Concerted measurements of free amino acids at the Cape Verde Islands: High enrichments in submicron sea spray aerosol particles and cloud droplets

Abstract

Abstract. This study presents measurements of free amino acids (FAA) in the marine environment to elucidate their transfer from the ocean into the atmosphere to marine aerosol particles and to clouds. FAA were investigated in seawater (underline water (ULW), sea surface microlayer (SML)), in ambient marine size-segregated aerosol particle samples at two heights (ground based at the Cape Verde Atmospheric Observatory (CVAO) and at the Mt. Verde, 744 m height) and in cloud water using concerted measurements. The ∑FAA concentration in the SML varied between 0.13–3.64 µmol L−1, in the ULW between 0.01–1.10 µmol L−1 and a strong enrichment of ∑FAA in the SML (EFSML: 1.1–298.4, average of 57.2) was observed. In the submicron (0.05–1.2 µm) aerosol particles at the CVAO, the composition of FAA was more complex and higher atmospheric concentration of ∑FAA (up to 6.3 ng m−3) compared to the supermicron (1.2–10 µm) aerosol particles (maxima of 0.5 ng m−3) were observed. The total ∑FAA concentration (PM10) was between 1.8–6.8 ng m−3 and tended to increase during the campaign. Averaged ∑FAA concentrations on the aerosol particles at the Mt. Verde were lower (submicron: 1.5 ng m−3, supermicron: 1.2 ng m−3) compared to the CVAO. A similar percentage contribution of ∑FAA to dissolved organic carbon (DOC) in the seawater (up to 7.6&tinsp;%) and to water-soluble organic carbon (WSOC) on the submicron aerosol particles (up to 5.3 %) indicated a related transfer process of FAA and DOC in the marine environment. The FAA were strongly enriched in the submicron aerosol particles (EFaer(∑FAA) 4∙102–3∙104, EFaer(WSOC) 2∙103–1∙104), possibly resulting from film droplet formation. The enrichment in supermicron aerosol particles was several orders of magnitude lower compared to supermicron size range with EFaer(∑FAA) 1∙101–2∙101, EFaer(WSOC) 3∙102–4∙102. A case study showed that several amino acids were transported from the ocean up to cloud level (e.g. aspartic acid, glutamic acid, proline) while other amino acids might not be transferred or quickly degraded (e.g. phenylalanine, tyrosine) or produced (e.g. GABA). The cloud water samples exhibited a similar composition of FAA compared to the SML but a strong variation of the atmospheric concentration of ∑FAA during the campaign (11.2–489.9 ng m−3). FAA in cloud water samples showed a strong enrichment by a factor of 4∙103 compared to the SML. The presence of high concentrations of FAA in general and of biologically produced FAA (aspartic acid) in particular together with the presence of inorganic marine tracers (sodium, methane sulfonic acid) demonstrates the influence of oceanic sources on marine clouds.

Supplementary material to "Marine organic matter in the remote environment of the Cape Verde Islands – An introduction and overview to the MarParCloud campaign"

“…After sampling, filters and aluminium foils were stored in aluminum boxes at -20 °C and transported in dry ice to the TROPOS laboratories in Leipzig, Germany. The chemical analysis of inorganic ions, the water soluble organic carbon (in the aerosol particles as well as in the ocean water and cloud water) and elemental carbon are described in detail in (van Pinxteren, et al 2017;van Pinxteren, et al 2015) and in Triesch, et al (2019).…”

Biotic and abiotic transformation of amino acids in cloud water: Experimental studies and atmospheric implications

“…Organic nitrogen compounds contribute a significant fraction to the total nitrogen in cloud water (18%) (Hill et al, 2007) and in aerosol particles 7 -10% in urban areas (Xu et al, 2017) or even exceed other nitrogen contributions in marine aerosol (Miyazaki et al, 2011). Among these organic nitrogen molecules, amino acids (AA) have been recently analyzed and quantified in cloud droplets collected at the puy de Dôme 5 station (Bianco et al, 2016a) and on the Cape Verde Islands (Triesch et al, 2020). AA were also quantified in rain collected in marine and sub-urban sites (Mace et al, 2003b(Mace et al, , 2003aMopper and Zika, 1987;Sidle, 1967;Xu et al, 2019;Yan et al, 2015), and in fog samples in Northern California (Zhang and Anastasio, 2003).…”

“…AA were also quantified in rain collected in marine and sub-urban sites (Mace et al, 2003b(Mace et al, , 2003aMopper and Zika, 1987;Sidle, 1967;Xu et al, 2019;Yan et al, 2015), and in fog samples in Northern California (Zhang and Anastasio, 2003). In cloud water, free AA concentrations range from 2.4±2.0 to 74.3±43.8 µg C L -1 at the rural site of the puy de Dôme (Bianco et al, 2016a) 10 and from 17 to 757 g C. L -1 at the marine site of Cape Verde (Triesch et al, 2020). These AA are from biological origin and are building blocks of peptides (also called 'combined AA') and…”

“…grassland (Scheller, 2001), ocean (Triesch et al, 2020) and agricultural activities (Song et al, 2017) were identified as major emission sources of amino acids.…”

“…(Scholes et al, 1965;Motohashi and Saito, 1993;Prütz and Vogel, 1976) , singlet oxygen ( 1 O2) (Kraljić and Sharpatyi, 1978;Matheson and Lee, 1979;McGregor and Anastasio, 2001;Michaeli and Feitelson, 1994;Miskoski and García, 1993 ;McGregor and Anastasio, 2001) or ozone (O3) (Ignatenko and Cherenkevich, 1985 ;Pryor et al, 1984). Based on such kinetic data, some studies have reported the time of life of amino acids in fog (McGregor and Anastasio, 5 2001) or in cloud water (Triesch et al, 2020). From these studies it is clear that some amino acids are transformed very rapidly, while others are almost never transformed within the time scale of fog or cloud life.…”