Diurnal Variations in Partitioning of Atmospheric Glyoxal and

Publication Date (Web): July 19, 2018. Copyright © 2018 American ... The dicarbonyls were also observed on Mt. Fuji (3776 m) in the free troposphere...
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Diurnal variations in partitioning of atmospheric glyoxal and methylglyoxal between gas and particles at the ground level and in the free troposphere Kasumi Mitsuishi, Masakazu Iwasaki, Masaki Takeuchi, Hiroshi Okochi, Shungo Kato, Shin-Ichi Ohira, and Kei Toda ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.8b00037 • Publication Date (Web): 19 Jul 2018 Downloaded from http://pubs.acs.org on July 21, 2018

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ACS Earth and Space Chemistry

Diurnal variations in partitioning of atmospheric glyoxal and methylglyoxal between gas and particles at the ground level and in the free troposphere

Kasumi Mitsuishi1, Masakazu Iwasaki1, Masaki Takeuchi2, Hiroshi Okochi3, Shungo Kato4, Shin-Ichi Ohira1, and Kei Toda1* 1

Department of Chemistry, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555, Japan

2

Faculty of Pharmaceutical Sciences, Tokushima University, 1-78-1, Shomachi, Tokushima 770-8505, Japan

3

Department of Resources and Environmental Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan

4

Department of Applied Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1, Minamiosawa, Hachioji, Tokyo 192-0397, Japan

*Corresponding author: [email protected]

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Abstract This work presents diurnal variations of gas- and particle-phase dicarbonyls (glyoxal (Gly) and methylglyoxal (Mgly)) in the atmosphere, which are important compounds that contribute to the formation and growth of atmospheric particulate matter. In order to obtain variations in partitioning, continuous collection of gaseous dicarbonyls was performed using a parallel plate wet denuder, and at the same time, the dicarbonyls in particle were collected using a spray-type particle collector downstream. Hourly samples were analyzed by high performance liquid chromatography–electrospray ionization–tandem mass spectrometry. This method is advantageous to monitor the gaseous and particulate carbonyls separately without loss during sampling. Sampling was performed in summer and winter in a midsize city (Kumamoto, Japan). The concentrations of the dicarbonyls increased in the summer daytime, which suggests that they are mostly formed by secondary production in the local atmosphere. The dicarbonyls and formaldehyde (HCHO) were found in both gas and particle phases, and partitioning to the particle phase was highest for Gly, followed by Mgly, and HCHO. It was observed that the compounds moved to the particle phase in the midnight and early morning hours according to the growth of hygroscopic aerosols in summer. The particle/gas ratio also increased in the presence of high PM2.5, which is transported from the Chinese Continent in winter. The dicarbonyls were also observed on Mt. Fuji (3,776 m) in the free troposphere. From back trajectory data and information on volatile organic compounds, they were most likely produced from relatively long-lifetime organic compounds from the Chinese Continent and biogenic volatile organic compounds emitted in the Japan Alps mountain range. Higher particle/gas ratios at the Mt. Fuji station indicate that low temperatures and high humidity precede the partition. The estimated effective Henry’s law constants for the dicarbonyls, 108 orders in mol/kgH2O/atm for summer data, were much higher than those for ideal liquid/vapor equilibrium but close to reported results obtained by chamber experiments. In the proposed method, oligomers in particle were also counted as the compounds. The dicarbonyl 2 ACS Paragon Plus Environment

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compounds existed up to sub-molar levels in real atmospheric aerosols, which suggests they undergo further reactions in the particle phase.

KEYWORDS: glyoxal, methylglyoxal, partition, particulate matter, Mt. Fuji, parallel plate wet denuder, dinitrophenylhydrazine derivatization, high performance liquid chromatography–tandem mass spectrometry.

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1. INTRODUCTION Carbonyl compounds are primarily emitted from anthropogenic sources and are also secondarily produced in the atmosphere from biogenic volatile organic compounds.1-3 The simplest and most abundant carbonyl (30–50% of atmospheric carbonyls) is formaldehyde (HCHO), which was classified as a Group 1 carcinogen in 2012 by the International Agency for Research on Cancer (IARC) of the World Health Organization.4,5 HCHO is a major component in atmospheric particles (~1% of fine particles (PM2.5)) as HCHO molecules in the atmosphere enter PM2.5 more during hygroscopic aerosol growth.6 In addition to monocarbonyls, dicarbonyls such as glyoxal (Gly) and methylglyoxal (Mgly) have attracted attention because of their unique physical and chemical properties. Gly and Mgly are produced from volatile organic compounds such as isoprene.7,8 It has been proposed that Gly can be formed from HCHO in ice particles. 9 The dicarbonyls play important roles in the series of photochemical reactions and formation of PM2.5 in the atmosphere, and in further reactions that produce secondary organic aerosol (SOA).10-12 Volatile carbonyls are relatively polar and can be captured in aerosols and contribute to the water-soluble organic carbon content of particles.1,13 Gas-phase hydration of the dicarbonyls accelerates their partitioning into the aerosol.14,15 Gly and Mgly are thought to exist in tetrol and geminal diol forms, respectively, and are transformed to glyoxylic acid hydrate and oxalic acid in the aerosol.7 The aldehydes accelerate particle growth via acid-catalyzed particle-phase reactions.16-19 The behaviors of Gly and Mgly in particles have been investigated recently, and they were found to produce light absorptive products in ammonium sulfate/nitrate solutions.20,21 These dicarbonyls may be incorporated into sulfate-based hygroscopic aerosols to produce brown carbon,22,23 and may react with ammonium and amino acids to produce imidazoles and imines. 24 - 26 Photochemical reactions in atmospheric particles reduce the Gly concentration in a hygroscopic aerosol.27 4 ACS Paragon Plus Environment

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Despite the interest in Gly and Mgly in atmospheric particles, detailed data for these compounds in the particle phase are not available. The above studies on Gly and Mgly in aerosols have mostly used model simulations and bulk water experiments. Few studies have measured dicarbonyl concentrations in real atmospheric particles. In one study, dicarbonyls in particles were collected on quartz fiber filters, extracted into water, derivatized to butyl acetals, and analyzed by GC/MS.28-30 Samples were collected for 7 days each and the dicarbonyls were analyzed together with dicarboxylic acids to investigate seasonal variations. Because dicarbonyls are highly volatile, some loss may occur during the filter sampling. So, Matsunaga et al. and Yan-Li et al. sampled airborne dicarbonyls using a system with a filter and derivatizing reagent-coated solid denuder, to obtain several sets of data for Gly and Mgly.31,32 The solid denuder was placed downstream of the filter to collect dicarbonyls desorbed from the trapped particles. Variations were studied with time resolutions of 4–6 h, but the data were limited, and diurnal variation was not investigated in detail. The aim of this work was to investigate the dynamics and partitioning of Gly and Mgly between gas and particle phases and to establish a method for the investigation. Gas- and particle-phase dicarbonyls were collected continuously using a parallel plate wet denuder (PPWD) and particle collector (PC), respectively. The PPWD collected gaseous species selectively, and dicarbonyls contained in particles passed through the PPWD and were extracted into nebulized water in the PC. The collected dicarbonyls were derivatized with dinitrophenylhydrazine (DNPH) for high-performance liquid

chromatography

coupled

with

electrospray

ionization–tandem

mass

spectrometry

(HPLC-ESI-MS/MS). The dicarbonyl molecules react with two molecules of DNPH to form Gly-(DNPH)2 and Mgly-(DNPH)2 in the presence of excess derivatizing reagent. Samples were collected at Kumamoto University (Japan), and on the top of Mt. Fuji, which is the highest point in Japan. Pollution from PM2.5 is one of the main environmental issues in west Japan due to its transportation from the Chinese Continent, and Kumamoto is a midsize city in the west end of 5 ACS Paragon Plus Environment

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Japan. In contrast to the long-distance transportation of atmospheric pollution, the contribution of locally produced particles is not well-discussed for Japanese ambient particles. Dicarbonyls at Kumamoto are good indicators of the secondary organic aerosols found in the representative city of western Japan. On the other hand, a station on Mt. Fuji is in the free troposphere where the effect of locally emitted compounds is expected to be negligible. Also, behavior of the dicarbonyls may be significantly different at the two stations due to relatively lower temperatures and higher humidity at the Mt. Fuji station. The comparisons would give basic information about atmospheric dicarbonyls, and our new tool for their analysis provides detailed information about variations in the partitioning.

2. EXPERIMENTAL 2.1. Analysis campaigns and sampling sites. Air monitoring was performed in a nine-story building (Faculty of Science, Kumamoto University) located at N 32.81 and E 130.73 during summer (May 12–16, 2016) and winter (December 6–10, 2016). Each air sample was aspirated from outside a laboratory on the ninth floor. The sampling site was in the suburban area to the northeast of Kumamoto city and beside Mt. Tatsuta forest area. There is no stationary pollutant source, and anthropogenic volatile organic compounds (AVOCs) are mostly from vehicles. Biogenic volatile organic compounds (BVOCs) such as isoprene were observed in summer daytime.33 NOx concentrations at Kumamoto are low in summer and high in winter, and 24-h averages are typically at several ppbv and around 20 ppbv, in the respective seasons.34 In winter, the westerlies bring PM2.5 from the Chinese Continent and pollutants such as polyaromatic hydrocarbons were observed at several ng/m3 in winter Kumamoto.35 The PM in this area sometimes consists of desert dust (Kosa) in a special season, but in most seasons secondarily-produced particles are dominant.36 Sampling was also performed during August 18–23, 2017 at a station located on the summit of Mt. Fuji (3,776 m, N 35.36, E 138.72, https://npofuji3776-english.jimdo.com/), which is a typical 6 ACS Paragon Plus Environment

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independent stratovolcano located in east Japan. Electricity was supplied from the base only in summer for the observation campaign.37

2.2. Reagents. An aqueous solution of DNPH (50 w/w%) was obtained from TCI (Tokyo, Japan). The DNPH was purified just before sampling using an established method.38 Briefly, 0.12 g of DNPH was dissolved in a mixture of 24 mL of concentrated HCl, 60 mL of water, and 12 mL of acetonitrile (ACN) to obtain a 6.2 mM DNPH solution. The DNPH solution was purified twice by extracting contaminated DNPH derivatives into 1 mL of carbon tetrachloride. Gly (39 w/w% in water, TCI) and Mgly (40 w/w% in water, Sigma-Aldrich, St. Louis., MO, USA) were diluted in water to obtain a mixed stock solution containing 100 mM of each of the dicarbonyls. The stock solution was further diluted to prepare working standard solutions (1–100 nM). Formaldehyde-d2 DNPH derivative (ChemService, West Chester, PA) was used as an internal standard. Milli-Q water prepared using a Simplicity UV water purification system (Merck Millipore, Darmstadt, Germany) was used throughout the experiments for the dicarbonyl absorbing solution, preparation of the standards, and in the eluent for chromatography.

2.3. Sampling apparatus for collection of gas- and particle-phase dicarbonyls. Gas-phase species were collected by a PPWD,39 and water-soluble species in aerosols were collected by a PC.40 The collection system is shown in Figure 1. The PPWD and PC were constructed in our laboratory. The PPWD was prepared using two acrylic plates, with the air-contacting areas textured to make the surfaces wettable. The effective area of each plate was 62 mm × 415 mm and the plates were placed 3 mm apart to allow for air flow between them. Sample air was introduced from the bottom into the space between the plates at a rate of 3 L/min using an air pump (DA-40S, ULVAC Kiko, Saito, Miyazaki, Japan) and a mass flow controller (SEC-B40, Horiba STEC, Kyoto, Japan). The absorbing solution 7 ACS Paragon Plus Environment

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was introduced from the top of the PPWD at a rate of 1.0 or 0.3 mL/min for each plate and aspirated from the bottom using an eight-port peristaltic pump (Rainin Dynamax RP-1, Mettler Toledo, Greifensee, Switzerland) with Pharmed® tubing (ø 1/32” × ø 5/32” for introduction, ø 1/16” × ø 3/16” for aspiration). The PC consisted of a cylindrical housing (64 mm i.d. × 93 mm height) with a nebulizer in the bottom to create an absorbing water mist from sample air coming out of the PPWD. Air passed through a hydrophobic membrane made of PTFE (PF020 ø 47 mm, Advantec, Tokyo, Japan), whereas water was blocked by the filter and collected. Water samples from the PPWD and PC were transferred to a fraction collector (CHF122SC, Advantec) and collected in 18-mL glass test tubes. The fraction collector was modified to simultaneously collect two solutions (dFC), one each for the gas and aerosol (Section 1 of Supporting Information).

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Figure 1. Gas/aerosol sample collection system using parallel plate wet denuder (PPWD) and particle collector (PC) sampling devices. A cross-sectional schematic of the PPWD is shown on the left, and a photograph taken from the front is shown on the right. Abbreviations: AP, air pump; MFC, mass flow controller; PP, peristaltic pump; dFC, dual fraction collector; and UPW, ultrapure water.

2.4. Analysis of collected dicarbonyls. A 1-mL aliquot of each water sample was placed in a vial and then 10 µL of 6.2 mM DNPH solution was added for HPLC analysis. The derivatized dicarbonyls were analyzed by HPLC-ESI-MS/MS41,42 (LCMS-8040, Shimadzu, Kyoto, Japan) equipped with a reversed-phase chromatography column (Sunfire, ø 2.1 mm × 150 mm, Waters, Milford, MA, USA), which was maintained at 40°C. The injection volume was 50 µL. The eluent was a water/ACN mixture, and the ACN proportion was initially 45% and then increased to 60% at 5 min, 75% at 8 min, and 100% between 15–25 min. From 25–40 min, the ACN proportion was reduced to 45% to condition the column for the next analysis. A diversion valve was used to introduce the eluent from 7–30 min into the MS/MS detector. Gly and Mgly eluted from the column at 13.3 and 14.4 min, respectively, and were ionized by ESI with nitrogen as the nebulizing gas (3 L/min) and drying gas (15 L/min). The desolvation temperature was 250°C.

3. RESULTS AND DISCUSSION 3.1. Collection and analysis of dicarbonyls. Sampling was performed based on selective gas collection followed by extraction of water soluble species into a sprayed absorbing solution from aerosol. The collection efficiency, f, of the PPWD for gaseous species was examined by passing the dicarbonyl vapors through two PPWDs connected in series. The f value was obtained from the amounts of dicarbonyls collected upstream (Q1) and downstream (Q2).  =1−

 (1) 

The f values experimentally obtained were 99.92 ± 0.12% for Gly and 99.91 ± 0.02% for Mgly (n = 3) at 9 ACS Paragon Plus Environment

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a sampling rate of 3 L/min. The absorbing solution on the PPWD walls acted as a good sink for both gaseous Gly and Mgly. Typical collection efficiencies for particles obtained in a spreadsheet calculation43 for aerodynamic particles were 0.044% for a 2.5 µm diameter and 0.146% for a 0.5 µm diameter. Thus the PPWD collects gaseous Gly and Mgly quantitatively and particles pass through it quantitatively. The results show that the compounds in the gas and particle phases can be collected separately by the PPWD and PC. The performance of filter sampling was also examined to compare the sampling methods. Gly, Mgly, and HCHO placed on glass fiber filters (ø 37 mm) were analyzed before and after air introduction at 1 L/min for 6 h. The proportions of Gly, Mgly, and HCHO remaining on the filter were only 51.3 ± 8.0, 7.51 ± 0.61, and 1.04 ± 0.05% (n = 3), respectively, of the original quantities after 6 h of air introduction. These results show that approximately half of the Gly was lost and the majority of the Mgly and HCHO did not stay on the filter. Therefore, a conventional filter sampling method is not suitable for collection of particle-phase dicarbonyls. A DNPH-coated denuder could be placed downstream of the filter to catch the dicarbonyl vapors that are lost from the trapped particles,31,32 but this method requires a long sampling time and would make the extraction process complicated. A DNPH-impregnated cartridge is sometimes used for analysis of carbonyls in polluted air,44 but this does not distinguish between gasand particle-phase species. Our method using the combination of PPWD, PC and dFC allows for collection of dicarbonyl compounds in the gas and particle phases separately in a manner similar to the use of PPWD/PC for inorganic acid/base species.39,40 Mass spectra were recorded for the DNPH-derivatized Gly and Mgly (Figure 2). Gly was monitored in negative ion mode at m/z 417 for the precursor ion and m/z 182 for the product ion with a collision energy of 22 eV. The (DNPH)2-Gly was broken into the dinitroaminobenzene anion (m/z 182) and mono-DNPH-derivatized Gly (m/z 235). The peak for m/z 235 was very small compared with that at m/z 182, probably because the mono-DNPH derivative further decomposed to the 10 ACS Paragon Plus Environment

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dinitroaminobenzene anion on collision. For Mgly, precursor and product ions were observed at m/z 431 and 182, respectively, with a collision energy of 24 eV. The HPLC-ESI-MS/MS method was advantageous for trace analysis compared with conventional solid phase extraction (SPE) preconcentration followed by HPLC-UV.45-49 The limits of detection, calculated from three times the baseline noise, for HPLC-ESI-MS/MS were 0.04 nM for Gly and 0.05 nM for Mgly, and these results were approximately 100 times those for HPLC-UV. The detection limit of HPLC-UV could be improved 50 times by SPE preconcentration but the SPE procedure might cause sample contamination. Importantly, the present analytical procedure is simpler than the SPE coupled HPLC methods, which reduces the risk of contamination for trace analysis. Blank values were below 0.5 nM (corresponding to < 0.05 ng/m3 for particulate), which were obtained by adding DNPH reagent to absorbing solutions passed out from PPWD and PC without air introduction. Glyoxal trimer was examined to derivatize with DNPH and the trimer was quantitatively transformed to Gly-(DNPH)2. Also, signal intensities for paraformaldehyde agreed with those for corresponding concentrations of the HCHO monomer. From the experiments, it can be said that oligomers in particle were counted as carbonyl monomers.

Figure 2. Mass spectra of the precursor and product ions for glyoxal and methylglyoxal derivatized with dinitrophenylhydrazine (DNPH). 11 ACS Paragon Plus Environment

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3.2. Variations of dicarbonyls in the atmosphere. The concentrations of Gly and Mgly were analyzed together with HCHO for 5 days (120 h) continuously in both summer and winter at Kumamoto (Figure 3). In the gas phase, the Mgly levels were higher than those of Gly in both summer and winter. The Gly levels were very low (< 50 ng/m3) for most of the winter samples. The levels of both dicarbonyls were higher in the daytime and lower at nighttime, and this indicates that these compounds are mostly produced by photochemical reactions at Kumamoto. Higher levels in summer support this interpretation of the data. Clear daily variation was observed for gaseous dicarbonyls in summer, whereas variation was irregular in winter. In the summer, the concentrations of gaseous dicarbonyls rapidly increased after sunrise, remained relatively high during the daytime, and then decreased in the afternoon. In previous work, we reported isoprene and oxidant levels increased in the summer morning every day at 1 km north of our university.3,33 These were considered as one of the main sources of the dicarbonyls in summer. The concentrations of gaseous Gly and Mgly did not increase in the morning on the last day of summer monitoring because it was raining (Figure S2), and these compounds were scavenged by rain droplets. In winter, while biogenic isoprene was negligible,33 NOx levels were much higher than in the summer and contribution from anthropogenic compounds may be dominant. Higher concentrations of nonmethane hydrocarbon and PM2.5 (see Figure S2 in Supporting Information) also suggested anthropogenic effects on the dicarbonyl production in winter. The concentrations of particle-phase Gly and Mgly were an order of magnitude smaller than the gaseous concentrations. Interestingly, diurnal variation was observed for the particle-phase dicarbonyls in summer, but the particulate HCHO did not show typical diurnal changes (Figure S2), which is consistent with our previous HCHO observations.6 The dicarbonyls might be less reactive than HCHO in particles, and HCHO trapped in particles may be quickly transformed to other 12 ACS Paragon Plus Environment

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compounds in summer daytime.

Winter

Gas

400

Gas

1200

2

Mgly

Insolation (W/m )

Summer 400

Gly

300

300

900

Mgly

Gly

3

Dicarbonyl concentration (ng/m )

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

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200

200

600

100

100

300

0

0 80 70

40

0

Particle

40

Particle

30

30

Mgly

Gly

20

20

10

Gly

10

Mgly

0

0

May 12

May 13

May 14

May 15

May 16

Dec 6

Dec 7

Dec 8

Dec 9

Dec 10

Figure 3. Concentrations of glyoxal (Gly) and methylglyoxal (Mgly) in the gas- and particle-phases in summer and winter at Kumamoto.

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Table 1.

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Daytime and nighttime concentrations of the dicarbonyls and HCHO in gas and particle

phases Summer (May)

Winter (December)

HCHO

Gly

Mgly

(ng/m3)

(ng/m3)

(ng/m3)

HCHO (ng/m3)

Gly

Mgly

(ng/m3)

(ng/m3)

Gas Daytime

1460 ± 520

Nighttime

1260 ± 420

Average

1360 ± 480

D/N ratio

1.16

105

± 45

165 ± 90

838 ± 283

66.9 ± 24.0

126 ± 60

910 ± 365

86.2 ± 40.7

146 ± 78

874 ± 327

1.31

0.921

1.58

14.0 ± 9.25 8.63 ± 8.48 11.3 ± 9.23 1.62

99.6 ± 58.4 59.8 ± 35.0 79.7 ± 52.0 1.67

Particle Daytime

77.9 ± 61.7

18.0 ± 5.8

Nighttime

96.3 ± 72.9

14.9 ± 4.6

Average

87.1 ± 67.9

16.5 ± 5.4

D/N ratio

0.809

1.21

Daytime

1540 ± 540

124 ± 49

Nighttime

1360 ± 450

Average

1450 ± 500

D/N ratio

1.13

12.9 ± 6.2 8.21 ± 3.36 10.5 ± 5.5 1.57

82.5 ± 41.9

2.55 ± 1.79

84.3 ± 57.3

1.92 ± 1.82

6.85 ± 8.20

83.4 ± 50.0

2.23 ± 1.83

9.98 ± 12.9

1.33

1.92

0.979

13.1 ± 15.7

Total 178 ± 94

921 ± 318

16.5 ± 10.2

134 ± 61

994 ± 418

10.6 ± 8.87

66.6 ± 37.3

103 ± 44

156 ± 82

957 ± 371

13.5 ± 10.0

89.7 ± 58.8

1.51

1.33

0.926

81.8 ± 25.6

1.56

113 ± 67

1.69

Daytime: 7 am–7 pm, nighttime: 7 pm–7 am.

3.3. Partitioning between the gas and particle phases. Particle/gas phase ratios (P/Gs, Figure 4) of the dicarbonyls were obtained from the hourly concentrations. Partitioning dramatically changed throughout the day. In summer, the P/G ratios were high at midnight and in the early morning, but low in the daytime. These variations were synchronized with changes in the relative humidity. Therefore, partitioning is likely related to the growth of hygroscopic aerosols. Concentrations of representative ions in the particle phase were 8.4 µg/m3 NH4+, 0.6 µg/m3 Cl-, 2.3 µg/m3 NO3-, and 15.4 µg/m3 SO42- on average during the summer campaign, which indicates the existence of hygroscopic aerosols. A 14 ACS Paragon Plus Environment

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similar pattern was observed in winter, but irregular increases in the P/G ratio were sometimes observed, for example, increases in the morning on December 6, around noon on December 9, and in the afternoon on December 10 were not associated with periods of high humidity. In the first and second of these periods, the PM2.5 level increased to 60 µg/m3 and the dicarbonyls were supposed to be captured in the fine particles. Winter particle ions were 0.23 µg/m3 NH4+, 1.3 µg/m3 Cl-, 7.7 µg/m3 NO3-, and 5.6 µg/m3 SO42-. Ammonia neutralized only part of the particle acids and nitrate was abundant compared to those in summer. These ion concentrations also increased in the events of high PM2.5, and probably they contributed to high partitioning of the dicarbonyls in particles.

Summer

100

RH

80

Gly

0.3

60

0.2

40

0.1

20

0.0

Mgly May 12

May 13

May 14

May 15

May 16

0

2.0

Winter

100

1.6

RH

80

1.2

Mgly

0.8

PM2.5

60

3

0.4

Humidity ( % ) PM2.5 ( µg/m )

0.5

Partition ( P/G ratio )

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

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40

Gly

0.4

20

0.0 Dec 6

Dec 7

Dec 8

Dec 9

Dec 10

0

Figure 4. Partitioning of dicarbonyls in summer and winter. The range on the y-axis for the summer results is different to that for the winter results because the summer P/G ratios were much smaller than those in winter.

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The average P/G ratios were 0.0673, 0.218, and 0.0793 for HCHO, Gly, and Mgly, respectively, in summer (Table 2). The P/G ratios for HCHO and Mgly were almost the same, and the Gly ratio was three times the HCHO and Mgly P/G ratios. These results can be explained using the water solubilities of these compounds. The Henry’s law constants, KH, of HCHO (3,200 M/atm) and Mgly (3,700 M/atm) are almost the same, whereas that of Gly (360,000 M/atm50) is 100 times the KH values of the other carbonyls. Thus, Gly is easily absorbed in hygroscopic aerosols. These KH values are also extremely high compared with known values for N2 (0.00061 M/atm) and O2 (0.0013 M/atm), even with those for water soluble inorganic gases SO2 (2.0 M/atm) and NH3 (54 M/atm). Thus, both Gly and Mgly easily dissolve into hygroscopic aerosols. In winter, the P/G ratios of Gly and Mgly were 0.288 and 0.127, respectively, and were about 1.5 times the ratios obtained in summer. The average temperatures during the summer and winter sampling campaigns were 21.3 and 9.0°C, respectively. Therefore, the KH values of HCHO (11,730 M/atm) and Mgly (15,503 M/atm) in winter were three times larger than in summer (HCHO 4,263 M/atm, Mgly 5,077 M/atm). These values were calculated from reported KH values at standard temperature and temperature coefficients (HCHO: KH° = 3200, ∆H/R = 680051; Mgly: KH° = 3700, ∆H/R = 7500 52 ). Effective Henry’s law constants were estimated from the obtained gas and particle concentrations and water content. Effective Henry’s law constant (effKH) is often used for the carbonyls, which is considered as a parameter showing liquid/vapor equilibrium and oligomerization in the aquatic particle. eff  =

   = × 10 … (2)    

Here, Caw is concentration in aerosol water (mol/kgH2O), P is partial pressure of the compound (atm), Cp is particulate carbonyl concentration (ng/m3), LW is aerosol liquid water (g/m3) obtained from ammonium sulfate and humidity,53 PT is total atmospheric pressure (atm), Cg is gaseous carbonyl 16 ACS Paragon Plus Environment

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concentration (ng/m3), R is gas constant (0.0821 L atm/(K mol)), and T is ambient temperature (K). Note that molecular weights required to calculate Caw and P from Cp and Cg are not shown in eq. 2 because they cancel out each other. The effKH values were on the order of 108, as shown at the bottom of Table 2. Though obtained values were extremely high relative to the physicochemical values for the ideal solution, they were close to laboratory experimental values (~ 108 in mol/kgH2O/atm) reported for (NH4)2SO4 solution.54 Ip et al. used 4 × 109 M/atm as effKH to explain the missing sink of Gly in Mexico City,55 which is a value much larger than our results. One of the reasons for the high effKH compared to the physicochemical value is that the particle was based on a condensed salt solution and the condition is far different from infinite dilute solution. Second, the carbonyl compounds interact with other aerosols, such as oxygenated organic aerosol54 as well as aerosol liquid water, and the estimation was conducted without excluding this. Another reason for the higher effKH in winter is due to adsorption on PM2.5 from the Chinese Continent transported by prevailing westerlies. Third, the compounds may change the existing species to oligomers and polymers in particle, even though they were supposed to be decomposed to monomers and react with DNPH in the absorbing solution with the added derivatizer as confirmed in 3.1. Oligomerizations are reversible reactions.53 Thus, particles hold the carbonyl compounds much more than the ideal simple gas-water equilibrium. The nighttime/daytime partitioning ratios (N/D) were mostly > 1.0 or around 1.0, which means that partitioning shifted to the particle phase more during nighttime. The N/D ratios of Gly in summer (1.35) and winter (1.63) were particularly high. This phenomenon can be explained by higher hygroscopic aerosol growth and higher vapor/aerosol equilibrium (higher KH) during nighttime than during daytime.

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Table 2. Partitioning (P/G ratios*) for the dicarbonyls and HCHO between the gas and particle phases and estimated effective Henry’s law constants Summer (May) HCHO

Winter (December)

Gly

Mgly

HCHO

Gly

Mgly

P/G ratios Daytime

0.0548 ± 0.0421

0.189 ± 0.0534

0.0836 ± 0.0304

0.0920 ± 0.0487

0.219 ± 0.152

0.127 ± 0.103

Nighttime

0.0797 ± 0.0602

0.251 ± 0.112

0.0749 ± 0.0328

0.0910 ± 0.0374

0.357 ± 0.470

0.126 ± 0.159

Average

0.0673 ± 0.0532

0.218 ± 0.093

0.0793 ± 0.0318

0.0915 ± 0.0434

0.288 ± 0.355

0.127 ± 0.134

N/D ratio*

1.45

1.35

0.896

0.988

1.63

0.990

4.4

1.3

41

21

8

Effective Henry’s law constant (x 10 ), mol/kgH2O/atm) 0.31

10

*Abbreviations: P/G ratio, particle/gas ratio; N/D ratio, P/G ratio at nighttime (7 pm to 7 am) versus daytime (7 am to 7 pm).

3.4. Dicarbonyl levels on top of Mt. Fuji and comparison with Kumamoto data. Sampling

was conducted for 4.5 days at the summit. Even on the independent peak, Gly and Mgly were detected from both the gas and particle phases. Clear diurnal variation was not observed during the sampling campaign (Figure 5). From August 22 until the morning of August 23, the dicarbonyl levels were relatively low in both the gas and particle phases. During this period, O3 and CO were mostly below 30 ppbv and 100 ppbv, respectively. By contrast, on August 19, the gas phase Gly and Mgly levels were high around 60 ng/m3 and the particle phase levels were near 20 ng/m3, while O3 and CO levels were higher (around 60 ppbv and 100–150 ppbv, respectively). When higher dicarbonyls were observed, atmospheric transport was from Northern China on August 19 and Southern China on August 20 and 21 (see back trajectory data in Figure S3 of Supporting Information). On August 22, atmospheric transport was from the Pacific Ocean, which is when the dicarbonyl levels were relatively low. Thus, the dicarbonyl levels on Mt. Fuji were related to the origin of air mass. The dicarbonyls produced in China may not be retained due to their short lifetime (lifetimes of Gly and Mgly are reported as 2.5 and 1.5 h, respectively. 56 ), but the transferred polluted air might enhance the secondary reactions to produce dicarbonyls around the Mt. Fuji summit. Acetylene is known as the 18 ACS Paragon Plus Environment

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major anthropogenic source of Gly.55 Such relatively stable compounds (lifetime = 12 days57) are part of the East Asia Continental pollution and might act as the source of Gly. Domestic BVOCs were possible sources as well. Isoprene was sometimes observed in high concentrations at Mt. Fuji. In fact, increases in isoprene levels up to several ppbv were observed on the nights of August 20 and 21. The air mass passed above Central and Southern Japan Alps mountain regions before reaching Mt. Fuji.58 The BVOCs pumped to the free atmosphere in the mountain range gathered in the air being transported from the Chinese Continent to act as sources of the dicarbonyls. Partitioning of Gly and Mgly dramatically changed during the Mt. Fuji sampling campaign. The typical ranges for the daytime and nighttime P/G ratios were 0.1–0.3 and 0.6–0.8, respectively, and some P/G ratios at nighttime were > 1.0. Overall, the ratios were lower in the daytime than at nighttime, which agreed with the data obtained in Kumamoto.

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Figure 5. Glyoxal (Gly) and methylglyoxal (Mgyl) concentrations found in samples from the top of Mt.

Fuji. Partitioning results for the dicarbonyls are presented together. In the top panel, “solar” indicates the hourly sunshine duration as a percent. The ambient temperature and levels of O3 and CO are shown together with the solar index. No data were recorded for Gly and Mgly from midnight to 7 am, August 20 because of an electrical fault at the Mt. Fuji summit station.

The results obtained in the three campaigns are summarized in Figure 6. The highest Gly and Mgly concentrations were obtained in Kumamoto in summer. In winter, the Gly levels in both the gas and particle phases were very low, at approximately 1/8th of the summer levels. The Mgly levels in winter were almost the same as those in summer, especially for particle-phase Mgly. The Gly/Mgly ratio was higher in summer (0.656) and lower in winter (0.149). In summer, biological origins such as isoprene were supposed to be dominant and they produce both Gly and Mgly. In winter, on the other hand, the majority of sources are anthropogenic and Gly concentrations were much lower while Mgly 20 ACS Paragon Plus Environment

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might be produced from anthropogenic acetone, isoalkanes, and alkenes. Acetone is one of the major compounds in diesel automobile exhaust,59 and the second largest origin of Mgly.55 Acetone was a possible major source in winter at Kumamoto to make the Gly/Mgly ratio small. Details of the components are not available, but nonmethane hydrocarbons during the summer and winter monitoring were 65 ± 28 and 169 ± 104 ppbv, respectively (Figure S2), which suggests higher anthropogenic VOCs in winter. The reason for the high Gly/Mgly ratio at Mt. Fuji (0.828) is uncertain, but the same tendency was observed in the preliminary monitoring conducted in August 2016. Photolysis is the main sink for both compounds55 and strong UV radiation may accelerate the decomposition of Mgly due to a higher quantum yield (0.107) than that of Gly (0.029).60 Weather on Mt. Fuji was mostly fine as the solar radiation time shows in Figure 5. Also, OH radical formations were supposed to be higher on the mountain due to the strong UV radiation, and an abundance of OH would lead to the removal of more Mgly than Gly, which have rate constants of 1.15 × 10-11 and 1.73 × 10-11 cm3/(molecule s) for Gly and Mgly, respectively.59 Even at the Mt. Fuji summit station, the dicarbonyls were present (total concentrations: Gly 30.9, Mgly 37.3 ng/m3 on average) in comparable levels to those in Kumamoto (Gly 103 and Mgly 157 ng/m3 in summer, Gly 13.4 and Mgly 89.7 ng/m3 in winter), and especially the levels of particle-phase Gly (7.1 ng/m3) and Mgly (7.7 ng/m3) in the free troposphere were close to those in Kumamoto (Gly 16.5 and Mgly 10.5 ng/m3 in summer, Gly 2.2 and Mgly 10.0 ng/m3 in winter). Possible origins of Gly and Mgly at Mt. Fuji have been discussed previously. The highest P/G ratio was obtained on the Mt. Fuji summit. The temperature at the Mt. Fuji summit station was between 4 and 8°C (5.6 ± 1.5°C), which is almost the same as that in winter in Kumamoto (8.9 ± 3.8°C). The average relative humidity (80.2 ± 17.3%) on Mt. Fuji was higher than that in winter in Kumamoto (72.3 ± 17.3%). The conditions on Mt. Fuji were more conducive to hygroscopic aerosol growth than in Kumamoto, and this would contribute to the higher partitioning. 21 ACS Paragon Plus Environment

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Mgly

150 100 50 0

May Dec Aug Kumamoto Fuji

May Dec Aug Kumamoto Fuji

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Particle

1.0 0.8

20 15 10

Gly

M gly

May Dec A ug

M ay Dec Aug Kumamoto Fuji

0.6 0.4 0.2

5 0

Partition

M gly

G ly

P/G ratio

Gly

3

200

Gas Gly, Mgly (ng/m )

250

3

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

Gly, Mgly (ng/m )

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M ay D ec A ug Kumam oto Fuji

M ay D ec A ug Kum amoto Fuji

0.0

Kumamoto Fuji

Figure 6. Comparison of the concentrations and partitioning of glyoxal (Gly) and methylglyoxal (Mgly).

3.5. Dicarbonyls in particles and at the air/particle interface. From our analytical results,

Gly and Mgly in particle were 0.17 ± 0.13 and 0.093 ± 0.058 % of PM2.5, respectively, in the summer of Kumamoto, and they were 0.011 ± 0.010 and 0.049 ± 0.058 % in winter. Gly and Mgly contributed to the particle matters more in summer. The dicarbonyls were abundant compounds of fine particles in summer while long transportation from China is the main origin of aerosols in winter. As mentioned before, oligomers and polymers in particles were detected as well as their monomers by the spray scrubbing followed by DNPH derivatization. Therefore, the dicarbonyls accumulated as oligomers were counted, and determined concentrations were much higher than those estimated from vapor liquid equilibrium. The oligomers become larger molecules, such as humic-like substances, which were detected in the sub-µg/m3 order at the Mt. Fuji station.61 They are part of large organic carbon molecules, and particulate organic carbon is in the µg/m3 order in early summer of Kumamoto.36 A graphic presentation of the behavior of Gly and Mgly in the gas and particle phases is presented in Figure 7. Concentrations of atmospheric Gly and Mgly were on the same order and an order smaller than that of HCHO. Diurnal variations suggest that the compounds were mostly 22 ACS Paragon Plus Environment

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secondarily produced in summer. The partitioning results showed that Gly and Mgly were absorbed in particles more so when the relative humidity was high. This movement was accelerated by hygroscopic aerosol growth and by the hydration of Gly and Mgly. Hygroscopic aerosol growth increases exponentially with increases in relative humidity, and pronounced growth is expected under saturated conditions.53 This would increase the capacity of the aerosol for Gly and Mgly. Kroll et al. reported that hydrated Gly and Mgly formed even in the gas phase,14 and the hydrated Gly and Mgly are expected to have higher affinity to water vapor and water droplets than anhydrous compounds. Thus, partitioning to the particle phase occurred under high relative humidity. In particles, Gly and Mgly are in tetrol and diol forms in acidic aerosols,16,17 and they may undergo further reactions. Gly and Mgly are present in very high concentrations in hygroscopic aerosols. Our estimated concentrations were up to the sub-molar order in hygroscopic aerosol particles (Figure S4 in Supporting Information). Interestingly, the calculated concentrations in the particles reached maximum around noon if the dicarbonyls existed only in hygroscopic aerosols. This suggests that dicarbonyls enter the particles during hygroscopic aerosol growth in the nighttime and early morning, the trapped dicarbonyls then are not released well to the gas phase when the hygroscopic aerosol shrinks. A vapor/aerosol equilibrium is not reached with the particulate dicarbonyls as in the gas/particle interface in Figure 7. The very high concentrations in the particle phase suggest that dimerization and oligomerization, as proposed by chamber experiments,10,19 occur. Gly and Mgly react with ammonium in the particles, which is present at a high concentration, to form nitrogen containing compounds such as imidazoles22-24 and further complicated compounds.62-64 These in-particle reactions confirmed from chamber experiments are supported by our atmospheric data, in which the concentrations of Gly and Mgly increase up to sub-molar levels and NH4+ at molar levels in the hygroscopic aerosol. Also, Gly and Mgly in such high concentrations in particle may react with sulfite to become hydroxyalkanesulfonate to keep tetravalent sulfur in aerosol.65,66 23 ACS Paragon Plus Environment

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Figure 7. Behavior of glyoxal (Gly) and methylglyoxal (Mgly) in the gas and particle phases.

Abbreviations: BVOCs, biogenic volatile organic compounds, and SOA, secondary organic aerosol.

4. CONCLUSION

We studied detailed variations of the levels of dicarbonyls and their partitioning between gas and particle phases in a city and on Mt. Fuji. In summer, the dicarbonyl levels were high and diurnal variations were observed. This suggests that Gly and Mgly were mainly produced by secondary formation in photochemical reactions in the summer. The P/G ratio in summer increased with hygroscopic aerosol growth. Dicarbonyl levels on Mt. Fuji were affected by atmospheric transport from China and probably by BVOCs produced in the Japan Alps mountains. Partitioning was higher on Mt. Fuji than in the city because the conditions were conducive for hygroscopic aerosol growth and increased the compounds’ water solubilities. The effKH estimated for the compounds in summer, ~108, are on the same order as that reported in chamber experiments, while they are much higher than the physicochemical values for the ideal solution. In winter, effKH are about five times larger. The physicochemical constants are three times larger because of lower temperature. In addition, the carbonyls adsorbed on particles other than hygroscopic ones might be counted and this might lead to 24 ACS Paragon Plus Environment

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the overestimation of effKH for winter where PM2.5 is coming from China. We estimated that dicarbonyls in the hygroscopic aerosol were present at sub-molar levels in the particle shrinking process, and these particles could act as condensed micro reactors for the dicarbonyls. Therefore, further reactions of the dicarbonyls could occur in the particles. The obtained results for the real atmosphere provide useful information to investigate the chemistry occurring in atmospheric aerosols. This information could support bulk solution-based experiments and theoretical approaches. The gaseous and particulate analytes were collected separately using PPWD, PC, and dFC, and were analyzed by HPLC-ESI-MS/MS. This method is useful for the analysis of atmospheric compounds existing in both gas and particle phases at trace levels and can be used to investigate the dynamics of these compounds in the atmosphere. It is an attractive method for investigation of atmospheric chemistry and for the monitoring of atmospheric polar and volatile organic compounds.



ACKNOWLEDGMENTS

This work was supported by KAKENHI, Grants-in-Aid for Basic Research (B) (Grant No.16H04168) from the Japan Society for the Promotion of Science. We thank all students who helped with the analyses, people who supported Mt. Fuji sampling, and members of NPO Mount Fuji Research Station. We thank professor Kazuhiko Miura and his student, Mr. Shintaro Yokoyama, for valuable information about upwind/downwind during the Mt. Fuji sampling, and Gabrielle David, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.



ASSOCIATED CONTENT

Supporting Information

The supporting information is available free of charge on the ACS Publications website at DOI: 10:1021/acsearthspacechem.xxxxxxx. 

AUTHOR INFORMATION 25 ACS Paragon Plus Environment

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Corresponding author

* Phone: +81-96-342-3389. E-mail: [email protected] ORCID

Kei Toda: 0000-0001-6577-1752 Shin-Ichi Ohira: 0000-0002-5958-339X Masaki Takeuchi: 0000-0001-6193-0074 Notes

The authors declare no competing financial interest.



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