Hydroxy fatty acids in remote marine aerosols over the Pacific Ocean

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Hydroxy fatty acids in remote marine aerosols over the Pacific Ocean: Impact of biological activity and wind speed Poonam Bikkina, Kimitaka Kawamura, Srinivas Bikkina, Bhagwati Kunwar, Kiichiro Tanaka, and Keisuke Suzuki ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.8b00161 • Publication Date (Web): 31 Jan 2019 Downloaded from http://pubs.acs.org on February 1, 2019

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ACS Earth and Space Chemistry

Hydroxy fatty acids in remote marine aerosols over the Pacific Ocean: Impact of biological activity and wind speed

by #Poonam

Bikkina1,2, Kimitaka Kawamura2,3,4,*, Srinivas Bikkina4, Bhagawati Kunwar4 Kiichiro Tanaka3 and Keisuke Suzuki5,6

1Graduate

School of Environmental Sciences, Hokkaido University, Sapporo 060-0810, Japan of Low Temperature Sciences, Hokkaido University, Sapporo 060-0819, Japan 3Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, Hachioji 192-0397, Japan 4Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan 5Department of Geography, Faculty of Science, Tokyo Metropolitan University, Hachioji 192-0397, Japan 6Faculty of Science, Shinshu University, Matsumoto 390-8621, Japan 2Institute

Submitted to “Earth and Space Chemistry” (January 30, 2019)

*Corresponding author [email protected]

1 ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Current parameterization of cloud-aerosol interactions of nascent sea-spray aerosols (SSA) in the climate models is hampered by our limited understanding on the constituents of organic aerosols. We investigated here the mass concentrations, molecular distributions and relative abundances of hydroxy fatty acids (FAs), ubiquitous lipid compounds in the SSA collected over the western Pacific Ocean (35°N-40°S). Detectable levels of methanesulfonic acid (an oxidation product of dimethyl sulfide) and high enrichment factors of Mg2+ and Ca2+ relative to Na+ emphasize the impact of the marine biological activity on the organic fraction of SSA. The molecular distributions of -hydroxy FAs with characteristic “odd-C” predominance (C9>C10>C11>C12) among short-chain homologs (C20)28, 29, whereas LMW-fatty acids and -hydroxy FAs (≤C20) are specific to soil-GNB9, 30, phytoplankton and marine-GNB/heterotrophic bacteria10, 31. Despite the source variability (terrestrial vs. marine), the molecular distributions of hydroxy FAs/fatty acids show strong even-C predominance due to their synthesis through biological pathway3, 6, 13. Likewise, the CPIhydroxy FAs, which is an abundance ratio of even/odd homologs, is also a useful proxy to identify their sources (i.e., higher plants or marine phytoplankton)13. Numerous researches have used these tracers to understand the possible sources of hydroxy FAs/n-fatty acids in marine aerosols3, 4, 8, 32. Chichijima, a remote island in the western North Pacific, aerosols have higher concentrations of C21-C34 n-fatty acids and C21-C31 hydroxy FAs in winter/spring than other seasons because of the input from terrestrial higher plant waxes4, 6. In contrast, LMW-fatty acids and hydroxy FAs (C8 - C20) are more abundant in summer over Chichijima because of the influence from marine-derived organic matter4, 6. Mochida et al.

5

documented a positive

correlation between LMW-fatty acids and sea salts along with a significant increase in the 4 ACS Paragon Plus Environment

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LMW-fatty acid/sea-salt ratio in spring/summer during high chlorophyll levels in the N. Pacific5. Furthermore, LMW-fatty acids occur in supermicron mode (i.e., association with sea salts) and HMW-fatty acids in the submicron mode (i.e., from biomass burning emission)16. All these observations are from the coastal ocean and along the longitudinal cruise tracks in the N. Pacific. However, no such information was available for better constraining the sea-toair emission of fatty acids and related compounds from the open ocean waters of the Pacific. Therefore, our study here focuses on the hydroxy FAs/fatty acids in marine aerosols over the western Pacific Ocean during KH92-4 expedition, covering the latitudes from 35°N to 40°S. The aim of this study is to assess the governing factors of atmospheric abundances, molecular distributions and relative abundances of hydroxy FAs/fatty acids over the western Pacific during September-October. 2. EXPERIMENTAL METHODS 2.1. Aerosol sampling and determination of water-soluble inorganic species Total suspended particulate (TSP) samples were collected during the cruise KH92-4 (16 September24 October 1992) in the western Pacific Ocean (Figure S1). High volume air sampler (Shibata HVC 1000; flow rate: 1.0 m3 min-1) was set up on the upper deck of the R/V Hakuho Maru (~14 m above sea surface). Each sample was collected for ~2448 h with a precombusted (450 ºC for 6 h) quartz fiber filter (PALLFLEX®TM, 20 x 25 cm). To assure the clean sample collection, we used wind speed/sector controlled (±45º and ≥5 ms-1) sampling system connected to high volume air sampler. The purpose of using this system is to avoid a potential contamination from the ship exhausts. However, this system does not detect a potential contamination from other ships, although there were no ships nearby the research vessel (R/V Hakuho Maru) because the cruise was operated on the remote open ocean. All meteorological parameters were obtained from the onboard weather station of the ship. The 5 ACS Paragon Plus Environment


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cruise track and surface wind conditions (>7 ms-1) at the time of sampling are shown in Figure S1. After sampling, all the filters were stored in a pre-cleaned glass bottle individually with a Teflon-lined screw cap at -20 ºC until analysis. Details of cruise track and aerosol sampling are reported in Sempéré and Kawamura33. A fraction of TSP sample was extracted in ultrapure deionized water by sonication and analyzed for water-soluble anions and cations by an ion chromatography as described in Suzuki et al. 34. 2.2. Extraction and measurement of hydroxy FAs Briefly, a fraction of the aerosol filter was extracted with 0.1 M KOH/methanol solution (10 ml x 3) under reflux, followed by subsequent ultrasonication with dichloromethane (DCM) (10 ml x 3). We combined methanol extracts with DCM extracts to obtain a better recovery for non-polar lipids such as n-alkanes. The combined extract was concentrated to ca. 1 ml using a rotary evaporator under vacuum and then divided into neutral and acidic fractions according to the method described in Kawamura 7. From the acidic fraction, carboxylic acids were extracted with DCM. By adding 0.5 ml of 14% BF3/methanol (SUPELCOTM) to the acidic fraction, carboxylic acids were converted to methyl esters at 100 °C. Excess derivatizing agent and hydrofluoric acid were removed by adding 10 ml of water and n-hexane/DCM (10:1). These derivatives were separated into (1) monocarboxylic acid, (2) dicarboxylic acid and (3) hydroxy fatty acid ester fractions using a silica gel (deactivated with 1% H2O) column chromatography. The hydroxy FA fractions were stored at -20 ºC in darkness until analysis. Prior to GC/MS

injection,

hydroxy

FAs

were

derivatized

with

N,O-bis-(trimethylsilyl)

trifluoroacetamide (BSTFA) (SUPELCOTM Analytical) at 80 °C for 1 h to convert hydroxyl groups to trimethylsilyl (TMS) ethers. After the reaction, 50 L of an n-hexane solution containing 1.43 ng L-1 of internal standard (C13 n-alkane/tridecane, Wako) was added to dilute the derivatives. We used a mass spectrometer (Hewlett-Packard Model 5975 C inert XL EI/CI 6 ACS Paragon Plus Environment

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mass-selective detector, MSD with Triple-Axis Detector) interfaced to a gas chromatograph (Agilent Technologies, Model 7890 GC) for compound identification and quantification. For the quantification of hydroxy FAs, HP-5 fused silica capillary column (Agilent; 25 m long × 0.20 mm i.d. x 0.5 μm film thickness) was used with GC oven temperature programmed from 50°C (2 min) to 120°C at 15°C min-1 then to 305°C (15 min) at 5°C min-1. The lipids were extracted with organic solvents (e.g., in methanol, n-hexane or dichloromethane). Because the solvents are toxic for bacteria being different from water samples, bacterial growth is very unlikely at temperatures ≤-20ºC. The protocol used for the lipid extraction is widely used for investigating the terrestrial input of organic matter in the deep-sea sediment, ice core, snow/snow pit and aerosol samples3,

4, 8, 35.

More detailed description of the analytical

procedures of these lipid biomarkers was reported in several of our previous publications3, 4, 8, 35.

2.3. Quality Assurance Identification of hydroxy FAs was performed by comparing retention times and mass spectra with those of TMS derivatives of authentic methyl esters of -hydroxy n-C12 and n-C16 FAs; β-hydroxy n-C12, n-C14, n-C15, and n-C16 FAs and ω-hydroxy n-C16, n-C20 and n-C22 FAs, which were also used as external standards. The pre-combusted blank quartz filters were spiked with known concentrations of hydroxy FAs and processed in a similar fashion as that of real samples. The recoveries of authentic β- and ω-hydroxy FAs standards were better than 60% and 70%, respectively. Procedural field blanks were also analyzed for hydroxy FAs and no signals were detected on the mass spectrum of the target compounds. We previously showed, using the same analytical protocol adopted here, that molecular distributions of - and hydroxy FAs in certified reference materials of Asian dust and Chinese loess matches with the TSP collected in 2001 over Gosan, Jeju Island during the influenced dust outbreaks from East 7 ACS Paragon Plus Environment


Asia3. Moreover, the reported lipid compounds are well-known proxies for the paleoclimatic studies. The extraction protocol includes various fractions and after derivatization, these aliquots were well preserved at -20ºC. Sample extraction and BF3/methanol derivatization procedures were completed in 1993, but TMS derivatization of hydroxyl groups and subsequent GC/MS measurements were performed in 2015. Because the extracted samples were kept in a 1.5 ml glass vial with a Teflon-lined screw cap in a dark freezer room at -20°C, chemical breakdown/oxidation of lipid compounds is very unlikely. In fact, based on the unpublished datasets from our group, we ascertained that the storage induced artifacts were not detected, as inferred from the repeated analyses of organic compounds (e.g., dicarboxylic acids) in 1991 Alert aerosols in 2010 using the same filter sample stored at 20 ºC (i.e., reproducible within 10%)36, 37. Therefore, it is unlikely to consider that the interpretations of the sources and molecular distributions of hydroxy FAs investigated in this study are affected by the storage artifacts of aerosol extracts. 3. RESULTS AND DISCUSSION 3.1. Air mass back trajectories and wind speed dependence of SSA To identify the sources/origin of air parcels collected during the cruise, 10-day isentropic air mass back-trajectories (AMBTs) were computed for every 12 hours at arrival heights of 100, 500 and 1000 m (Figure S2) using hybrid single particle lagrangian integrated trajectory model (HYSPLIT version-4)38, 39. By combining the origin of AMBTs with the abundances of levoglucosan (i.e., a biomass burning tracer)40, we classified the TSP into “continental” and “marine” types. Though levoglucosan can be degraded during transport and, hence, undermine the influence of continental impact to TSP collected here, the composition and relationships of major water-soluble inorganic ions are consistent with seawater source. Only the TSP collected near Japan, Papua New Guinea, and Australia (N = 7) have shown


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slightly higher abundances of levoglucosan (i.e., >1 ng m-3; data obtained from Kunwar et al., manuscript in preparation), which are referred here as “continental” and the rest is referred to “marine”. Therefore, the “continental” samples are likely to have contributions of hydroxy FAs from terrestrial biogenic sources. For all other samples, the AMBTs originated mostly from the Southern Ocean. As the AMBTs for most of the samples showed marine origin (Table 1), sea-salts and associated organic compounds can contribute to aerosol total carbon (TC) during the cruise. We found the predominance of Cl- and Na+ among other ions and their significant correlations with Mg2+, K+, and Ca2+ (Table S1), which are derived from sea-salts. Notably, the slope of the linear regression between Cl- and Na+ is ~1.8 (≈ [Cl-/Na+]seawater; R2 = 0.93; Figure 1a), further suggesting a lack of heterogeneous processing of sea-salt by the atmospheric acidic species (HNO3 and H2SO4) that are usually abundant in continental outflows. However, we observed rather low concentrations of Cl- in three TSP samples due to high SO42- contribution from nearby volcanoes and, therefore, excluded those from the linear regression. We also found a significant linear relation between average surface wind speed during TSP collection and the sea-salt load (i.e., Na+aero × [Salinity/Na+]seawater; Figure 1b). Several other studies have also observed a similar relationship over the remote oceans41-43. These observations highlight the wind speed driven sea-salt contribution in marine aerosols. 3.2. Organic matter association with SSA Biological activity in the sunlit surface waters (e.g., phytoplankton bloom) affects the composition of organic mass in the SSA44-47. This effect can be traced by the enrichment factors of aerosol-Mg2+ and Ca2+ (EFMg2+/Ca2+ ≈ (X/Na+)aerosol/(X/Na+)seawater; here X = Mg2+ or Ca2+) due to their association with biogenic carbonaceous particles in seawater (e.g. gel type substances, phytoplankton exudates, and phytodetritus)44-47. EFMg2+ (~1.2±0.2) and EFCa2+ 9 ACS Paragon Plus Environment


(~1.8±0.8) in the TSP during KH92-4 (Figure 1c) are comparable with those reported in the literature44-47. Keene et al.

46

observed a median and maximum EFCa2+ is ~1.2 and 4 in the

nascent SSA. Salter et al. 44 detected high EFCa2+ (>1 – 10) for the submicron SSA from the N. Atlantic seawater. Likewise, fine mode SSA from the natural seawater during a mesocosm are coated with organic compounds enriched in Mg45. In seawater, Ca2+ and Mg2+ have a tendency to deprotonate and reacts with COOH moieties of surface-active fatty acids and hydroxy FAs4850.

Gaston et al.

47

observed organically bound Mg2+ and Ca2+ particles in SSA, particularly

when wind speeds are ≥10 ms-1, over different oceanic regions characterized by an increase in chlorophyll-a and DMS levels due to high biological activity. Wang et al. 51 observed an enrichment of aliphatic rich lipids (e.g. fatty acids), amino acids, proteins, and saccharides in the SSA compared to those in surface seawater and SSML during a phytoplankton bloom. Jayarathne et al.

52

documented a selective enrichment of

saccharides relative to Na+ in both sea spray and sea salt aerosols compared to that in the SSML during a phytoplankton bloom. Therefore, observed EFMg2+/Ca2+ during the KH92-4 cruise signify the role of ocean biological activity in the western Pacific in controlling the composition of organic mass associated with sea-spray/sea salt emissions. Due to a lack of measurements on in situ productivity during the KH92-4 cruise (September-October 1992), we used satellitebased chlorophyll-a data from 1998 – 2001 as a surrogate (Figure S3) to support the influence of biological activity in seawater. 3.3. Latitudinal variability We detected the presence of methanesulfonic acid (MSA), an oxidation product of dimethyl sulfide (DMS) originated from phytoplankton exudates53-55, but with no latitudinal variability (Figure 1d). The non-sea-salt SO42-/MSA ratios between 20°S and 40°S (56±25) are lower than other TSP samples (Figure 1e). These ratios perhaps represent the marine 10 ACS Paragon Plus Environment

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biogenic signature, which are consistent with those reported over the Atlantic Ocean (37±16)56. Sea-to-air emission of isoprene during phytoplankton bloom could lead to the formation of glyoxylic acid (C2) in deliquescent marine aerosols57. Therefore, we compared the latitudinal distributions of MSA and C2 (Figure S4), which are gas- and aqueous phase oxidation products of DMS58 and isoprene59, respectively. No similarity was found for the latitudinal distributions, perhaps due to relative stability of MSA over C, which further oxidizes to form more stable oxalic acid in marine aerosols60. The impact of marine-derived organic matter on TSP is also evident by the lower relative abundance of water-soluble organic carbon (WSOC) in TC (median: 37%; mean: 40%; Figure 1f) compared to that in the East Asian outflow to the western North Pacific (48%61). Marine-derived organic matter is characterized by lower WSOC/TC (~35%62; ~39%63, ~20%64) in remote marine aerosols due to the contribution from colloidal aggregates of phytodetritus/bacteria19, 65. These findings are in accordance with those of O’Dowd et al. 65, emphasizing the predominance of water-insoluble organic matter (here hydroxy FAs) in remote marine aerosols. However, Miyazaki et al.

62

have recently documented a somewhat higher

percentage contribution of WSOC/TC (~60%) over the productive open ocean waters of the western Pacific. We also found slightly higher values of up to 55% in samples collected near Australia, where surrogate chlorophyll-a maps showed phytoplankton blooms during September – October (Figure S3). Overall, the relative influence of continental versus marine sources on TSP collected here are diverse and difficult to interpret. We detected the homologous series of C9–C20 -hydroxy FAs in some samples (Table S2) and C9-C31 -hydroxy FAs in merely three TSP samples collected near Japan, Papa New Guinea, and Australia (Table S3). The LMW -hydroxy FAs are specific to LPS of marine GNB/heterotrophic bacteria10 and/or soil GNB3. The long-range transport of Asian dust (i.e., a 11 ACS Paragon Plus Environment


carrier of soil GNB) to the western North Pacific is dominant during late spring - early summer but not in autumn (i.e., September-October)3, 4, 8. On a similar note, terrestrial plant waxes and soils contribute to HMW -hydroxy FAs but LMW homologs (e.g., C16) originate from both continental/marine emissions3, 4. Based on the predominance of C16 and C22 -hydroxy FAs in remote marine aerosols and deep-sea sediments, Kawamura7 suggested their contribution from both oceanic and terrestrial sources. Hence, if -hydroxy FAs in TSP are from higher plant waxes, we would expect a significant contribution of both HMW and LMW homologs (i.e., evident only for 3 TSP). However, we observed only the C16 -hydroxy FAs in another six samples among which one TSP sample also contain C10 and C14 -hydroxy FAs. Overall, these results emphasize a significance of LMW - and -hydroxy FAs derived from marine organic matter in the MABL (see for statistical summary Table S4). To evaluate the relative source strength of marine/continental sources, we examined the pollution Roses (i.e., using “openair” package in R) of total - and -hydroxy FAs according to their wind direction/speed (Figure S5). The pollution Roses of - and -hydroxy FAs, consistent with those of n-fatty acids and n-alkanes, revealed influence from SW/SE direction (i.e., Pacific/Southern Ocean), which are associated with high wind speeds (av. 7.1 m s-1). These high wind speeds could result in increased emissions of surface-active compounds (e.g., fatty acids, hydroxy FAs) associated with SSA66-68. In particular, LMW -hydroxy FAs have been detected in the ultra-filtered dissolved organic matter (UDOM) from the surface waters of the Pacific Ocean, Gulf of Mexico, and North Sea10; contributed mainly from the LPS of microbial lipids (i.e., marine GNB species). Therefore, the presence of LMW hydroxy FAs signifies the importance of marine-derived organic matter (i.e., phytoplankton/microbial detritus, dissolved organic matter, etc.).


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We could not observe any significant latitudinal variability for both total mass loadings of - and -hydroxy FAs (Figure 1g, h). However, the TSP sample collected around 32ºN shows high loadings of - and -hydroxy FAs compared to the sample collected around 32ºN (Table 1), which could be explained by a strong influence from East Asian outflow (including Japanese islands) for the 32°N sample vs. 28°N sample. The total mass concentrations of hydroxy FAs showed no significant differences (unpaired two-tailed t-score: 1.16; df = 13; P > 0.05) between “continental” and “marine” type samples. In seawater, concentrations hydroxy FAs are rather low compared to n-fatty acids. This is due to the specific origin of hydroxy FAs from the membrane lipids (i.e., LPS) of marine GNB/heterotrophic bacteria compared to LMW-fatty acids and mono/polyunsaturated fatty acids in bulk dissolved/particulate organic matter fractions 10, 69, 70. Therefore, we observed a strong latitudinal variability for LMW n-fatty acids (C8–C20; Figure 1i) but not for hydroxy FAs. However, unsaturated fatty acids are less abundant than nfatty acids in seawater due to their rapid photooxidation to result in -oxocarboxylic acids and aldehyde analogs71, 72, which are further oxidized to yield dicarboxylic acids73, 74. Consequently, the sea-air emission of organic compounds associated with SSA are likely a mixture of more abundant fatty acids, dicarboxylic acids, -oxocarboxylic acids and less abundant hydroxy FAs. Azelaic acid, a specific photochemical oxidation product of marine biogenic unsaturated fatty acids73-75, also exhibited similar latitudinal variability with LMW-fatty acids in TSP (Figure 1j) due to a common source contribution from ocean surface. However, these latitudinal trends are contrary to those of sea-salt (Figure 1k), which showed higher concentrations in the TSP from southern latitudes due to prevailing high wind speed. Consequently, the mixing of lipids in the SSML with the underlying ocean waters of the South Pacific results in overall lower abundances of these n-fatty acids associated with sea-salt particles.



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3.4. Molecular distributions of hydroxy FAs The molecular distributions of -hydroxy FAs revealed a predominance of C9 over C10 and C11 over C12 homologs (Figure 2a). However, these distributions are contrary to those observed over Chichijima Island in the N. Pacific (i.e., C16 > C12 and/or C14)4, where we found higher abundances for even-C numbered -hydroxy FAs. This could be due to differences in the impact of ocean biological activity (e.g., phytoplankton bloom), which affects both the abundances and molecular distributions of the lipids in the SSA31,

52, 68, 76.

The

phytoplankton/bacterial cells lyse during bubble bursting process and release LPS-bound hydroxy FAs31, 77 and n-fatty acids into the water-column47, 78. Likewise, microbial oxidation of n-fatty acids within the sunlit surface ocean could also form corresponding -hydroxy FAs10, 11, 70, 79.

Consequently, hydroxy FAs (i.e., specific to bacterial/phytoplankton cells) occur in

lower abundance than n-fatty acids (i.e., originate from bulk of the phytodetritus) in seawater, SSML, and SSA. Cochran et al. 31 detected C5-C18 -hydroxy FAs and witnessed a sudden shift in the molecular distribution of n-fatty acids in the SSA (i.e., higher concentrations of some odd-C homologs) during a phytoplankton bloom. Trichodesmium blooms usually occur in the western Pacific during summer/autumn seasons80, 81. Therefore, higher abundances of odd-C numbered -hydroxy FAs (C9>C10 & C11>C12) in marine aerosols could be due to microbial/chemical degradation of n-fatty acids associated with SSA. Similar distributions for all the TSP during KH92-4 along with the presence of only LMW hydroxy FAs ( C12 > C14; Figure 2b) along with the predominance of LMW-homologs (C9-C20). However, concentration of -hydroxy C11 FA exceeded to that of C16 in one TSP collected near Australia (QFF554). The epicuticular plant waxes of cutin contain -hydroxy 14 ACS Paragon Plus Environment

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C16 and C18 FAs, whereas suberin is composed of -hydroxy C16C26 FAs

29, 79.

In general,

marine-derived organic matter contributes only to LMW -hydroxy FAs, while plant waxes also account for HMW -hydroxy FAs. Overall, similar trends in the molecular distributions between continental and marine type samples along with the occurrence and/or predominance of LMW hydroxy FAs suggest a major input from marine sources. This finding is further corroborated by the molecular distributions of other lipids (e.g., n-fatty acids and n-alkanes) emitted from surface seawater (Figure 2c and 2d). The molecular distributions of n-fatty acids (Figure 2c) have revealed a predominance at palmitic acid (C16) followed by stearic acid (C18) and myristic acid (C14). We found rather low concentrations for HMW n-fatty acids (C21-C32) than LMW homologs. These results are consistent with other studies from the Pacific Ocean31, 35, 60, 82. The carbon preference index of n-fatty acids (CPIn-FAs ≈ (C8+C10+C12+C14+C16+C18+C20+C22)/ (C9+C11+C13+C15+C17+C19+C21+C23))31 is useful for underpinning their origin (i.e., whether anthropogenic or biogenic). Here, the CPIn-FAs >1 indicates more biogenic origin through biological synthesis of even-C homologs of n-fatty acids. The CPIn-FAs values (6 – 17) in TSP suggest the biogenic sources and are comparable to those documented for the nascent sea salt particles (2 – 14)17, 31. Furthermore, the impact of ocean biological activity on n-fatty acid composition in marine aerosols is evident by the mass ratio of oleic acid (C18:1) to stearic acid (C18). The C18:1/C18 ratio in marine aerosols serves as a proxy to evaluate the relative significance of terrestrial versus marine input of biogenic n-fatty acids (i.e., higher plants vs. marine planktonic/microbial sources). Oleic acid is less stable and oxidized to result in dicarboxylic acids during long-range transport72, 74. Although the C18:1/C18 ratios are lower for the aged aerosols transported from E. Asia to the N. Pacific (av. 0.4213, 0.1517), the sea-to-air emission of fatty acids could cause somewhat higher values (0.7583, 1.3584, 1.08384) in pristine marine 15 ACS Paragon Plus Environment


aerosols. Therefore, the C18:1/C18 ratio is useful for assessing the photochemical aging of fatty acids (i.e., whether “fresh” or “old”)17. Here, we found lower C18:1/C18 ratios between 35ºN and 20ºS (0.35±0.30) compared to those between 20ºS and 40ºS (1.5±0.6). This observation implies a strong influence of continental lipids from E. Asia and/or the mixing with those of oceanic origin over the tropical Pacific during KH92-4 cruise. Nevertheless, the HYSPLIT backward air mass trajectories originated mostly from the pelagic ocean (Figure S2). This result means that marine microbial lipids are probably the dominant source of airborne hydroxy FAs and n-fatty acids during KH92-4. These contrasting features (lower ratios of C18:1/C18 over the WNP with marine origin of AMBTs) may suggest that marine derived unsaturated fatty acids are subjected to atmospheric oxidation during atmospheric transport72. Interestingly, we found that C18:1/C18 ratios inversely correlated with ambient temperature (Figure S7a). Relatively high ambient temperatures over the WNP during KH92-4 might have resulted in a lower C18:1/C18 ratios. Overall, the C18:1/C18 ratios from this study (0.09–2.62; av. 0.91; Table 1) highlight a significant contribution from marine biogenic lipids in the SSA followed by photochemical oxidation in the atmosphere. Another useful proxy for assessing the terrestrial versus marine lipid contribution in TSP in the MABL is molecular distributions and CPI of n-alkanes (i.e., defined as (C21+C23+C25+C27+C29+C31+C33+C35)/(C20+C22+C24+C26+C28+C30+C32+C34))6. However, the distributions of n-alkanes from biogenic plant waxes, in general, exhibit strong odd carbon predominance with CPIn-alkanes (4-15)85, 86, while such feature is absent for those originate from fossil-fuel combustion source (CPIn-alkanes: ~0.8±0.1)87. Additionally, the weak odd-C predominance in the molecular distributions with a CPIn-alkanes close to unity (1-2) in remote marine aerosols also indicate contributions from oceanic microorganisms/recycled organic matter88. The molecular distributions of n-alkanes in TSP during the KH92-4 cruise showed


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weak odd-C predominance between C23 and C31 (Figure 2d). These CPIn-alkanes (1.07 – 1.84; av. 1.37±0.25) values, however, suggest a pronounced influence of oceanic biological sources and/or contribution from traces of petroleum derived hydrocarbons in the slicks of surface seawater. 3.5. Relative abundances of hydroxy FAs We have examined the relative abundances of LMW (i.e., C9C20) and HMW (i.e.,C21C30) -hydroxy FAs in total mass concentrations of (C9C30) to assess the significance of continental versus oceanic sources. LMW homologs (C9C20) accounted for ~58100% of total -hydroxy FAs ((C9C31); Table 1), suggesting the marine biogenic origin. In the case of -hydroxy FAs, we could observe only LMW homologs (C8-C20) due to a specific contribution from LPS of marine GNB/heterotrophic bacteria. We observed a predominance of -hydroxy FAs in total hydroxy FAs (61100%, av. 92%) over the remote Pacific Ocean (Figure 3a). The absence of -isomers and the predominance of -hydroxy FAs followed by -hydroxy FAs over the western Pacific (i.e., contrary to those distributions in the East Asian outflow3,

4, 8, 32),

emphasize a contribution from oceanic sources. We also observed higher

relative abundances of LMW n-fatty acids during KH92-4 cruise, again suggesting a major input from oceanic sources (Figure 3b). In the MABL, LMW n-fatty acids (C9 – C20) can be derived from either plant waxes or marine-derived organic matter6. In contrast, HMW n-fatty acids are mostly originated from higher plant waxes but not from oceanic phyto detritus/microbial organic matter6. Therefore, mass

ratios

of

terrestrial

to

aquatic

n-fatty

acids89

(TARn-FAs

≈

(C22+C24+C26+C28+C30+C32)/(C10+C12+C14+C16+C18+C20)) and -hydroxy FAs (TAR-hydroxy-FAs: (C22+C24+C26+C28+C30)/(C12+C14+C16+C18+C20)) are useful for deciphering the contribution



from land-derived versus marine-derived lipids. If TARn-FAs/-hydroxy-FAs is greater than unity, it implies a major input of n-fatty acids/hydroxy FAs from allochthonous sources (i.e., from terrestrial plant waxes). If the ratio is less than unity, it indicates a minor input from marine sources (i.e., the Pacific Ocean). The ratios of TARn-FAs range from 0.01 to 0.66 (Table 1), emphasizing important marine sources (the North Atlantic: 0.07 – 0.1317; California coast: 0.004-1.117; North Pacific: 0.00; Yellow Sea: 0.417; the values were estimated from fatty acid data from the round-the-world cruise17). However, the TAR-hydroxy-FAs ratios are computed for the TSP samples in which both HMW and LMW -hydroxy FAs were detected (QFF538: 0.3, collected near Japan; QFF553: 1.5, QFF555: 0.7, both were collected near Australia). For all other samples, we could observe only LMW -hydroxy FAs. The advantage of these ratios for the qualitative source apportionment, for instance, is evident by the relatively high TAR-hydroxy FAs

(1.4) in a TSP influenced by air masses from Australia, possibly indicating the input from

terrestrial plant waxes. 3.6. Factors affecting the distributions of n-fatty acids and hydroxy FAs Hydroxy FAs and n-fatty acids, the ubiquitous surfactants crucial for the formation of the SSML89-92, are autochthonous lipid components produced by marine phytoplankton and/or microbial degradation of organic matter93, 94. The trapped air bubbles in the surface waters, because of the wind stress, readily scavenge these lipids16, 66, 82, 95, 96. Volkman et al.70 suggested that hydroxy FAs are the oxidative products of relatively more abundant and corresponding long chain fatty acids in the SSML. Based on the origin of AMBTs, the predominance of LMW homologs in both hydroxy FAs and n-fatty acids as well as their TARhydroxy FAs/n-FAs, we thus hypothesize that hydroxy FAs in marine aerosols originate from the microbial/photochemical oxidation of microbial/plankton-derived n-fatty acids.


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Mochida et al. 82 found that most abundant fatty acids (C16, C18, C14, C16:1, C18:1) are in the coarse mode (i.e., 1 -10 µm) with a positive linear relationship of LMW n-fatty acids with wind speed and sea-salt abundances from the North Pacific5, 16. However, their study suggested that n-fatty acids are not the major surfactants associated with SSA over the western North Pacific based on their estimated surface area coverage.

16, 82

In contrast, we observed here a

weak but significant (R2 = 0.32; P8 m s-1) often results in the destruction of SSML (i.e., rich in n-fatty acids) by mixing with the underlying surface ocean. Therefore, we observed that low mass ratios of LMW n-fatty acids to sea-salt decreased significantly over the South Pacific (i.e., due to high wind speed) compared to those over the North Pacific (Figure S6a). The predominance of LMW homologs and molecular distributions of n-fatty acids (i.e., even-C predominance) clearly indicate a major input from oceanic microbial/planktonic lipids to MABL. If both TC and LMW n-fatty acids were originated from the marine-derived organic matter, then we could a good correlation between them. However, we found a moderate linear regression between TC and LMW n-fatty acids (R2 = 0.34; see Figure S7b). Therefore, both the abscissa and ordinate are more or less normalized with the Na+ in TSP (here, sea-salt ≈ [Salinity/Na+]seawater × [Na+]aero; salinity/Na≈3.2). This normalization process somewhat minimizes the compositional changes of organic compounds associated with SSA due to any physical/chemical processes occurring in the marine atmosphere. We found a significant linear relationship (R2=0.81) between LMW-fatty acids/sea-salt and TC/Na+ (Figure 4b). Because TSP samples (QFF538) collected near Japan showed high TC content due to a likely influence from East Asian outflow, we excluded the data from the regression analysis. We found a significant correlation (R2=0.85) between the total mass of LMW n-fatty acids and azelaic acid in TSP (Figure 4c). Remineralization of the dissolved/particulate organic matter by heterotrophic bacteria releases the surface-active lipids (e.g., n-fatty acids, unsaturated fatty acids) into the water column10, 69, 70. However, the mono/polyunsaturated fatty


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acids (e.g., oleic acid) in seawater rapidly oxidizes to form initially oxocarboxylic acids71, 72, which are later converted to dicarboxylic acid (e.g., azelaic acid)73. Therefore, the linear relationship between LMW n-fatty acids and azelaic acid (Figure 4d) in TSP could be due to their common origin from marine-derived organic matter. We also found that oleic acid/stearic acid ratio (C18:1/C18) exhibited a nonlinear (power) anti-correlation with azelaic acid (Figure 4c). In particular, the C18:1/C18 ratios showed opposite latitudinal trends to that of LMW n-fatty acids/sea-salts (Figure S5b). High surface winds prevailed over South Pacific during KH92-4, coincide with an increase in high C18:1/C18 ratio and sea-salt load but with lower mass ratios of LMW n-fatty acid/sea-salt. A comparison of total mass concentrations of n-fatty acids and hydroxy FAs with other compound classes (e.g., dicarboxylic acids and oxocarboxylic acids33 and sugars) in TC demonstrates that n-fatty acids and dicarboxylic acids are the two major organic components in the remote Pacific Ocean aerosols (Figure 4e). However, Russell et al.

18

documented

relatively high abundances of saccharides in the SSA from the high latitudinal oceans. This could be due to differences in the ocean biological activity and the influence of wind speed on the SSML. On the contrary, recent mesocosm experiments have revealed the predominance of fatty acids in the nascent SSA from a productive ocean31. Likewise, Fu et al. 17 observed that n-fatty acids were more abundant than sugars/anhydrosugars in marine aerosols collected during a round-the-world cruise. Therefore, spatial heterogeneity in the ocean biological activity along with variability in wind speed are the likely factors governing the atmospheric abundances of hydroxy FAs/n-fatty acids over the Pacific Ocean. The impact of biological activity on the organic compounds of SSA is evident by (i) presence of MSA, a gaseous-phase oxidation product of marine DMS, (ii) high EFMg2+/Ca2+, (iii) correlation of LMW n-fatty acids with azelaic acid due to their origin from phytodetritus,



(iv) high C18:1/C18 ratios in TSP, and (v) surrogate chlorophyll-a based maps during SeptemberOctober period for the years 1998-2001 (Figure S3). Under these conditions, the observed shifts in the molecular distributions of -hydroxy FAs (i.e., C9>C10 & C11>C12) could be due to the influence of biological activity in the seawater. Moreover, wind speed can affect the transfer of material from the surface ocean to the marine atmosphere but cannot explain such shifts in the molecular distributions of hydroxy FAs/n-fatty acids. Cochran et al. 31 observed a similar abrupt variability in the molecular distributions of fatty acids in SSA during a phytoplankton bloom. Therefore, oceanic biological activity and wind speed combinedly govern the atmospheric abundances and molecular distributions of hydroxy FAs and n-fatty acids over the western Pacific. Climate models often use the parameterizations of wind speed driven sea-salt production and biogenic non-sea-salt SO42- concentrations (i.e., DMS oxidation product) over the open ocean to constrain the indirect effects of natural aerosols due to their hygroscopic nature and link with cloud nucleation processes99. However, the transmission electron microscope (TEM) images of pristine oceanic aerosols from the high and low latitudes have revealed ubiquitous coatings of organic compounds in the SSML on deliquescent sea-salt particles100, 101. In this study, the wind speed dependence of both sea-salt concentrations and LMW n-fatty acids/sea-salt ratios as well as the biological activity in the surface ocean clearly affect the sea-to-air emission of fatty acids over the Pacific Ocean. If fatty acids in the SSML are, indeed, coated on nascent sea spray aerosols as monolayers, they might hinder the wateruptake of the particles (barrier effect)82 as evident by the recent laboratory experiments focusing on the CCN activity of palmitic (C16) and stearic (C18) acids21, 102. Understanding the relative proportions and molecular distributions of hydroxy FAs and n-fatty acids in marine aerosols from the remote ocean, as described in this study, under varying biological activity in the ocean surface is fundamental for better parameterization/representation of climate models. 22 ACS Paragon Plus Environment

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ASSOCIATED CONTENT Supporting Information Three supporting figures are provided to better understand the surface wind directions, the origin of air mass back trajectories and pollution rose diagrams of investigated lipid compounds and the latitudinal variability of characteristic fatty acid ratios along with their wind speed data. Additionally, another supporting table explains significant linear correlations among the chemical constituents presented in this study. AUTHOR INFORMATION Corresponding Author E-mail: [email protected] (K.K.) Present Address #National

Institute of Oceanography, Visakhapatnam, Andhra Pradesh 530-003, India.

ACKNOWLEDGEMENTS Authors thank the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT, Monbukagakusho) for the Ph. D scholarship of PB. Experimental work was mostly completed at Department of Chemistry, Tokyo Metropolitan University (TMU) when KK was a faculty member of TMU. The authors acknowledge the financial support from the Japan Society for the Promotion of Science (JSPS) through Grant-in-Aid No. 24221001.



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A.; Berkowitz, C. M.; Tyliszczak, T.; Gilles, M. K.; Laskin, A., Chemical speciation of sulfur in marine cloud droplets and particles: Analysis of individual particles from the marine boundary layer over the California current. Journal of Geophysical Research: Atmospheres 2008, 113, (D4). doi.org/10.1029/2007JD008954 59. Carlton, A. G.; Turpin, B. J.; Lim, H.-J.; Altieri, K. E.; Seitzinger, S., Link between isoprene and secondary organic aerosol (SOA): Pyruvic acid oxidation yields low volatility organic acids in clouds. Geophysical Research Letters 2006, 33, (6). doi.org/10.1029/2005GL025374 60. Kawamura, K.; Sakaguchi, F., Molecular distributions of water soluble dicarboxylic acids in marine aerosols over the Pacific Ocean including tropics. Journal of Geophysical Research: Atmospheres 1999, 104, (D3), 3501-3509.


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Kawamura, K.; Gagosian, R., Implications of ω-oxocarboxylic acids in the remote marine atmosphere for photo-oxidation of unsaturated fatty acids. Nature 1987, 325, (6102), 330. 73. Kawamura, K.; Bikkina, S., A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation. Atmospheric Research 2016, 170, 140-160. 74. Tedetti, M.; Kawamura, K.; Narukawa, M.; Joux, F.; Charriere, B.; Sempéré, R., Hydroxyl radicalinduced photochemical formation of dicarboxylic acids from unsaturated fatty acid (oleic acid) in aqueous solution. Journal of Photochemistry and Photobiology A: Chemistry 2007, 188, (1), 135-139. 75. Zahardis, J.; Petrucci, G., The oleic acid-ozone heterogeneous reaction system: products, kinetics, secondary chemistry, and atmospheric implications of a model system–a review. Atmospheric Chemistry and Physics 2007, 7, (5), 1237-1274. 76. Pham, D. Q.; O’Brien, R.; Fraund, M.; Bonanno, D.; Laskina, O.; Beall, C.; Moore, K. A.; Forestieri, S.; Wang, X.; Lee, C., Biological Impacts on Carbon Speciation and Morphology of Sea Spray Aerosol. ACS Earth and Space Chemistry 2017, 1, (9), 551-561. 77. Passeri, A.; Schmidt, M.; Haffner, T.; Wray, V.; Lang, S.; Wagner, F., Marine biosurfactants. IV. Production, characterization and biosynthesis of an anionic glucose lipid from the marine bacterial strain MM1. Applied Microbiology and Biotechnology 1992, 37, (3), 281-286. 78. Cherry, R. S.; Hulle, C. T., Cell Death in the Thin Films of Bursting Bubbles. Biotechnology Progress 1992, 8, (1), 11-18. 79. Volkamer, R.; Jimenez, J. L.; San Martini, F.; Dzepina, K.; Zhang, Q.; Salcedo, D.; Molina, L. T.; Worsnop, D. R.; Molina, M. J., Secondary organic aerosol formation from anthropogenic air pollution: Rapid and higher than expected. Geophysical Research Letters 2006, 33, (17), (L17811).doi:10.1029/2006GL026899. 80. 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82. Mochida, M.; Kitamori, Y.; Kawamura, K.; Nojiri, Y.; Suzuki, K., Fatty acids in the marine atmosphere: Factors governing their concentrations and evaluation of organic films on sea-salt particles. Journal of Geophysical Research: Atmospheres 2002, 107, (D17), AAC 1-1-AAC 1-10. 83. Hoque, M. M. M.; Kawamura, K., Longitudinal distributions of dicarboxylic acids, ω-oxoacids, pyruvic acid, α-dicarbonyls, and fatty acids in the marine aerosols from the central Pacific including equatorial upwelling. Global Biogeochemical Cycles 2016, 30, (3), 534-548. 84. Kunwar, B.; Kawamura, K., Seasonal distributions and sources of low molecular weight dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid, α-dicarbonyls and fatty acids in ambient aerosols from subtropical Okinawa in the western Pacific Rim. Environmental Chemistry 2014, 11, (6), 673-689. 85. Mandalakis, M.; Polymenakou, P. N.; Tselepides, A.; Lampadariou, N., Distribution of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons and organochlorinated pollutants in deep-sea sediments of the southern Cretan margin, eastern Mediterranean Sea: A baseline assessment. Chemosphere 2014, 106, 28-35. 86. Bendle, J. A.; Kawamura, K.; Yamazaki, K., Seasonal changes in stable carbon isotopic composition of n-alkanes in the marine aerosols from the western North Pacific: implications for the source and atmospheric transport. Geochimica et Cosmochimica Acta 2006, 70, (1), 13-26. 87. Karanasiou, A. A.; Sitaras, I. E.; Siskos, P. A.; Eleftheriadis, K., Size distribution and sources of trace metals and n-alkanes in the Athens urban aerosol during summer. Atmospheric Environment 2007, 41, (11), 23682381. 88. Kennicutt, M. C.; Barker, C.; Brooks, J. M.; DeFreitas, D. A.; Zhu, G. H., Selected organic matter source indicators in the Orinoco, Nile and Changjiang deltas. Organic Geochemistry 1987, 11, (1), 41-51. 89. Waterson, E. J.; Canuel, E. A., Sources of sedimentary organic matter in the Mississippi River and adjacent Gulf of Mexico as revealed by lipid biomarker and δ13CTOC analyses. Organic Geochemistry 2008, 39, (4), 422-439. 90. Cunliffe, M.; Engel, A.; Frka, S.; Gašparović, B.; Guitart, C.; Murrell, J. C.; Salter, M.; Stolle, C.; UpstillGoddard, R.; Wurl, O., Sea surface microlayers: A unified physicochemical and biological perspective of the air– ocean interface. Progress in Oceanography 2013, 109, 104-116. 91. Frka, S.; Kozarac, Z.; Ćosović, B., Characterization and seasonal variations of surface active substances in the natural sea surface micro-layers of the coastal Middle Adriatic stations. Estuarine, Coastal and Shelf Science 2009, 85, (4), 555-564. 92. Mazurek, Z. A.; Pogorzelski, J. S.; Boniewicz-Szmyt, K., Evolution of natural sea surface film structure as a tool for organic matter dynamics tracing. Journal of Marine Systems 2008, 74, S52-S64. 93. Slowey, J. F.; Jeffrey, L. 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Figure 1. Linear regression analyses between mass concentrations of (a) Cl- and Na+ (b) sea salt and wind speed (m s-1), (c) Mg2+ (blue circles) and Ca2+ (red squares) versus Na+. Latitudinal variability in the mass concentrations of (d) methanesulfonic acid (MSA), (e) nonsea-salt-SO42-/MSA, (f) relative abundance of water-soluble organic carbon (WSOC) and total carbon (TC), (g) -hydroxy FAs, (h) -hydroxy FAs, (i) low molecular weight (LMW)-fatty acids (C8-C19), (j) azelaic acid, and (k) sea-salt in marine aerosols collected over the western Pacific Ocean during KH92-4 cruise. 29 ACS Paragon Plus Environment


Figure 2. Molecular distributions of (a) -hydroxy fatty acids (FAs), (b) -hydroxy FAs, (c) n-fatty acids, and (d) n-alkanes in marine aerosols (TSP) collected during KH92-4 cruise in the Pacific Ocean during September-October 1992. 30 ACS Paragon Plus Environment

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Figure 3. Relative abundances of (a) -, - and - hydroxy fatty acids (FAs), (b) low (LMW) versus high molecular weight (HMW) fatty acids in their total mass concentration in TSP collected over the Pacific Ocean during KH92-4 cruise (generated using open source software R)103.



Figure 4. Correlation plots for (a) low molecular weight fatty acids (LMW-FAs) to sea-salt ratio (LMW-FAs/Sea-salt) and wind speed, (b) LMW-FAs/Sea-salt and total carbon to sodium ratio (TC/Na+), (c) azelaic acid (i.e., C9 dicarboxylic acid) and Oleic acid/Stearic acid (C18:1/C18) and (d) azelaic acid and LMW-FAs, (e) Percentage contributions of various organic compound classes to TC (equivalent-C basis) in the marine aerosols from the Pacific Ocean. The filled squares in Figure 4a represent three samples collected near Japan for which air mass back trajectories showed mixed influence of continental versus oceanic air masses and, therefore, not included for the regression analysis (generated using open source software R)103. 32 ACS Paragon Plus Environment

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Table 1. Geographical location of samples collected along with the origin of air mass back trajectories (AMBT) and characteristic parameters of hydroxy fatty acids and n-fatty acids in TSP collected during KH92-4 campaign (September – October 1992) onboard R/V Hakuho Maru. Lat (ºN)

Long (ºE)

ID

AMBT origin

(C9-C20) -OH FAs

(C9-C20) -OH FAs

(C21-C30) -OH FAs

(C9-C30) -OH FAs

%LMW -OH FAs

CPI -OH FAs

CPI -OH FAs

TAR -OH FAs

(C8-C20) n-FAs

(C21-C36) n-FAs

TAR n-FAs

CPI n-FAs

C18:1/ C18

Azelaic acid

31.6

141.2

538

WNP, EA

6.651

1.40

0.35

1.75

80

0.6

3.6

0.3

39.0

9.4

0.19

9.0

0.26

6.8

28.3

142.5

539

WNP

0.240

0.01

0.00

0.01

100

0.3

-

-

31.9

1.0

0.03

11.3

0.20

6.3

23.7

143.1

540

WNP

1.518

n.d.

n.d.

n.d.

-

0.4

-

-

49.6

1.1

0.02

13.4

0.10

8.7

13.9

143.3

541

WNP

0.308

n.d.

n.d.

n.d.

-

1.0

-

-

34.8

0.5

0.01

17.1

0.09

6.2

0.06

15.1

0.23

6.2

3.6

148.6

543

WNP, PNG

0.128

0.08

0.00

0.08

100

2.7

-

-

22.4

2.0

-4.2

152.8

544

WNP

0.887

0.02

0.00

0.02

100

0.6

-

-

40.8

3.4

0.07

15.5

1.05

6.0

-12.3

154.2

545

SP

0.114

0.00

0.00

0.00

-

0.6

-

-

23.4

1.0

0.04

13.5

0.20

3.4

-15.4

159.6

546

WNP, PNG

0.254

0.01

0.00

0.01

100

1.5

-

-

26.5

2.2

0.07

9.7

0.42

2.3

0.11

11.1

0.56

3.0

-18.2

165.9

547

WNP, PNG

0.063

0.01

0.00

0.01

100

0.8

-

-

20.1

2.5

-23.7

172.4

548

SO, SP

0.010

n.d.

n.d.

n.d.

-

-

-

-

10.5

0.8

0.07

7.1

1.29

1.2

-30.7

175.3

549

SO, SP

0.020

n.d.

n.d.

n.d.

-

-

-

-

11.6

0.8

0.06

6.8

1.33

0.6

-32.7

170.9

550

SO, SP

nd.

n.d.

n.d.

n.d.

-

-

-

-

6.8

0.4

0.06

7.9

2.62

0.6

0.06

6.4

1.25

0.7

-33.0

166.3

551

SO, SP

0.008

n.d.

n.d.

n.d.

-

-

-

-

5.6

0.4

-37.8

158.2

552

SO, SP

0.397

0.01

0.00

0.01

100

0.4

-

-

5.4

0.5

0.09

5.6

0.90

0.4

-37.4

154.9

553

SO, AU

1.089

0.27

0.19

0.46

58

0.8

1.5

1.5

5.2

3.8

0.66

5.7

0.98

0.9

-32.1

155.1

554

SO, AU

0.047

0.00

0.00

0.00

-

-

-

-

8.1

0.7

0.08

6.2

1.90

1.2

0.39

6.7

1.96

0.7

0.03

6.8

1.01

1.5

-26.9 -21.3

155.1 154.6

555 556

SO, AU SO

0.724 0.024

0.25 0.00

0.11 0.00

0.37 0.00

69

0.9

-

-

3.4 -

0.7 -

7.1 8.7

WNP = W. North Pacific, EA = E. Asia, PNG = Papa New Gunea, AU = Australia, SO = Southern Ocean

2.9 0.4

%LMW -FAs = LMW -OH FAs/(-OH FAs + -OH FAs); CPI-OH FAs = (C10+C12+C14+C16+C18+C20)/(C9+C11+C13+C15+C17+C19) CPI-OH FAs = (C10+C12+C14+C16+C18+C20+C22+C24+C26+C28+C30)/(C9+C11+C13+C15+C17+C19+C21+C23+C25+C27+C29) CPIn-fatty acids = (C10+C12+C14+C16+C18+C20+C22+C24+C26+C28+C30+C32+C34+C36)/ (C9+C11+C13+C15+C17+C19+C21+C23+C25+C27+C29+C31+C33+C35) TAR-OH FAs = (C22+C24+C26+C28+C30)/(C12+C14+C16+C18+C20); TARn-FAs = (C22+C24+C26+ C28+C30+C32)/(C10+C12+C14+C16+C18+C20) 33 ACS Paragon Plus Environment


1 2 3

TOC art:

4 5 6 7 8 9 10 11 12


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Figure 1. Linear regression analyses between mass concentrations of (a) Cl-and Na+ (b) sea salt and wind speed (m s-1), (c) Mg2+ (blue circles) and Ca2+ (red squares) versus Na+. Latitudinal variability in the mass concentrations of (d) methanesulfonic acid (MSA), (e) non-sea-salt-SO42-/MSA, (f) relative abundance of water-soluble organic carbon (WSOC) and total carbon (TC), (g) -hydroxy FAs, (h) -hydroxy FAs, (i) low molecular weight (LMW)-fatty acids (C8-C19), (j) azelaic acid, and (k) sea-salt in marine aerosols collected over the western Pacific Ocean during KH92-4 cruise. 148x188mm (300 x 300 DPI)

ACS Paragon Plus Environment


Figure 2. Molecular distributions of (a) -hydroxy fatty acids (FAs), (b) -hydroxy FAs, (c) n-fatty acids, and (d) n-alkanes in marine aerosols (TSP) collected during KH92-4 cruise in the Pacific Ocean during September-October 1992. 203x273mm (300 x 300 DPI)


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Figure 3. Relative abundances of (a) -, - and - hydroxy fatty acids (FAs), (b) low (LMW) versus high molecular weight (HMW) fatty acids in their total mass concentration in TSP collected over the Pacific Ocean during KH92-4 cruise. 254x190mm (300 x 300 DPI)



Figure 4. Correlation plots for (a) low molecular weight fatty acids (LMW-FAs) to sea-salt ratio (LMWFAs/Sea-salt) and wind speed, (b) LMW-FAs/Sea-salt and total carbon to sodium ratio (TC/Na+), (c) azelaic acid (i.e., C9 dicarboxylic acid) and Oleic acid/Stearic acid (C18:1/C18) and (d) azelaic acid and LMW-FAs, (e) Percentage contributions of various organic compound classes to TC (equivalent-C basis) in the marine aerosols from the Pacific Ocean. The filled squares in Figure 4a represent three samples collected near Japan for which air mass back trajectories showed mixed influence of continental versus oceanic air masses and, therefore, not included for the regression analysis (generated using open source software R)103. 127x189mm (300 x 300 DPI)


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Hydroxy fatty acids in remote marine aerosols over the Pacific Ocean

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