Environ. Sci. Technol. 2005, 39, 4729-4738
Detailed Study of Factors Controlling Atmospheric Concentrations of PCNs ROBERT G. M. LEE,* GARETH O. THOMAS, AND KEVIN C. JONES Department of Environmental Science, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster LA1 4YQ, U.K.
Atmospheric concentrations of polychlorinated naphthalenes (PCNs) (108 samples in total) were measured at two rural/ semirural sites in England and one remote site on the west coast of Ireland in the years 2001 and 2000, respectively. Detailed analysis of the factors affecting concentrations is performed. At Mace Head (MH) Ireland, concentrations of ΣPCNs ranged between 1.7 and 55 pg m-3 with a mean of 15 pg m-3 and were controlled primarily by advection. ΣPCNs concentrations at Hazelrigg (HR), northwest England, ranged between 31 and 310 pg m-3 with a mean of 110 pg m-3, and at Chilton (CH), southwest England, ranged between 31 and 180 pg m-3 with a mean of 85 pg m-3. Data from the HR site shows that PCN concentrations have not declined between the early 1990s and 2001, while PCB concentrations have declined. The ratio of the ΣPCNs/ ΣPCBs was close to or greater than 1 at all sites. From air mass back trajectories, it is clear that local/regional sources influenced concentrations of PCNs at all sites, particularly at MH. At the two English sites during the summer, concentrations of PCNs were strongly influenced by temperature, indicating that air-surface exchange processes play an important role. Advection became more influential during winter, particularly at CH, where a different homologue profile was observed in some samples when air masses approached from the southwest and PCN concentrations increased. The average mixture profile of PCNs in air was similar to that observed in other studies and different from that in Halowax 1014.
Introduction Polychlorinated naphthalenes (PCNs) have been identified in a range of environmental media including Arctic air at both land and sea based sampling locations (1); air from urban, rural, and remote sites in North America and Germany (2-6); in marine mammals (7); pelagic environments and food chains (8-10); fish and birds from the Great Lakes (11, 12); and human adipose tissue and breast milk (13). They have similar physicochemical characteristics to PCBs and have been produced commercially as technical mixtures, such as Seekay Waxes (ICI, U.K.), Nibren Waxes (Bayer, Germany), and Halowaxes (Koppers, U.S.A.). The latter company voluntarily ceased production in 1977 (14). In the U.S.A. and Europe they were used in similar wide ranging applications to PCBs. In the 1970s in the U.K. those uses that were documented suggest that most PCN technical mixtures * Corresponding author phone: (+44 1524) 592578; fax: (+44 1524) 593985; e-mail:
[email protected]. 10.1021/es048156c CCC: $30.25 Published on Web 05/27/2005
2005 American Chemical Society
were used in capacitor paper impregnation, and as a wood preservative (14). In addition to direct sources of PCNs resulting from the uses of technical mixtures, a number of indirect sources/inputs to the environment have been identified. For instance, PCNs are present as contaminants in PCB products (15) and may be produced during combustion processes and metal refining (16, 17). Several of the PCN congeners exhibited dioxin-like toxicity and have been ascribed relative potencies (REPs) (18, 19). Global production of PCNs is estimated as being 10% that of PCB production (14, 20). PCNs have been proposed as potential candidate POPs for inclusion into the UNECE POPs Protocol (21). However, in the U.K. very little information exists on environmental levels, emissions, production, and possible present uses. A number of studies have been undertaken in North America and the Arctic to assess atmospheric concentrations of PCNs and identify sources; however, little data are available for the U.K. and Western Europe as a whole. The paucity of atmospheric concentration data for PCNs has inhibited investigations into the long-term temporal trends of PCNs in the atmosphere. In addition investigations into the short-term trends can be hampered by practical considerations (e.g. studies are often limited to a few samples taken during limited periods). This study was therefore conducted, with the aim of establishing the following: background concentrations of PCNs and their variability in the atmosphere of a potential source country (U.K.); in European background air (Western Ireland); and some of the factors that control ambient PCN concentrations. This builds on a number of similar studies which have been carried out on other POPs in the U.K. atmosphere (6, 22-26).
Method A more detailed description of the sites used in this study and the sampling regime are given elsewhere (26), hence only a brief outline will be provide here. Sampling Sites. Mace Head (MH) is an atmospheric research station on the west coast of Ireland (53°20′ N, 9°54′ W) operated by the Department of Physics at the National University of Ireland, Galway. It is a European background/ remote site, ca. 50 m from the Atlantic Ocean. To the north, south, and east, the area is mostly rural. The nearest major town is Galway, about 55 km east. The majority of air systems that affect the site approach from the west. Hazelrigg (HR) is a field station belonging to Lancaster University (54°2′ N, 2°45′ W), situated on the northwest coast of England in a semirural area outside Lancaster, a town of ca. 70 000 inhabitants. The site is approximately 5 km from the Irish Sea. Much of the land within 50 km of the site is rural. However, a number of towns and cities are also within the area. The weather at the site is dominated by low-pressure systems from the west. Chilton (CH) (51°40′ N, 1°20′ W) is situated ∼20 km south of Oxford and ∼70 km west of London. The site is ∼120 km inland, with numerous villages, towns, and urban areas, within a 100 km radius. The site is affected more by weather systems approaching from the SW, with more southerly origins than at MH and HR. CH can be influenced by urban and industrial inland areas of the U.K. and can be classed as a semirural inland site (see Supporting Information Figure S1). Sampling Regime. General Metal Works GPS1 samplers were used at all sites to collect the air samples. The particulate fraction was trapped on a Whatman glass microfiber filter (GFF) (grade GF/A, 10 cm diameter) and the gas-phase fraction on two polyurethane foam plugs (PUF) (length 5 cm, diameter 6.5 cm, density 0.030 g cm-3). Two samplers VOL. 39, NO. 13, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Concentrations of PCNs at Hazelrigg (HR), Chilton (CH), and Mace Head (MH) (pg m-3)a IUPAC
HR mean
HR max.
HR min.
CH mean
CH max.
CH min.
MH mean
MH max.
MH min.
19 23 24 15 16 17/25 42 28/29/43 27/30 35 38/40 46 33/34/37 47 36/45 52/60 53 59 58 61 50 57 62 66/67 64/68 69 71/72 63 65 73 74 75 Σtri-CN Σtetra-CN Σpenta-CN Σhex-CN Σhepta-CN octa-CN ΣPCN
2.4 15 20 1.7 1.1 2.9 2.4 9.9 1.0 7.5 15 5.9 15 4.3 2.7 0.6 0.4 0.7 0.1 0.9 0.2 0.3 0.5 0.1 0.1 0.1 0.2 0.1 0.1 0.1 0.1 0.1 43 64 3.6 0.3 0.1
