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Spatio-temporal distributions of dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid, α-dicarbonyls and fatty acids in the marine aerosols from the North and South Pacic Mir Md. Mozammal Hoque a,b,1 , Kimitaka Kawamura a, ,2 , Mitsuo Uematsu c a Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-ku, Sapporo, Japan b Graduate School of Environmental Science, Hokkaido University, N11 W5, Kita-ku, Sapporo, Japan c Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba, Japan abstract article info Article history: Received 5 April 2016 Received in revised form 12 October 2016 Accepted 26 October 2016 Available online 28 October 2016 Aerosol samples (TSP) were collected during a cruise in the North (3°05N34°02N) and South (6°59S25°46S) Pacic to investigate the spatio-temporal distributions of water-soluble dicarboxylic acids and related com- pounds. The molecular distributions of diacids were characterized by the predominance of oxalic (C 2 ) acid followed by malonic (C 3 ) and then succinic (C 4 ) acid. However, we found a predominance of C 4 over C 3 in the aerosol sample that was collected in the western North Pacic Rim with a heavy inuence from continental air masses. Atmospheric abundances of short chain diacids (C 2 C 4 ) are 23 times higher in the North Pacic than in the South Pacic. During the cruise, abundances of C 2 in the western North Pacic are 5 times higher than those in the rest of the samples collected. Moreover, the aerosol samples collected in the western North Pacic demonstrated that glyoxylic (ωC 2 ) acid and methylglyoxal (MeGly) were dominant together with C 2 . We found a strong correlation between C 2 and ωC 2 (r = 0.87) and C 2 and MeGly (r = 0.97) in the western North Pa- cic aerosols but the correlations are signicantly weak in the samples from the central North Pacic and South- ern Ocean. Diacids were found to account for 1.6 to 14% of organic carbon with higher values in the western North Pacic. These results, together with 7-day backward air mass trajectories, indicate that ωC 2 and MeGly are both originated from the photochemical oxidation of continent-derived organic precursors including isoprene, which can serve as precursors for the production of C 2 during long-range atmospheric transport. © 2016 Elsevier B.V. All rights reserved. Keywords: Aerosols Spatio-temporal distributions Dicarboxylic acids Oxalic acid Glyoxylic acid 1. Introduction Atmospheric aerosols are composed of various organic compounds, which can signicantly contribute to the aerosol mass loading and alter the chemical and physical properties (Mochida et al., 2003; Legrand et al., 2007). Marine-derived primary organic aerosols (POA) are produced by bubble bursting and wave breaking processes that are driven by the wind actions over the surface ocean (Rinaldi et al., 2010). On the other hand, marine secondary organic aerosols (SOAs) are essentially produced by the atmospheric reactions of anthropogenic and biogenic volatile organic compounds (BVOCs) with oxidants such as ozone (O 3 ), nitrogen oxides (NO x ) and OH radicals (Claeys et al., 2004, 2007; Jaoui et al., 2005). However, the fate of marine organic aerosols is highly uncertain (Miyazaki et al., 2014). Organic matter in primary marine organic aerosols may act as an important precursor/ source and sink for OH radicals, leading to their degradation and pro- duction of low molecular weight (LMW) dicarboxylic acids (Zhou et al., 2008). LMW dicarboxylic acids have potential inuences on the physical properties of organic particles thus play an important role in the hygroscopic growth of particles (Prenni et al., 2003) and the activa- tion of cloud condensation nuclei (Liss and Lovelock, 2007; Booth et al., 2009). Both of the primary and secondary sources of LMW dicarboxylic acids and related compounds are well documented in literatures (e.g., Kawamura and Bikkina, 2016). Water-soluble dicarboxylic acids may also be produced from photochemical and aqueous phase oxida- tion of biogenic unsaturated fatty acids and volatile organic compounds (VOCs) such as isoprene emitted from the ocean surface (Bikkina et al., 2014; Sempéré and Kawamura, 2003) coupled with gas-to-particle con- version (Zhang et al., 2010). As illustrated in Fig. 1, in-cloud processing of isoprene is an important contributor to SOA production in the marine atmosphere, which can alter the global distribution of hygroscopic organic aerosol. Atmospheric Research 185 (2017) 158168 Corresponding author. E-mail address: [email protected] (K. Kawamura). 1 Now at Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail, Bangladesh. 2 Now at Institute for Advanced Studies, Chubu University, Kasugai, Aichi, Japan. http://dx.doi.org/10.1016/j.atmosres.2016.10.022 0169-8095/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmosres

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  • Atmospheric Research 185 (2017) 158–168

    Contents lists available at ScienceDirect

    Atmospheric Research

    j ourna l homepage: www.e lsev ie r .com/ locate /atmosres

    Spatio-temporal distributions of dicarboxylic acids, ω-oxocarboxylicacids, pyruvic acid, α-dicarbonyls and fatty acids in the marine aerosolsfrom the North and South Pacific

    Mir Md. Mozammal Hoque a,b,1, Kimitaka Kawamura a,⁎,2, Mitsuo Uematsu ca Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-ku, Sapporo, Japanb Graduate School of Environmental Science, Hokkaido University, N11 W5, Kita-ku, Sapporo, Japanc Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba, Japan

    ⁎ Corresponding author.E-mail address: [email protected] (K. Kawa

    1 Now at Department of Environmental Science and ReBhashani Science and Technology University, Tangail, Ban

    2 Now at Institute for Advanced Studies, Chubu Univers

    http://dx.doi.org/10.1016/j.atmosres.2016.10.0220169-8095/© 2016 Elsevier B.V. All rights reserved.

    a b s t r a c t

    a r t i c l e i n f o

    Article history:Received 5 April 2016Received in revised form 12 October 2016Accepted 26 October 2016Available online 28 October 2016

    Aerosol samples (TSP)were collected during a cruise in the North (3°05′N–34°02′N) and South (6°59′S–25°46′S)Pacific to investigate the spatio-temporal distributions of water-soluble dicarboxylic acids and related com-pounds. The molecular distributions of diacids were characterized by the predominance of oxalic (C2) acidfollowed by malonic (C3) and then succinic (C4) acid. However, we found a predominance of C4 over C3 in theaerosol sample that was collected in the western North Pacific Rim with a heavy influence from continental airmasses. Atmospheric abundances of short chain diacids (C2–C4) are 2–3 times higher in the North Pacific thanin the South Pacific. During the cruise, abundances of C2 in the western North Pacific are 5 times higher thanthose in the rest of the samples collected. Moreover, the aerosol samples collected in the western North Pacificdemonstrated that glyoxylic (ωC2) acid and methylglyoxal (MeGly) were dominant together with C2. Wefound a strong correlation between C2 andωC2 (r= 0.87) and C2 andMeGly (r= 0.97) in thewestern North Pa-cific aerosols but the correlations are significantly weak in the samples from the central North Pacific and South-ernOcean.Diacidswere found to account for 1.6 to 14% of organic carbonwith higher values in thewesternNorthPacific. These results, together with 7-day backward air mass trajectories, indicate that ωC2 and MeGly are bothoriginated from the photochemical oxidation of continent-derived organic precursors including isoprene, whichcan serve as precursors for the production of C2 during long-range atmospheric transport.

    © 2016 Elsevier B.V. All rights reserved.

    Keywords:AerosolsSpatio-temporal distributionsDicarboxylic acidsOxalic acidGlyoxylic acid

    1. Introduction

    Atmospheric aerosols are composed of various organic compounds,which can significantly contribute to the aerosol mass loading andalter the chemical and physical properties (Mochida et al., 2003;Legrand et al., 2007). Marine-derived primary organic aerosols (POA)are produced by bubble bursting and wave breaking processes thatare driven by the wind actions over the surface ocean (Rinaldi et al.,2010). On the other hand, marine secondary organic aerosols (SOAs)are essentially produced by the atmospheric reactions of anthropogenicand biogenic volatile organic compounds (BVOCs) with oxidants suchas ozone (O3), nitrogen oxides (NOx) and OH radicals (Claeys et al.,2004, 2007; Jaoui et al., 2005). However, the fate of marine organic

    mura).source Management, Mawlanagladesh.ity, Kasugai, Aichi, Japan.

    aerosols is highly uncertain (Miyazaki et al., 2014). Organic matter inprimary marine organic aerosols may act as an important precursor/source and sink for OH radicals, leading to their degradation and pro-duction of low molecular weight (LMW) dicarboxylic acids (Zhouet al., 2008). LMW dicarboxylic acids have potential influences on thephysical properties of organic particles thus play an important role inthe hygroscopic growth of particles (Prenni et al., 2003) and the activa-tion of cloud condensation nuclei (Liss and Lovelock, 2007; Booth et al.,2009).

    Both of the primary and secondary sources of LMW dicarboxylicacids and related compounds are well documented in literatures(e.g., Kawamura and Bikkina, 2016). Water-soluble dicarboxylic acidsmay also be produced from photochemical and aqueous phase oxida-tion of biogenic unsaturated fatty acids and volatile organic compounds(VOCs) such as isoprene emitted from the ocean surface (Bikkina et al.,2014; Sempéré and Kawamura, 2003) coupledwith gas-to-particle con-version (Zhang et al., 2010). As illustrated in Fig. 1, in-cloud processingof isoprene is an important contributor to SOA production in themarineatmosphere, which can alter the global distribution of hygroscopicorganic aerosol.

    http://crossmark.crossref.org/dialog/?doi=10.1016/j.atmosres.2016.10.022&domain=pdfhttp://dx.doi.org/10.1016/j.atmosres.2016.10.022mailto:[email protected]://dx.doi.org/10.1016/j.atmosres.2016.10.022http://www.sciencedirect.com/science/journal/01698095www.elsevier.com/locate/atmosres

  • Fig. 1. In-cloud isoprene chemistry for the formation of major diacids: glyoxylic acid, pyruvic acid, and oxalic acid (modified from Lim et al., 2005).

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    Distributions of LMW diacids in remote marine aerosols are con-trolled by long-range transport of continental aerosols (Kundu et al.,2010; Fu et al., 2013a, b; Kawamura and Sakaguchi, 1999) and photo-chemical oxidation of BOVCs emitted from the ocean surface (Bikkinaet al., 2014; Hoque et al., 2015).

    Although several studies have been performed in a single hemi-spheric region over the Pacific, intra-hemispheric distributions ofLMW diacids and related compounds have rarely been conducted dur-ing a single oceanic cruise (Sempéré and Kawamura, 2003). In thepresent study, remote marine aerosol samples were collected during acruise of M/V Bousei Maru to cover the North and South Pacific duringFebruary to April 1994. This cruise is unique because of the dissimilar-ities of the hemispheres in terms ofmeteorology, wind patterns, and cli-mate aswell as biological productivity. For example, the coastal westernNorth Pacific is highly influenced by polluted continental air massestransported from north China, Mongolia, Russia and Siberia. In contrast,the central North Pacific that is significantly influenced by the oceanicair masses (e.g., Bikkina et al., 2014) as it is far away from the pollutionsources in the continents. The aerosol samples collected from the SouthPacific can be influenced by the inward continental air masses fromPapua-New Guinea, Southern Australia and New Zealand.

    In this study, we conducted organic aerosol studies to characterizelow molecular weight dicarboxylic acids, ω-oxoacids, pyruvic acids, α-dicarbonyls and fatty acids as well as organic carbon (OC), elementalcarbon (EC) andwater-soluble total nitrogen in themarine aerosol sam-ples from the North and South Pacific. The objectives of the presentstudy are to (1) characterize the molecular compositions of diacidsand related polar compounds over the North and South Pacific Ocean,and (2) clarify the spatial distributions of water-soluble dicarboxylicacids and related compounds and their contributions to OC in the ma-rine boundary layer of the North and South Pacific.

    2. Methods

    During the cruise of T/V Bousei Maru from 16 February to 1 April1994, a total of 17 marine aerosol (TSP) samples were collected in theNorth Pacific (3°05′N–34°02′N, 144°52′E–173°49′W) and South Pacific(6°59′S–25°46′S, 154°28′E–173°55′W). A high volume air sampler wasset up at the upper deck of the ship using pre-combusted (500 °C)quartz fiber filters (Pallflex-2500QAT-UP, 20 × 25 cm). The samplerwas controlled by a wind sector (±60°) and wind speed (≥5 m s−1)

    system to avoid potential contamination from the ship exhausts(Kawamura and Sakaguchi, 1999). Sampling time was 48 to 72 h.Fig. 2 shows the cruise track. Total aerosol mass was determined byweighing the filter before and after the sample collection. Each filterwas then stored individually in a pre-combusted clean glass jar with aTeflon-lined screw cap at−20 °C in darkness prior to analysis. Althoughthe sample filters had been stored for a long time, degradation of or-ganics on the filters should be insignificant under such a low tempera-ture (Wang et al., 2006; Kawamura et al., 2010). Blank filters wereexposed to the marine air in the sample shelter for a few seconds with-out pumping and then recovered into the glass jar (Sempéré andKawamura, 2003).

    Water-soluble diacids, ω-oxoacids, pyruvic acid, and α-dicarbonylsas well as fatty acids were determined using an improved method ofMochida et al. (2007) and Kawamura and Ikushima (1993). In brief, al-iquots of filter samples were extracted with organic-free ultra purewater (5 ml × 3, N18 MΩ) under ultrasonic agitation for the isolationof diacids and other water-soluble organic compounds. The extractswere passed through a glass column (Pasteur pipet) packedwith quartzwool for removingfilter debris and particles. The extractswere adjustedto pH= 8.5–9.0 using a 0.05 M KOH solution and then concentrated toalmost dryness using a rotary evaporator (~40 °C) under vacuum. Afterthe dryness in N2 blow down system, diacids, oxoacids, α-dicarbonylsand fatty acids in the concentrates were derivatized to butyl estersand dibutoxy acetals with 14% borontifluoride in n-butanol at 100 °Cfor 1 h.

    The derivatives were extracted with n-hexane (~5 ml) after addingpure water (~5 ml). The hexane layer was concentrated to about 50 μlusing a rotary evaporator, transferred to a glass vial (1.5 ml), conse-quently dried by N2 blow down and dissolved in 100 μl of n-hexane.The derivatives (2 μl) were injected into a capillary gas chromatograph(GC) system (Agilent 6890) equipped with a split/splitless injector,fused silica capillary column (HP-5, 25 m × 0.2 mm i.d., 0.5 μm filmthickness) and flame ionization detector (FID). Identifications of estersand acetals were confirmed by comparing GC retention times andmass spectra with those of authentic standards. Mass spectral analysiswas conducted with a GC/mass spectrometry system (Agilent MS) andquantification of compounds was performed by GC/FID. Fig. S1 showsa typical capillary gas chromatogram of the identified diacids in theaerosol sample (QFF 592) collected during the North-South Pacificcruise. Similar procedure was also performed for recovery and blank

  • Fig. 2. Cruise track of T/V Bousei Maru in 1994. The numbers and thick black marks in the map represent sample identification numbers and sample location, respectively.

    Table 1Aerosol mass, concentrations of various carbonaceous and nitrogenous components, theirconcentration ratios and contributions of diacid-C to OC in the North and South Pacificaerosol samples.

    Components Minimum Maximum Average Median

    Aerosol mass (μg m−3) 36 95 64 63TC (μg m−3) 0.2 1.9 0.6 0.4OC (μg m−3) 0.1 1.4 0.5 0.3WSTN (μg m−3) 0.01 0.8 0.2 0.1TC/aerosol mass (%) 0.2 4.5 1.1 0.8WSTN/aerosol mass (%) 0.02 1.0 0.3 0.1Diacid-C/OC (%) 1.4 11 4.2 4.0

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    tests. We got a recovery of 85% for oxalic acid and N90% for malonic,succinic and adipic acids. Triplicate analyses of ambient aerosol sampleshowed analytical error of b10% for major diacids. Field blanks showedvery small peaks for oxalic, pyruvic and phthalic acids in the GC chro-matograms; they are b5% of the real samples. The reported concentra-tions for the samples were corrected for the field blanks.

    Water-soluble organic carbon (WSOC) and total nitrogen (WSTN)were measured using a Shimadzu total carbon/total nitrogen analyzer(TOC-VCSH) (Miyazaki et al., 2011). First, a filter disc of 3.14 cm2was ex-tracted with organic-free ultra pure water under ultrasonication for 15min. The extracts were then passed through a syringe filter (Millex-GV, 0.45 μm, Millipore). For the removal of inorganic carbon, the ex-tracts were acidified with 1.2 M HCl and purged with pure air. Theblank levels were b5% of the real samples. The analytical errors ofWSOC andWSTNmeasurements during triplicate analyses were within5%. WSOC concentrations reported here are corrected for the fieldblanks.

    Concentrations of organic carbon (OC) and elemental carbon (EC)were measured using a Sunset Laboratory carbon (OC/EC) analyzer fol-lowing Interagency Monitoring Protected Visual Environments (IM-PROVE) thermal/optical evolution protocol (Wang et al., 2005). Totalcarbon (TC) was calculated as TC = OC + EC. A filter disc of 1.4 cm2

    punchwas put in quartz boat placed in the thermal desorption chamberand applied to stepwise heating in a helium flow, and then helium gaswas switched to He/O2. Finally, evolved CO2 during the oxidation ateach temperature step was measured with non-dispersive infrared(NDIR) detector. For the setting up the OC/EC split point and OC correc-tion, a transmittance of light (red 660 nm) was applied through the fil-ter punch. The analytical error in duplicate analysis for OC and EC of thefilter sample were within 10% and the reported concentrations arecorrected for the field blanks. The blank levels were b10% of the realsamples.

    During the periods of aerosol sampling, 7-day backward air masstrajectories were calculated every 6 h using the Hybrid Single-ParticleLagrangian Trajectory (HYSPLIT)model developed by the National Oce-anic and Atmospheric Administration (NOAA) air resource laboratory

    (http://ready.arl.noaa.gov/HYSPILT.php). Each back trajectory wascalculated at 500 m above the ground for aerosol samples collectedduring the cruise.

    3. Results and discussion

    3.1. Composition and general characteristics of marine aerosols

    Marine organic aerosols composed of primary (POA) and secondaryorganic aerosol (SOA). POA is mechanically produced as sea spray aero-sols by the interaction of wind with the ocean surface, which is com-posed of sea salts and organics (Rinaldi et al., 2010). On the contrary,SOA can form in themarine boundary layer through a number of differ-ent processes. Biogenic volatile organic compounds (BVOCs) emittedfrom sea surface and the subsequent oxidation products may be in-volved in new particle formation through nucleation process. BVOCsand related oxidation products can also condense on preexisting parti-cles and droplets, which can contribute to the particulate mass. SOAcan also derive from the chemical transformation of primary or second-ary components present in the condensed phase and atmospheric oxi-dation of isoprene (Rinaldi et al., 2010). Such transformations maytake place at the particle surface (Eliason et al., 2004; Maria et al.,2004) or in the aqueous phase (Ervens et al., 2003; Warneck, 2003).

    http://ready.arl.noaa.gov/HYSPILT.php

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    As shown in Table 1, aerosolmass concentrations over theNorth andSouth Pacific ranged from36 to 95 μgm−3 (av. 64 μgm−3,median 63 μgm−3) and 28 to 92 μg m−3 (av. 54 μg m−3, median 50 μg m−3), respec-tively. Such values are comparative to those reported previously for thewestern to central Pacific (range: 19–404 μg m−3, av. 48 μg m−3)(Kawamura and Sakaguchi, 1999), western Pacific (11–68 μg m−3)(Sempéré and Kawamura, 2003) and North Pacific (11–232 μg m−3,av. 44 μg m−3) (Hoque et al., 2015) but higher than those reported forthe tropical Indian Ocean (av. 15 μg m−3) (Krishnamurti et al., 1998)and the Atlantic Barbados (11–31 μg m−3) (Li et al., 1996). In theNorth Pacific, spatio-temporal distributions of aerosols mass showedhigher values over thewesternNorth Pacific Rim,where the continentalair masses are transported significantly during the study period (seeFigs. 3 and 4a). Interestingly, over the South Pacific, higher aerosolsmass concentrations are observed in the samples that were collectednear the islands (Tasmania and Papua New Guinea), suggesting thatcontinental aerosols have been transported long distances along the re-mote areas of the North and South Pacific.

    Concentrations of total carbon (TC) for the remote aerosol samplesranged from 0.15 to 1.9 μg m−3 (av. 0.62 μg m−3, median 0.36 μgm−3). The relative abundances of TC to aerosol mass ranged from 0.2%to 4.5% (av. 1.1%, median 0.8%) (see Table 1). Spatial distributions ofTC and TC% of the aerosols also showedpatterns similar to those of aero-sols mass, supporting a significant atmospheric transport of continen-tally derived organics over the remote marine atmosphere (Hoqueet al., 2015).

    Abundances of water-soluble total nitrogen (WSTN) in aerosolsranged from 0.01 to 0.80 μg m−3 (av. 0.16 μg m−3, median 0.10 μgm−3). These values are in the same order of magnitude of those report-ed previously for theNorth Pacific (range: 0.02–0.90 μgm−3, av. 0.20 μgm−3) (Hoque et al., 2015), but are ca. 3 times lower than those (0.07–3.02 μg m−3, 0.58 μg m−3) reported for the ambient aerosols collectedfrom Okinawa Island in the western North Pacific Rim (Kunwar andKawamura, 2014). The water-soluble nitrogenous fraction (WSTN%) in

    Fig. 3. Seven-day backward airmasses trajectories at 500m above the groundwere drawnwithsee Fig. 2.

    aerosols mass ranged from 0.02 to 1.0% (av. 0.25%, median 0.10%) (seeTable 1). These values are similar to those reported in our previousstudy from the North Pacific (Hoque et al., 2015) and Pacific Ocean in-cluding tropics (Kawamura and Sakaguchi, 1999), but significantlylower than those reported for TN from urban Tokyo (Kawamura andIkushima, 1993). Concentration of WSTN and mass fraction of WSTNin aerosols also showed similar spatial distributions that are obtainedfor TC and TC% of aerosol mass with higher values over the westernNorth Pacific, which may happen due to the strong influences of airmasses from the Asian Continent (see Fig. 3). This finding may implythat particulate nitrogen is of continental origins, which are transportedlong distances to the remote western North Pacific.

    In contrast, the samples collected in the central North Pacific and inremote South Pacific showed lowest concentration of WSTN. Thesesamples are free from continental influences (Fig. 3), suggesting thatsea-to-air emissions of aerosols are not the main source of water-soluble organic nitrogen over the remote ocean.

    3.2. Molecular distributions of diacids,ω-oxoacids, pyruvic acid, fatty acidsand α-dicarbonyls

    During the expedition, LMWdicarboxylic acids (C2–C11),ω-oxoacids(C2–C9 except for C6), pyruvic acid, fatty acids (C14, C16, C18, C18:1) andα-dicarbonyls (Gly and MeGly) were detected. The molecular distribu-tions of diacids were characterized by the predominance of oxalic (C2)acid followed by malonic (C3) and succinic (C4) acids (Fig. 5a), beingsimilar to those reported previously in the different locations from thePacific Ocean (Bikkina et al., 2014; Hoque et al., 2015). On average, at-mospheric abundances of C2, C3 and C4 are 2–3 times higher in theNorth Pacific than those in the South Pacific (Table 2). Specifically, theconcentrations of C2 in aerosol samples collected from the westernNorth Pacific Rim are 5–10 times higher than those obtained from thecentral North Pacific and South Pacific (Fig. 5a, b and c).

    NOAAHYSPLITmodel. The black line indicates cruise tracks. For details of the cruise tracks,

  • Fig. 4. Spatio-temporal distributions of (a) total aerosol mass, and (b) total diacids in the marine aerosols collected from the North and South Pacific.

    162 M.M.M. Hoque et al. / Atmospheric Research 185 (2017) 158–168

    Glyoxal (Gly) is formed by the oxidation of acetylene, toluene and ofglycolaldehyde from isoprene and ethene (Warneck, 2003; Ervens et al.,2004) and glyoxylic (ωC2) acid is produced by the oxidation of glyoxal(Kawamura, 1993). Methylglyoxal (MeGly) are nearly ubiquitous andare photochemically generated through oxidation of VOCs (Henryet al., 2012). As proposed by Galloway et al. (2011), 2.1% of glyoxaland 4.2% of methylglyoxal are of direct yields from isoprene. Gly andMeGly that do not come from isoprene are originated from acetylene,acetone, alkenes and aromatics emitted from the continent due to an-thropogenic activities as well as from marine anthropogenic sourcethrough ship emission (Tuazon et al., 1984; Fu et al., 2008; Chan et al.,2009; Volkamer et al., 2007; Galloway et al., 2011). Interestingly,glyoxylic acid and methylglyoxal are relatively abundant in the aerosolsamples where C2 is dominant (Fig. 4c, d) because oxalic acid could beproduced from methylglyoxal in cloud droplets in the marine atmo-sphere (Carlton et al., 2006).

    Interestingly, those samples (QFF 605, 606) having higher concen-tration of ωC2 and MeGly are influenced by the continental air massesoriginated fromNorth China and Siberiawhere coal and biofuel burningare very intensive (see Fig. 3). It is of noteworthy that in the sample sets

    from the western North Pacific we found a strong correlation betweenC2 andωC2 (r= 0.87) and C2 andMeGly (r= 0.97), but the correlationsare significantly weak for the rest of samples collected from the centralNorth and South Pacific. Hence, we conclude that ωC2 and MeGly areboth derived via the photochemical oxidation of organic precursors inthe continental air masses and can serve as a precursor of C2 duringlong-range atmospheric transport.

    However, the molecular distributions of diacids in one sample (QFF606) that was collected in the coastal western North Pacific near theJapanese Islands, showed a predominance of C2 followed by C4 and C3(Fig. 5d). Such a molecular distribution is different from those of othersamples, which exhibit C3 N C4 (Fig. 5a, b, c and d). The C3/C4 ratios b1have been reported in winter aerosol samples from urban Tokyo(Kawamura and Ikushima, 1993), although the ratios are N1 in theurban samples during summer and warmer seasons due to the photo-chemical production of C3 from C4. The sample (QFF 606) may bestrongly influenced by the urban aerosols from Japan. Similarmoleculardistribution pattern of C4 N C3 has been reported in the continentalaerosols collected during the 1997 Indonesian forest fires (Narukawaet al., 1999) and for marine aerosols collected during a round the

  • Fig. 5.Molecular composition of lowmolecular weight dicarboxylic acids (C2–C11),ω-oxoacids, pyruvic acid,α-dicarbonyls and fatty acids in selectedmarine aerosols from the North andSouth Pacific. For the details of samples QFF 594, 602, 605 and 606, see Fig. 2. For the abbreviations of the compounds, see Table 2.

    163M.M.M. Hoque et al. / Atmospheric Research 185 (2017) 158–168

    world cruise (Fu et al., 2013a), where influence of biomass burningwas significant.

    Among ω-oxoacids, glyoxylic (ωC2) acid is most abundant, whoseconcentrations in the North Pacific are almost 6 times higher thanthose from the South Pacific (Table 2). This result clearly indicates thatanthropogenic emissions are more significant in the North Pacific thanin the South Pacific, because glyoxylic acid ismainly produced by the at-mospheric oxidation of aromatic hydrocarbons (Smith et al., 1999;Kleindienst et al., 2004). Methylglyoxal was found as foremost α-dicarbonyl species, comprising 88% and 77% of total α-dicarbonylsfrom the North and South Pacific, respectively. Such a findingmay indi-cate that anthropogenic hydrocarbons are the important precursor ofmethylglyoxal in the trans-hemispheric Pacific Ocean (Kleindienstet al., 2004). However, atmospheric abundances of total fatty acids are~2 times higher in the South Pacific than in the North Pacific(Table 2). In fact, azelaic acid (C9), a tracer of photochemical oxidation

    Table 2Concentrations (ng m−3) of dicarboxylic acids, ω-oxoacids, pyruvic acid, α-dicarbonyls and fa

    North Pacific (n = 11)

    Compounds Range Average MedianOxalic acid, C2 12–163 44.4 32.8Malonic acid, C3 2.3–34.4 9.1 4.5Succinic acid, C4 0.4–26.2 6.2 3.7Glutaric acid, C5 BDL-7.1 1.5 0.6Adipic acid, C6 0.1–4.3 0.8 0.4Pimelic acid, C7 BDL-1.2 0.3 0.2Suberic acid,C8 BDL-0.7 0.2 0.2Azelaic acid, C9 BDL-1.6 0.4 0.3Sebacic acid, C10 BDL-0.2 0.1 0Undecanoic acid, C11 BDL-0.2 0.1 0.1Phthalic acid, Ph 0.2–10 2 1.1Glyoxylic acid, ωC2 0.3–20.3 3.5 0.9Glyoxal, Gly BDL-3.4 0.7 0.3Methylglyoxal, MeGly 0.1–13.7 4.5 1.1Total diacids 17–207 68 50Total ω-oxoacids 0.6–28 5.3 2.2Total α-dicarbonyls 0.1–15 5 1.4Total fatty acids 0.1–2.1 0.7 0.6

    a RA, average relative abundance in each group.b BDL, below detection limit (0.005 ng m−3).

    of biogenic unsaturated fatty acids (Kawamura et al., 1996; Kawamuraand Sakaguchi, 1999), also showed increased levels in the South Pacificwhere unsaturated fatty acids maximized (Fig. 5a).

    3.3. Spatial distributions of diacids and related compounds and contribu-tions (%) of diacids to aerosol OC over the Pacific

    Concentration ranges of total diacids, ω-oxoacids, pyruvic acid, α-dicarbonyls and fatty acids are 17–207 ngm−3 (av. 54.4 ngm−3, medi-an 25.2 ngm−3), 0.6–28 ngm−3 (4.0 ngm−3, 1.3 ngm−3), 0.04–10 ngm−3 (1.0 ng m−3, 0.2 ng m−3), 0.1–15 ng m−3 (3.7 ng m−3, 1.2 ngm−3), and 0.1–3 ngm−3 (0.8 ngm−3, 0.6 ngm−3), respectively. Atmo-spheric abundances of diacids and related polar compounds (ω-oxoacids andα-dicarbonyls) in the North Pacific were 2–5 times higherthan those from the South Pacific (Table 2). In contrast, fatty acids in theSouth Pacific are more abundant by 42% than in the North Pacific (see

    tty acids in the marine aerosol from the North (n = 11) and South (n = 6) Pacific.

    South Pacific (n = 6)

    RA (%) Range Average Median RA (%)65.5 11–41 19.3 15.6 64.513.4 3.2–7.3 4.6 4.1 15.49.1 0.7–3.8 1.9 1.5 6.42.2 0.1–0.6 0.2 0.1 0.71.2 0.2–0.5 0.3 0.3 10.4 0.1–0.3 0.1 0.1 0.30.3 0.1–0.6 0.2 0.1 0.70.6 0.2–2.6 0.7 0.4 2.30.01 BDL-0.1 0.1 0.1 0.30.01 BDL-0.3 0.2 0.2 0.73 0.3–1.0 0.8 0.9 2.766 0.4–1.0 0.6 0.5 4013.8 0.1–0.5 0.2 0.1 22.288.2 0.1–2.0 0.7 0.3 77.8– 18–62 30 25 –– 1.2–2.2 1.5 1.3 –– 0.2–2.1 0.9 0.5 –– 0.3–3.0 1 0.7 –

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    Table 2), suggestingmore algal activities in the South Pacific and subse-quent emissions to the atmosphere during the cruise (Mochida et al.,2002). Fig. 4b shows a spatio-temporal variability of total diacids overthe North and South Pacific during the study period. As expected, con-centrations of diacids were several times lower in the pelagic oceansthan those in the coastal areas in the western North Pacific. This findingmay support an idea that the AsianContinent has a significant impact onthe atmospheric abundances of diacids over the oceanic regions.

    During the cruise, the highest concentration of diacids was obtainedover the North Pacific (Table 2 and Fig. 4b). ω-Oxoacids, pyruvic acidsand α-dicarbonyls are abundant in the marine aerosols when diacidsshow high abundances. Higher levels of diacids and related compoundswere observed over the western North Pacific where polluted airmasses are transported from East Asia together with more VOCs, soot,mineral dusts, and O3 (see Fig. 3). The concentrations of diacids signifi-cantly decreased when the ship moved to lower latitudes (Fig. 4b). Theseven-day backward air mass trajectories also indicate that there are nocontinental influences during the sampling in the low latitudinal re-gions of the subtropical North Pacific (Fig. 3). In contrast, spatial distri-butions of diacids over the South Pacific were noticeably uniform,except for one sample that was collected near the Suva port in Fiji. Diac-id concentrations over the South Pacific are twice lower than those ofthe North Pacific (Fig. 4b). The lower diacid concentrations should bedue to limited anthropogenic activities in the Southern Hemisphere ascompared to the Northern Hemisphere (Jaward et al., 2004).

    In this study, diacids and related polar organic compoundsaccounted for 1.6–14% (av. 5.2%, median 5.2%) of OC, where diacidswere the major contributor accounting for 1.4–11% (4.2%, 4.0%)(Table 1) followed by α-dicarbonyls (0.03–2.1%, av. 0.4%, median0.3%), ω-oxoacids (0.1–0.9%, 0.4%, 0.3%) and pyruvic acids (0.01–0.3%,0.05%, 0.03%) of OC. Diacid-C/OC ratios are similar to those reported inthe western North Pacific (5.7–11.2%), North Pacific (3.6–16.8%), andSouth China Sea (av. 18.7%) (Fu et al., 2013a, b), but are several timeshigher than those reported in urban/continental aerosols from China(av. 1.3%) (Ho et al., 2007) and Mongolia (av. 0.9%) (Jung et al., 2010).Higher diacid-C/OC ratios in the marine aerosols than those fromChina and Mongolia suggest that photochemical aging of organic aero-sols is significant in the remote marine atmosphere during long-rangetransport (Fu et al., 2013a, b).

    Fig. 6 shows spatio-temporal distributions of relative abundances ofdiacid-C in aerosol organic carbon (OC). In general, higher diacid-C/OCratios were detected in the North Pacific than those in the South Pacific.In the North Pacific, higher diacid-C/OC ratios were obtained in thewestern North Pacific Rim, where the influences of polluted continental

    Fig. 6. Spatio-temporal distributions of contributions of total diacids to organic

    air masses are important than the central North Pacific (see Figs. 6 and3). Previous studies reported that atmospheric transport of O3 and itsprecursors such as NOx and VOCs from East Asia to the western NorthPacific have increased significantly (Hoell et al., 1996; Naja andAkimoto, 2004). Tropospheric O3 plays a crucial role in controlling theoxidizing capacity of the marine atmosphere. Hence, we suspect thatdiacid-C/OC ratios may be intensified over the western North Pacificunder highly oxidizing atmospheric condition.

    Among the North Pacific aerosol samples, the highest diacid-C/OCratio (10.6%) was observed in the central North Pacific around 29°N(Fig. 6), where contribution of oxalic (C2) acid to aerosol OCmaximized(6.6%). 7-day backward air masses trajectory revealed that the samesample (29°N) is highly impacted by the continental air mass fromMongolia (Fig. 3). Among the South Pacific samples, highest diacid-C/OC ratio was observed around 25°46′S as shown in Fig. 6, which is influ-enced by the continental air masses from Tasmania (see Fig. 3). Theseresults again support that photochemical aging of continental aerosolsand precursors is significant during long-range atmospheric transportover the ocean.

    3.4. High abundances of oxalic acid and its precursors over the westernNorth Pacific associated with continental outflow

    Oxalic acid was the most abundant diacid species during the cruise,which comprises 65% of total diacids. The five samples (QFF 590 and603–606) that were collected in the western North Pacific (35°N–25°N) are highly influenced by continental air masses (see Figs. 2 and3). In these samples, abundances of oxalic acid (C2) are 5 times higherthan the rest of samples from the North and South Pacific (Fig. 8a). Inthe western North Pacific, we found higher abundances of C2 togetherwith glyoxylic acid (ωC2) andmethylglyoxal (MeGly). In the same sam-ples, ωC2 is 8 times more abundant than the rest of samples from theNorth Pacific and 6 timesmore abundant than those from the South Pa-cific (Fig. 8b). Likewise, abundances of MeGly in the same samples are16 times higher than the remaining samples from the North Pacificand 10 times higher than the South Pacific samples (Fig. 8c). Interest-ingly, samples enriched withωC2 andMeGly are influenced by the con-tinental outflows fromNorth China, Japanese Islands and Siberia, wherefossil fuel and biomass burning emissions are very intensive. Asdiscussed earlier, abundances of C2 in those samples are well correlatedwithωC2 andMeGly, indicating thatωC2 andMeGly are photochemical-ly produced from continent-derived VOCs and their aqueous-phasephotooxidation may considerably contribute to the significant

    carbon in the marine aerosols collected from the North and South Pacific.

  • 165M.M.M. Hoque et al. / Atmospheric Research 185 (2017) 158–168

    production of oxalic acid during long-range atmospheric transport(Zhang et al., 2010).

    3.5. Secondary formation of short chain (C2–C3) diacids over the remotePacific

    Oxalic (C2) acid was the dominant diacid species in themarine aero-sols studied. However, abundances of C2 were found to fluctuate in theaerosols from the North and South Pacific (Fig. 5a, b, c), which might beoccurred due to the variability of the ambient air temperature, photo-chemistry and the availability of precursor organic compounds. For ex-ample, the dominant presence of succinic (C4) acid has been reported inthe Antarctic aerosols (Kawamura et al., 1996), spring snowpack sam-ples from the Arctic (Narukawa et al., 2002), winter aerosols fromTokyo (Sempéré and Kawamura, 1994), and Los Angeles aerosol sam-ples (Kawamura et al., 2001). Thus, higher relative abundance of C4 isa common trend in the cold environmental condition (Sempéré andKawamura, 2003). But in themarine aerosols, succinic acid is often con-verted to oxalic and malonic acids due to photochemical degradation(Kawamura and Sakaguchi, 1999; Hoque et al., 2015). Fig. 7a showsspatio-temporal distributions of C2/C4 ratios. The C2/C4 ratios are higherin the equatorial regions of the North and South Pacific than those of thehigher latitudes. These results indicate that photochemical degradationof C4 to C2 maximized in the warmer regions of the central Pacific.

    Moreover, correlation between relative abundance of C4 diacid andambient air temperature has been reported to be negative by Sempéréand Kawamura (2003). As reported by Miyazaki et al. (2010), C2 was

    Fig. 7. Spatio-temporal distributions of the concentration ratios of (a) oxalic/succinic acid (C2/Cduring T/V Bousei Maru cruise.

    strongly correlated with C4 (r2 = 0.83), where C4 has been oxidized toproduce C2. In contrast, our data set showed aweak correlation betweenC2 and C4 diacid (r2 = 0.29). This result may indicate that photochemi-cal degradation of C4 is not themain source of C2 in this study. However,Bikkina et al. (2014) proposed that glyoxylic (ωC2) acid, glyoxal (Gly),methylglyoxal (MeGly) and pyruvic (Pyr) acid, which are the oxidationproducts from marine and continent, are derived from volatile organiccompounds (VOCs). These oxidation products are further oxidized toproduce oxalic acid (Carlton et al., 2006, Nguyen et al., 2010). Abun-dances of VOC oxidation products are 2–16 times higher in the samplesinfluenced by continental air masses than the rest of samples collectedfrom the North and South Pacific (see Figs. 2, 3 and 9). It is of interestto note that, based on backward airmass trajectories, 86%of theVOCox-idation products are originating from continental sources. Moreover,sum of these oxidation products (Pyr + Gly + ωC2 + MeGly) showeda strong correlation with C2 (r2 = 0.84). This finding suggests that pho-tochemical oxidation of VOCs is themajor source of C2 (28%) in the pres-ent study rather than photochemical degradation of C4 to C2 (14%).

    In the ambient atmosphere, succinic (C4) acid can be degraded tomalonic (C3) acid due to the abstraction of its hydrogen atom by hy-droxyl radicals followed by subsequent decarboxylation and thus C3/C4 ratios can be used as an indicator of enhanced photochemical agingof diacids (Kawamura and Ikushima, 1993). The C3/C4 ratios in the cur-rent study varied from 0.8 to 7.6 (av. 3.0, median 2.0). These values arecomparable to those (av. 4.0) reported for the Pacific Ocean aerosols(Kawamura and Sakaguchi, 1999), marine aerosols collected during around-the-world cruise (0.9–5.8, av. 2.3) (Fu et al., 2013a, b), and

    4), and (b) malonic/succinic acid (C3/C4) in the North and South Pacific aerosols collected

  • Fig. 8. Latitudinal distributions of (a) oxalic acid, (b) glyoxylic acid, and (c) methylglyoxalin the marine aerosols collected from the North and South Pacific.

    Fig. 9. Latitudinal distributions of (a) pyruvic acid, (b) glyoxal, (c) glyoxylic acid, and(d) methylglyoxal in the marine aerosols collected during the North and South Pacific.

    166 M.M.M. Hoque et al. / Atmospheric Research 185 (2017) 158–168

    Chichijima Island aerosols in the western North Pacific (av. 2.1)(Mochida et al., 2003), but are several times higher than those ofurban aerosols from Tokyo (av. 1.6) (Kawamura and Ikushima, 1993),Chinese cities (0.74) (Ho et al., 2007), Chennai, India (av. 1.4)(Pavuluri et al., 2010), and New Delhi (av. 0.6) (Miyazaki et al., 2009).Higher C3/C4 ratios in the marine aerosols than in the urban aerosolssuggest that C3 is photochemically produced from C4 during long-range atmospheric transport from the continents to the remote marineatmosphere or in their source region (Fu et al., 2013a, b).

    As shown in Fig. 7b, spatial distributions of C3/C4 ratios show pat-terns similar to those of C2/C4 ratios with higher values in lower lati-tudes of the North and South Pacific. This result suggest that anenhanced photochemical production of C3 from its precursor (C4) inthe warmer regions. Similar occurrences have been reported in the ma-rine aerosols collected from Gosan site of Jeju Island in the westernNorth Pacific Rim, where C3/C4 ratios were enhanced in summer(Kundu et al., 2010). During the present expedition, succinic (C4) acidwas found to strongly correlate withmalonic (C3) acid (r2= 0.89), indi-cating that photochemical degradation of C4 is the source of C3.

    4. Conclusions

    We report the spatial distributions of water-soluble dicarboxylicacids and related compounds (ω-oxoacids, pyruvic acid, and α-dicarbonyls) and fatty acids in the atmospheric aerosols from theNorth and South Pacific. The abundances of diacids and related com-pounds were found to be 3–6 times higher over the North Pacific thanthe South Pacific. Molecular distributions of dicarboxylic acids in themarine aerosols showed the predominance of oxalic (C2) followed bymalonic (C3) and succinic (C4) acids. Abundances of oxalic acid in the

    aerosols from the western North Pacific are 5 times higher than therest of samples collected during the cruise. The western North Pacificis most likely influenced by the East Asian outflows, which may leadsto higher abundances of water soluble-organics in the oceanic region.Although C3 is more abundant than C4, one sample collected in thecoastal western North Pacific showed a predominance of C4 over C3,where a continental influence was significant from the Mongolian re-gion due to air mass backward trajectory.We found a strong correlation(r2 = 0.89) between C3 and C4 diacids, indicating that photochemicaldegradation of C4 is the source of C3 in the remote marine atmosphere.Diacids accounted for 1.6 to 14% of OCwith higher values in thewesternNorth Pacific. This finding together with 7-day backward air mass tra-jectories indicates that photochemical aging of continental aerosolshave been preceded during a long-range atmospheric transport to theoutflow regions of Asian dusts and precursors.

    Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.atmosres.2016.10.022.

    Acknowledgments

    This studywas in part supported by the Japan Society for the Promo-tion of Science (JSPS) through grant-in-aid No. 24221001.We acknowl-edge the cruise members for the technical supports during the cruise ofT/V Bousei Maru of Tokai University.

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    Spatio-temporal distributions of dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid, α-dicarbonyls and fatty acids ...1. Introduction2. Methods3. Results and discussion3.1. Composition and general characteristics of marine aerosols3.2. Molecular distributions of diacids, ω-oxoacids, pyruvic acid, fatty acids and α-dicarbonyls3.3. Spatial distributions of diacids and related compounds and contributions (%) of diacids to aerosol OC over the Pacific3.4. High abundances of oxalic acid and its precursors over the western North Pacific associated with continental outflow3.5. Secondary formation of short chain (C2–C3) diacids over the remote Pacific

    4. ConclusionsAcknowledgmentsReferences