Total organic carbon and the contribution from speciated organics in cloud water: Airborne data analysis from the CAMP2Ex field campaign

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 0.2-6.8ĝ€¯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 13.66ĝ€¯ppmĝ€¯C with a mean of 0.902ĝ€¯ppm C. The highest TOC values are observed below 2ĝ€¯km with a general reduction aloft. An exception is samples impacted by biomass burning for which TOC remains enhanced at altitudes as high as 6.5ĝ€¯km (7.048ĝ€¯ppmĝ€¯C). Estimated total organic matter derived from TOC contributes a mean of 30.7ĝ€¯% to total measured mass (inorganics + organics). Speciated organics contribute (on a carbon mass basis) an average of 30.0ĝ€¯% to TOC in the study region and account for an average of 10.3ĝ€¯% 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 (14.7ĝ€¯±ĝ€¯20.5ĝ€¯%), formate (5.4ĝ€¯±ĝ€¯9.3ĝ€¯%), oxalate (2.8ĝ€¯±ĝ€¯4.3ĝ€¯%), DMA (1.7ĝ€¯±ĝ€¯6.3ĝ€¯%), succinate (1.6ĝ€¯±ĝ€¯2.4ĝ€¯%), pyruvate (1.3ĝ€¯±ĝ€¯4.5ĝ€¯%), glycolate (1.3ĝ€¯±ĝ€¯3.7ĝ€¯%), adipate (1.0ĝ€¯±ĝ€¯3.6ĝ€¯%), MSA (0.1ĝ€¯±ĝ€¯0.1ĝ€¯%), glutarate (0.1ĝ€¯±ĝ€¯0.2ĝ€¯%), and maleate (