Total organic carbon and the contribution from speciated organics in cloud water: airborne data analysis from the CAMP2Ex field campaign
Authors: Stahl Connor , Crosbie Ewan , Bañaga Paola Angela , Betito Grace , Braun Rachel A. , Cainglet Zenn Marie , Cambaliza Maria Obiminda , Cruz Melliza Templonuevo , Dado Julie Mae , Hilario Miguel Ricardo A. , Leung Gabrielle Frances , MacDonald Alexander B. , Magnaye Angela Monina , Reid Jeffrey , Robinson Claire , Shook Michael A. , Simpas James Bernard , Visaga Shane Marie , Winstead Edward , Ziemba Luke , Sorooshian Armin 
Published: September 2021

Abstract. This work focuses on total organic carbon (TOC) and contributing species in
cloud water over Southeast Asia using a rare airborne dataset collected
during NASA's Cloud, Aerosol and Monsoon Processes Philippines Experiment
(CAMP2Ex), in which a wide variety of maritime clouds were studied,
including cumulus congestus, altocumulus, altostratus, and cumulus.
Knowledge of TOC masses and their contributing species is needed for
improved modeling of cloud processing of organics and to understand how
aerosols and gases impact and are impacted by clouds. This work relies on
159 samples collected with an axial cyclone cloud-water collector at
altitudes of 0.2–6.8 km that had sufficient volume for both TOC and
speciated organic composition analysis. Species included monocarboxylic
acids (glycolate, acetate, formate, and pyruvate), dicarboxylic acids
(glutarate, adipate, succinate, maleate, and oxalate), methanesulfonic acid
(MSA), and dimethylamine (DMA). TOC values range between 0.018 and 13.66 ppm C with a mean of 0.902 ppm C. The highest TOC values are observed below 2 km
with a general reduction aloft. An exception is samples impacted by biomass
burning for which TOC remains enhanced at altitudes as high as 6.5 km (7.048 ppm C).
Estimated total organic matter derived from TOC contributes a mean of
30.7 % to total measured mass (inorganics + organics). Speciated
organics contribute (on a carbon mass basis) an average of 30.0 % to TOC in
the study region and account for an average of 10.3 % to total measured
mass. The order of the average contribution of species to TOC, in decreasing
contribution of carbon mass, is as follows (±1 standard deviation):
acetate (14.7 ± 20.5 %), formate (5.4 ± 9.3 %), oxalate (2.8 ± 4.3 %), DMA (1.7 ± 6.3 %), succinate (1.6 ± 2.4 %), pyruvate (1.3 ± 4.5 %), glycolate (1.3 ± 3.7 %),
adipate (1.0 ± 3.6 %), MSA (0.1 ± 0.1 %), glutarate (0.1 ± 0.2 %), and maleate (< 0.1 ± 0.1 %). Approximately
70 % of TOC remains unaccounted for, highlighting the complex nature
of organics in the study region; in samples collected in biomass burning plumes,
up to 95.6 % of TOC mass is unaccounted for based on the species detected.
Consistent with other regions, monocarboxylic acids dominate the speciated
organic mass (∼ 75 %) and are about 4 times more
abundant than dicarboxylic acids. Samples are categorized into four cases based on back-trajectory history,
revealing source-independent similarity between the bulk contributions of
monocarboxylic and dicarboxylic acids to TOC (16.03 %–23.66 % and
3.70 %–8.75 %, respectively). Furthermore, acetate, formate,
succinate, glutarate, pyruvate, oxalate, and MSA are especially enhanced
during biomass burning periods, which is attributed to peat emissions transported
from Sumatra and Borneo. Lastly, dust (Ca2+) and sea salt
(Na+/Cl-) tracers exhibit strong correlations with speciated
organics, supporting how coarse aerosol surfaces interact with these
water-soluble organics.