Wet Deposition of Polychlorinated Biphenyls in Urban and

Table 1 gives a list of the sampling stations with their abbreviations and latitude ... a characterization of each site based on population and the lo...
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Research Wet Deposition of Polychlorinated Biphenyls in Urban and Background Areas of the Mid-Atlantic States DARYL A. VAN RY, CARI L. GIGLIOTTI, THOMAS R. GLENN, IV, ERIC D. NELSON, LISA A. TOTTEN, AND STEVEN J. EISENREICH* Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, New Jersey 08901

Spatial and temporal trends of polychlorinated biphenyl (PCB) concentrations in precipitation were measured at urban and background sites as part of the New Jersey Atmospheric Deposition Network (NJADN). The volume weighted mean concentration (VWM) of ΣPCBs (sum of PCBs) based on precipitation measurements at three background sites was in the range of 0.30-0.50 ng/L. Concentrations in precipitation at two urban-industrial sites were on average 7-43 times higher than background concentrations. Wet deposition fluxes of ΣPCBs at the two urbanized sites were 16 ( 3.4 and 3.9 ( 0.72 µg/m2-yr, while the background flux was approximately 0.30 µg/m2yr. On average, 97% of the total atmospheric washout (WT) of PCBs resulted from particle scavenging. The fraction of atmospheric PCBs on particles was the best predictor of atmospheric washout in both urban (log WT ) 0.71 ((0.049) log φ + 4.9 ((0.11); r2 ) 0.81) and nonurban areas (log WT ) 0.77 ((0.083) log φ + 5.6 ((0.16); r2 ) 0.64). Wet deposition fluxes of ΣPCBs are of the same order of magnitude as dry-particle deposition fluxes in all land-use regimes.

Introduction Atmospheric deposition is a major mechanism by which semivolatile organic contaminants (SOCs) enter many aquatic ecosystems (1-8). This is of particular importance for polychlorinated biphenyls (PCBs), which are transported from sources to background areas and subsequently removed from the atmosphere by depositional processes (e.g., wet, dry particle, gas absorption) and reaction with OH radical (9, 10). Wet deposition, or the removal of contaminants from the atmosphere by precipitation hydrometeors, is a significant, if not major fraction of the total atmospheric deposition of SOCs to many ecosystems, particularly those that lie distant from local sources (1, 4, 5, 11-17). While a considerable amount of work has been done to assess wet deposition of PCBs to aquatic systems (e.g., refs 1, 16, 18, 19), little work has been done to assess wet deposition across terrestrial gradients. Furthermore, few measurements of PCBs in rain have been made in the Mid-Atlantic States (8), with the exception of the Chesapeake Bay area (1, 20). Additionally, while many researchers have investigated the relative importance of gas and particle phase scavenging of SOCs from the atmosphere by precipitation (20-27), our understanding of the washout process in the environment is still relatively incomplete. * Corresponding author phone: +39-0332-78 90 37; fax: +390332-78 93 28; e-mail: [email protected]. 10.1021/es0158399 CCC: $22.00 Published on Web 06/22/2002

 2002 American Chemical Society

FIGURE 1. Map showing seven NJADN sampling sites where precipitation samples were collected. Abbreviations and other site information are listed in Table 1. Lightened areas indicate urban areas by population density. This research is part of the continuing New Jersey Atmospheric Deposition Network (NJADN), a research and air monitoring network which has the following as objectives: (i) to characterize the regional atmospheric levels of hazardous air pollutants, (ii) to estimate atmospheric loadings to aquatic and terrestrial ecosystems, (iii) to identify and quantify regional versus local sources and sinks, and (iii) to identify environmental variables controlling atmospheric concentrations of PCBs, polycyclic aromatic hydrocarbons (PAHs), chlorinated pesticides, trace metals, Hg, and nutrients. This paper focuses on spatial and temporal trends of wet deposition and atmospheric scavenging of PCBs at NJADN sampling sites, which represent a range of land-use regimes.

Experimental Section Sampling Stations. NJADN sampling stations are located throughout the state of New Jersey in different geographical land-use regimes including urban, suburban, and background areas of the region. Figure 1 shows a map of the region and identifies NJADN sites where precipitation was collected. Table 1 gives a list of the sampling stations with their abbreviations and latitude and longitude and gives a characterization of each site based on population and the local environment. Camden (CC) and Jersey City (JC) sampling sites are located within the urban-industrial stretches surrounding Philadelphia and New York City, respectively. New Brunswick (NB) and Chester (XQ) are suburban sites in densely- and lightly-populated areas, respectively. Sandy Hook (SH) and Tuckerton (TK) are coastal sites, where SH is located on the coastal fringe of the NY/NJ VOL. 36, NO. 15, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. NJADN Sampling Sites Collecting Precipitation site Camden Jersey City New Brunswick Chester Pinelands Sandy Hook Tuckerton a

CC JC NB XQ PL SH TK

characterization

lat./long.

urban-industrial (Philadelphia) urban-industrial (New York City) suburban light suburban background forest coastal (urban impacted) coastal (light residential)

39.93-75.12 40.71-74.05 40.48-74.43 40.79-74.68 39.96-74.63 40.46-74.00 39.60-74.37

date commenced

na

total vol (L)

July 15, 1999 Jan 8, 1999 Jan 24, 1998 July 21, 2000 June 1, 1999 Feb 6, 2000 Aug 7, 2000

28 36 59 12 27 18 13

495 510 591 128 414 267 152

Total number of samples. Collected in 12-, 18-, and 24-day intervals.

urban-industrial area in the lower Hudson River Estuary. The coastal TK site is characterized by a light residential population and is located 23 km north of Atlantic City, NJ. The Pinelands (PL) site is located in the northern portion of the Pinelands National Reserve, a protected pine/oak ecosystem with a sparse population (as low as 10 people per square mile (28)). Sampling of precipitation at each of the sites was initiated at different times throughout the NJADN project (Table 1), and PCB data reported in this work correspond to the period 1998 through May 2001 (except at NB, which ends March 2001). Precipitation Sampling Methodology. Integrated precipitation samples were collected at each of the sites using wet-only precipitation collectors (Meteorological Instrument Centre (MIC) Co.). The sampler is fitted with a moisture sensor that when activated operates a hood to pivot open to reveal a square-topped stainless steel collection funnel (46 cm × 46 cm). The electronic components are heated to allow for sampling during cold weather events and to prevent freezing. The funnel was fitted with a threaded glass column (approximately 30 cm × 1.5 cm i.d.) packed with XAD-2 (Supelco, mesh size 20-60) as a sorbant and held in place with glass wool plugs. A low wattage light bulb was used to heat the lower compartment below the funnel to keep the column from freezing during extremely cold weather. Samples were integrated over 12-day (Jan 1998-Sept 1998), 18-day (thru August 1999), and 24-day intervals at each of the sites. At the end of the sampling period, a swab of glass wool moistened with Milli-Q water was used to wipe the stainless steel funnel in order to collect any residual particles that may have sorbed to the funnel surface. These swabs were later extracted with the XAD and glass wool from the columns. Air Sampling Method. In a later section of this paper, the relative importance of gas and particle phase PCBs on the precipitation phase PCB concentration is examined using atmospheric data from an intensive field campaign conducted in August 7-11, 2000 at four of the NJADN sampling sites (CC, PL, NB, and TK). Twelve-hour integrated air samples (08:00-20:00 and 20:00-08:00 EDT) were taken at each of the sites using modified high volume air samplers (Tisch Environmental, Inc.) fitted with precleaned Polyurethane foam (PUF) plugs to collect gas phase and quartz fiber filters (QFF, Whatman, 8 in. × 10 in., QMA grade) to collect the particle phase. A single integrated rain sample was collected at each of the four sites during this 5-day period to coincide with the air samples. Further details of this field experiment are presented elsewhere (29). Sampling Media Pretreatment. XAD-2 was precleaned in a large Soxhlet apparatus by a sequential extraction method using (in successive order) methanol, acetone, hexane, acetone, and then methanol for 24 h each. The XAD-2 was then rinsed several times with Milli-Q water and stored in a sealed container at room temperature with an excess of Milli-Q water to keep the XAD-2 saturated. Glass wool was extracted overnight in 1:1 acetone:hexane. Details of pretreatment of media used for air sampling can be found elsewhere (10, 30). 3202

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FIGURE 2. Volume weighted mean (VWM ( SEM) concentrations (ng/L) of ΣPCBs in rain at NJADN sites and from other field studies ((SEM where available). Cheasapeake Bay data from ref 1; IADN Great Lakes data from ref 18; Galveston Bay data from ref 16; Chicago value is from unpublished IADN data (31). Hashed bars indicate urban-industrial areas. Analytical Method. After sampling, glass columns and corresponding glass wool swabs were returned to the laboratory and stored in a refrigerator at approximately 7 °C. The XAD-2 and glass wool were later extracted together in a Soxhlet apparatus for 24 h using 1:1 acetone:hexane. This was followed by a liquid-liquid extraction in a separatory funnel with Milli-Q water followed by back-extraction of the water fraction 3× with 50 mL of hexane. The sample was reduced by rotoevaporation (Bu ¨ chi), transferred to ∼12 mL amber vials, and further reduced to about 1 mL under a steady stream of N2 gas (Air Products). The sample was then fractionated by applying the sample to 4 g of 3% Milli-Q water deactivated alumina packed into a glass pipet and topped with Na2SO4. Two fractions were eluted with 12 mL of hexane (F1) and 15 mL of 2:1 dichloromethane:hexane (F2). The F1 contained the PCBs and some chlorinated pesticides (CPs), while the F2 contained PAHs and other CPs. For PCB analysis, the F1 was reduced under N2 gas, transferred to 2 mL injection vials, and reduced again to ∼0.5 mL. The methodology used for analysis of air samples was identical, except for the absence of the liquid-liquid extraction step, as described elsewhere (10, 30). Samples were analyzed on a Hewlett-Packard 6890 gas chromatograph (GC) with electron capture detection (µ-ECD) using a 0.32 mm i.d. × 60 m HP-5 capillary column (0.25 µm film thickness). The temperature program was as follows: 70 °C to 180 °C at 7 °C/min; 180 °C to 225 °C at 1.05 °C/min; 225 °C to 285 °C at 5.75 °C/min; 285 to 300 at 11.50 °C/min;

TABLE 2. ΣPCB Concentrations, Fluxes, and Homologue Group Contributions in Precipitation at NJADN Sites Camden (CC)

Jersey City (JC)

New Brunswick (NB)

Chester (XQ)

Pinelands (PL)

Sandy Hook (SH)

Tuckerton (TK)

ΣPCBs VWM ( SEM (ng/L)a 13 ( 2.8 ΣPCBs flux ( SE (µg/m2-yr)b 16 ( 3.4

3.9 ( 0.72 3.9 ( 0.72

1.3 ( 0.18 1.1 ( 0.16

0.52 ( 0.10 0.33 ( 0.061

0.38 ( 0.076 0.37 ( 0.075

0.80 ( 0.23 0.75 ( 0.22

0.35 ( 0.11 0.31 ( 0.097

winter spring summer fall

28 15 8.0 11

4.4 6.6 2.4 1.7

0.30 0.81 0.35 0.37

0.53 0.72 1.09 0.43

0.23 0.17 0.59 0.32

2 3 4 5 6 7 8 9

0.87 3.4 7.3 15 14 4.3 35 20 a

Seasonal Fluxes (µg/m2-yr)b 1.8 0.29 1.4 0.45 1.1 0.56 0.52 0.31

Homologue Group - Relative Percent Contributionsc 3.0 2.9 2.6 10 12 20 11 11 19 19 27 20 22 23 22 22 22 19 19 19 11 8.3 7.6 7.5 9.8 7.4 9.1 8.3 1.1 1.0 1.7 1.5

3.7 12 34 20 15 8.8 6.2 0.87

1.1 7.8 20 32 20 6.7 9.6 1.6

SEM calculated using eq 1; total number of samples can be found in Table 1. b Calculated from the VWM. c Volume weighted.

hold 300 °C for 8 min. For greater peak resolution, the pressure was also programmed as follows: 170 kPa to 210 kPa at 40 kPa/min; hold 210 kPa for 14.5 min; 210 to 170 kPa at 40 kPa/min. Surrogate standards were added to each of the precipitation samples prior to extraction. The PCB congeners 14, 23, 65, and 166 were used as surrogate compounds. The PCB congeners 30 and 204 were added to the sample extract as internal standards prior to GC-analysis. Calibration standards were run with field samples and contained all the congeners of interest and a single point calibration was applied. The congeners and coelutions that were analyzed can be found in GC elution order in Figures 4 and 5 that follow. Where coelution of congeners occurred, the most abundant congener (first congener listed) was used to assign the peak to a homologue group or to apply a chemical-physical property. Quality Assurance. Samples were corrected for surrogate recovery using PCB 23 to correct congeners eluting before PCB 45, PCB 65 to correct congeners eluting from PCB 45 to 85+136, and PCB 166 to correct all those eluting thereafter. The surrogate PCB congener 14 had frequent chromatographic interferences, so PCB 23 was added to the surrogate mixture about halfway through the field study. Where PCB 23 was not added, PCB 65 was used for correction. Recoveries of PCBs 23 and 65 were almost always the same or within a few percentage points. The average surrogate recoveries in all rain samples including blanks were 79 ( 11%, 79 ( 14%, and 85 ( 15%, for congeners 23, 65, and 166, respectively (n ) 193, n ) 89 for congener 23). The average recovery of ΣPCBs in XAD-2 matrix spikes was 100 ( 28% (n ) 5). Some columns and their corresponding glass wool swabs were extracted separately, and 46% to 89% of the total mass of PCBs was derived from the wipe. The profile of PCB congeners in the funnel wipe resembled the particle phase, suggesting that the wipe contained particles deposited to the funnel surface and not any minute amount of gas-phase congeners that may have leaked into the funnel compartment. This also suggests that the wipe is an important operational element of this method and that the wipe is necessary to capture particle bound PCBs on the funnel surface. Laboratory blanks, taken to assess contamination of samples, contained an average ΣPCB mass of 0.97 ( 0.49 ng, whereas the mass of ΣPCBs found in rain samples ranged from 2.4 to 900 ng (n ) 18). Samples were routinely corrected on a congener basis by subtracting the average mass from laboratory blanks from the total mass found in individual samples. A method detection limit defined as the mean mass

of ΣPCBs in blanks + 3 standard deviations was 0.97 + 1.5 ng. Meteorology. The precipitation collectors measured integrated precipitation at each site. Temperature and other ancillary data were collected from various meteorological stations. For New Brunswick, data was collected on-site. For the Camden and Pinelands sites, data were obtained from NOAA meteorological stations located at Philadelphia International Airport and Mount Holly, NJ, respectively. Data for the Tuckerton site were obtained from the Rutgers Ocean Data Access Network (RODAN) tower located on-site. The 10-m values were used for each site.

Results and Discussion Wet Deposition of PCBs. Spatial Variations. Values for the volume weighted mean (VWM, ng/L) concentrations of ΣPCBs in rain samples collected at NJADN sites are summarized in Table 2 and Figure 2. The standard error of the volume-weighted mean (SEM) was calculated using the following expression (19)

(SEM)2 )

[∑(P X -PX ) ∑P ) ∑(P -P)(P X -PX ) + X ∑(P -P) ] n

2

2XW

i i

2

(n-1)(

w

i

2

i

i i

W

W

2

i

(1)

where n is the number of samples, Pi is the precipitation amount (L) in a given sample, Xi is the concentration in a given sample (ng/L), XW is the VWM (ng/L), and variables with a bar represent the average value of that variable. The highest VWM concentrations of ΣPCBs were observed at the urban-industrial sites (13 ( 2.8 and 3.9 ( 0.72 ng/L at CC and JC site, respectively). Concentrations were lower at sites presumably impacted by urban-industrial activities though located on the fringes of urban areas (1.3 ( 0.18 and 0.80 ( 0.23 ng/L at suburban NB and coastal SH). The lowest VWM concentrations of ΣPCBs were observed at sites distant (>45 km) from urban-industrial areas (0.52 ( 0.10, 0.38 ( 0.076, and 0.35 ( 0.11 ng/L for XQ, PL, and TK, respectively). These data suggest that urban areas are the most important sources for the observed concentrations and that urban emissions of PCBs dominate the local signal of rain concentrations within ∼30 km of sources. Similar spatial trends in air concentrations have been observed for PCBs in this region, particularly in the lower Hudson River Estuary (8, 10). While the area around the forested PL site has the lowest population density, precipitation concentrations of PCBs at PL were of VOL. 36, NO. 15, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Temporal trends in the flux of ΣPCBs over time at each of the NJADN stations. The width of the bar represents the length of time over which the sample was integrated. Also given is the annualized flux (µg/m2-yr) calculated from the VWM. Note scale differences at Camden and Jersey City. the same order of magnitude as those at XQ and TK sites, which each have a light residential population. Background concentrations of ΣPCBs in rain in this region were approximately 0.30-0.50 ng/L. The similarity in the PL, TK, and XQ values suggest that these nonurban and coastal sites represent a regional background signal. Concentrations in precipitation at the two urban-industrial sites were, on average, 7 to 43 times higher than background values. The annual wet deposition fluxes (Fwet) of ΣPCBs (µg/ m2-yr) at each NJADN site were calculated by multiplying the VWM by the total volume of rain collected (Table 1) and dividing by the total time of sampling and the cross-sectional area of the collection funnel (0.212 m2) Table 2. Spatial trends in the flux of ΣPCBs were similar to those observed for the VWM concentrations (CC > JC > NB > SH > XQ ∼ PL ∼ TK): urban > suburban > background/coastal. Figure 2 shows VWM concentrations of ΣPCBs for the NJADN sites compared to those reported elsewhere. Leister and Baker (1) report a VWM concentration of 1.6 ng/L (range 0.04-34 ng/L for 1990-1991) in Chesapeake Bay, ∼150 km to the south. This concentration is similar to concentrations measured at the urban-impacted NJADN sites, NB and SH. The authors describe the sample site as rural but acknowledge that emission sources are located within a few kilometers (1). VWM concentrations of ΣPCBs in precipitation around the Great Lakes (IADN (18)) were 2.0 ( 0.36 ng/L for Lake Superior (Eagle Harbor) and 1.3 ( 0.17 ng/L for Lake Michigan (Sleeping Bear Dunes), while an ensemble average for all Great Lakes was 2.0 ( 0.23 ng/L (18). While the IADN 3204

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concentrations for this time period (1991-1997) are somewhat higher than urban-impacted NJADN sites (NB and SH), concentrations in precipitation were slowly decreasing around the Great Lakes region as of 1997 (18). Park et al. (16) reported a VWM ΣPCB concentration of 1.3 ng/L around Galveston Bay, TX for 1995-1996. VWM concentrations of ΣPCBs measured in Chicago, IL from 1998 through 2000 were 6.6 ( 0.86 ng/L (wipes not included after June 1999 (31)), which is similar to concentrations measured at the urban JC and CC sites. Offenburg and Baker (19), in event-based precipitation sampling in Chicago, IL and over-water in Lake Michigan (1994-1995) as part of AEOLOS, report VWM concentrations of 29 ( 24 ng/L for ΣPCBs in downtown Chicago (not shown in Figure 2). While this concentration is roughly double that of the urban CC site, VWM value reflects only five samples, one of which had a significantly higher concentration leading to the large SEM (19). Overall, concentrations of PCBs in precipitation collected at the NJADN sites are of the same order of magnitude or lower than concentrations measured in other parts of North America with similar land-use. Temporal Variations. Figure 3 shows the flux of ΣPCB (ng/m2-day) in all precipitation samples collected during NJADN (Jan 1998-May 2001). In Figure 3, the bar-width represents the length of time over which precipitation events were integrated (generally 12-24 days). The highest degree of overall variability in the flux came from urban or urbanimpacted sites (CC, JC, NB, SH; average relative standard deviation (relSD) ) 107%), while nonurban sites exhibited

FIGURE 4. Volume weighted wet deposition profiles of PCB congeners at four NJADN sites. Note differences in concentration scales for the different stations. significantly less variability (XQ, PL, TK; average relSD ) 69%). No statistically significant correlations between the ΣPCB fluxes or concentrations and the precipitation rate or amount were found for any of the sites. This is not surprising since scavenging of gases and especially particles occurs on short characteristic time scales (on the order of seconds) (23, 24). While the amount of precipitation is important to the magnitude of the flux amount on some level, other factors also drive the observed fluxes and concentrations. The frequency and intensity of precipitation events during the integrated periods are important factors (23). The type of precipitation (rain, snow, sleet, mixed, etc.) at each site plays an important role in the magnitude of the wet deposition flux (12, 23, 27). These notions, coupled with the spatially variable weather and precipitation patterns in NJ, make sample-to-sample comparisons between NJADN sites difficult. The Chester site, for example, which is located at a higher elevation than all other sites, received more snow and freezing rain during the same winter time period (20002001). Conversely, TK, a site warmed by coastal waters in the winter, was more likely to see rain when other sites were receiving snow. Certainly, an important factor controlling the magnitude of the wet deposition flux is the concentration of PCBs in air. The role of atmospheric gas and particle concentrations on precipitation will be discussed later. Table 2 shows the seasonal flux of ΣPCBs (µg/m2-yr) for each NJADN site calculated from the VWM for each season. The highest fluxes of ΣPCBs were observed in spring for JC and PL and in winter for CC and NB. The annualized ΣPCB

fluxes at XQ were similar over all seasons. Seasonal trends in VWM concentrations were identical to those for fluxes at each site. While the wet season for this region is usually during winter and spring, this trend was highly variable for this data set. For example, Hurricane Floyd in early September 1999 and a series of heavy rains in mid-August 2000 raised the overall summer precipitation rate, which in turn lowered the VWM concentration for this season. Since atmospheric ΣPCB concentrations are generally higher during warmer temperatures (10), one might expect a high mass flux during summer. However, these rain events were continuous and intense. In these and similar events the atmospheric particles and gases were presumably washed out to the greatest extent at the start of the event, followed by a period of lower air concentrations during the length of the extended event. This would lead to an overall dilution in PCB concentration (over increasing volume) and PCB flux (over time). Interestingly, the coastal SH and TK sites, which were less affected by these storms during their respective collection periods, did show their highest fluxes of ΣPCBs during summer when air concentrations were also higher because of higher air temperatures (10). PCB Deposition Profiles. Table 2 provides the volume weighted relative percent contribution of homologue groups 2-9 for each NJADN site for all data collected. The relative contribution of highly chlorinated congeners (sum of homologues 7, 8, and 9) was greatest for the urban sites, Camden (59%) and Jersey City (22%), whereas all other sites had smaller relative contributions of these congeners (range 16VOL. 36, NO. 15, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 5. Comparison of PCB profiles in rain, particle phase, and gas phase at the urban Camden site during the intensive period (August 7-11, 2000). Particle and gas-phase profiles represent the average for the week (n ) 9). 19%). The highest contribution of lower molecular weight congeners (homologue groups 2 and 3) was measured at NB and PL (22% and 21%). At increasing distances away from emission sources, the relative importance of higher chlorinated PCBs in environmental samples is diminished because the heavier congeners tend to be associated with aerosols and have correspondingly shorter atmospheric residence times. That is, particle-bound PCBs are more efficiently removed from the atmosphere than gas phase PCBs. While this trend is frequently observed for total air samples, it becomes less pronounced for total precipitation samples where gas and particle phases are acted on differently by the precipitation event(s) (20-23). The characteristic PCB profile is also a function of the emission strength of the individual PCB congeners from local sources. Figure 4 shows volume weighted congener profiles for all PCB congeners measured. Four of the NJADN sites have been chosen as examples for comparison of different land-use regimes (CC - urban; NB - suburban; PL - background, terrestrial; TK - background, coastal). The profile from the urban CC site was enriched in highly chlorinated species, while congeners from the suburban NB site were more evenly distributed throughout the homologue groups. The profiles from PL and TK were similar and correlated well (linear r2 ) 0.60; p < 0.0001 with PCB 8+5 removed as an outlier), which is consistent with the notion that PCBs at these two nonurban sites either have similar types of sources and/or that PCBs are being removed from the atmosphere by similar processes prior to and/or during wet deposition. Atmospheric Washout of PCBs. Intensive Sampling Campaign. The congener distributions measured in precipitation are dependent on the distribution and speciation of PCBs in air (20-22, 25). Therefore the relative abundances of PCBs in gas and particle phases and the efficacy of precipitation to remove PCBs from the atmosphere via these 3206

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different phases is important. During the 5-day period of August 7-11, 2000, an intensive sampling campaign was carried out whereby concentrations in gas and particle phases were continuously measured in air samples collected over 12-h periods at four NJADN sites (CC, NB, PL, and TK). A rain sample was also collected at each site integrated over the 5-day period. At most sites it rained almost each day (or night), with most precipitation events occurring as short bursts of a half hour or less with no extended downpours. The integrated volume of rain collected at each site ranged from 0.8 to 3 L. Table 3 summarizes concentration data from the intensive period in rain, gas and particle phases (averages over 5 days for 9 day/night sample periods). At each site, the spatial trend in rain concentrations followed the same spatial trends in the gas and particle phases (CC > NB > PL), the exception being TK where the rain concentration was lowest of the four, but air sample concentrations there were slightly higher than PL. Figure 5 shows the average congener profile distributions at the urban CC site in the rain, particle and gas phases for the 5-day period. The congener profiles are statistically similar (r2 ) 0.70, p < 0.0001) with a large contribution from highly chlorinated species (7-9 chlorines). Washout of particle-bound PCBs is apparently the dominant removal mechanism by rain, consistent with previous observations (19, 20, 25). Washout Ratios and Coefficients. Washout ratios describe scavenging of SOCs by precipitation (5, 11, 13, 21, 22, 24, 26, 27). The total washout ratio (WT) is defined as

WT )

CR,T CA,T

(2)

where CR,T is the total PCB concentration in rain (pg/m3 water) and CA,T is the total concentration in air (pg/m3). WT is,

TABLE 3. Average Concentrations and Atmospheric Washout of PCBs during the August 2000 Intensive Camden (CC) rain (ng/L)a gas (pg/m3)b,c particle (pg/m3)b,c logWG (range)d logWP, calc (range)e logWT (range)f wet flux dry particle fluxg

19 6600 ( 2200 57 ( 33

New Brunswick (NB) Concentration (ΣPCBs) 4.3 730 ( 320 8.7 ( 3.5

Washout Coefficients for PCB Congeners 1.2-2.2 1.2-2.1 4.4-6.5 4.8-6.7 2.2-5.3 2.5-5.5 53 25

Deposition (ng/m2-day) 3.3 3.7

Pinelands (PL)

Tuckerton (TK)

2.3 340 ( 85 2.3 ( 0.83

0.87 470 (120 3.5 ( 1.0

1.3-2.3 5.2-7.2 2.8-5.9

1.3-2.3 4.2-6.8 2.6-4.4

3.9 1.0

1.7 1.5

a Single sample collected for 5 days. b Average of 12-h integrated samples taken during the week (n ) 9). c TK gas phase (n ) 8, one sample not taken); TK particle phase (n ) 7; one sample lost, one not taken). d WG ) 1/H′; temperature corrected range for all PCB congeners. e Calculated using eq 3; range for all PCB congeners. f WT ) CR,T/Ca,T; range for all PCBs. g Estimated by assuming a particle deposition velocity of 0.5 cm/s.

FIGURE 6. Correlations between the washout ratios (logWT) and the fraction on particles (log O) for PCB congeners during the August intensive, Camden, NJ. therefore, dimensionless. The relative importance of gas and particle phases in rain scavenging is described by

WT ) WG(1 - φ) + WP(φ)

(3)

where WG and WP are the gas and particle phase scavenging coefficients, respectively, φ is fraction associated with atmospheric particles, and WG is equal to the inverse of a compound’s dimensionless Henry’s Law Constant (H′) at the appropriate temperatures.

Results for washout ratio calculations are given in Table 3 and were calculated using the rain and average air PCB concentrations during the August 2000 campaign. Henry’s Law constants, and the temperature corrections used to calculate WG, were obtained from refs 32 and 33. The overall range of WT for all PCB congeners at all four sites was 158 to 790 000 (log WT ) 2.2-5.9). WG values are a function of the average temperature at a given site and are spatially similar (range: log WG ) 1.2-2.3). The relative importance VOL. 36, NO. 15, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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of gas or particle scavenging of PCBs is reflected in the relative magnitude of the two terms on the right-hand side of eq 3. For all sites and congeners, the WP(φ) term represented 0-99% of the magnitude of WT and on average represented 97% of WT. This fact reflects quantitatively the overwhelming importance of the particle phase and its interaction with falling hydrometeors on total scavenging. Higher values for log WT were found at the forested PL site (2.8-5.9) than at the urban CC site (2.2-5.3) because of the relatively greater enrichment of PCBs on particles at the PL site (see Figure 6 for range). This observation reflects the importance of source strength at the urban CC site. Since evaporative sources of PCBs are proximate to the CC site, the gas phase is enriched in PCBs relative to the particle phase, even though particle mass concentrations were on average higher at urban than at the forested site. Since the particulate PCB concentrations are a larger contributor to the concentration in rain, the relative magnitude of WT is lower for sites with relatively less PCB mass in the particle phase. This also occurred at the coastal TK site where φ values were lower than those at PL and log WT values were higher than those at PL (2.6-4.4). Explanations for this observation may be that local emission sources of PCBs are near the TK site or that the assumption regarding Henry’s Law equilibrium is not adequately valid in this situation. Values for log WT at the suburban NB site (2.5-5.5) fall roughly between urban CC and forested PL. Particle washout ratios, WP,calc, calculated using WT, WG, and φ, followed the same spatial trends as WT. The log WP,calc values overall ranged from 4.4-6.5 at the urban CC site and 5.2-7.2 at the remote PL site or roughly an order of magnitude greater at the remote site than at the urban site. The overall values of the washout ratios were not different from published values (5, 11-13, 21, 22, 25, 26, 34). Washout ratios are frequently used to estimate probable PCB concentrations in rain, especially in the context of mass balance modeling (2, 17, 34). Conversely, if measurements of concentrations in precipitation are available, and the extent of PCB partitioning between gas and particle phases is known (i.e., φ), washout ratios may be used to estimate concentrations in air (eq 3). A value of approximately 105 is recommended for WP for PCBs in urban areas, and approximately 106 is recommended for WP in more remote regions. For total scavenging (WT) of PCBs in this study, the fraction on particles (φ) was the best predictor. Figure 6 provides the linear regressions for log WT vs the log φ at each of the four sites during the intensive. The highest correlation between log WT and log φ was found at sites with the highest concentrations in rain and air (CC and NB, r2 ) 0.81 and 0.78, respectively, p < 0.0001). Correlations were poorer at the remote sites (PL and TK, r2 ) 0.64 and 0.28, respectively). Slopes of the relationships between log WT and log φ (m ( SE) are similar at each of the sites even though these are two distinct land-use types. Franz et al. (27) report a slope of 0.71 ( 0.08 for snow scavenging of PCBs. The similarity of these slopes may suggest that the inherent process of scavenging of PCB congeners from the atmosphere may be reasonably consistent across concentration gradients. To estimate WT from φ we recommend using the regression equation from CC for urban areas (log WT ) 0.71 ( 0.049 (logφ) + 4.9 ( 0.11) and the regression equation from PL for nonurban areas (log WT ) 0.77 ( 0.083(logφ) + 5.6 ( 0.16). Importance of Wet Deposition. Dry particle deposition fluxes were estimated for ΣPCBs at each of the four sites during the August 2000 intensive by applying a particle deposition velocity (ν) ) 0.5 cm/s (8, 29, 34). Table 3 shows the resultant dry particle and wet deposition fluxes for the week (ng/m2-day). Wet and dry particle fluxes of ΣPCBs at all sites were of the same order of magnitude and spatially followed similar trends between urban and nonurban areas. While the wet deposition flux (53 ng/m2-day) at the urban 3208

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CC site exceeded the dry particle flux (25 ng/m2-day) by a factor of ∼2, this difference may not be significant since the particle deposition velocity chosen may be conservative (35). Nonetheless, these results imply that wet deposition is at least as important as dry particle deposition in across land uses. The ratio of the magnitude of wet deposition to dry particle deposition in this study ranged from 0.88 to 3.85, which is similar to results found in other ecosystems.

Acknowledgments The following individuals are kindly acknowledged for their field and laboratory assistance: C. Schauffle, Dr. J. Y. Shin, I. Koelliker, S. Yan, Dr. P. A. Brunciak (deceased), D. Gray, D. Roberts, J. Oxley, S. Piotrowski, M. Danko, and J. Liming. The NJADN project is funded by the NJ Department of Environmental Protection (Project Officer, Michael Aucott) and the NJ Agricultural Experiment Station (NJAES). Early work on the Network was funded in part by the Hudson River Foundation (Project Officer, Dennis Suzskowski). D. Van Ry gratefully acknowledges an Air Pollution Research and Education Grant (APERG) from the Air & Waste Management Association, Mid-Atlantic States Section (A&WMAMASS).

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3 November 1994, Denver Colorado; Baker, J. E., Ed.; Pensacola, FL, 1997; pp 51-72. Poster, D. L.; Baker, J. E. Environ. Sci. Technol. 1996, 30, 349354. Dickhut, R. M.; Gustafson, K. E. Environ. Sci. Technol. 1995, 29, 1518-1525. Franz, T. P.; Gregor, D. J.; Eisenreich, S. J. In Atmospheric Deposition of Contaminants to the Great Lakes and Coastal Waters: Proceedings from a session at the SETAC 15th annual meeting 30 October - 3 November 1994, Denver Colorado; Baker, J. E., Ed.; Pensacola, FL, 1997; pp 77-107. Forman, R. T. T. In Pine Barrens: Ecosystem and Landscape; Forman, R. T. T., Ed.; New Brunswick, NJ, 1998. Van Ry, D. A.; Glenn, T. R. I.; Gigliotti, C. L.; Totten, L. A.; Eisenreich, S. J. Environ. Sci. Technol. 2002, in review. Gigliotti, C. L.; Dachs, J.; Nelson, E. D.; Brunciak, P. A.; Eisenreich, S. J. Environ. Sci. Technol. 2000, 34, 3547-3554.

(31) Hites, R. A.; Basu, I. Indiana University, unpublished data, 2001, personal communication. (32) Bamford, H. A.; Poster, D. L.; Baker, J. E. J. Chem. Eng. Data. 2000, 45, 1069-1074. (33) Bamford, H. A.; Poster, D. L.; Baker, J. E. Environ. Sci. Technol. 2002, In Review. (34) Van Ry, D. A.; Dachs, J.; Gigliotti, C. L.; Brunciak, P. A.; Nelson, E. D.; Eisenreich, S. J. Environ. Sci. Technol. 2000, 34, 24102417. (35) Franz, T. P.; Eisenreich, S. J.; Holsen, T. M. Environ. Sci. Technol. 1998, 32, 3681-3688.

Received for review December 12, 2001. Revised manuscript received April 2, 2002. Accepted May 21, 2002. ES0158399

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