Article pubs.acs.org/est
Semivolatile Organic Contaminants in the Hawaiian Atmosphere Xianming Zhang,† John Barnes,‡ Ying D. Lei,† and Frank Wania*,† †
Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Ontario M1C 1A4, Canada Mauna Loa Observatory, National Oceanic and Atmospheric Administration, Hilo, Hawaii 96720, United States
‡
S Supporting Information *
ABSTRACT: An air sampling campaign on the Island of Hawaii aimed to assess background concentrations of semivolatile organic compounds (SVOCs) over the Central Northern Pacific and to explore their distribution along an altitudinal transect. XAD-resin-based passive air samplers were deployed from May to September 2011 at six sites along a transect from the northeastern coast to the Mauna Loa Observatory and at three other island sites. By crossing the trade wind inversion, the transect comprised the marine boundary layer and free troposphere. At the two ends of the transect, flow-through samplers simultaneously sampled air at monthly resolution. Elevated levels of dieldrin, chlordane- and DDT-related pesticides, polycyclic aromatic hydrocarbons (PAHs), and polybrominated diphenyl ethers (PBDEs) at two urban sites indicated contributions from local sources. The composition of chlordane and DDT-related residues indicated recent emissions. PAHs concentrations that decline more rapidly with increasing elevation than those for PBDEs are consistent with faster atmospheric degradation of PAHs. SVOC levels on Mauna Loa were generally at the lower end of concentration ranges reported for remote sites, including the Arctic. However, in contrast to the Arctic, long-range atmospheric transport is deemed less important than human-induced material flow as the source of SVOCs to the island’s atmosphere. ing.7,13,14 However, HVAASs require electricity and frequent operator visits and are difficult and expensive to deploy at multiple sites to study the spatial variations of SVOCs in the air of remote regions.13 To overcome these disadvantages, passive air samplers (PASs) are increasingly used to obtain timeintegrated SVOC air concentrations in various types of environment.15−17 PASs are especially useful in providing high spatial resolution data to elucidate the fate of SVOCs in remote regions such as mountains.10,18−22 Although PASs have many advantages and have been widely used, passive sampling rates are potentially influenced by many factors. Understanding these factors is necessary in order to properly interpret and compare PAS-derived air concentrations. A few studies have investigated potentially influential factors such as wind, temperature, properties of the target chemicals, and sampler configuration.23−26 While time-integrated sampling is an advantage of PASs, the sampling rates are generally low (15 m3/d) and has proven useful for monitoring SVOCs in remote areas with a much higher temporal resolution than PAS.28 In this study, an air sampling campaign using PASs and FTSs was conducted on the Island of Hawaii with the aim of exploring the vertical variations of SVOCs from sea level to the top of the Mauna Loa volcano to assess the occurrence of several groups of SVOCs in the free troposphere over the central northern Pacific and compare their concentrations with those in the marine boundary layer.
2. MATERIALS AND METHODS 2.1. Sampling Sites. Located in the Central Northern Pacific, the archipelago of Hawaii is relatively easily accessed, despite being more than 3000 km from the nearest continent. The air sampling campaign was conducted on the Island of Hawaii (Figure 1), which is a volcanic island covering 10432 km2.29,30 Less than 1.5 million people live within a 3000 km radius of the island, which itself has a population of 185000.29 The elevation on the island rises by more than 3000 m over a horizontal distance of less than 60 km. Prevailing northeasterly trade wind bring marine air to the island. A persistent trade wind inversion caps the atmospheric planetary boundary layer at approximately 2000 m above sea level.31 These geographical features make the island an ideal place to study LRAT of SVOCs in the tropical region. 2.2. Sampling Campaign. Cylindrical PASs using XADresin filled mesh cylinders as the passive sampling medium were deployed to conduct time-integrated sampling at nine sites (labeled A-I in Figure 1) from May to September 2011. Six of these sites form a transect from the northeastern coast (Site A, elevation: 0 m) to the Mauna Loa Observatory (Site F, elevation: 3400 m) and extend from the planetary boundary layer (sites A−D) to the free troposphere (sites E and F). For comparison PAS were also deployed at sites on the east end of the island (G), in Volcano Village (H), and in the northeast of the island close to the village of Waimea (I). Two FTSs with vortex sensors for wind speed measurements were deployed at B
DOI: 10.1021/acs.est.7b03841 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 2. Spatial distributions of (a) hexachlorobenzene (HCB), (b) hexachlorocyclohexanes (HCHs), (c) chlordanes, (d) dieldrin, (e) dichlorodiphenyltrichloroethane (DDT), and (f) endosulfan derived by passive air samplers (PASs, 20 cm-long XAD filled mesh cylinder as the sampling medium) on the Island of Hawaii. Dash lines indicate the altitude of the sampling sites.
isooctane, blown down with high purity nitrogen, transferred to a vial, and further reduced to 0.5 mL. To the vial, 10 μL of 10 ng/μLmirex and 20 μL of 1 ng/μL each of BDE-75, 116, 205 (not present in air) were added to quantify the recovery of surrogates. 2.4. Sample Analysis. Selected PAHs, PBDEs, and pesticides were analyzed using an Agilent 7890A gas chromatograph coupled to an Agilent 7000A triple quadrupole mass spectrometer with electron-impact ion source. Instrumental settings and parameters for analysis of the three groups of compounds are listed in Table S3. All compounds were detected using multiple reaction monitoring mode with helium (2.25 mL/min) as the quench gas and nitrogen (1.5 mL/min) as the collision gas. The precursor ions, product ions, and collision energies selected for multiple reaction monitoring of PAHs, PBDEs, and pesticides are listed in Tables S4−6. 2.5. Quality Assurance. Sampling and analysis followed routine QA/QC practice. We quantified field blanks, analytical procedure blanks, and recoveries of isotope-labeled spikes added prior sample extraction. Ratios of quantifier and qualifier
ions had to be within 30% of the expected value to confirm the target peaks from the chromatogram. Eight field blanks of the XAD-filled mesh cylinder were collected. Ten field blanks (one for each site every month) were originally planned for the FTSs during the whole sampling campaign. However, two glass jars broke while being transported to the lab, so the number of field blanks for the FTSs was reduced to eight. Field blanks of the sampling media were exposed to air at the sampling sites for 1 min and stored and transported the same way as the samples until analysis. Of the chemicals analyzed, only fluorene and phenanthrene were detected in the field blanks for the FTSs. The blank levels (1− 10 ng/sample) were
