Environ. Sci. Techno/. 1995, 29, 2405-2413
PAHs in Air Adjacent to Two Inland Water Bodies BRIAN GARDNER, C. NICHOLAS HEWITT, AND KEVIN C. JONES*
Environmental Science Division, Institute of Environmental and Biological Sciences, Lancaster University, Lancaster LA1 4YQ, U.K.
Air PAH concentration data have been obtained adjacent to two U.K. water bodies, as part of a study to quantify atmospheric deposition inputs. The sites are 'semiurban' (Castleshaw) and 'rural' (Esthwaite Water, EW), based on PAH air concentrations, compound ratios, and characteristics of the ambient aerosol derived from sorption data analysis. Both sites experienced increased atmospheric loadings of total suspended particulate and PAH in winter. Particle size distributions indicated a seasonal shift in the age of the air mass, suggesting fresher aerosol and increased emissions in winter. Vehicle emissions probably make a greater contribution in non-winter periods, while heating production sources dominate in winter. Particle size data indicate that aging of combustion aerosol occurs by both coagulation and elution of the more volatile compounds to background aerosol of greater mass median diameter (MMD). Precipitation strongly influenced air concentrations and phase distributions; particulate scavenging of PAH is more rapid than vapor-phase removal. Consistent with this, statistical analysis indicated that winter air concentrations were more heavily influenced by precipitation rates than temperature; in summer, the reverse was true, There is evidence of a significant source of low molecular weight PAH in the vapor phase in summer months. This is thought to be due to volatilization of PAHs that have previously been deposited from soils and vegetation surfaces.
Introduction Recent European Union legislation aimed at controlling the input of certain chemicals to the aquatic environment has emphasized the importance of the anthropogenic organic contribution to the overall contaminant loading of water bodies. One specific aim is to try and account for 'diffuse' source inputs (1). Indeed, for many water bodies it is considered likely that diffuse sources-aerial inputs essentially-of priority organic chemicals are often more important than point sources, such as agricultural or road runoff, and industrial effluents. Eisenreich etal. ( 2 , 3 ) for , example, concluded that '85% of the total input of PCBs to Lake Superior was from atmospheric deposition.
0013-936X/95/0929-2405$09.00/0
1995 American Chemical Society
There has been little attempt to estimate atmospheric contributions to freshwater bodies in the U.K. Reservoirs are of particular interest in this regard. Little information is available on the atmospheric inputs to the many small lakes and reservoirs feeding U.K. population centers. Most of these are situated within tens of kilometres of urban areas and large-scale emissionsources (industry,transport). In addition, reservoirs will not receive urban run-off and sewerage discharges. The overall objectives of this investigation were first to quantify and assess atmospheric deposition inputs for a group of organic contaminants to two U.K. inland water bodies. To achieve this, it was necessary to establish wet and dry deposition fluxes to the water surface and to relate these in turn to overlying air concentrations. Secondly,by investigating the relevant compound-dependent parameters and environmental processes involved in wet and dry deposition, our objective was to develop a model for deposition to natural water bodies. A range of polynuclear aromatic hydrocarbons (PAHs) was selected for detailed study because they are of relevance to water quality issues and because individual compounds within the group vary widely in terms of their gasparticle distribution in air. They therefore display a range of depositional characteristics. This paper presents data on the PAHs in air at the two study sites frommid-1990to mid-1991. Asubsequentpaper will present data on deposition processes and fluxes prior to the development of a process and mass balance model.
Materials and Methods Sample Sites. Two sample sites were selected in northwest England. The first was on the north shore of Castleshaw Upper Reservoir near Oldham, in industrialized Lancashire (OS Grid Ref SJ 997 103). This is an upland water supply reservoir in a semi-urban location 18 km northeast of the city of Manchester. Two small towns are within 5 km of this site: the large towns of Oldham and Rochdale are 10 km to the north. The site is owned by North West Water plc, who maintain a rain gauge at the site. Additional meteorological data were available from Manchester Airport, ca. 25 km from Castleshaw. Land use is for grazing, and no wind shadowing obstructions exist. The surface area of the reservoir is approximately 0.4 km2. The second site was established at Esthwaite Water, Cumbria, on land owned by the Institute for Freshwater Ecology, Windermere. The nearest potential sources of airborne PAHs are a minor road that circumscribes the lake and some houses within 50- 100m. Two small villages are located within a distance of 3 km, and a number of small towns are within a 20 km radius. The nearest large town is Barrow, 40 km to the south. Esthwaite Water is a small lake approximately 1km2in surface area. It has been extensively used for scientific studies, and consequently no motorized boats are allowed on it. It is consideredtypical of the many small lakes in the Lake District used solely for recreational purposes. The Institute for Freshwater Ecology maintains a full meteorologicalmonitoring station on-site. Air Sampling. High VolumeAirSampling. Air sampling was carried out using a standard high-volume air sampler modified to incorporate a backup cylinder downstream of the Whatman GFlA glass fibre fdter. Polyurethane foam
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(PUF)plugs were contained in the cylinder to absorb vaporphase compounds. Flow rates of 0.4 and 0.6 m3 min-' measured with a Kurz hot wire aneomometer were used. Simultaneous sampling of material deposited by dry deposition was carried out over periods of at least 7 (and typically 10-14) days. Air sampling was intermittent by means of a timer, which stored up to 28 different onloff commands during any one period. Samples of -1000 m3 were obtained over ca. 36 hll4-day sample period. The production and emission of PAH can exhibit a diurnal cycle depending upon what sources dominate at the particular site (4). To ensure the sampled air was representative of the air masses over the site during the whole period, the following program was used to weight the sample equally around the clock and over the whole week Monday06.0009.00 h; Tuesday 10.00-13.00; Wednesday 14.00-17.00; Thursday 18.00-21.00; FridaylSaturday 22.00-01.00; Sunday 02.00-05.00. Two PUF plugs were used for each sample; these were analyzed separately to check for breakthrough of vapor-phase compounds. Sampling was carried out at both sites from July 1990 to July 1991. Meteorological data (rain, ambient temperature) and total suspended particulate measurements were also recorded. The most important sampling artifact reported for highvolume sampling is due to vapor-particulate phase redistribution (5).Changes in the air concentration of each phase during a sampling period and changes in the ambient temperature can lead to volatilization losses (where condensed-phase semivolatile compounds collected onto the filter are blown off and sorbed by the PUF plug) or to sorption of part of the vapor-phase component from the airstream onto the filter or particulate material already collected on the filter. The blow-off artifact is considered to be more common (10). A recent comparative study of sampling methods suggests a less drastic artifact for traditional filter-sorbent sampling trains (7). Typically, the backup contained '25% of the total vapor phase component, with greater penetration to the second plug observed for the lighter compounds, as expected. Size Fractionated Sampling. Approximately every 3 months, a seasonal air sample was taken at each site to fractionate atmospheric particulate material into different size ranges and to obtain information on the distribution of PAH over the size range of atmospheric aerosol. A 4-stage high-volume cascade impactor (Anderson 2000), mounted on a high-volume sampler and operated continuously at a constant flow rate for 6-7 days, was used to obtain five fractions: '7.0pm (aerodynamic diameter);3.3-7pm; 2.03.3 pm; 1.1-2.0 pm; '1.1 pm. PAH Analysis. All samples were extracted for 8 h with dichloromethane on a Buchi Soxhlet extractor system prior to analysis by high-performance liquid chromatography (HPLC) with fluorescence and diode array detection as described previously (13). The following compounds were routinely determined: acenaphthenel fluorene (co-elutors) (Ace/Fl), phenanthrene (Phen), anthracene (Anth), fluoranthene (Fluor), pyrene (Py), benzanthracenelchrysene (BalCh),benzo [b]fluoranthene (BbF),benzo[klfluoranthene (BkF), benzo[a]pyrene (BaP), and dibenz[ah]anthracene (Dib). Percentage recoveries of PAHs spiked at appropriate concentrations onto filters and PUFs are given in Table 1. The accuracy and precision of the method were assessed by analysis of the NIST reference urban dust (CRM 1649). Data were as follows: Fluor = 7.7 pg g-' (2% RSD) [quoted 2406
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VOL. 29, NO. 9,1995
TABLE 1
Percentage Recoveries of Spiked Matrices (YORSD) PAH
filter
PUF
Ace/Flr Phen Anth Fluoranth PV Batch BbF BkF BaP DiB
13 (51) 53 (44) 23 (69) 62 (33) 43 (38) 71 (17) 78 (11) 62 (5) 35 (31) 84 (9)
62 (4) 71 (11) 78 (12) 64 (8) 30 (7) 84 (9) 66 (14) 61 (3) 80 (17) 86 (13)
value 7.1 f 0.51; BaP = 3.6 (37% RSD) [2.9 i 0.51; Phen = 5.3 (12% RSD) [4.5 & 0.31; Py = 6.7 (3% RSD) [6.3 i 0.41; BbF = 6.7 (3% RSD) [6.2 f 0.31; and BkF = 2.2 (3% RSD) [2.0f0.1]. OnlyFluorandBaParefullycertified;theother values are provided by NIST for information only. Results indicated that the method slightly but consistently overestimated PAH content for the two referenced compounds and four additional PAHs. One result (Py) is within the uncertainty bounds corresponding to the 95% confidence interval; all the other results correspond to the NIST values at the 85 or 90% confidence level. Sample detection limits, calculated on the basis of an air volume of 1000 m3, an extract volume of 300 pL and an injection of 5 pL were of the order 2-10 pg m-3 in air for all the compounds.
Results and Discussion General Comments on Concentrations. The median, mean, and range of concentrations for each compound and the total (C) PAH are reported in Table 2 for both sites. Median CPAH concentrations-the better indication of general ambient levels-are similar at the two sites: 18.6 ng m-3 at Esthwaite Water and 16.9 ng m-3 at Castleshaw. Mean CPAH concentrations at Esthwaite Water (40ng m-3), on the other hand, were roughly double those at Castleshaw (22 ng m-3), largely due to the effect of two high concentration events at Esthwaite Water between July 31 and August 14,1990 (254ng of CPAH m-?, and between January 27 and February 5, 1991 (120 ng of CPAH m-9). CPAH concentrations at Castleshaw had a narrower range (9-52 ng m-3) than at Esthwaite Water (6-254 ng rn-"). These values compare with ZPAH concentrations measured at 4 U.K.urban sites of between 11 and 735 ng m-3 in 1991; annual median concentrations in London, Manchester, Cardiff, and Stevenage city center sites were 164, 134, 125, and 98 ng m-3, respectively (14). Background air concentrations of PAH reported at remote sites are 1-2 orders of magnitude lower: the Swedish background air concentration for CPAH,,=15has been established at 2.5-11 ng m-3 (mean = 4.1 ng m-j) (10). Niehaus et al. (11) found nonurban levels for TPAH,,16 of 0.1- 10ng m-3 in Germany. Continental background air was measured at 3.8 ng m-3 for XPAHn=13 by Baker and Eisenreich (12). Sampling at a remote wilderness site in North America, McVeety and Hites (13) typically obtained XPAH,=11 levels of '2.0 ng m-3. Esthwaite Water and Castleshaw are generally between the background and urban levels, indicating that these sites are semirural/semiurban locations. The median mixture of compounds was quite similar at the two sites. Phenanthrene was easily the most abundant compound, averaging 44 and 49% of the ZPAH at the two sites. Acenaphthenelfluorene (12-14%), Fluor (13-14%),
TABLE 2
Median, Mean, and Range of Individual PAHs and ZPAH Concentrations Measured at Esthwaite Water and Castleshaw during the Study Period (EW, n = 19; C, n = 18 samples) (ng m-3)e Esthwaite Water
Castleshaw
compound
median
mean
range
acenaphth/fluor phenanthrene anthracene fluoranthene pyrene benz[alanth/chrys benz[b]fluoranthene benz[klfluoranthene benzblpyrene dibenzla,hlanthracene
2.3 (12) 8.2 (44) 1.1 (6) 2.5 (13) 2.4 (13) 0.38 (2) 0.97 (5) 0.30(2) 0.31 (2) 0.08( < I ) 18.6
6.2 15.7 1.6 3.7 5.7 1 .o 2.3 0.64 2.8 0.38 40.1
0.08-39 0.35- 107 0.08-7.5 0.38-23 0.26-62 0.04-6.2 0.1-17 0.02-3.7 7.0
lo*-6
FIGURE 4. Particle size distribution of total suspended particulate at (a) Castleshaw and (b) Esthwaite Water.
for this apparently anomolous seasonal particle size distribution are discussed below. Particle size distributions are consistent with literature reports of TSP particle size distributions in urban and rural areas, indicating bimodality of particle volume (also mass, assuming constant density) around 0.2-0.3 and 3-10 pm aerodynamic diameter size ranges (22). Most studies indicate a maximum involume concentration for the larger mode, which is not suggested by impactor results for Castleshaw and Esthwaite. However, Willeke and whitby (22)note that, above about 5 pm aerodynamic diameter, different capture efficiencies for larger particles can be significant. Mass median diameters (MMD) for TSP are given in Table 5. These have been computed from the gravimetric data for each stage by plotting the cumulative percent mass concentration < particle diameter against particle diameter on log-probability paper in the usual manner (23). The geometric standard deviation obtained for the ratios of the distribution at 84 and 50% values are also quoted. The figures for TSP MMD should be treated with caution owing to the bimodality of some of the samples. The number of resolvable size fractions of the Anderson impactor is insufficient to confidently assess log normality for each mode by comparison of the 8476150% to 50%/ 16% ratio. Modes are typically located in size ranges captured by the first or final impactor stages only. Despite this, a
TABLE 5
Mass Median Diameters (,urn)
for P A P
Esthwaite Water autumn winter
spring
compound
MMD
GSD
MMD
GSD
MMD
GSD
Ace/FI Phen Anth Flr PYr BaCh BbF BkF BaP DiB tot PA14 TSP
0.32 50.03 50.04 0.40 0.21 0.02 0.05 0.02 0.05
