Abstract

Polycyclic aromatic hydrocarbons (PAHs), their alkylated (RPAHs), nitrated (NPAHs) and oxygenated (OPAHs) derivatives are air pollutants. Many of these substances are long-lived, can undergo long-range atmospheric transport and adversely affect human health upon exposure. However, the occurrence and fate of these air pollutants has hardly been studied in the marine atmosphere. In this study, we report the atmospheric concentrations over the Mediterranean Sea, the Red Sea, the Arabian Sea, the Gulf of Oman and the Arabian Gulf, determined during the AQABA (Air Quality and Climate Change in the Arabian Basin) project, a comprehensive ship-borne campaign in summer 2017. The average concentrations of ∑27PAHs, ∑19RPAHs, ∑11OPAHs and ∑17NPAHs, in the gas and particulate phase, were 2.85 ± 3.35 ng m−3, 0.83 ± 0.87 ng m−3, 0.24 ± 0.25 ng m−3 and 4.34 ± 7.37 pg m−3, respectively. The Arabian Sea region was the cleanest for all substance classes, with concentrations among the lowest ever reported. Over the Mediterranean Sea, we found the highest average burden of ∑26PAHs and ∑11OPAHs, while the ∑17NPAHs were most abundant over the Arabian Gulf (known also as Persian Gulf). 1,4 Naphthoquinone (1,4-O2NAP) followed by 9-fluorenone and 9,10-anthraquinone were the most abundant studied OPAHs in most samples. The NPAH composition pattern varied significantly across the regions, with 2 nitronaphthalene (2-NNAP) being the most abundant NPAH. According to source apportionment investigations, the main sources of PAH derivatives in the region were ship exhaust emissions, residual oil combustion and continental pollution. All OPAHs and NPAHs except 2-NFLT, which were frequently detected during the campaign, showed elevated concentrations in fresh shipping emissions. In contrast, 2-nitrofluoranthene (2-NFLT) and 2-nitropyrene (2-NPYR) were highly abundant in aged shipping emissions due to secondary formation. Apart from 2-NFLT and 2-NPYR, also benz(a)anthracene-7,12-dione and 1,4-O2NAP had significant photochemical sources. Another finding was that the highest concentrations of PAHs, OPAHs and NPAHs were found in the sub-micrometre fraction of particulate matter (PM1).

Highlights

  • Air pollution contributes to the global burden of respiratory and cardiovascular diseases (Shiraiwa et al, 2017; Lelieveld et 40 al., 2019)

  • Apart from 2-NFLT and 2-NPYR, benz(a)anthracene-7,12-dione and 1,4-O2NAP had significant photochemical sources. Another finding was that the highest concentrations of polycyclic aromatic hydrocarbons (PAHs), OPAHs and NPAHs were found in the sub-micrometre fraction of particulate matter (PM1)

  • The highest average concentrations of the PAHs and the OPAHs were detected in the Mediterranean Sea, while the NPAHs were most abundant in the Arabian Gulf

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Summary

Introduction

Air pollution contributes to the global burden of respiratory and cardiovascular diseases (Shiraiwa et al, 2017; Lelieveld et 40 al., 2019). PAHs, OPAHs, NPAHs and RPAHs are formed by incomplete combustion of fossil fuels, biomass and waste (Baek et al, 1991; Lee et al, 2003; Walgraeve et al, 2010; Bandowe and Meusel, 2017) Apart from these pyrogenic sources, PAHs, especially low-molecular-weight PAHs and RPAHs, and some PAH derivatives can originate from petrogenic sources and spills of petroleum hydrocarbons (Andersson and Achten, 2015; Zhao et al, 2015; Abbas et al, 2018). In addition to these 60 so-called primary emissions, NPAHs and OPAHs can be formed by secondary formation by reactions of PAHs with atmospheric oxidants (Finlayson-Pitts and Pitts, 1999; Keyte et al, 2013). The ratio 2-NFLT/1-NPYR can be used as an indicator for the relative contributions of secondary 65 formation reactions in the gas phase compared to primary emitted compounds (Bamford and Baker, 2003)

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