Polycyclic aromatic hydrocarbons (PAHs) and 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 have 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
Air pollution contributes to the global burden of respiratory and cardiovascular diseases (Shiraiwa et al., 2017; Lelieveld et al., 2019). The Red Sea and especially the Arabian Gulf region are prone to major risks by air particulate matter (PM) and gas-phase pollutants due to the hot and arid climate, leading to high dust concentrations and photochemical activity (Lelieveld et al., 2009). In combination with high anthropogenic emissions from highly populated cities, intense marine traffic due to major trade routes (Johansson et al., 2017) and a strong petrochemical industry, air pollution can be significant in these regions (Lelieveld et al., 2015).
One major class of air pollutants is polycyclic aromatic hydrocarbons (PAHs) and their alkylated (RPAHs), nitrated (NPAHs) and oxygenated (OPAHs) derivatives. Several of these substances are classified as carcinogenic or possibly carcinogenic (IARC, 1983, 2012a, b, 2018; OEHHA, 2021). Moreover, many polycyclic aromatic compounds (PACs) show strong mutagenic (Durant et al., 1996; Clergé et al., 2019; Idowu et al., 2019) and ecotoxic effects (El Alawi et al., 2002; Sverdrup et al., 2002a, b; WHO, 2003). Quinones, a major subgroup of OPAHs, have received more attention in recent years due to their potential to contribute to oxidative stress on the cell level (Bolton et al., 2000; Xiong et al., 2017; Lyu et al., 2018). Although some PAH derivatives show even higher toxicity than their parent PAHs (Durant et al., 1996; Collins et al., 1998; WHO, 2003; Turcotte et al., 2011; Lee et al., 2017; IARC, 2018; Clergé et al., 2019; Idowu et al., 2019), their atmospheric concentrations and their cycling and fate are not well studied. Alkylated 3-ring PAHs are more persistent, bioaccumulative and toxic than the parent 3-ring PAHs, which have been identified as substances with persistent, bioaccumulative, and/or toxic properties (PBT) (ECHA, 2021; Wassenaar and Verbruggen, 2021).
PAHs, OPAHs, NPAHs and RPAHs are formed by incomplete combustion of fossil
fuels, biomass and waste (Baek et al., 1991; Yunker et al., 2002; Ravindra
et al., 2008; Bandowe and Meusel, 2017; Abbas et al., 2018). 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 so-called primary emissions,
NPAHs and OPAHs can also be formed by secondary formation by reactions of
PAHs with atmospheric oxidants (Finlayson-Pitts and Pitts, 1999; Tsapakis
and Stephanou, 2007; Walgraeve et al., 2010; Keyte et al., 2013; Bandowe and
Meusel, 2017; Abbas et al., 2018). For most PAH derivatives, the
contribution from secondary formation is not known. It was shown that
2-nitrofluoranthene (2-NFLT) is formed in gas-phase reactions and was not
found in direct emissions, while the opposite was reported for 1-nitropyrene
(1-NPYR) (Arey et al., 1986; Atkinson et al., 1990; Bamford and Baker,
2003). Therefore, the ratio
The concentration of PAHs in ambient air as well as other environmental compartments has been studied quite extensively in the last decades (Baek et al., 1991; Srogi, 2007; Ravindra et al., 2008), especially for the 16 U.S. EPA-prioritised PAHs (Keith, 2015). However, our knowledge about the distribution of PAH derivatives is still limited (Andersson and Achten, 2015; Lammel, 2015; Bandowe and Meusel, 2017; Jin et al., 2020). There are several studies reporting atmospheric concentrations of OPAHs and NPAHs in the particulate and the gas phase at urban and semi-urban sites (Bamford and Baker, 2003; Albinet et al., 2007, 2008; Garcia et al., 2014; Li et al., 2015; Tomaz et al., 2016; Alves et al., 2017; Kitanovski et al., 2020). Rural/continental background and remote continental sites were investigated in a small number of studies, indicating that several NPAHs and OPAHs are ubiquitous (Ciccioli et al., 1996; Tsapakis and Stephanou, 2007; Albinet et al., 2008; Brorström-Lundén et al., 2010; Scipioni et al., 2012; Tang et al., 2014; Nežiková et al., 2021). Their detection in the Arctic (Drotikova et al., 2021) and the Antarctic (Vincenti et al., 2001; Minero et al., 2010) confirms the long-range transport potential (Keyte et al., 2013). This is supported by global modelling studies of NPAHs (Wilson et al., 2020; Kelly et al., 2021). However, fewer studies have determined the pollutant concentrations in the marine environment, in polluted sea regions or in marine background air. Tsapakis and Stephanou (2007) and Lammel et al. (2017) measured NPAHs and OPAHs at an eastern Mediterranean marine background location, while Zhang et al. (2018) sampled air on Tuoji Island in the Yellow Sea. To the best of our knowledge, there is no study measuring NPAHs and OPAHs over the open ocean. Knowledge about the sources of pollution and the atmospheric fate processes such as gas–particle partitioning, photochemical degradation and deposition in the marine environment is crucial for understanding the distribution and fate of these pollutants, although very little is known (Keyte et al., 2013). In addition, these processes in marine air are crucial for modelling the distribution of these substances, and the concentrations are needed for the validation of modelling results (Wilson et al., 2020; Kelly et al., 2021).
The objective of this study was to determine the concentrations in the gas and particulate phase of the PAHs, RPAHs, NPAHs and OPAHs in the Mediterranean Sea and around the Arabian Peninsula including the Red Sea, Arabian Sea and the Arabian Gulf region. We aimed to study the mass size distributions of PACs in the atmosphere of a hot marine environment. Furthermore, we provide information about the sources of air pollution in these regions.
The Air Quality and Climate in the Arabian Basin (AQABA) campaign took place
in summer 2017 from 25 June until 1 September 2017, sailing
on a research vessel (
The air pollutants were sampled separately in gas and particulate phases in
polyurethane foams (PUFs; Molintan a.s., Břeclav, Czech Republic) and on
quartz microfibre filters (QFFs; QMA type, Whatman, Sheffield, United
Kingdom), respectively, by active air sampling on the observation deck (in
the front part of the vessel, around 7.7 m a.s.l. and 55 m away from the
stack). The aerosol was sampled as PM
All filters were pre-baked at 300
A total of 43 air (gas- and particulate-phase) samples for the determination of PAHs and
alkylated PAHs and three field blanks (three PUFs and three QFFs) were collected on the
monkey deck of the research vessel (around 4 m higher and 5 m less far away
from the stack compared to the samplers for PAHs, OPAHs and NPAHs) during
the campaign, using a high-volume air sampler (GMWL-2000H; General Metal
Works, Cleves, USA). After sampling, the filters and PUFs were stored
similarly as the Digitel high-volume samples. In contrast to the Digitel
high-volume sampler, total suspended particles (TSP) instead of PM
PUFs and QFFs were extracted using automated Soxhlet extraction (40 min Soxhlet extraction followed by 20 min of solvent rinsing) with DCM (JT Baker, Avantor group, Poland), pesticide residue grade) in a B-811 extraction unit (Büchi, Flawil, Switzerland). Prior to extraction, the samples were spiked with the surrogate standards: deuterated nitro-PAHs (1-nitronaphthalene-d7, 2-nitrofluorene-d9, 9-nitroanthracene-d9, 3-nitrofluoranthene-d9, 1-nitropyrene-d9, 6-nitrochrysene-d11, 6-nitrobenzo[a]pyrene-d11) and deuterated PAHs (naphthalene-d8, phenanthrene-d10, perylene-d12). All analytical standards were purchased from Sigma Aldrich (Darmstadt, Germany) or Chiron (Trondheim, Norway).
The extract was cleaned up using a silica column (with 1 cm i.d. as open
tube using 5 g of silica (Merck, Darmstadt, Germany), 0.063–0.200 mm,
activated at 150
Polycyclic aromatic compounds (PACs) in the sample extracts were analysed at the Trace Analytical Laboratory of the research centre RECETOX at the Masaryk University in Brno, Czech Republic, similar to the method described by Nežiková et al. (2021). The target compounds in this analysis were 26 PAHs, 1S-heterocycle, 1 RPAH, 17 NPAHs and 11 OPAHs. All target PAHs, OPAHs and NPAHs including their acronyms are shown in Table 1. The physico-chemical properties of all targeted compounds are shown in Table S2.
The analysis of PAHs was performed by a gas chromatograph (GC; 7890A,
Agilent, Santa Clara, USA) equipped with a 60 m
NPAHs and OPAHs were analysed by GC atmospheric pressure chemical ionisation
tandem mass spectrometry (GC-APCI-MS/MS) on a Waters Xevo TQ-S MS (Waters,
Mildford, USA) coupled to a GC (GC 7890, Agilent, Santa Clara, USA). The MS
was operated under dry source conditions in multiple reaction monitoring
(MRM) mode (N
For alkylated PAHs, particulate- and gas-phase samples were extracted
separately following a procedure described in detail elsewhere (Iakovides et
al., 2021) with certain modifications. Briefly, each sample was spiked
before the extraction with a known amount of surrogate standard (2–15 ng of phenanthrene-d10, Dr. Ehrenstorfer) and Soxhlet-extracted with 1 : 1
The analysis was carried out on a GC (7890N GC, Agilent, Santa Clara, USA)
equipped with a deactivated fused silica guard column (5 m, Agilent, Santa
Clara, USA) followed by a 30 m
Target compounds and their acronyms. CAS numbers and physicochemical properties are shown in Table S2.
Further description of analytical methods and other supporting parameters
such as meteorological data, PM
Positive matrix factorisation (EPA PMF 5.0) was applied to the PM
In addition, principal component analysis (PCA) was performed. Similar to
the PMF, all samples were included in the analysis. The concentrations of
the selected substances (based on detection frequency and importance for
interpretation; i.e. 2-NNAP; 2-NFLT; 1-NPYR; 2-NPYR; 7-NBAA; 1-(CHO)NAP;
9-OFLN; 9,10-O
Residence time distributions of air mass histories, 10 d backward in
time, were studied using the FLEXPART Lagrangian particle dispersion model
(FLEXPART version 10.4; Pisso et al., 2019), with ECMWF meteorological data
(0.5
More information about the analytical quality assurance such as the
filtering of the samples against contamination by the own ship exhaust, the
detailed quality control of the analysis of the PAH derivatives (recoveries
of the surrogate standards, blank correction, detection frequencies, limits
of quantification (LOQs)) and a summary of PMF diagnostics is given in the
Supplement (Sect. S1.5). In short, the recovery of the surrogate standards
of the high-volume samples ranged 41 %–119 %. The reported concentrations
are blank-corrected using the average of three field blanks but not
recovery-corrected. The instrumental limits of quantification (iLOQs) of the
PAHs, OPAHs and NPAHs ranged 0.10–53, 0.11–1.96 (ignoring 9,10-phenanthrenequinone) and 0.02–8.33 ng per sample, respectively. For the evaluation, the maximum of the iLOQ and
the LOQ of field blank samples (fbLOQs) were used. The fbLOQs of the PAHs, OPAHs and
NPAHs ranged 0.12–54.64,
The separation of the isomers 2-NFLT and 3-NFLT is incomplete using the 5MS GC column ((5 %-phenyl-)methylpolysiloxane GC stationary phase). In this study, the separation of the two isomers was inadequate to quantify both isomers separately but sufficient to qualitatively report that 3-NFLT was either not detected or only detected as a small shoulder of the 2-NFLT peak, which was not integrated for the peak area of 2-NFLT.
The average total (sum of gas- and particulate-phase) concentrations of
the pollutants in the different sea regions are shown in Fig. 1. The average
total concentrations (range in brackets) of the sum of one pollutant class
from all high-volume air samples of the
Total concentration (gas
The spatial distribution of the concentrations of the different substance
classes in both legs is shown in Fig. 2. The plot only shows the average
concentration of each sampling stretch, which could also be impacted by
individual local plumes at distinct times and locations. Furthermore, it
needs to be considered that the method uncertainty at very low
concentrations can be relatively high (up to 28 %, see Sect. S1.5.2.2), similar to some of the spatial gradients indicated in Fig. 2. As visible in Figs. 1 and 2, the cleanest region, with the lowest
concentration of all substance classes, was the Arabian Sea in the Indian
Ocean. The average air concentrations over the Arabian Sea were 0.59 ng m
Total concentration (logarithmic scale) of
The concentration of the
The average concentration of the
The concentration of the
As shown in Fig. 1, the Gulf of Oman and the Arabian Gulf were similarly
polluted as the northern Red Sea. The concentrations of the
The concentrations of the PAH derivatives in a few samples in the remote sea
regions were among the lowest ever reported in air (Walgraeve et al., 2010;
Bandowe and Meusel, 2017; Abbas et al., 2018), while other samples reached
concentration levels previously found at suburban sites. The samples from
near Sicily and Sardinia in the Mediterranean Sea, near the Suez Canal and
over the Gulfs showed a total concentration of 0.1–1.4 ng m
NPAHs and OPAHs have rarely been examined in the marine environment. A study
by Lammel et al. (2017) investigated the 3–4-ring NPAHs in the eastern
Mediterranean under the influence of long-range transport from central and
eastern Europe in summer 2012. The concentration of the
The concentrations of NPAHs (40, 90 and 60 pg m
Harrison et al. (2016) measured PAHs and their derivatives at three sites
along the east coast of the Red Sea, in a plume of a major point source
(petrochemical complex). 9,10-O
Few studies report MPHE and M
The results of the
The substance patterns of PAHs in the six different sea regions are shown in Fig. 3a. PHE was by far the most abundant PAH in all regions (average contribution of 49 %), followed by FLN, ACE, FLT and PYR, with average contributions of 24 %, 10 %, 6 % and 5 %, respectively. The predominance of 3-ring PAHs was also found in earlier studies of the marine atmosphere (Ding et al., 2007; van Drooge et al., 2010; Lohmann et al., 2013; Kim and Chae, 2016; González-Gaya et al., 2019). It can be noted that the PAH composition patterns were similar in all regions. However, the patterns of the Mediterranean Sea and the southern Red Sea differed from the other regions. The contribution of PHE in the southern Red Sea was higher than the average, while it was lower than the average in the Mediterranean Sea. The opposite could be observed for FLN. The different pattern in the Mediterranean Sea was mainly caused by the samples from the second leg with high influence of aerosols from Europe.
Relative amount of
The distribution pattern of RPAHs among the campaign regions is presented in
Fig. 3b. The RPAHs did not show significant regional differences in the
composition pattern. 2-MPHE, 1-MPHE and 3-MPHE were the most abundant
alkylated PAH species throughout the campaign, making up 22 %, 16 %
and 12 % of the total RPAHs measured. Among the M
As shown in Fig. 3c, the regional differences between the OPAH composition
patterns are more pronounced than the regional average PAH and RPAH
patterns. 1,4-O
In the Gulf of Oman, the contribution from high-molecular-weight OPAHs
(4-ring OPAHs) was higher compared to the other regions. The composition
pattern of the samples from the Arabian Sea differed from the other samples
because of a lower share of 9,10-O
Similar to the OPAHs, the regional differences in the NPAH composition
pattern are more pronounced than the PAH and RPAH patterns. As illustrated
in Fig. 3d, the most abundant NPAHs were 2-NNAP, 3-NPHE, 2-NFLT and 1-NPYR,
with an average contribution of 45 %, 18 %, 15 % and 12 %,
respectively. The contribution of 2-NNAP ranged between one-third and one-half
in all regions. However, it was not detected above the LOQ in the gas phase of
samples from the Arabian Sea. Due to the total detection frequency of
The fractional contribution of 1-NPYR is high in the Gulf of Oman and the Arabian Gulf. This can be explained by a significant amount of 1-NPYR in the exhaust of fossil fuel combustion (IARC, 2018; Zhao et al., 2015) and its high abundance near petrochemical industries (Caumo et al., 2018). It is used as a marker for primary emissions since it does not have significant secondary sources (Arey et al., 1986). The relatively short estimated lifetime of 1-NPYR in air due to photodegradation (Fan et al., 1996; Feilberg and Nielsen, 2000) and the small reaction rate with OH (Table S2, US EPA, 2019) could explain its low contribution in the Mediterranean Sea, since we sampled relatively aged air samples in that region. The relatively high contribution of 1-NPYR in the Arabian Sea might be due to bypassing ships (Table S18) as we found 1-NPYR highly abundant in the ship exhaust (Sect. 3.3.1). The high contribution of 1-NPYR in samples D40–42, in or close to the Gulf of Aden, is possibly due to pollution from coastal cities in the northeastern province of Somalia. The continental influence of these samples is also shown in the results of the PMF analysis (Fig. 4b). The large contribution of long-range-transported aerosols in the Mediterranean Sea is also illustrated by the high contribution of 2-NFLT, which is formed in secondary processes (Arey et al., 1986) and undergoing long-range transport on even a global basis (Wilson et al., 2020). The contribution of 2-NFLT is also high in the southern Red Sea, a region with minor influence of primary emissions but higher fraction of long-range-transported aerosols. 3-NPHE, which has primary (primary: Bamford et al., 2003; mainly primary: Zhuo et al., 2017) and secondary sources (secondary: Atkinson and Arey, 1994; Ringuet et al., 2012a; mainly secondary: Tomaz et al., 2017), has an almost similar contribution in all regions. This could be explained by various different sources or a long mean atmospheric lifetime.
As shown in Figs. 4 and S4 as well as described in the Supplement (Sect. S2.4.1), the PMF analysis revealed five different source factors, namely fresh and aged shipping emissions, continental emissions, residual oil combustion and desert dust.
The PAHs, NPAHs and OPAHs in the air over the Mediterranean Sea and in the
seas around the Arabian Peninsula are believed to originate primarily from
fresh and aged shipping emissions. Fresh shipping emissions, mainly from the
ship stack of our research vessel
PMF group 2.
Another important source of PAH derivatives was continental emissions. Based on the distribution of residence times of air masses during these sampling times, we could conclude that these emissions mainly came from Europe (especially received in the Mediterranean Sea but also in the Arabian Gulf), countries around the Arabian Gulf (mainly received there) and Egypt (mainly received in the northern Red Sea). Furthermore, the PACs originated from residual oil combustion. High factor contributions (Figs. 4b and S4b) in the period between 24 July and 6 August 2017 were linked to the samples collected in the Gulf of Oman and the Arabian Gulf and influenced by the emissions in the coastal areas and offshore (Fig. S3e and f), as also reported by Bourtsoukidis et al. (2019), Eger et al. (2019), Pfannerstill et al. (2019) and Wang et al. (2020). The source factor identified with minimum contributions of NPAH and OPAHs was desert dust. The finding of PAH derivatives in the factor desert dust could be explained by mixing of dust with other emissions sources such as continental pollution or shipping emissions. The concentration of the factor desert dust peaked primarily during a period of Sahara dust outbreaks (from 13–18 July 2017), while samples were collected over the Red Sea and over the western part of the Gulf of Aden (Fig. S3c and d, see also Eger et al., 2019). Dust emitted on the Arabian Peninsula is evident during the sail in the Gulf of Oman and the Arabian Gulf (24 July and 6 August 2017, Fig. S3d and e) but mixed with several other sources.
The contribution of the individual OPAHs and NPAHs can be seen in PMF group 2 in Figs. 4 and 5, showing the relative contributions of each factor to the
concentration of each substance. All PACs targeted in the PMF run (group 2)
had a significant contribution from fresh shipping emissions as their
source. Moreover, by comparing several samples with a significant influence
of the exhaust from the own stack (samples D16; 17; 20; 22; 23; 28; 37; 38;
see Table S4 and Fig. S4) to the stack-filtered regional average
concentrations, we could show that almost all detected PAHs, NPAHs and OPAHs
were elevated in the samples with fresh shipping emissions (Table S17).
1-NPYR showed the highest ratio of contaminated to filtered samples among
the NPAHs, while 11-OBaFLN and 1-(CHO)NAP had the highest ratio among the
OPAHs. All targeted OPAHs showed a ratio higher than 1. For the NPAHs, only
2-NFLT was not elevated, except for a ratio of 5 in the Arabian Sea. 2-NFLT
had been reported to be present in diesel particulate matter (Bamford et
al., 2003; Zimmermann et al., 2012). However, this was explained by the gas-phase formation of 2-NFLT after emission during sample collection.
Surprisingly, the concentration of 2-NPYR was significantly elevated in the
fresh shipping emissions. This is unexpected, as 2-NPYR was reported absent
in diesel exhaust (Bamford et al., 2003) and believed to be formed through
secondary formation only (Finlayson-Pitts and Pitts, 1999; Wilson et al.,
2020). Zhao et al. (2019, 2020) found significant amounts of 2-NPYR in ship
exhaust gas depending on the fuel type and the engine loading. They report
high emissions of this compound, especially with heavy fuel oil use and
mainly under low engine speeds. The abundance of 2-NPYR was explained by
secondary formation due to higher NO
Relative contribution of the five factors resolved by PMF to the concentration of each substance in PMF group 2.
The large contribution of aged shipping emissions to the concentration of
2-NFLT and 2-NPYR (Fig. 5) illustrates the importance of secondary formation
of these two NPAHs. In contrast, 1-NPYR is not abundant in the aged
shipping emissions, showing that there is no significant secondary formation.
It has been reported that 1-NPYR arises solely from primary emissions
(Bezabeh et al., 2003; Reisen and Arey, 2005). The contribution of aged
shipping emissions to the occurrence of 3-NPHE could either be explained by
the higher atmospheric half-life of 79 h compared to 2-NFLT, 1-NPYR and
2-NPYR (Table S2, US EPA, 2019) or by secondary formation, as previously
suggested (Tomaz et al., 2017). All detected OPAHs were abundant in the aged
shipping emissions. Their abundance points to a long lifetime or formation
in the atmosphere. The relative contributions of 11-OBaFLN, BAN and
7,12-O
1-NPYR and 3-NPHE seem to be good tracers for oil combustion, hence the
correlation with emissions from the petrochemical industry in the Gulf of
Oman and the Arabian Gulf. 1-NPYR and 3-NPHE are known to be emitted during
combustion of oil (Streibel et al., 2017). In addition, all OPAHs included
in the PMF, except for 1,4-O
Except for 11-OBaFLN, all considered PAHs, OPAHs and NPAHs are partly from
continental pollution (Fig. 4a). The abundance of these air pollutants in
continental pollution, including 11-OBaFLN, has been shown in many studies
(Bamford and Baker, 2003; Albinet et al., 2007, 2008; Wei et al., 2015;
Tomaz et al., 2016; Drotikova et al., 2020; Lammel et al., 2020;
Nežiková et al., 2021). The missing contribution of continental
pollution to the concentration of 11-OBaFLN might be because of its
comparably low atmospheric half-life due to degradation by OH (Table S2, US
EPA, 2019). Continental pollution was highly abundant in the Mediterranean
Sea (Fig. 4b), where we found the highest concentrations of the OH radical
of the entire AQABA campaign. 1,4-O
The ratio of the particulate concentration of BAP to BAP
The relatively low ratios in all other regions might be explained by the low
number of primary sources of air pollutants at sea except for ship traffic
and some emissions from the offshore oil and gas industry. Thus, the
pollution from urban and industrial areas, which are located mostly on the
coast, is already slightly aged when reaching the sampler on the ship,
depending on the proximity to the emission sources. This could also be the
explanation why the second highest regional average values were found in the
southern and the northern Red Sea, receiving the emissions from the nearby
coast as well as from the intense ship traffic in the region. The lowest
regional average
The RPAHs could not be included in any multivariate analysis since the
RPAH sampling followed another sampling protocol than the PAHs, OPAHs and
NPAHs, with only very few similar sampling times. The ratio of
Similar to the ratio of
Box-and-whisker plot of the ratios
The reason for the low incidence of high ratios could be that the
concentrations of atmospheric oxidants OH and NO
The ratio of
In contrast to the regions with polluted air, a low ratio was observed in
air over the Arabian Sea and in the parts of the Mediterranean Sea far from
the coast. The average ratio in the Arabian Sea was only 0.36. This points
to primary sources (as indicated in Sect. 3.3.2) and/or very low NO
Since 2-NPYR is almost entirely formed by the reaction of PYR with OH
radicals during daytime, while 2-NFLT can be formed by daytime reaction
with OH as well as by night-time reaction with NO
As illustrated in Fig. 6b, the lowest average ratio (9.5) was found in the
northern Red Sea, while the ratio of 15.8 (first leg: 22.3; second leg:
13.4) in the Mediterranean Sea was the highest regional average value. The
high value in the Mediterranean Sea during the first leg was due to two
exceptionally high values in samples D1 and D5 (coordinates in Table S1).
The formation of these NPAHs will be largely determined by the accumulated
night-time NO
A high ratio of the secondarily formed PAH derivatives 2-NPYR and 2-NFLT
(Arey et al., 1986; Bamford and Baker, 2003; Reisen and Arey, 2005) to their
parent PAHs PYR and FLT, respectively, indicates long-range-transported
aerosols with a significant concentration of the atmospheric oxidants OH and
NO
Distribution of residence times of air masses received in the
Arabian Gulf:
Another sample with a high ratio of secondarily formed NPAHs is sample D48
in the northern Red Sea nearby the Suez Canal. Similar to the first night in
the Arabian Gulf, Wang et al. (2020) determined a high OH exposure during
the first night in the Gulf of Suez (22–23 August 2017) accompanied by a
high mixing ratio of acetone. The finding that aerosols sampled between the
22 and 23 August 2017 (D48) were atmospherically aged is supported
the high PAH derivative
Generally, low and high
We found significant positive correlations (
The highest concentrations of PAHs, OPAHs and NPAHs are found in the
sub-micrometre fraction of particulate matter, PM
Figure 8 shows the campaign average mass size distributions (MSDs) of the PAHs
and PAH derivatives. The MSDs of PAHs, NPAHs and OPAHs are mainly unimodal
given the coarse size resolution of the impactor with six size ranges within
PM
Campaign average mass size distributions (MSDs) of
The ratio between the concentrations in particles
Since the process of redistribution depends on time, a shift of the MMD to larger particles sizes is found for aged aerosols (see exemplary Fig. S10). For instance, Lammel et al. (2017) found two maxima for the 4-ring PAHs at a marine background site (same cascade impactor as the one used in this study). The second maximum was explained by aged aerosols at the marine site. The samples showing a maximum of the sum of PAHs at higher particle diameters in our study can also be attributed to aged aerosols (aged samples C6 and C7 in Arabian Gulf; C27, C28 in Mediterranean Sea without close primary emission sources; C22 in very clean air over the Arabian Sea, C24 in southern Red Sea possibly because of Saharan dust).
For compounds with similar vapour pressures and polarity (or sorption to the
PM matrix), differences in the MSDs could point to a different origin and/or
time elapsed since release or formation of the compounds. The relative
amount of the primarily emitted 1-NPYR in the fraction with a particle size
of
For the first time, PAHs and their derivatives were measured in the marine
environment around the entire Arabian Peninsula in a comprehensive ship
campaign. The atmospheric average concentrations of
Source apportionment showed that the PAHs and their nitrated and oxygenated
derivatives mainly originated from fresh and aged shipping emissions. All
OPAHs and NPAHs except 2-NFLT, which were frequently detected during the
campaign, showed elevated concentrations in fresh shipping emissions. 1-NPYR
among the NPAHs and 11-OBaFLN and 1-(CHO)NAP among the OPAHs showed the
highest relative increase in their concentration. In contrast, 2-NFLT and
2-NPYR were highly abundant in aged shipping emissions due to secondary
formation. 1-NPYR, 3-NPHE and several OPAHs had a significant contribution
from residual oil combustion. PAH derivatives were clearly enriched in
long-range-transported plumes from polluted regions in Egypt, the Arabian
Gulf, and southern and eastern Europe. Throughout the campaign, the highest
concentrations of PAHs, OPAHs and NPAHs were found in the sub-micrometre
fraction of particulate matter (PM
The data used in this study are archived and distributed through the KEEPER
service of the Max Planck Digital Library (
The supplement related to this article is available online at:
MW evaluated the data and wrote the manuscript. GL supervised this study.
MI and RP did the sampling. MK, MI and EGS provided the data about alkylated
PAHs and wrote this part. PPo performed the PMF and wrote the part. BN
created the FLEXPART Lagrangian particle dispersion model results. JK
provided the data about metals. PK and PPř performed the PAH, NPAH and OPAH
sample preparation and analysis. IT created GPS plots and provided NO
At least one of the (co-)authors is a member of the editorial board of
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We thank Hays Ships Ltd, Captain Pavel Kirzner and the
This research was supported by the Max Planck Society, the Czech Ministry of Education, Youth and Sports – Research Infrastructure RECETOX RI (no. LM2018121 and CZ.02.1.01/0.0/0.0/16_013/0001761), the project CETOCOEN EXCELLENCE (no. CZ.02.1.01/0.0/0.0/17_043/0009632) and the Czech Science Foundation (GACR 20-07117S). This project was supported by the European Union's Horizon 2020 Research and Innovation programme under grant agreement no. 857560.The article processing charges for this open-access publication were covered by the Max Planck Society.
This paper was edited by Sergey A. Nizkorodov and reviewed by two anonymous referees.