Observations of Sharp Oxalate Reductions in Stratocumulus Clouds at Variable Altitudes: Organic Acid and Metal Measurements During the 2011 E-PEACE Campaign

Abstract

This work examines organic acid and metal concentrations in northeastern Pacific Ocean stratocumulus cloudwater samples collected by the CIRPAS Twin Otter between July and August 2011. Correlations between a suite of various monocarboxylic and dicarboxylic acid concentrations are consistent with documented aqueous-phase mechanistic relationships leading up to oxalate production. Monocarboxylic and dicarboxylic acids exhibited contrasting spatial profiles reflecting their different sources; the former were higher in concentration near the continent due to fresh organic emissions. Concentrations of sea salt crustal tracer species, oxalate, and malonate were positively correlated with low-level wind speed suggesting that an important route for oxalate and malonate entry in cloudwater is via some combination of association with coarse particles and gaseous precursors emitted from the ocean surface. Three case flights show that oxalate (and no other organic acid) concentrations drop by nearly an order of magnitude relative to samples in the same vicinity. A consistent feature in these cases was an inverse relationship between oxalate and several metals (Fe, Mn, K, Na, Mg, Ca), especially Fe. By means of box model studies we show that the loss of oxalate due to the photolysis of iron oxalato complexes is likely a significant oxalate sink in the study region due to the ubiquity of oxalate precursors, clouds, and metal emissions from ships, the ocean, and continental sources.

Impact of emissions from shipping, land, and the ocean on stratocumulus cloud water elemental composition during the 2011 E-PEACE field campaign

“…Eighty one samples had sufficient volume for elemental and ionic composition analysis. One fraction of the liquid volumes was analyzed with inductively coupled plasma mass spectrometry (ICP-MS), details of which are provided by Sorooshian et al (2013). The reported measurements of all elements in each sample represent the average of three measurements.…”

Inorganic salts interact with oxalic acid in submicron particles to form material with low hygroscopicity and volatility

“…They may then be oxidized in the particle aqueous phase to produce OxA (Warneck, 2003), which can then react with mineral ions in the particle to produce insoluble material (e.g., calcium oxalate), reducing particle hygroscopicity. OxA has also been found to be significant in particles dominated by non-hygroscopic material (e.g., mineral dust) (Sullivan and Prather, 2007). For these particles, solubilizing reactions, such as uptake of nitric acid, may occur at the particle surface, and subsequent water exposure creates conditions ripe for reaction between OxA and di-valent cations (Laskin et al, 2012).…”

“…Since the contribution of sea salt (or other mineral salts) in submicron particles at continental forest sites far from the sea is minor (Saarikoski et al, 2005), ammonium or aminium salts are likely main contributors to the growth of aerosol particles, even at sub-20 nm sizes (Barsanti et al, 2009;Smith et al, 2010). However, at marine sites or other mineral-rich areas the contribution of organic salts from mineral-salt-organicacid reactions may have a significant effect on aerosol chemical properties and further cloud processing (Furukawa and Takahashi, 2011;Laskin et al, 2012;Rinaldi et al, 2011; G. Drozd et al: Inorganic salts interact with organic di-acids 5207 Sorooshian et al, 2013). These results emphasize the fact that atmospheric species, both organic and inorganic, can undergo drastic changes when they react with each other and these changes can alter the chemical and physical properties of particles.…”

Characterization of Atmospheric Iron Speciation and Acid Processing at Metropolitan Newark on the US East Coast

“…Results showed that there was a significant good correlation (p < 0.05, R > 0.5, n = 8) between dissolved iron (Fe(II) and Fe(TD)) and sulfate in the coarse mode, but there was no good correlation between dissolved iron and oxalate in both mode, which may result from the low concentration of oxalate in the ambient environment. Sorooshian et al (2013) [59] conducted filed work in northeastern Pacific Ocean by collecting stratocumulus cloud water and examining the organic acid and metal concentrations; they found an inverse relationship between oxalate and Fe. Thus, the oxalate sink in this study could be explained to some extent by the photolysis of iron oxalato complexes.…”