Only seen when doing vertical profiles• This split is seen in six (of twelve) SEAC4RS flights, with the same MS signature in each
case• Enhanced C3H7O2 (m/z 75) is seen in the higher up/CHxO rich factor every time
BL FactorO: C 0.70
RL FactorO: C 0.74
C5H6OC3H7O2
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C3H7O2 as an RL IEPOX-SOA marker?
• C3H7O2 (m/z 75) enhancements relative to m/z 82 is a good tracer of IEPOX-SOA under more humid conditions aloft
• Hence this marker is significantly lower in ground measurements• IEPOX-OS is formed under less humid conditions, hence some
anticorrelation is expected
13
Conclusions The contribution of IEPOX-SOA to SE OA was substantial for both
DC3 and SEAC4RS (20-50%)
IEPOX, inorganic sulfate & aerosol water correlate with IEPOX-SOA.
A cleaner SE US will have more IEPOX (due to lower NO), but maybe not more IEPOX-SOA (as SO4 is also lower)
Organosulfates correlate reasonably well with IEPOX-SOA at low liquid water content/high ionic strength
IEPOX-SOA in the residual layer has a distinct chemical signature Formation under higher humidity or in-cloud?