Distributions of Polycyclic Aromatic Hydrocarbons, Aromatic Ketones

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Distributions of Polycyclic Aromatic Hydrocarbons, Aromatic Ketones, Carboxylic Acids and Trace Metals in Arctic Aerosols: Long-Range Atmospheric Transport and Photochemical Degradation/Production at Polar Sunrise Dharmendra Kumar Singh, Kimitaka Kawamura, Ayako Yanase, and Leonard Barrie Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b01644 • Publication Date (Web): 21 Jul 2017 Downloaded from http://pubs.acs.org on July 23, 2017

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Environmental Science & Technology

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Distributions of Polycyclic Aromatic Hydrocarbons, Aromatic Ketones, Carboxylic Acids

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and Trace Metals in Arctic Aerosols: Long-Range Atmospheric Transport and

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Photochemical Degradation/Production at Polar Sunrise

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Dharmendra Kumar Singha, Kimitaka Kawamura*a,b, Ayako Yanaseb and Leonard Barriec

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a

11

b

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c

13

*

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TEL: +81-568-51-9330, FAX: +81-568-51-4736

Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo, Japan

Bolin Centre Research, Stockholm University, Stockholm, Sweden Corresponding author: E-mail address: [email protected]

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ACS Paragon Plus Environment


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Abstract

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The distributions, correlations and source apportionment of aromatic acids, aromatic ketones,

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polycyclic aromatic hydrocarbons (PAHs) and trace metals were studied in Canadian high Arctic

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aerosols. 19 PAHs including minor sulphur-containing heterocyclic PAH (dibenzothiophene)

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and major 6 carcinogenic PAHs were detected with a high proportion of fluoranthene followed

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by benzo[k]fluoranthene, pyrene and chrysene. However, in the sunlit period of spring, their

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concentrations significantly declined likely due to photochemical decomposition. During the

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polar sunrise from mid-March to mid-April, benzo[a]pyrene to benzo[e]pyrene ratios

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significantly dropped and the ratios diminished further from late April to May onwards. These

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results suggest that PAHs transported over the Arctic are subjected to strong photochemical

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degradation at polar sunrise. Although aromatic ketones decreased in spring, concentrations of

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some aromatic acids such as benzoic and phthalic acids increased during the course of polar

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sunrise, suggesting that aromatic hydrocarbons are oxidized to result in aromatic acids. However,

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PAHs do not act as the major source for dicarboxylic acids of low molecular weight (LMW)

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diacids such as oxalic acid that are largely formed at polar sunrise in the arctic atmosphere

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because PAHs are one to two orders of magnitude less abundant than LMW diacids. Correlations

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of trace metals with organics, their sources and the possible role of trace transition metals are

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explained.

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Keywords: Alert aerosols; PAHs; aromatic ketones; aromatic acids; polar sunrise;

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photochemical decomposition; anthropogenic emission; long-range atmospheric transport, trace

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elements

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1. Introduction

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The Arctic, which is covered by the Eurasian and North American continents, is known

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to receive polluted air masses containing organic and inorganic contaminants from the northern

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mid-latitudes by long-range atmospheric transport.1,2 Sea-to-air flux of marine organic materials

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are limited during winter due to the coverage of sea ice in the Arctic Ocean and atmospheric

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transport of aerosols and their precursor gases are only the sources of the arctic winter aerosols.

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In spring around mid-March when polar sunrise begins, photochemical reactions modify the

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atmospheric composition of arctic aerosols; for example, formation of sulphate via gas-to-

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particle conversion is enhanced2,3 as well as secondary production of water-soluble dicarboxylic

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acids.4,5 The previous polar sunrise experiments showed that organic pollutants transported to the

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Arctic from mid-latitudes of Eurasia, Asia and North America are severely subjected to

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photochemical oxidation in the arctic atmosphere.2,6

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Fu et al.1 reported that, during winter-spring season, sudden appearance of solar

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irradiance and long-range atmospheric transport are the key components regulating the chemical

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composition of organic aerosols in the atmosphere of the Arctic. Furthermore, a distinct rise in

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ambient temperature from winter to spring substantially impacts the partitioning of semivolatile

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organic compounds between gas and particle in the atmosphere.

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Aromatic hydrocarbons are one of the typical organic pollutants emitted from fossil fuel

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combustion and biomass burning processes. They should be long-range transported in the

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atmosphere to the Arctic in winter and spring. Latitudinal distributions of PAHs in the deep-sea

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sediments from the equatorial to northern North Pacific at 175°E transect showed that

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concentrations of PAHs increase from the equatorial Pacific to the northern North Pacific nearby

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the Bering Sea7, suggesting that anthropogenic PAHs are long-range transported over the high

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altitudes in the Northern Hemisphere although they are deposited by wet/dry processes during

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the transport across the ocean and are perched in the deep-sea ocean floor via sedimentation

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processes. Zhou et al.8 reported that interment of PAHs by solid organics is a feasible mechanism

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to restrain the heterogeneous/multiphase reaction during long-range atmospheric transport for

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several days to weeks. Although the heterogeneous reactivity of surface-bound PAHs is

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exceedingly fast in the atmosphere, the above-mentioned mechanism may substantially extend

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the lifetime of PAHs, allowing them to experience long-range transport to distant locations.8



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The PAHs that escape the wet/dry deposition in the atmosphere are long-range

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transported to the Arctic. Deposition of PAH from the atmosphere to snow and ice sheets has

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persisted in the Canadian high Arctic over the last 20 years.9 However, there are only a few

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studies10,1 on PAHs that have been carried out in aerosols of the arctic atmosphere.

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In present study, we analyzed the samples of atmospheric aerosols collected from Alert,

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Canada in the high Arctic to determine PAHs employing a gas chromatography (GC) and

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GC/mass spectrometry (GC/MS). We also measured aromatic ketones, aromatic carboxylic acids

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and trace metals in the arctic aerosols. Here, we investigate seasonal and temporal variations of

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these aromatic compounds with the variations in benzo[a]pyrene to benzo[e]pyrene

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concentration ratios and carcinogenic PAHs from winter to early summer and discuss their

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photochemical behaviours. In addition to speciation and distributions of detected organic species,

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we found unique correlations of trace metals with organic species detected.

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2. Experimental Section

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2.1. Aerosol Samples

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Total suspended particles (TSP) were collected at Alert (82.5°N; 62.3°W) alfresco

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adjacent to the Special Study Trailer Laboratory (175 m a.s.l.) from 19 February to 10 June 1991

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employing a high volume air sampler (without a denuder). Quartz fiber filter (Pallflex 2500

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QAT-UP, 20 x 25 cm), which was pre-combusted at 450 °C for 3 hours to eliminate potential

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organic contaminants. Samples were collected on a weekly basis and field blank filters were

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procured once every four weeks. Average ambient surface air temperature during sample

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collection ranged from -34.9°C in February to -1.9°C in June. The sun fully rises to 24 hours

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above the horizon by April 1 and polar sunrise starts March 5. Before and after sampling, filters

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were stored in a pre-cleaned glass jar (150 ml) with a Teflon-lined screw cap. Samples were

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transported to Tokyo in a cooler at temperature below 0°C and stored in darkness at -20°C until

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the analyses. Details of sampling site and sampling method are provided elsewhere.11,4 Since

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sampling phase (a week) is long, a positive artifact by the adsorption of gaseous organics on the

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quartz filter would be insignificant and not alter their concentrations. We simultaneously

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collected TSP samples using nitrocellulose filters for the analyses of metals at the same site.

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2.2 Extraction and Derivatization

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PAHs, aromatic acids and ketones were extracted with 0.1 M KOH in methanol,

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containing ca. 5% distilled water from sample filters. A pre-cleaned Whatmann GF/A filter was

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used for separation of extracts by filtration. Under ultrasonication the filtrate was further

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extracted with methanol and then dichloromethane. Rotary evaporator was employed for

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concentration of the combined extracts under vacuum and divided into neutral and acidic

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fractions; the neutrals were extracted with n-hexane containing 10% dichloromethane (DCM)

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whereas carboxylic acids isolated by extraction with DCM after acidification with 6 M HCl.

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Four fractions of (1) alkanes, (2) PAHs, (3) ketones/aldehydes and (4) fatty alcohols were

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separated from neutral fraction on a silica gel column chromatography. PAHs and aromatic

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ketones/aldehydes were determined using a Carlo Erba MEGA 5160 gas chromatograph (GC)

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equipped with an on-column injector, a fused silica HP-5 column and an FID detector and

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GC/mass spectrometer (Finnigan MAT ITS-40).12

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The acidic fraction containing various types of carboxylic acids was derivatized with

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14% BF3 in methanol to corresponding methyl esters. The esters were isolated with n-hexane and

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then further separated into three fractions using a silica gel column chromatography;

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monocarboxylic acids, dicarboxylic acids and ketoacids, and hydroxy fatty acids. Carboxylic

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acid methyl esters were determined using a Carlo Erba MEGA 5160 GC as above.12 The desired

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compounds were identified by comparing the GC retention times with those of authentic

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standards. The compound identification was confirmed by the examination of mass spectra

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obtained by a mass spectrometer (Finnigan-MAT ITS-40). All the chemical analyses were

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completed by 1995.

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2.3 Chemical Analysis of Trace Elements

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Vanadium (V), aluminium (Al) and manganese (Mn) were determined using instrumental

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neutron activation analysis (INAA) whereas other trace metals (Zn, Mg, Pb, Fe, Ni, Cu, and Ca)

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were assessed by inductively coupled plasma emission (ICP) spectroscopy. Analysis with INAA

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was executed at the University of Toronto Slowpoke Reactor using short irradiation of 1/8 filter

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in plastic vials followed by counting of the samples in separate nonirradiated vials. Calibration is

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checked by analysis of National Institute of Standards and Technology (NIST) fly ash standards.

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ICP analysis was conducted on the residue of 1/8 of a filter. Filters were ashed at 475°C and



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mixture of ultrapure hydrochloric and nitric acid were used for extraction. Final extracts were

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prepared in 1 mL of concentrated HNO3 and 30 mL distilled deionized water. All the metal

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analyses were completed by 1992.

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2.4 Quality control and Quality assurance

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Field blank filters (n=4) were analyzed for the above-mentioned organic compound

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classes. However, any major peaks were detected for the target compounds on GC

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chromatograms and GC/MS traces. The data shown here are rectified for the field blanks. The

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detection limits were typically < 0.005 pg m-3. Recoveries for authentic standards using the

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analytical procedure presented > 80%. The data were not corrected for the recoveries. Analytical

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errors of major species by duplicate analyses of samples were < 10%. Based on composite

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solutions of metals or on standard reference materials such as NBS1648 urban particulate matter,

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NBS1633a trace elements in coal fly ash, and NRCC MESS-1 marine sediment reference

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material were performed through the ashing digestion and analysis procedure on a routine basis

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for several quality control samples. Loss of elements attributable to volatilization during ashing

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of the sample was less than 10%. Extraction efficiency of metals from the ash residue in the acid

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digestion step was better than 98%.

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With varimax rotation, principle component analysis (PCA) was also performed for

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clarification of complex data that can be abridged by decreasing a set of variables, called factors

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or components. Reducing the dimensionality for a set of variables, PCA can be applied as an

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appropriate statistical procedure. According to Galarneau13, PCA separates observed ambient

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concentrations corresponding to groups of covarying elements and evaluating those groups to

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doubted source profiles.

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3. Results and Discussion

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Thirty aromatic species (19 PAHs, 6 carboxylic acids and 5 ketones) were identified in

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the arctic aerosol samples. Among them, aromatic acids were the most abundant compound

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class, followed by aromatic ketones and PAHs. The molecular formulas, ring numbers, and

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abbreviations of detected PAHs are given in Table 1.

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3.1. Seasonal and Temporal Variations in Concentrations and Molecular Distributions of

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PAHs, Aromatic Acids and Ketones with Total Carbon (TC)


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Temporal variations in mass concentrations of PAHs and aromatic acids with total

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carbon (TC) detected in the Alert aerosols are shown in Figure 1. The trend of TC mass

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concentrations showed a rise and fall in different sampling weeks, with the utmost concentration

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(639 ng m-3) during the first week of sampling in February (before polar sunrise) and the lowest

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concentration (91 ng m-3) in the last week in June (well after polar sunrise). The mean

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concentration of TC was found to be 360±176 ng m-3. We observed that all PAHs were not

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present in all the sampling weeks, higher concentrations of PAHs were obtained in late February

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(before polar sunrise) and concentrations generally decreased during the polar sunrise (Figure

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1a). These results may be caused by photochemical degradation of airborne PAHs into their

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derivatives with additional functional groups.1 The another reason is an increase in the

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concentration of ozone (O3), which could augment the ozonolysis in the atmosphere, leading to a

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decrease in particulate PAH concentrations.14 In contrast, concentrations of aromatic acids were

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correspondingly

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dimethylphenyl)butanoic acid (Figure 1b).

higher

even

after

polar

sunrise

with

dominance

of

γ-(2,4-

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Average mass concentrations of each PAH measured in total suspended particulate

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matter before and after polar sunrise are ranked in the following order, ANTH < FLUO
9,

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10-anthracenedione > 4H-cyclopenta(def)phenanthren-4-one > diphenylmethanone. The highest

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concentration of 9-fluorenone was 39.3 pg m-3 (Figure 2). Oxygenated PAHs are produced in the

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atmospheric reactions of PAHs with O3 and hydroxy radicals.19

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Chen et al.20 reported the characteristics of secondary organic aerosol (SOA)

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production from naphthalene, 1-methylnaphthalene and 2-methylnaphthalene under the

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conditions of high and low NOx and the absence of NOx in a chamber study and observed that

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yields of SOA from naphthalene and methylnaphthalenes are more with increasing yields of 1-

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methylnaphthalene > naphthalene > 2-methylnaphthalene. They concluded that OH radicals,

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NOx levels, initial PAH/NO ratios, NO2/NO ratios influence the system reactivity, and all

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affected the SOA formation from the PAH precursors. Similarly, Chan et al.21 stated that SOA

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was semivolatile under high-NOx and effectively non-volatile under low-NOx conditions, owing

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to the greater fraction of ring-retaining outcomes produced under low-NOx conditions. They

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reported that PAHs are estimated to yield SOA 3–5 times higher than light aromatic compounds


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over photooxidation and PAHs can comprise up to 54% of the total SOA from the oxidation of

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diesel emissions, playing a potentially large source of urban SOA.

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The increased concentrations of aromatic acids from mid-April to late April and from

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mid-May to late May potentially support an augmented photochemical production in the Arctic

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and surroundings. The winter maximum of PAHs suggests that the Arctic receives air masses

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with polluted aerosols and their precursors produced from the midlatitudes through long range

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atmospheric transport1. According to Halsall et al.10, PAH concentrations during October to

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April were highest in high Arctic Alert due to the predominance of haze. The multiple peaks in

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aromatic acids are shown in May onwards as a result of plausible photochemical degradation of

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PAHs and other sources including local pollution. Aerosol elimination rates are minimum in

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winter because of the absence of solar radiation under stagnant meteorological conditions with

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surface based inversion.22

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Figure 3 displays box-plots of monthly variations in total concentrations of PAHs and

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aromatic acids. Average concentrations of ∑19-PAHs and ∑6-aromatic acids are 112 and 727 pg

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m-3, respectively. A seasonal fluctuation was noticed in the concentrations of PAHs. Before polar

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sunrise (late February-early March), box plots display higher concentrations of PAHs than the

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warmer months (April-June). The median concentration of ∑PAHs during the cold episode was

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much higher than the rest of the months. Enhanced intrusion of air masses originated from the

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Eurasian and North American continents was due to meteorological conditions.10 Furthermore,

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the existence of intense temperature inversions in the boundary layer, predominantly due to the

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presence of sea ice in the Arctic Ocean, inhibits the deposition and dispersal of pollutants.23 As a

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result of these processes, atmospheric PAHs peak in winter.10 The seasonal pattern of variations

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in total mass concentration of aromatic acids was opposite to that of PAHs (Figure 3);

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concentrations of ∑6-aromatic acids increased from late February to May and then decreased in

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June.

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3.2. Relative Abundances of PAHs in Terms of Number of Rings

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Figure 4 shows the relative abundances of 3-, 4-, 5-, 6- and 7-aromatic ring PAHs in

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the Alert aerosols during late February to early June (before and after polar sunrise). The

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percentage contributions are 7% (3-rings), 48% (4-rings), 33% (5-rings), 10% (6-rings) and 2%

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(7-rings). Thus, the dominant contributors to total PAHs in the Alert aerosols were 4-, 5- and 6-



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ring PAHs, which is in agreement with previous research carried out in the Canadian Arctic,

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Alert.1,10 High molecular weight PAHs are the main contributor in the particulate phase.24

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Heavier PAHs are predominantly associated with the particulate phase at ambient temperatures

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normally in the Arctic; the preponderance of PAHs (70–90 %) are adsorbed on suspended

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particles whereas lighter PAHs (2–3 benzene rings) are predominantly found in gas phase.24

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Emission of PAHs to the atmosphere from heavy duty diesel engines are predominantly 4-ringed

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structures whereas gasoline engines emit higher molecular weight PAHs with more ring

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structures.25 Wood burning and coal combustion sources are also possible in the arctic air mass

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source regions.16,1,10

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The reduced height of the atmospheric surface-based mixing layer, decreased

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atmospheric reactivity of PAH compounds, greater emissions (biomass, wood, and coal burning),

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weaker solar radiation flux and increased atmospheric stability are likely factors contributing to a

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peak of PAHs in the winter season in the Arctic.26,27 As a result of residential heating in winter,

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atmospheric emissions were found to increase marked by higher levels of 4-ring PAHs28, which

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supports the measured highest concentration (48%) of 4-ring PAHs in the present study.

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Lowered atmospheric mixing height and strong stability in the lower arctic atmosphere together

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with a fall in ambient temperature further indicate to an entrapment of pollutants near the ground

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surface.29

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3.3. Speciation of Carcinogenic PAHs and Variations in the Ratio of Benzo[a]Pyrene to

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Benzo[e]Pyrene

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The United States Environmental Protection Agency30 and International Agency for

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Research on Cancer (IARC)31 classify 7-PAHs such as B[a]A, B[a]P, B[b]F, B[k]F, CHR,

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D[ah]A, and INDP to be possible carcinogens for humans. Seven PAHs are recognized as Group

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B2 carcinogens.32 In this study, six of the seven carcinogenic PAHs (B[a]A, B[a]P, B[k]F, CHR,

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D[ah]A, and INDP) were detected. Figure 5a displays the seasonal mass concentrations of these

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six carcinogenic PAHs. The mean concentration of carcinogenic PAHs ranked as follows: B[k]F

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> CHR > INDP > B[a]P > B[a]A > D[ah]A. The average concentration of these six carcinogenic

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PAHs in Alert aerosols is 46.8 pgm-3, accounting for ∼41.7% of total concentration of 19 PAHs

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measured. Most PAHs generate their products, for example, nitro- and oxygenated-PAHs upon

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reaction with radicals and other chemicals (e.g., SO2, NOx and O3) in the atmosphere, which are


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even more toxic.25 It was observed that in general comparison with SO2, NO2 has a feebler

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correlation with particle bound PAHs, because of their reactive nature and complex mechanism

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of source and sink.14 It was reported that SO2 and NO2 someway apportion a common emission

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source such as vehicular emission.14

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High solar radiation and ambient temperature enhance the formation of O3,

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consequently, the O3 level is noticed to become highest throughout summer.14 The O3

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concentration increases with a rise in ambient temperature and solar radiation during clear

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days.33 It was found that PAHs can react with O3 and NO2 through ozonolysis and nitration,

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respectively, forming products that are more reactive than the parent compounds.34 Conversely,

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it has been confirmed that ozonolysis can take place in a laboratory condition similar to the

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ambient atmosphere, subsequently forming various oxy-PAHs.34 Nevertheless, as a result of the

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severe complicated atmospheric conditions, findings on the real atmosphere have hitherto to be

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ascertained. Particle-borne B[a]P with extra O3 display pseudo-first-order kinetics in terms of

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selective loss of B[a]P over B[e]P, and reactions with a liquid organic coating ensue by the

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mechanism of Langmuir−Hinshelwood.8 Kwamena et al.35 investigated the surface-bound PAHs

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kinetics with O3 and suggested that the O3 partitioning constant is a signifier of the O3-aerosol

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surface contact, being independent of the amounts of PAHs adsorbed.

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Figure 5b displays progressive variations in the concentration ratios of B[a]P to B[e]P

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in the Alert aerosols. B[a]P and B[e]P have similar physical properties, since they are a pair of

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isomers. The ratio of B[a]P to B[e]P was used to understand the fresh and aged inputs of PAHs

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from their different sources into the Canadian high arctic region. B[a]P relative to B[e]P shows

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the reactiveness or stability of PAHs. The ratios peaked on March 1st and April 19th weeks of the

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sampling period. During the polar sunrise from mid-March to mid-April, the B[a]P to B[e]P

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ratios drop and further diminish from late April to June. These results indicate that PAHs carried

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over the Arctic are subjected to strong photochemical degradation at polar sunrise and after.

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Average mass concentration of B[e]P is higher than that of B[a]P, which is in agreement with

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another study10 accomplished in the Alert region. The B[a]P to B[e]P ratios ranged from 0.0 to

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0.9 with an average of 0.3 during the period of February to June. In the week of April 19, the

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B[a]P to B[e]P ratio is relatively high (0.91), which may be associated with a local emission

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from the military base’s incineration although we do not have such records.



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It was reported that a higher concentration ratio of reactive/stable PAHs is prominent

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in winter months, which is a sign of new inputs of PAHs into the Arctic. This specifies that only

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partial breakdown of B[a]P relative to B[e]P occurs in the arctic atmosphere in winter, with the

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accumulation of PAHs during possible long-range transport to the Arctic.10 PAHs, containing a

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predominantly toxic species B[a]P, are present in pristine areas, e.g., the Arctic and Antarctic

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regions, which are long-range transported from distant combustion sources as reported in field

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measurements and modeling studies.36 During PAHs transport, a loss of PAHs takes place via

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both heterogeneous and gas-phase photo-oxidation reactions. Up to date laboratory35 and

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modeling studies37 propose that heterogeneous reactions may be the major atmospheric loss

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process of PAHs.

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3.4 Effects of Polar Sunrise on PAHs and Aromatic Acids at Alert

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Concentrations and molecular distributions of PAHs and aromatic acids before

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(February 19-25) and after polar sunrise (April 1-8) are displayed in Figure 6. Concentrations of

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all PAHs were found to significantly decrease after polar sunrise. Total mass concentration of the

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nineteen PAHs measured was 850 pg m-3 before polar sunrise and, after polar sunrise, it became

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~27 times lower at 31.7 pg m-3. The dominant PAHs, FLA and B[k]F, became ~36 and ~18 times

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less abundant after polar sunrise than those before polar sunrise. Similarly, concentrations of

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B[a]P and B[e]P are ~53 and ~43 times lower than those before sunrise, respectively. The B[a]P

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to B[e]P ratio decreased greatly during polar sunrise, strongly consistent with a process of

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photochemical degradation of PAHs in sunlight during polar sunrise in the Arctic. The prevailing

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PAHs are fluoranthene, benzo[k]fluoranthene, pyrene, phenanthrene and chrysene (Figure 6).

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Before polar sunrise aromatic acids were detected in high abundances, implying that

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they are formed by photochemical processes in the midlatitudes and long-range transported to

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the Arctic.1 Their concentrations decreased after polar sunrise. In contrast, benzoic acid, salicylic

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acid, phthalic acid and γ-(2,4-dimethylphenyl)butanoic acid did not show a significant decline

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after polar sunrise. However, similar to aromatics, 2-carboxybenzaldehyde and 2,6-

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naphthalenedicarboxylic acid were found to be degraded with concentrations ~72 and ~18 times

335

lower after polar sunrise than before polar sunrise. This is probably due to the oxidation of

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aldehyde group and naphthalene structure in increasing sunlight.


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The concentrations of aromatic acids increased in mid-May to late May. They are very

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likely formed by in situ photochemical oxidation of organic precursors such as naphthalenes,

339

toluene and xylenes.38 Oxidation of PAHs can produce secondary compounds such as fluorenone

340

and phenanthroquinone during combustion and photo-oxidation processes. They can also be

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formed by the oxidation of phenanthrene or benzofluorenones, which are oxidation products of

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benzofluorene.39 Li et al.40 investigated the influence of methyl group to formation of SOA in the

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photooxidation of aromatic hydrocarbons under low NOx condition. They concluded that

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oxidation products of methyl group carbon of aromatic compounds have a lower rate of

345

partitioning to the particle-phase than the products derived from the ring opening of aromatic

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hydrocarbons.

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3.5. Source Apportionment of Organic Aerosols

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Many investigators in the recent past have employed diagnostic ratios of 3- to 7-ring

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PAHs categorized on the origin of various sources, some of which have been summarized in

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Table S1. Pyrolytic products from coal and wood burning and diesel/gasoline engine exhausts,

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and aged aerosols of combustion emission origin are the major sources of PAHs and related

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compounds observed in this study based on diagnostic ratios (Table S1). The average ratio of

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B[e]P/(B[e]P+B[a]P) is 0.65, suggesting that combustion-derived aerosols are more aged41

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because the concentration ratio of B[e]P/(B[e]P+B[a]P) for freshly emitted PAHs is equal to

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0.50.42 The most abundant PAH’s diagnostic ratio, FLA/(FLA+PYR), is >0.5, indicating the

356

contributions from coal, grass and wood burning (Table S1).

357

Principle component analysis provides the replacement of a large set of inter-correlated

358

original variables with reduced number of independent variables or principal components.43 An

359

emission source can be recognized by these components or factors. Eigen values > 1 were

360

considered for retention of principal components. Principal components with greater than 5% of

361

total variance of data set were utilized as components. Loadings affected most PAHs (Table S2)

362

and aromatic acids (Table S3) in each component and a value greater than 0.5 was selected.

363

SPSS (version 24) was used to enhance the variance of the squared elements in the column, a

364

factor matrix was generated (Tables S2 and S3). Three principal components or factors for PAHs

365

and two for aromatic acids were set by the scree tests and their component plots in rotated space

366

are displayed in Figure S1a and b.



Page 14 of 32

14

367

Table S2 shows the outcomes of factor analysis on the concentrations of total PAHs.

368

Three factors explain 98.4% variability in the PAHs data. Factor 1 account for 62.4% of the total

369

variance, which is loaded with B[b]FLUO, B[a]A, B[ghi]P, PYR, CORO, B[a]P, IndP, CHR,

370

B[k]F, B[ghi]FLA, B[e]P, FLA, D[ah]A and PHEN; these are indicators of coal and organic

371

matter combustion, traffic emission, coal, grass and wood burning and their long range

372

transport.1,44 Factor 2 explain 30.6% of the total variance, which is loaded with FLA, D[ah]A,

373

PHEN, DBTH, FLUO, PERY, and ANTH. These PAHs are derived from traffic emission, coal

374

and organic matter combustion via long range transport.1,44 Factor 3 accounts for 5.3% of the

375

total variance and is loaded with only BINAP, which is possibly transported long distances to the

376

Arctic from low and mid latitudes.

377

Table S3 shows the outcomes of factor analysis of concentrations of total aromatic

378

acids. Two factors account for 82.5% variability in the acid data. Factor 1 accounts for 59.3% of

379

the total variance, which is loaded with 2,6-naphalenedicarboxylic acid, 2-carboxybenzaldehyde,

380

salicylic acid and phthalic acid; these compounds are derived from the oxidation of various

381

organic precursors containing aromatic structures. Phthalic acid was found to be a proxy to

382

understand the organic aerosol formation via secondary oxidation.1 Factor 2 accounts for 23.2%

383

of the total variance and is loaded with γ-(2,4-dimethylphenyl)butanoic acid and benzoic acid,

384

which are the products derived from motor exhausts and photochemical degradation of organic

385

precursors. Benzoic acid has been regarded as a primary pollutant released from exhausts of

386

motors and a photochemical degradation of toluene, other alkyl benzenes and naphthalenes

387

emitted by automobiles.38,45 Oxygenated PAHs are produced via photo-oxidation of PAHs with

388

oxidants (ozone, OH radicals and nitrogen oxides) present in the atmosphere.19 Moreover, these

389

compounds have been originated in brake lining wear particles, road dust and emissions of

390

particulate exhaust from heavy duty diesel trucks.46, 47

391

3.6. Speciation and Variation in Mass Concentrations of Trace Elements and Their

392

Correlations with Detected Organic Species

393

Trace elements were categorised in two groups: major and minor elements. Major

394

elements are comprised of those metals whose mass concentrations are > 3 ng m-3 such as Al,

395

Mg, Fe and Ca while minor elements such as V, Zn, Pb, Ni, Cu and Mn are considered as those

396

with concentrations < 3 ng m-3. Figure 7 shows the mass concentrations with relative


Page 15 of 32


15

397

contribution (%) of major and minor trace elements detected in the Alert aerosols. We found that

398

among the major trace elements, Al is most abundant (29%) followed by Mg (28%), Ca (27%)

399

and Fe (16%) whereas Zn is most abundant (43%) among the minor elements followed by Pb

400

(20%), Cu (17%), Mn (12%), V (5%) and Ni (3%).

401

Four major (Al, Mg, Fe and Ca) and six minor (V, Zn, Pb, Ni, Cu and Mn) metal

402

elements were selected for ensuring the correlations and their plausible role with detected

403

organic species. Table S4 shows correlations of Mg and Pb with some PAHs (pg m-3) before

404

(n=5) and after polar sunrise (n=11) during sampling period. We found that Mg and Pb are

405

highly correlated (R2 = 0.67 to 0.94; p < 0.05) with FLA, PYR, CHR, and PHEN before polar

406

sunrise whereas after polar sunrise the correlations are weak (R2 = 0.04 to 0.78; p >0.05). The

407

Durbin–Watson statistic for all significantly correlated species is found to be < 2, which

408

determines the well autocorrelation between species. The contrary correlations before and

409

after polar sunrise suggest that photodegradation of PAHs that takes place during polar

410

sunrise and after. Reduction of metal mass concentration from “before” to “after polar

411

sunrise” could be explained by another reason for contrary correlations. The higher

412

correlations before polar sunrise also suggest same sources of Mg, Pb, FLA, PYR, CHR, and

413

PHEN by either long range transport from mid-latitude or local sources.

414

Table S4 shows the correlations of 5 aromatic acids (γ-(2,4-dimethylphenyl)butanoic

415

acid, phthalic acid, 2-carboxybenzaldehyde, salicylic acid and 2,6-naphthalene dicarboxylic acid)

416

with 7 trace metals (Mg, V, Mn, Al, Zn, Pb and Ca) before and after polar sunrise during

417

sampling period. We observed that these 5 aromatic acids were highly correlated (R2 = 0.60 to

418

0.99; p < 0.05) with 7 trace metals before polar sunrise, whereas the correlations were declined

419

(down to R2 = 0.0017 to 0.67; p > 0.05) after polar sunrise, signifying photo

420

oxidation/degradation of aromatic acids, signifying that those species were transported from

421

similar sources to the Arctic. We observed that γ-(2,4-dimethylphenyl)butanoic acid was

422

negatively correlated with V (R2 = 0.88; p < 0.05), Mn (R2 = 0.95; p < 0.01) and Al (R2 = 0.60; p

423

=0.06), indicating that those species were transported from dissimilar source regions to the

424

Arctic before polar sunrise (supplementary Table S4). Siois and Barrie48 reported that Al, Mn

425

and V are found in soil component of aerosols in spring likely due to long range transport of dust

426

from Gobi desert.



Page 16 of 32

16

427

Positive correlations (R2 = 0.43 to 0.90; p =0.39 to 0.05) of V, Mg, Pb, Zn, Fe, Ca and Ni

428

with total carbon and n-docosane were found (Figure S2a, b), proposing that those species were

429

also transported from similar source regions to the Arctic before polar sunrise. n-Alkanes such as

430

n-docosane are typically ascribed to the emission of fossil fuel.49 Coal combustion is also

431

contributed as a dominant source for n-docosane.50

432

PHEN, CHR, B[a]A, B[k]F, B[b]FLUO, FLA, B[e]P and B[a]P also showed strong

433

correlations with Mg, Ni, Zn, Pb and Ca (R2 = 0.44 to 0.89; p = 0.37 to 0.05) before polar sunrise

434

(Figure S3). Similarly, aromatic acids (benzoic acid, salicylic acid, 2-carboxybenzaldehyde,

435

phthalic acid, 2,6-naphthalenedicarboxylic acid and γ-(2,4-dimethylphenyl)butanoic acid) gave

436

good correlations (R2 = 0.41 to 0.64; p = 0.38 to 0.05 ) with trace metals (mainly Fe, Cu, Ni, Zn,

437

Ca, Mg and Pb) as shown in Figure S4. Figure S4 depicts fair correlations of benzoic acid with

438

Fe (R2 = 0.58; p < 0.05) and γ-(2,4-dimethylphenyl)butanoic acid with Cu (R2 = 0.64; p < 0.05).

439

Based on these correlations, we can propose here a plausible role of Fe and Cu as important

440

reagents in Fenton chemistry with these organic acids in dark reaction (before polar sunrise).

441

All 5 aromatic ketones (diphenylmethanone, 4H-cyclopenta[def]phenanthren-4-one,

442

9,10-anthracenedione, benz[de]anthracen-7-one, and 9-fluorenone) are also highly correlated (R2

443

= 0.41 to 0.97; p = 0.36 to 0.01) with Mg, Ni, Zn, Pb, Zn, Ca and Mn. We found strong

444

correlations of 4H-cyclopenta[def]phenanthren-4-one with 9,10-anthracenedione (R2 = 0.99) and

445

benz[de]anthracen-7-one (R2 = 0.92; p < 0.05). 9,10-Anthracenedione had also a strong

446

correlation (R2 = 0.94; p < 0.05) with benz[de]anthracen-7-one as shown in Figure S5. The above

447

correlations signify that these species are also originated from similar sources to the Arctic

448

before polar sunrise.

449

Vanadium (V) and aromatic acids are useful tracers of fossil fuel combustion, while V

450

is in part released from natural source, for example, wind-blown dust.51 The detected trace

451

transition metals may be interesting to better understand the role of transition metals such as Fe,

452

Cu and Mn in the interaction with organic compounds (acid, ketones and their derivatives),

453

because a recent aerosol study52 from the central Indo-Gangetic Plain reported strong

454

correlations of water soluble organic carbon with transition metals and stated the role of Fenton

455

reagent (Fe, Cu/H2O2) in the formation of secondary organic aerosols. Table S4 also displays the

456

correlations of 6 carcinogenic PAHs with Ni, a carcinogenic transition metal (cancer slope factor


Page 17 of 32


17

457

= 0.84)41 before and after polar sunrise in the Alert aerosols. We found stronger correlations (R2

458

= 0.86 to 0.92; p < 0.05) after than before polar sunrise, suggesting that these (6 PAHs and Ni)

459

carcinogenic species were evolved from the same sources. It was reported that Ni primarily

460

originates from total vehicular emissions as a result of burning of lubricating oil53. Cu, Zn, Ni

461

and Fe primarily originate from anthropogenic sources, for example, industries, petroleum, coal

462

combustion and fine soil dust re-suspension.54

463

In conclusion, higher concentrations of PAHs and aromatic acids in the Alert aerosols

464

before polar sunrise provide clues to better understand the role of photochemical processes in the

465

mid latitudes and long distance transport to the Arctic. Lower concentrations of PAHs and

466

aromatic acids after polar sunrise suggest a photochemical degradation of combustion-derived

467

PAHs and secondary production of organic aerosols in the presence of oxidants in the Arctic

468

atmosphere. 2,6-Naphthalenedicarboxylic acid declined from late April onwards like other

469

PAHs, thus we can conclude that dicarboxylic acids (e.g., oxalic acid) and their derivatives are

470

not photochemical products of PAHs at arctic polar sunrise. The possible sources of PAHs are

471

coal and organic matter combustion, traffic emission, coal/grass/wood burning and long range

472

transport whereas several aromatic acids were the photochemical oxidation products of aromatic

473

compounds derived from various sources including motor exhausts. Predominance of

474

fluoranthene (21%), γ-(2,4-dimethylphenyl)butanoic acid (66%) and 9-fluorenone (39%)

475

demonstrated the highest contributor to their respective class of compounds (PAHs, aromatic

476

acids and ketones). Relative contribution of 4-ring PAHs in total PAHs showed the highest value

477

(48%) followed by 5-, 6-, 3- and 7-ring PAHs. Lowest degree of sulphur containing heterocyclic

478

PAH (dibenzothiophene) and high abundances of 6-carcinogenic PAHs were identified in the

479

Alert aerosols. A comparison of correlations of aerosol organics and metals before and after

480

polar sunrise provides independent evidence that in situ production or destruction of organics is

481

occurring for many compounds during polar sunrise and after. This process weakens correlations

482

between organics and metals during the sunlit period.

483

Acknowledgements

484

This study was partly endorsed by the Japanese Ministry of Education, Culture, Sports, Science

485

and Technology (MEXT) and the Japan Society for the Promotion of Science (JSPS) by grant-in-

486

aid Nos. 17340166, 19204055 and 24221001.

487



Page 18 of 32

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489 490 491 492 493 494 495 496 497 498

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(47) Enya, T.; Suzuki, H.; Watanabe, T.; Hirayama, T.; Himasatsu, Y. 3-Nitrobenzanthrone, a powerful bacterial mutagen and suspected human carcinogen found in diesel exhaust and airborne particulates. Environ. Sci. Technol. 1997, 31, 2772–2775.

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(49) Schauer, J. J.; Kleeman, M. J.; Cass, G. R.; and Simoneit, B. R. T. Measurement of emissions from air pollution sources. 5. C1–C32 organic compounds from gasoline-powered motor vehicles. Environ. Sci. Technol. 2002, 36, 1169–1180.

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(52) Singh, D.K.; Gupta, T. Role of transition metals with water soluble organic carbon in the formation of secondary organic aerosol and metallo-organics in PM1 sampled during post monsoon and pre-winter time. J. Aerosol. Sci. 2016, 94, 56–69.

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Page 22 of 32

22 644

List of Figures

645 646

Figure 1. Weekly variations in mass concentrations of total carbon (TC) with (a) PAHs and (b) aromatic acids detected in the Alert aerosols.

647 648

Figure 2. Average mass concentrations of individual PAHs, aromatic acids and ketones detected in the Alert aerosols.

649

Figure 3. Temporal variations in the total mass concentrations of PAHs and aromatic acids.

650 651

Figure 4. Mass concentrations and relative contribution (%) of PAHs based on the number of aromatic rings.

652 653

Figure 5. (a) Variations in mass concentrations and relative contribution of carcinogenic PAHs and (b) temporal variations in ratio of B[a]P to B[e]P detected in the Alert aerosols.

654 655

Figure 6. Concentrations and molecular distributions of PAHs and aromatic acids before (Feb. 19-25, left) and after polar sunrise (Apr. 1-8, right).

656 657

Figure 7. Concentrations with (%) relative contribution of major and minor trace metals detected in the Alert aerosols.

658


Page 23 of 32


23 659 660 661

Table 1. Concentrations of polycyclic aromatic hydrocarbons (PAHs) and their molecular formula with abbreviations and number of rings.

PAHs

Concentration (pgm-3) Molecular Ring Abbreviation formula number Range (Average±STD)

Fluorene

FLUO

C13H10

3

0-0.2

0.014±0.045

Dibenzothiophene

DBTHP

C12H8S

3

0-0.8

0.087±0.22

Phenanthrene

PHEN

C14H10

3

0-51

7.4±13.7

Fluoranthene

FLA

C16H10

4

0-189

24.0±52.7

Pyrene

PYR

C16H10

4

0-97.4

13.3±29.1

Benzo[b]fluorene

B[b]FLUO

C17H12

4

0-7.4

0.94±2.24

1,1'-Binaphthalene

BINAP

C20H14

4

0-3.6

0.68±1.18

Benzo[a]anthracene

B[a]A

C18H12

4

0-40.4

4.76±11.7

Chrysene

CHR

C18H12

4

0-20.1

2.76±6.56

Benzo[k]fluoranthene

B[k]F

C20H12

5

0-93.0

12.6±27.2

Benzo[e]pyrene

B[e]P

C20H12

5

0-160

21.9±46.6

Benzo[a]pyrene

B[a]P

C20H12

5

0-47.3

5.84±13.4

Perylene

PERY

C20H12

5

0-24.6

3.17±7.35

Benzo[ghi]fluoranthene B[ghi]FLA

C18H10

5

0-14.7

0.92±3.67

Dibenz[a,h]anthracene

D[ah]A

C22H14

5

0-44.0

5.6±13.0

Benzo[ghi]perylene

B[ghi]P

C22H12

6

0-5.3

0.52±1.48

Anthanthrene

ANTH

C22H12

6

0-37.9

5.3±11.6

Indeno[1,2,3-cd]pyrene

INDP

C22H12

6

0-0.2

0.012±0.049

Coronene

CORO

C24H12

7

0-17.0

2.01±5.16

662 663



Page 24 of 32

24 664

(a)

665 666 667 668 669 670 671 672 673 674 675 676 677 678

(b)

679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694

Figure 1. Weekly variations in mass concentrations of total carbon (TC) with (a) PAHs and (b) aromatic acids detected in the Alert aerosols.


Page 25 of 32


25 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717

Figure 2. Average mass concentrations of individual PAHs, aromatic acids and ketones detected in the Alert aerosols.

718 719



Page 26 of 32

26 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743

Figure 3. Temporal variations in the total mass concentrations of PAHs and aromatic acids

744 745 746 747 748 749 750 751 752 753 754


Page 27 of 32


27 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775

Figure 4. Mass concentrations and relative contribution (%) of PAHs based on the number of aromatic rings.

776 777 778 779 780 781



Page 28 of 32

28 782 783

(a)

784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799

(b)

800 801 802 803 804 805 806 807 808 809 810 811 812 813

Figure 5. (a) Variations in mass concentrations and relative contribution of carcinogenic PAHs and (b) temporal variations in the ratio of B[a]P to B[e]P detected in the Alert aerosols.

814 815 816


Page 29 of 32


29 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842

Figure 6. Concentrations and molecular distributions of PAHs and aromatic acids before (Feb. 19-25, left) and after polar sunrise (Apr. 1-8, right).

843 844 845 846 847 848 849 850 851



Page 30 of 32

30 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870

Figure 7. Concentrations with (%) relative contribution of major and minor trace metals detected in the Alert aerosols.

871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887


Page 31 of 32


31 888 889 890 891 892 893 894

Graphical abstract

895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916



Page 32 of 32

32 917

Research Highlights

918

• Predominance of fluoranthene followed by benzo(k)fluoranthene, pyrene and chrysene in

919

winter and their declines in spring onwards.

920

• 4-Ring PAHs were highly contributed (48%) followed by 5, 6, 3 and 7–rings.

921

• Benzo[a]pyrene/benzo[e]pyrene ratios dropped from early-March to mid-April and further

922 923 924 925 926 927 928

diminish from mid-April to May. • PAHs transported over the Arctic are subjected to severe photochemical degradation at polar sunrise. • High concentrations of aromatic acids before polar sunrise hint an important role of photochemical processes in the mid latitudes and transported long distances to the Arctic. • Dominance of γ-(2,4-dimethylphenyl)butanoic acid (66%), 9-fluorenone (39%) and fluoranthene (21%) were the highest contributor in their respective compound classes.

929

• 6-Carcinogenic PAHs were identified in the Alert aerosols.

930

• Strong correlations of trace metals with organic species were found.

931 932 933

• Trace metals played a potential role in the oxidation of primary organic aerosols as a result of dark reaction (before polar sunrise) like other transition metals (Fe, Cu) through Fenton reaction.

934 935 936


Distributions of Polycyclic Aromatic Hydrocarbons, Aromatic Ketones

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