Integrated Atmospheric Deposition Network Research Articles

Spatial and temporal trends of chlorinated epoxides in the atmosphere near the North American Great Lakes

Dieldrin, heptachlor epoxide, and oxychlordane are highly chlorinated, persistent, bicyclic epoxides that are widely present in the environment. Given the long-standing restrictions on the production and use of these compounds, it is appropriate to wonder if their environmental levels have decreased over time, and if so, how fast. The Integrated Atmospheric Deposition Network (IADN) provides this information by measuring the concentrations of these compounds in the atmosphere at six sites near the Great Lakes once every 12 days. During the period 1990–2021 (inclusive), a total of 4125 samples have been collected. The median concentrations at the six sites are significantly different from one another. The concentrations of all three compounds at Chicago (population: 3,900,000) are significantly higher than those at most other sites, and those at Eagle Harbor (population: 1330) are significantly lower than those at most other sites. This concentration trend reflects the use of these compounds as termiticides and insecticides in cities as opposed to their use in agriculture. Multivariate statistical analyses of the spatially- and time-resolved data indicate that the atmospheric concentrations of these compounds are decreasing by a factor of two every 14 ± 5 years. Although the atmospheric levels of these three highly chlorinated epoxides are decreasing slowly, it is clear that they are environmentally persistent. It is also clear that our earlier reported halving times (1–10 years) for dieldrin were overly optimistic. To determine reliable long term temporal trends, it is essential to have long term concentration measurements.

Disentangling Source Profiles and Time Trends of Halogenated Flame Retardants in the Great Lakes.

Thirty-five polybrominated diphenyl ethers (PBDEs) and eight other alternative flame retardants were measured in air samples (vapor plus particles) collected at six sites near the North American Great Lakes between 2005 and 2019 as part of the Integrated Atmospheric Deposition Network (IADN). These data were analyzed using a multiple linear regression model to determine spatial and temporal trends. Overall, the levels of flame retardants remain significantly higher in urban sites compared to rural and remote sites except for pentabromoethylbenzene (PBEB), hexabromobenzene (HBB), and total Dechlorane Plus (ΣDP). Here, we report the first findings of decreasing levels of ΣDP at Sturgeon Point, New York. The atmospheric levels of total PBDEs remain unchanged over time near Lakes Michigan and Superior and declined near Lakes Erie and Ontario, with rate constants at the latter two lakes revealing halving times of approximately 7 to 14 years. This work presents results from the first investigation of PBDE source apportionment in the Great Lakes atmosphere. Source apportionment by use of positive matrix factorization (PMF) identified two legacy commercial technical mixtures (i.e., penta-BDE and deca-BDE mixes) and elucidated a factor representing ambient degradation. Our results show that weathered local sources of technical commercial mixtures, and their photolysis contribute most to the total PBDE burden in the Great Lakes atmosphere.

Design and Analysis of An Data-Driven Intelligent Model for Persistent Organic Pollutants in the Internet of Things Environments

The targeted compounds included Polychlorinated Biphenyls (PCBs), Pesticides (PESTs), Polycyclic Aromatic Hydrocarbons (PAHs) and so on in the Great Lakes Integrated Atmospheric Deposition Network (IADN), which is a platform based on the IoT (Internet of Things) technology to collect environmental pollutants data. While previous studies usually employed traditional statistical approaches to analyze the IADN results, we performed a complete modeling workflow of the total concentrations of PCBs, PESTs, and PAHs (which is referred to as $\sum $ PCBs, $\sum $ PEST s and $\sum $ PAHs orderly) in 1990–2016 samples by using a machine learning algorithm combined with data-driven research method, which lets the model fit the data, so as to change the model to achieve the effect. The main results of this article are as follows, 1) identifying the spatial and temporal trends of POPs (Persistent Organic Pollutants) in the air of the Great Lakes; 2) An appropriate data-driven intelligent model was constructed for the data at EH (Eagle Harbor) and STP(Sturgeon Point) sampling sites, via which we estimated their $\sum $ PCBs, $\sum $ PESTs, and $\sum $ PAHs in the following 4–5 years, showing the concentrations will continue declining with slight fluctuations; 3) The important role which IoT played in smart environmental protection was pointed out.

Using diagnostic ratios to characterize sources of polycyclic aromatic hydrocarbons in the Great Lakes atmosphere

The present study characterized source profiles of polycyclic aromatic hydrocarbons (PAHs) for the Great Lakes atmosphere using nine PAH diagnostic ratios (DRs). The samples were collected from six sites in the Great Lakes basin during 1996–2018 within the Integrated Atmospheric Deposition Network (IADN). In general, pyrogenic sources, including coal combustion and vehicular emissions, were the most important contributors to atmospheric profiles, in particular at the urban sites. Diesel emissions accounted for a larger portion of the traffic-originated PAHs than gasoline emissions at all sites, but this compositional pattern was less obvious at the urban sites. Temporal analyses for DRs revealed that the relative contribution of petrogenic sources and volatilization from surfaces has been increasing gradually, and that the gaps in PAH emissions between diesel- and gasoline-engines appeared to be further amplified in recent years.Coal combustion and non-pyrogenic emissions were the main PAH sources for winter and summer air, respectively, but none of the DRs responded to these changes. DRs were generally different between vapor and particle phases. Our findings shed light on spatial and temporal trends of PAH DRs and PAH source characterization in the Great Lakes basin. Additionally, this study confirmed the usefulness of DRs, especially when combined with the PMF analysis, while also highlighting the limitation of multiple DRs.

Atmospheric concentrations of hexabromocyclododecane (HBCDD) diastereomers in the Great Lakes region

The concentrations of α-, β-, and γ-hexabromocyclododecane (HBCDD) diastereomers in atmospheric particle phase samples were determined at four United States Integrated Atmospheric Deposition Network (IADN) sites located in the North American Great Lakes basin collected between 1 January and 31 December 2014. The concentrations ranged from 0.37 to 8.9 pg/m3, 0.12–4.0 pg/m3, and 0.26–22 pg/m3 for α-, β-, and γ-HBCDD, respectively among the four sampling sites. The median ΣHBCDD concentrations for the four sites were 2.0 pg/m3, 2.1 pg/m3, 1.7 pg/m3 and 5.2 pg/m3 for Chicago, Cleveland, Sturgeon Point and Sleeping Bear Dunes, respectively. Higher levels of ∑HBCDD were observed at the remote site of Sleeping Bear Dunes with comparable levels at the remaining three sites. α-HBCDD and γ-HBCDD were the dominant isomers with an average contribution of about 40% and 50% to ΣHBCDD concentrations, respectively. These HBCDD concentrations were compared with the levels of other brominated flame retardants measured in these samples, including polybrominated diphenyl ethers (PBDEs), 2,3,4,5-tetrabromoethylhexyl benzoate (EHTBB), bis(2-ethylhexyl) tetrabromophthalate (BEHTBP), and decabromodiphenylethane (DBDPE). ∑HBCDD concentrations were significantly lower than or indistinguishable from those of PBDEs, EHTBB, BEHTBP, and DBDPE at all sites except Sleeping Bear Dunes. No significant correlations were found between ΣHBCDD and ΣPBDE, EHTBB, BEHTBP, and DBDPE concentrations, suggesting a different source of HBCDD contamination. This is the first study reporting concentrations of HBCDD isomers in the Great Lakes ambient air, and our results indicate that HBCDD is ubiquitous in the Great Lakes basin, including at remote sites.

Trends in the levels of halogenated flame retardants in the Great Lakes atmosphere over the period 2005–2013

Air (vapor and particle phase) samples were collected every 12days at five sites near the North American Great Lakes from 1 January 2005 to 31 December 2013 as a part of the Integrated Atmospheric Deposition Network (IADN). The concentrations of 35 polybrominated diphenyl ethers (PBDEs) and eight other halogenated flame retardants were measured in each of the ~1,300 samples. The levels of almost all of these flame retardants, except for pentabromoethylbenzene (PBEB), hexabromobenzene (HBB), and Dechlorane Plus (DP), were significantly higher in Chicago, Cleveland, and Sturgeon Point. The concentrations of PBEB and HBB were relatively high at Eagle Harbor and Sturgeon Point, respectively, and the concentrations of DP were relatively high at Cleveland and Sturgeon Point, the two sites closest to this compound's production site. The data were analyzed using a multiple linear regression model to determine significant temporal trends in these atmospheric concentrations. The concentrations of PBDEs were decreasing at the urban sites, Chicago and Cleveland, but were generally unchanging at the remote sites, Sleeping Bear Dunes and Eagle Harbor. The concentrations of PBEB were decreasing at almost all sites except for Eagle Harbor, where the highest PBEB levels were observed. HBB concentrations were decreasing at all sites except for Sturgeon Point, where HBB levels were the highest. DP concentrations were increasing with doubling times of 3–9years at all sites except those closest to its source (Cleveland and Sturgeon Point). The levels of 1,2-bis(2,4,6-tribromophenoxy)ethane (TBE) were unchanging at the urban sites, Chicago and Cleveland, but decreasing at the suburban and remote sites, Sturgeon Point and Eagle Harbor. The atmospheric concentrations of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EHTBB) and bis(2-ethylhexyl)-tetrabromophthalate (BEHTBP) were increasing at almost every site with doubling times of 3–6years.

A Statistical Approach for Left-Censored Data: Distributions of Atmospheric Polychlorinated Biphenyl Concentrations near the Great Lakes as a Case Study

Polychlorinated biphenyl (PCB) congener concentrations were measured in atmospheric samples collected once every 12 days at six sites on the shores of the North American Great Lakes. These data have been obtained as part of the Integrated Atmospheric Deposition Network (IADN), which began in 1991. This data set now consists of ∼2900 samples, each of which has been measured for ∼80 PCB congeners. Some of these congeners are present at levels sufficiently high to be quantitated in almost every sample, while others are detected in fewer than two-thirds of the samples. These latter congeners represent an example of left-censored environmental measurements. This paper offers a simple approach to dealing with uncensored and censored atmospheric PCB concentration data based on a careful examination of the distribution function of the data and using the curve fitting power of the Solver feature of Excel.

Differences in spatiotemporal variations of atmospheric PAH levels between North America and Europe: Data from two air monitoring projects

Atmospheric concentrations of high molecular weight polycyclic aromatic hydrocarbons (PAHs) were measured at five sites for almost two decades near the North American Great Lakes, as part of the Integrated Atmospheric Deposition Network (IADN), and at three remote sites around Europe, as part of the European Monitoring and Evaluation Programme (EMEP). The primary objectives were to reveal the spatial distributions, long-term temporal trends, and seasonal variations of atmospheric PAH concentrations and to investigate potential differences between these two regions. Atmospheric PAH concentrations at the urban sites in Chicago and Cleveland near Great Lakes were about 20 times (depending on PAH congener and sampling site) greater than those at the rural sites except for Košetice in the Czech Republic. Atmospheric PAH concentrations at Košetice, also a rural site, were about one-third of those at Chicago and Cleveland, but 10 times higher than those at other rural sites (Sturgeon Point, Sleeping Bear Dunes, Eagle Harbor, Aspvreten, and Spitsbergen). Significant long-term decreasing trends of all these PAH atmospheric concentrations were observed at Chicago and Cleveland. For the other sites, either less significant or no long-term decreasing trends were observed. Clear seasonality was observed at Sturgeon Point, Sleeping Bear Dunes, Košetice, and Spitsbergen, with the highest PAH concentrations observed in mid-January.

Has the Phase-Out of PBDEs Affected Their Atmospheric Levels? Trends of PBDEs and Their Replacements in the Great Lakes Atmosphere

Air and precipitation samples were collected every 12 days at five sites near the North American Great Lakes from 2005 to 2011 (inclusive) by the Integrated Atmospheric Deposition Network (IADN). The concentrations of polybrominated diphenyl ethers (PBDEs) and selected alternative brominated flame retardants [pentabromoethyl benzene (PBEB), hexabromobenzene (HBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (TBE or BTBPE), decabromodiphenylethane (DBDPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and bis(2-ethylhexyl)-tetrabromo-phthalate (TBPH)] were measured in these samples. The concentrations of almost all of these flame retardants were related to the number of people within a 25 km radius of the sampling site, except for HBB, the concentrations of which were relatively high at Sturgeon Point, and PBEB, the concentrations of which were relatively high at Eagle Harbor. The temporal trends of all of these concentrations were variable. For example, BDE-47 vapor phase concentrations were increasing with doubling times of 5-10 years at Sturgeon Point, Sleeping Bear Dunes, and Eagle Harbor, but these concentrations were slowly decreasing in all phases at Chicago. The most consistent trend was for TBE, which showed concentrations that were unchanging or decreasing in all phases at all sites. TBPH concentrations in particles and HBB concentrations in precipitation were rapidly increasing at most sites with doubling times of ~2 years. The concentrations of DBDPE and BDE-209 were strongly and positively correlated, and the concentrations of TBB and TBPH were also strongly and positively correlated. The concentrations of TBB plus TBPH (representing Firemaster 550) and BDE-47, 85, 99, 100, 153, plus 154 (representing the withdrawn penta-BDE commercial mixture) were also strongly and positively correlated. These positive relationships indicate that the replacement of the deca-BDE commercial product by DBDPE and the penta-BDE product by Firemaster 550 have not yet become evident in the Great Lakes' atmospheric environment.

Source Apportionment of Polychlorinated Biphenyls in Chicago Air from 1996 to 2007

While the overall atmospheric polychlorinated biphenyl (PCB) levels in many urban areas are declining, it is not clear whether this decline is due to control strategies or merely due to natural attenuation. To investigate this issue, Positive Matrix Factorization (PMF) was used to identify the dominant sources of gas-phase PCBs in the atmosphere of Chicago, IL using a data set collected from 1996 to 2007 by the Integrated Atmospheric Deposition Network (IADN). Both the older PMF2 software and the newer EPA-sponsored PMF 3.0 software were employed. Both models resolved 5 factors, but they yielded somewhat different results in terms of the congener patterns of the factors and their temporal variation. The PMF2 software resolved factors that better resembled the original Aroclor formulations. While it is possible to apply an exponential decay model to this data set and derive statistically significant rate constants that indicate that ΣPCBs and some of the resolved factors are declining in Chicago air, examining plots of the 365-day moving average concentrations shows that they do not decrease in a fashion consistent with exponential decay. Instead, they display periods of decline as well as periods of increase. Thus an exponential decay model is not appropriate, and long-term time trends identified from this 12-year data set cannot be used to predict the future trends in PCB concentrations in the air of Chicago. Two of the five resolved factors resemble low MW Aroclors, and declined from 1996 to 2007. The other three factors, which represent the majority of the mass in the data set, are either not declining or actually increasing over time. Thus past efforts to eliminate PCBs from the Great Lakes ecosystem have been only marginally effective, if at all. Additional effort is needed to identify and eliminate atmospheric PCB sources in Chicago.

Dechlorane Plus in the Atmosphere and Precipitation near the Great Lakes

Air (vapor and particle) and precipitation samples were collected at five sites (two urban, one rural, and two remote) on the shores of the Great Lakes from January 1, 2005 to December 31, 2009 as a part of the Integrated Atmospheric Deposition Network (IADN). The concentrations of the syn and anti isomers of Dechlorane Plus (DP), a highly chlorinated flame retardant, were measured in these samples. The highest concentrations of these compounds were generally observed at the rural site at Sturgeon Point, New York, which is located near DP's manufacturing facility in Niagara Falls, New York, and at the urban site at Cleveland, Ohio. A multiple linear regression model was applied to the concentrations of these compounds in the vapor phase, particle phase, precipitation, and for the three phases combined. This regression resulted in an overall (three phases combined) doubling time for the anti-DP isomer of 9.5 ± 3.6 years, but for the syn- and total DP (syn + anti) concentrations, the overall regression was not statistically significant. These results suggest that there has been no significant change in the atmospheric concentrations of these compounds over the 2005-2009 time period. The effect of distance from the source in Niagara Falls was highly significant; for example, doubling the distance from Niagara Falls decreased the DP concentrations by about 30%. The effect of the number of people living and working within a 25-km radius of the sampling site (population density) was also highly significant but small; for example if this population doubled or halved, then the atmospheric DP concentrations would increase or decrease by only a few percent.

Discontinued and Alternative Brominated Flame Retardants in the Atmosphere and Precipitation from the Great Lakes Basin

Air (vapor and particle) and precipitation samples were collected at five sites (two urban, one rural, and two remote) around the Great Lakes during 2005-2009 as a part of the Integrated Atmospheric Deposition Network (IADN). The concentrations of polybrominated diphenyl ethers (PBDEs), decabromodiphenylethane (DBDPE), hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) were measured in these samples. The highest concentrations of these compounds were generally observed at the two urban sites-Chicago and Cleveland-with a few exceptions: The remote site at Eagle Harbor had particularly high levels of PBEB in all three phases, and the rural Sturgeon Point site had the highest HBB concentrations in the vapor phase. The sources of HBB and PBEB to these sites are unknown. A multiple linear regression model was applied to the concentrations of these compounds in the vapor phase, particle phase, precipitation, and the three phases combined. This regression resulted in overall (three phases combined) halving times for total PBDE concentrations of 6.3 ± 1.1 years. The overall halving times for HBB and BTBPE were 9.5 ± 4.6 years and 9.8 ± 2.8 years, respectively. For PBEB and DBDPE, the regression was not statistically significant for the combined phases, indicating that the atmospheric concentrations of these compounds have not changed between 2005 and 2009.

Time Trend Analysis of Atmospheric POPs Concentrations in the Great Lakes Region Since 1990

Using a multiple linear regression model of the concentrations of several persistent organic pollutants in the atmospheric vapor and particle phases and in precipitation, we have analyzed a data set of about 700,000 values to determine the rate at which these concentrations are decreasing. These concentrations were measured as part of the Integrated Atmospheric Deposition Network (IADN), which has operated several sites near the North American Great Lakes since 1991. The pollutants measured include 83 polychlorinated biphenyl congeners, 17 polycyclic aromatic hydrocarbons, and 24 organochlorine pesticides. In the approach used here, for each of the three phases, the concentrations of a specific chemical at all the sites were combined and fitted with a regression incorporating the sine and cosine of the Julian Day (relative to 1 January 1990 and with a periodicity of one year) and the population living and working within a 25-km radius of the sampling site. Partial residuals were then calculated for each datum, all of the residuals for the three phases were combined, and an overall halving time was calculated from them. This relatively simple approach indicated that the concentrations of PCBs in air around the Great Lakes are decreasing with an overall halving time of 17 ± 2 years, which is slow for a substance that was banned about 35 years ago. Phenanthrene, chrysene, and endosulfan showed halving times on the order of 10 years. The concentrations of several organochlorine pesticides were decreasing more rapidly; for example α- and γ-HCH (lindane) have halving times of about 3.5 years.

Evaluation of Tree Bark as a Passive Atmospheric Sampler for Flame Retardants, PCBs, and Organochlorine Pesticides

To investigate the relationship between the levels of persistent organic pollutants in tree bark (a passive sampler) and those in air and precipitation, tree bark and air and precipitation samples were collected during the same time period at the five U.S. Integrated Atmospheric Deposition Network (IADN) sites located in Great Lakes basin. The concentrations of polybrominated diphenyl ethers, Dechlorane Plus, decabromodiphenyl ethane, polychlorinated biphenyls, DDTs, and chlordanes were measured in these samples. Overall, the pollutant concentrations in tree bark are significantly related to the concentrations of these compounds in the air and precipitation collected where the tree was growing. Generally, the highest tree bark and air pollutant concentrations were observed at urban sites, and the lowest concentrations were observed at remote sites. The overall correlation between bark and atmospheric and precipitation concentrations for all the compounds measured in this study was highly significant (P < 0.0001) over 3-4 orders of magnitude. In addition, bark-air partition coefficients, measured for all the chemical categories in this study, were about 10(6), which was in good agreement with previously estimated bark-air partition coefficients for corresponding pollutant groups.

A captured episode of γ-hexachlorocyclohexane air pollution in the Toronto area after the Canadian lindane ban

A Canadian ban on lindane for agricultural use came into effect on December 31, 2004. In the years leading up to this ban, air concentrations of γ–HCH, the active ingredient of lindane, decreased gradually over the Great Lakes region. Typical mean concentrations were about 5 and 10 pg m-3 for Lakes Huron and Ontario, respectively, during the summer of 2005. However, during the period June 27–28, 2005, a γ–HCH air pollution episode was captured in Toronto by three independent sampling programs [Episodic Pesticide Transport (EPT) Study, Integrated Atmospheric Deposition Network (IADN) and Canadian Atmospheric Network for Currently Used Pesticides (CANCUP)], with concentrations of 586 and 3 070 pg m-3 measured in north and downtown Toronto, respectively – an increase of about two orders of magnitude above typical levels. This episode was not observed at any of the regional IADN sites on the same day, suggesting a localized emission in the city from an unknown and episodic source. This study demonstrates the value in continued monitoring of persistent organic pollutants (POPs) beyond their phase–out period and highlights the importance of combining information from different projects to discover environmental pollution events.

Findings from quality assurance activities in the Integrated Atmospheric Deposition Network

A series of experiments were conducted among the laboratories participating in the Integrated Atmospheric Deposition Network (IADN) monitoring program to evaluate comparability of the reported persistent organic pollutant concentrations. This quality assurance activity is essential because a variety of methods are currently used for sample collection, extraction, and analysis by the IADN laboratories. The experiments included analyses of a common reference standard (CRS), analyses of split samples, and analyses of samples collected with co-located samplers at the Point Petre IADN measurement station. The analytes included polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs). For virtually all compounds, the laboratories produced generally comparable results for the CRS samples, the split samples and the co-location samples, although some differences were observed. Analysis of the methods may pinpoint areas where variations in the methods will result in the differences observed in the reported data. These differences can be due to the field sampling process, the analytical method, field blank values, or a combination of all these factors. This study points out the importance of QA activities at every step of an environmental monitoring process so that areas where improvements may be needed or where inconsistencies may exist can be identified.

Multimedia Emissions Inventory of Polychlorinated Biphenyls for the U.S. Great Lakes States

Polychlorinated biphenyls (PCBs) were banned in the United States in 1979, and since then a significant decline in their release to the environment has been observed. This decline has now reached a plateau. Several new regulatory programs have been put in place to further reduce PCB emissions/releases. However, our ability to measure the effectiveness of these regulatory/voluntary programs and to support regional fate/transport and source/receptor modeling efforts depend on reliable emission information. In this study, we attempt to improve the emission inventory for PCBs by compiling and analyzing the multimedia total PCB emission/release data reported for the U.S Great Lakes states for each year from 1990 to 2000. Although Toxic Release Inventory (TRI), National Emissions Inventory (NEI), Great Lakes Regional Air Toxic Emissions Inventory (GLRATEI), and Integrated Atmospheric Deposition Network (IADN) data formed the basis of estimating air emissions, we used the TRI, National Response Center (NRC), and PCB transformer inventory data to estimate PCB releases to land. We used the Permit Compliance System and NRC data to obtain estimates of PCB discharges to water systems in the Great Lakes states.The Remedial Action Plans for each area of concern were the primary source for estimating PCB loads of dredged sediments. On the basis of the NEI, IADN, and GLRATEI data, the total air emissions within the decade were approximately 126 t. The regionwide discharges to water systems and releases to land in the form of landfills and accidental spills in 1990–2000 were estimated as approximately 170 and 3225 t, respectively. We estimated that approximately 1.3 million t of PCB-contaminated sediment were removed or targeted for removal in five lakes of the U.S. portion of the Great Lakes basin. We stress that these estimates were based on reported amounts and the unreported PCB releases/emissions could result in significantly higher estimates.

Flame Retardants in the Atmosphere near the Great Lakes

As part of the Integrated Atmospheric Deposition Network (IADN), air samples were collected at five sites around the Great Lakes (two urban, two rural, and one remote) every 12 days during 2005-2006, and the concentrations of polybrominated diphenylethers (PBDEs), 1,2-bis(2,4,6-tribromophenoxy)-ethane (TBE), Dechlorane Plus (DP), and decabromodiphenyl ethane (DBD PE) were measured. The highest mean concentrations of total PBDEs were found at the urban sites in Chicago and Cleveland (65 +/- 4 and 87 +/- 8 pg/m3, respectively), and the lowest at the remote site in Eagle Harbor (5.8 +/- 0.4 pg/m3). With the exception of Chicago, the atmospheric concentrations of BDE-47 and 99 (summed over the gas and particle phases) are decreasing rapidly with half-lives of approximately 2 years, but the concentrations of BDE-209 are not decreasing at any of the five sites. The atmospheric partial pressures of BDE-47 and 99 showed a strong Clausius-Clapeyron relationship with reciprocal atmospheric temperature. TBE, DBDPE and DP were detected at all sites, but with the exception of Chicago, there were insufficient data to determine temporal trends for these compounds. The influence of human population density and synoptic atmospheric transport patterns was explored to explain the relatively high concentrations of BDE-209 in Cleveland.

Atmospheric Atrazine at Canadian IADN Sites

Atrazine is one of the most widely used herbicides in North America and has been primarily applied to corn production in the Great Lakes basin for over 30 years. During 1996-2002, atrazine concentrations in the atmospheric gas and particle phases were investigated at three Canadian Integrated Atmospheric Deposition Network (IADN) sites including two lakeside sites (Burnt Island and Point Petre) and a rural inland site (Egbert). Strong seasonality with peak concentrations occurring in late April-early July was observed. An atrazine usage map for Canada (sum: 870 t) and the United States (sum: 34 500 t) in 2002 was created. Local application and regional atmospheric transport both appear to contribute to its atmospheric occurrence, while the latter might episodically result in high concentrations events. No strong temperature dependence was observed for atrazine particle-gas partitioning. Recent measurement results of atrazine in precipitation samples collected at Egbert and another agricultural site, Vineland, through the Canadian Atmospheric Network for Currently Used Pesticides (CANCUP), are also presented, Dry, wet, and gas exchange deposition all contribute to atmospheric inputs of atrazine to the Great Lakes. For Lake Ontario, gas exchange is estimated to be of similar magnitude to dry and wet deposition.

Temporal and Spatial Trends of Atmospheric Polychlorinated Biphenyl Concentrations near the Great Lakes

Polychlorinated biphenyl (PCB) concentrations were measured in the atmosphere at six regionally representative sites near the five Great Lakes from 1990 to 2003 as part of the Integrated Atmospheric Deposition Network (IADN). Concentration data for several individual PCB congeners and for total PCBs were analyzed for temporal and spatial trends after correcting for the temperature dependency of the partial pressures. Atmospheric PCB concentrations are decreasing relatively slowly for tetra- and pentachlorinated congeners, an observation that is in agreement with primary emissions modeling. Relatively rapid decreases in PCB concentrations at the sites near Lakes Michigan and Ontario may reflect successful reduction efforts in Chicago and Toronto, respectively. Atmospheric PCB concentrations near Lakes Superior and Huron are now so low that the air and water concentrations may be close to equilibrium. Atmospheric PCB concentrations at sites near Lakes Michigan, Erie, and Ontario are relatively higher than those measured at sites near Lakes Superior and Huron. The highest PCB level was observed at the site near Lake Erie, most likely due to nearby urban activity. However, this relatively higher concentration is still 6-10 times lower than that previously reported at the Chicago site. A correlation between average gas-phase PCB concentration with local population indicates a strong urban source of PCBs. The temperature dependence of gas-phase PCB concentrations is similar at most sites except at Burnt Island on Lake Huron, where very low concentrations, approaching virtual elimination, prevent reliable temperature correlation calculations.