although new bedford 
 harbor ( nbh ) , ma , is one of the largest polychlorinated 
 biphenyl ( pcb ) superfund sites in the united states , it has not been studied as an important source of airborne 
 pcbs . in 1983
, nbh was placed on the national priorities list of superfund 
 cleanup sites because of the extremely high levels of pcbs in the 
 sediments .
aroclors 1242 and 1016 were discharged into the harbor 
 for more than 30 years ( 1940s1970s ) .
pcb concentrations 
 of 1 g g in flounder and 10000 
 g g ( dry weight ) in sediments have been 
 reported .
these high 
 pcb levels motivated release of seafood consumption advisories starting 
 in 1979 and sediment dredging since 1994 .
concentrations of pcbs in air have been 
 measured and reported by 
 the u.s .
environmental protection agency ( u.s . epa ) since 1999 , and although concentrations are elevated , the magnitude of the harbor 
 as an emission source is unclear and the potential risk by inhalation 
 caused by emissions is unknown .
while remediation is driven by pcb 
 levels in the sediments , pcbs are mobilized from sediment to overlying 
 water and air , contributing to human exposure via inhalation .
it 
 is important to understand the specific contribution of nbh to local 
 levels of airborne pcbs as part of the risk - based decision making 
 regarding remediation .
we recently developed a strategy for 
 predicting concentrations 
 of airborne pcbs as a function of emissions from contaminated water .
we measured pcbs in water , calculated the emissions 
 as gross volatilization flux , and predicted dispersion into the surrounding 
 region . in northwest indiana , we found that pcbs released from the 
 indiana harbor and ship canal ( ihsc ) accounted for 15% of the observed 
 pcb concentrations in the adjoining neighborhoods .
the community surrounding 
 the ihsc is one of the most industrially dense regions in the united 
 states and has a long history of environmental contamination . using 
 this two - pronged strategy of calculated emissions and atmospheric 
 dispersion modeling
, we concluded that there were many sources of 
 airborne pcbs in this region in addition to ihsc .
pcb concentrations in nbh water are at least 10 times 
 higher than 
 in ihsc , and its area is 3 times larger than that of ihsc , which could 
 dramatically increase the contribution of airborne gas - phase pcbs 
 to the local atmosphere .
therefore , we hypothesized that pcb emissions 
 from nbh explain ambient air concentrations of pcbs in the surrounding 
 communities .
to address our hypothesis , in response to and in 
 collaboration 
 with community and environmental organizations , we launched a field 
 effort in 2015 to evaluate the effect of emissions from nbh on airborne 
 pcbs .
we calculated congener - specific pcb emissions from nbh as a 
 function of reported water concentrations , chemical properties , and 
 local meteorology .
we used an atmospheric dispersion model to predict 
 gas - phase pcb concentrations in the region surrounding nbh .
in addition , 
 we compared our predictions to measured values from our own samplers 
 and those measured by the u.s .
lastly , we examined the long - term 
 trends in pcb emissions and air concentrations for 20062015 
 using historical data reported by the u.s . epa .
airborne pcbs 
 were measured using polyurethane foam passive air samplers ( puf - pas ) 
 as previously described .
the puf - pas collects both gas and particle phases , 
 but because pcbs are mostly in the gas phase ( 90% ) , the values 
 reported here are assumed to be the gas phase .
samplers were placed 
 at the same 18 locations for three consecutive periods , from july 
 to november of 2015 in new bedford , fairhaven , dartmouth , and acushnet , 
 ma ( figure s1 ) , except for one location 
 where we sampled two rounds .
the sampling locations were selected 
 by community members following discussions about study objectives 
 and the need for the spatial distribution of pcb monitors .
all but 
 two selected locations are near residential homes . prior to 
 placement ,
puf disks were cleaned in a soxhlet apparatus for 24 h 
 with hexane , followed by 24 h with acetone , and finally with a 1:1 
 ( v / v ) hexane / acetone solution for 24 h. pufs were dried for 1 h in 
 a ventilated fume hood , wrapped in combusted aluminum foil within 
 ziploc bags , and stored at 4 c .
hourly sampling rates ( r ) specific to each sampler 
 and pcb congener were modeled from local meteorology , ranging from 
 2 to 3 m day .
these sampling rates 
 were used to calculate effective sampling volumes ( veff ) for each sampler and pcb congener , ranging from 25 
 to 110 m. we used these volumes 
 to calculate the concentration of airborne pcb from the mass collected 
 in the passive samplers .
additional details , including the qa / qc for the airborne pcb measurements , 
 airborne pcb emission calculations , air dispersion model aermod , and 
 meteorological data utilized in this investigation , are provided in 
 the supporting information .
pcb concentrations 
 in water and from high - volume air sampling were reported elsewhere , 
 and details are also provided in the supporting information .
concentrations of airborne 
 pcb ranged from 0.4 to 38 ng m , with a 
 geometric mean of 3.1  3.8 ng m. the values 
 of > 10 ng m ( n = 9 ) are the 
 highest 
 values reported for outdoor pcb puf - pas samples by our laboratory 
 ( chicago , cleveland , and east chicago ) and also by others ( toronto , 
 on ) .
epa large - volume air sampler ( hi - vol ) gas - phase 
 measurements for the same months of 2015 
 ( mann  whitney ; p = 0.32 ) ( figure 1 ) . u.s .
epa high - volume 
 ( hi - vols ) and puf - pas measurements for comparison 
 of the gas phase .
no significant difference was found between the methods ( mann  whitney ; p = 0.32 ) .
epa hi - vol 
 samplers used in this comparison are given in figure 3 .
a clear and large spatial variability was found , with the 
 highest 
 values located closest to the water ( figure 2 ) .
indeed , no statistical difference was found among the 
 three sampling period average concentrations ( kruskal  wallis ; p = 0.83 ) .
samples from the same location varied by a factor 
 of <3 , whereas puf - pas samples in chicago varied in average > 6-fold 
 for the same location .
in addition , the 
 highest value showed the lowest variability ( 10% ) , suggesting a single 
 and constant pcb source .
spatial and temporal distributions of airborne 
 pcb ( nanograms 
 per cubic meter ) in new bedford harbor . sampling round 1 ( green ) from 
 july 9 , 2015 , to august 20 , 2015 , sampling round 2 ( blue ) from august 
 20 , 2015 , to october 1 , 2015 , and sampling round 3 ( yellow ) from october 
 1 , 2015 , to november 12 , 2015 .
the inset shows the box - and - whisker 
 plot for the concentration distribution of the three sampling periods . 

map source : office of geographic information ( massgis ) , commonwealth 
 of massachusetts , massit .
very similar pcb congener profiles were found in all the 
 samples , 
 dominated by low and middle chlorinated congeners ( < pentachlorobiphenyls ) . 

the majority of the congeners found in the samples are present in 
 aroclor mixtures ( figure s4 ) .
the samples 
 have strong aroclor 1242 and 1016 profiles , consistent with numerous 
 reports of sediment contamination with these two commercial mixtures and a consistent congener profile ( sample average cos  = 
 0.97 ) .
samples collected farther from nbh exhibit 
 a larger relative contribution of non - aroclor pcb11 ( figure s5 ) .
the pcb11 fraction in the samples 
 exhibits one of the highest variabilities ( standard error ) of the 
 171 pcb congeners measured , suggesting that nbh is not the major source 
 of this congener .
these results suggest a single and continuous source 
 of airborne pcbs , consistent with our hypothesis that the water of 
 nbh is a large source of pcbs to the local atmosphere . pcb
gross volatilization fluxes 
 ranged from 160 to 1200 g m day for the 2015 samples .
these fluxes result in pcb emissions 
 from the upper and lower harbor areas ranging from 90 to 140 kg year , with an average of 110 kg year .
the only previous pcb emission calculations for nbh were published 
 by garton et al . using their data from 
 1983
, we were able to predict a gross volatilization flux of 70 g 
 m day , which is on the same 
 order of magnitude as the lower - end estimates reported here ( 2015 
 water data ) .
nbh fluxes are higher than those of other well - known 
 pcb - contaminated water systems in the united states . for example , 
 gross volatilization fluxes from green bay in 1989 ranged from 0.2 
 to 5.3 g m day .
the values for the hudson river estuary in 19992001 
 ranged from 0.05 to 0.9 g m day .
the values for the delaware river 
 in 20012003 ranged from 0.2 to 2.5 g m day .
although it is very difficult to compare pcb 
 fluxes between different studies , all these fluxes are at least 2 
 orders of magnitude lower than the 2015 nbh values .
nbh fluxes are 
 a result of the notably high concentrations of dissolved pcbs measured 
 in nbh , which in some cases were in the hundreds of nanograms per 
 liter ( table s1 ) .
indeed , some values are 
 only a factor of 100 below the water solubility limit .
we excluded from consideration 
 any water samples that were collected while there was active dredging , 
 as indicated in the u.s .
although some values are extremely high , 
 a clear decrease in emission over time was observed ( figure s6 ) .
this reduction is consistent with the observed 
 decline in air and sediment pcb concentrations over time .
aermod is an epa model for 
 predicting the dispersion of airborne pollutants from a source , in 
 this case nbh .
we applied aermod to compare the measured pcb concentrations 
 to those predicted as a function of our calculated emissions .
the 
 aermod predictions exhibit a pcb spatial distribution consistent with 
 our field measurements and validate our hypothesis that nbh waters 
 are the source of pcb in the nearby surrounding air ( figure 3 ) .
aermod prediction map for mean pcb concentrations ( nanograms 
 per cubic meter ) from july to november 2015 .
circles represent our 
 puf - pas samplers , and squares represent high - vol samples placed by 
 the u.s .
pink circles and squares represent the samplers used 
 for comparison of methods ( figure 1 ) .
both puf - pas and hi - vol samplers were active between 
 july and november 2015 , although the puf - pas samplers were continuously 
 collecting while the hi - vol samplers were sampling in 24 h periods . 

aermod predicted pcb within a factor of 2 of our 
 puf - pas 
 measurements 50% of the time ( 9 of 18 samples ) ( figure 4 ) .
interestingly , all the locations where 
 the prediction exceeded the measurements by a factor of > 3 were 
 located 
 close to the water and east of nbh . in general
, the predictions exceeded 
 our field measurements by an average factor of 2.6 , ranging from 0.5 
 to 11 .
epa has been monitoring airborne pcbs in nbh since 
 1999 using hi - vol samplers .
their hi - vol measurements 
 for the same period of time were somewhat closer to the predicted 
 concentrations with an average factor of 2.1 , ranging from 0.7 to 
 5 , with only one location with an average factor of > 4.0 . given 
 that 
 the range of pcb concentrations is large and a factor of 100 , 
 we conclude that the modeling approach we used is appropriate and 
 accurately predicts the effect of nbh emissions on ambient pcbs in 
 the air of the surrounding communities .
circles represent mean puf - pas measurements ( n = 3 ) , and triangles represent geometric means of hi - vol measurements 
 from the u.s .
error bars represent 
 one standard deviation for the puf - pas samplers and one geometric 
 standard deviation for the hi - vol samplers .
the black line represents 
 the 1:1 line , and the red lines represent the 1:2 and 2:1 lines ( i.e. , 
 factor of 2 ) .
the 
 results of this study support our 
 working hypothesis : pcb emissions from nbh explain nearby air concentrations . 

first , we note the 
 large spatial variation in measured airborne pcbs , with much higher 
 concentrations close to the shoreline .
second , we found that the profiles of pcb congeners in the air samples 
 are remarkably similar , and also similar to those of the commercial 
 mixtures aroclor 1016 and aroclor 1242 .
third , we found 
 that our predicted and measured air concentrations exhibit similar 
 ranges of values and similar spatial distributions , both decreasing 
 in magnitude with distance from the water . to the best of our knowledge , 

this is the first study to show that a pcb - contaminated waterway is 
 responsible for the nearby measured pcbs .
it is likely that 
 pcbs have been emitted from nbh water for many years .
using the same 
 modeling approach , we predicted airborne pcb concentrations from u.s . 

our calculations illustrate a decrease 
 in pcb emissions as well as airborne pcb concentrations ( figure 5 ) .
our findings indicate 
 that nbh is one of the largest ongoing sources of airborne pcbs in 
 the united states and the cause of the highest concentrations in the 
 neighborhoods surrounding the harbor .
it is likely that nbh has been 
 an important source of airborne pcbs in the new bedford area since 
 it was contaminated with aroclors .
asterisks indicate a significant difference between 2006 
 predicted concentrations and 2011 and 2014 ( mann  whitney ; p = 0.004 ) .
 qualitatively and 
 quantitatively , we have demonstrated that airborne 
 polychlorinated biphenyl ( pcb ) concentrations in the air surrounding 
 new bedford harbor ( nbh ) are caused by its water pcb emissions . 
 we 
 measured airborne pcbs at 18 homes and businesses near nbh in 2015 , 
 with values ranging from 0.4 to 38 ng m3 , with 
 a very strong aroclor 1242/1016 signal that is most pronounced closest 
 to the harbor and reproducible over three sampling rounds . 
 using u.s . 
 
 environmental protection agency ( u.s . 
 epa ) water pcb data from 2015 
 and local meteorology , we predicted gas - phase fluxes of pcbs from 
 160 to 1200 g m2 day1 . 
 fluxes were used as emissions for aermod , a widely applied u.s . 
 epa atmospheric dispersion model , to predict airborne pcb concentrations . 
 
 the aermod predictions were within a factor of 2 of the field measurements . 
 
 pcb emission from nbh ( 110 kg year1 , average 2015 ) 
 is the largest reported source of airborne pcbs from natural waters 
 in north america , and the source of high ambient air pcb concentrations 
 in locations close to nbh . 
 it is likely that nbh has been an important 
 source of airborne pcbs since it was contaminated with aroclors more 
 than 60 years ago . 
Introduction
Materials and Methods
Results and Discussion