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

5

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

6

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

7

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

9

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

10

SEAC4RS:Many sources, different regimes

11

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

12

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?