Keri C. Hornbuckle
Assistant Professor
Department of Civil Engineering
212 Ketter Hall
University at Buffalo. Buffalo, NY 14260
Phone: (716) 645-2114 ext 2328
FAX: (716) 645 3667
email: kchorn@eng.buffalo.edu

October 17, 1996

BACKGROUND: Because of the large surface area and organic carbon content of plants, vegetation is expected to be an important participant in the fate and transport of semi-volatile organic compounds (POPs). This is especially likely for compounds that have been widely used, are resistant to degradation, and have low water solubilities. These compounds, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), are taken up by plants primarily through vapor adsorption. The compounds' low water solubilities prevent translocation through the plant vascular system. Due to the ubiquitous nature of vapor-phase POPs, these compounds have been measured in vegetation all over the world. Unfortunately the nature and controls on POP vapor exchange with plants is not well understood. For example, it is not yet known whether exchange between vapor POPs and plant surfaces results in removal of the chemicals from the environment or transport through the environment. Two complementary predictive hypotheses have arisen. First, recent publications by Simonich and Hites have suggested that plants serve as sinks for POPs. Plants are expected to be efficient scavengers of vapor-phase POPs because of their high lipid content. POPs are highly lipophilic; for example, the octanol-water partition coefficients (K_ow) for PCBs range from 10⁵ to 10⁸, K_ows for PAHs range from 10^3.5 to 10⁷. Simonich and Hites have predicted that more than 40% of the PAHs released to the atmosphere in the northeast one-third of the United States will be buried with the vegetation of the region (Figure 1). Whether a compound will be retained hear its original source or transported long distances is dependent on the dynamics of gas-phase exchange with suspended atmospheric particles and exchange with terrestrial and aquatic surfaces. An analysis of these expectations has been detailed by Wania and Mackay, who suggest that the earth's surfaces act as conduits for the transfer of POPs from warmer regions to cooler regions (Figure 2). Their model hypothesis states that the deposition of POPs to surfaces of the globe may be envisioned as a process not unlike chromatographic separation, whereby compounds are removed from the gas-phase as a function of their gas/surface partitioning coefficient and temperature. According to this hypothesis, compounds are transported world-wide via a 'grasshopper' effect of deposition and volatilization as a function of regional climate. By this mechanism, the ultimate fate of the more volatile POPs is the cold surfaces of the Arctic and Antarctica. The validity of this hypothesis is of great concern since many industrially developing countries, some with poor pollution controls, lie in warmer regions of the world. It is likely that POPs are both permanently and temporarily captured by plants depending on the nature of the POP, the plant surface, and especially the local climate.

Our studies of the behavior of atmospheric POPs over Lake Superior , Lake Michigan and, most recently, in a forest in northern Minnesota have shown the importance of seasonal and diurnal climate change on vapor-phase POPs in North America. Over Lake Superior, for example, seasonal variation in vapor POP concentrations determined the direction of air-water exchange. This could not be attributed to local source variation or changes in water temperature so it has been hypothesized that vapor exchange with terrestrial surfaces controls regional vapor-phase concentrations. If this is the case, and given the likelihood of continuing POP release and global climate change, an systematic examination of the effect of climate on POP mobilization is warranted.

The interaction between climate, surface type, and POP characteristics is not well understood. This is largely due to the limitations of field and laboratory experiments. Field experiments, while reflective of real-world chemical behavior, are difficult to interpret due to our inability to control single factors. Laboratory experiments suffer from the unintended elimination of natural phenomena that may control chemical behavior and the necessity of operating at much higher concentrations and smaller scales than normally found in the environment.

OBJECTIVES: A investigation using a large (600m³) environmental chamber is proposed. The overall objective of this work is to investigate the natural processes by which vapor-phase organic chemicals partition to plant surfaces. The specific objectives include:

STATEMENT OF IMPACT AND BENEFITS: The results of this project include a predictive relationship between vapor POP concentrations and/or POP mass flux and measurable parameters of climate. This relationship could be coupled to an atmospheric dispersion model for use in predicting transport of atmospheric pollutants from their original source to a target site. It is anticipated that such a model will be useful to regulators and policy makers who are interested in pollution sources that originate outside of the usual regulatory boundaries (states, nations). Our results will be useful for risk assessment models as well. Currently, there are very large uncertainties in predicting the long-term risks of low level toxic release from incinerators or other atmospheric sources. Part of this uncertainty is due to estimating atmospheric residence times, which are a function of vapor deposition and volatilization rates. The results of this project may also be useful to studies of the effects of global climate change. It is expected global climate change, which will probably include changes in relative humidity as well as temperature, will increase the availability of many toxic compounds. This project will help us determine the possible magnitude of that increase. (See also Future Directions section on page 13).

LITERATURE BACKGROUND: The goal of this study is to identify the unique effect of local climate, as quantified by temperature, relative humidity, and UV light incidence, on the dynamics of vapor-phase POP concentrations ([POP_v]). The study is designed to examine the dynamics of chemical vapor in a large controlled environmental chamber. The compounds proposed for study, PCBs and PAHs, originate from a variety of mostly anthropogenic sources and are of special interest because of their global distribution, persistence, tendency to bioaccumulate, and known or suspected toxicity. PCBs consist of ~110 congeners which were manufactured between 1929 and 1977. Of the approximately 635 million kilograms produced, up to 10% may continue to cycle through the atmosphere . PCBs remain in the environment due to slow degradation and continued release from sediments, landfills, urban areas, and other previously contaminated sites. In contrast to PCBs, PAHs are generally released to the atmosphere as unintended byproducts of natural and anthropogenic combustion processes . It is therefore difficult to estimate the total PAH mass released, although on would expect it to increase with industrialization and decrease with the use of pollution control technology. Ramdahl et al. estimated that about 7.5 million kg were released from United States sources in 1983.

Mathematical modeling, laboratory studies, and field work have been used in the examination of vapor-plant exchange of POPs. The modeling work of Paterson et al. , McLachlan and others have shown the importance of vapor-exchange with leaves. Translocation through the plant vascular system is not important for POPs due to their low water solubilities and the compounds are expected to accumulate in plant leaves cuticles to a degree proportional to their hydrophobicity. The POP hydrophobicity has been characterized by the compound's octanol/water partition coefficient, Kow, and octanol/air partition coefficient, Koa. Because Koa is a function of temperature, this model thermodynamically predicts that accumulation is a function of local temperature. Vapor exchange with plant surfaces has also been examined in a manner analogous to vapor/particle partitioning. Partitioning between atmospheric vapors and particles has been theoretically and empirically examined in more detail than partitioning with plant surfaces and so is a good theoretical base for developing theory about vapor/leaf exchange . The focus of this field is on surface adsorption phenomena rather than absorption into the whole solid. Therefore, factors that influence the surface and surface dynamics are expected to control the distribution of POPs between vapor and surfaces. In addition to temperature, the effects of surface area and polarity and POP surface area and polarity must be considered. There has also been some work examining the role of biological activity in the exchange of POPs between air and leaves. For example, Deinum and coworkers have theorized that the opening and closing of stomata will determine the uptake of vapor phase organic compounds. Since stomatal activity is due in part to solar radiance, it was predicted that plant burdens of organic compounds should increase during the day and decrease at night. Although there is no evidence to support such a concentration change, there is also little to refute it. Additional examination into the effect of light on POP vapor/leaf exchange is indicated.

Partitioning of POPs between a leaf and the vapor phase is expected to be a strong function of temperature. The effect of temperature on any equilibrium is thermodynamically predicted as follows:

(1)

where K is the equilibrium partition coefficient, DH_vol is the enthalpy of volatilization (kJ/mol) and C includes entropic contributions which are not a function of temperature, and unit conversions. Because DH_vol is near constant for POPs at ambient temperatures, this equation establishes the theoretically predicted relationship between the partitioning of POPs to plants as a function of temperature -when the system is at equilibrium. It is important to note that this analysis is valid for equilibrium with the surface (an adsorption mechanism) or for equilibrium with the whole leaf (an absorptive mechanism). Equilibrium with the surface is expected to be rapid while equilibrium with the whole plant matrix is achieved on a much slower scale, and limited by diffusion of the compound through the waxy plant cuticle.

A recent field investigation of the dynamics of gas-phase POPs in a remote forest indicated that exchange between plant surfaces and the atmosphere is rapid and responds to temperature as predicted by the van't Hoff relationship (equation 1) . The study in a semi-remote bog in northern Minnesota was designed to minimize confounding factors such as mixing, anthropogenic interference, seasonal variation, and heterogeneity in vegetation type. Air was sampled over short time periods, in a dense forest populated by a narrow variety of vegetation, far from local sources. Sampling was conducted over 3 to 5 days in four seasons. Strong diurnal variation was observed, corresponding to the diurnal variation in local air temperature (Figure 3). This diurnal variation reflects a change in local vapor concentrations of up to a factor of seven for many POPs. This variation could not be attributed to mixing, chemical reactivity or biological change.

     Figure 3. Vapor-phase concentrations of total PCB varies            
     diurnally with temperature. This trend is least 
     pronounced in  March, when snow covered most plant 
     surfaces, and on July 18, when the effect of relative 
     humidity appeared to change the nature of vapor sorption 
     (see text). The scale for PCB vapor is on the right 
     (ng/m3), the scale for air temperature is on the left 
     (°C). Time of day is plotted on the horizontal axis.

The diurnal variation is strongly correlated to climatic factors, including temperature. Construction of plots of the log (vapor concentration) versus inverse temperature suggest that temperature is controlling the vapor-phase concentrations. In fact, for samples collected in September, temperature could explain most of the variation in vapor phase concentration. However, for samples collected in March, May, and July, the relationship between gas-phase concentrations and inverse temperature is weak. During these times, factors other than temperature controlled gas-phase concentrations. Much of the variance in gas-phase concentrations measured in the bog could be accounted for if relative humidity was included.

The effect of water vapor on vapor POP exchange with plant surfaces is largely unknown. Previous theoretical and empirical investigations into the effect of humidity have focused on mineral surfaces and semi-polar organics. For these systems, an increase in relative humidity translates to an increase in adsorbed water and subsequent displacement of organics . For mineral surfaces, a linear relationship between relative humidity and displacement of POPs is expected . A linear relationship for sorption of nonpolar compounds to nonpolar surfaces like plants is not expected for two reasons. First, water has not been expected to develop a film, but rather to from droplets which expand in height and then in diameter . Recent reports have seriously challenged this expectation. Burkhardt and Eiden used an electrical current to show that films, not just droplets, can form on the waxy surface of a spruce needle at relative humidities as low as 50% . This is a result of previous deposition of atmospheric particles loaded with sulfates or other polar inorganics. It is therefore evident that the development of water films on plant surfaces must be considered when modeling their uptake and release of vapor-phase POPs. Second, work by Chiou and Shoup and others have shown that sorption to a waxy or organic surface is so much more important than sorption of POPs to water, or mineral surfaces, that the latter can be ignored up until almost total water coverage. It is therefore unlikely that relative humidity would show a linear correlation with vapor/leaf partition coefficients.

A few studies have commented on the relationship between relative humidity and partition coefficients for atmospheric particles. Thibodeaux et al. predicted enhanced sorption of POPs by aerosols when no water was present (0% relative humidity; all sites are available for organic sorption) and when the surface is completely covered with water (100% relative humidity; organics dissolve in the water film). They found the lowest POP sorption to the aerosol at intermediate values of relative humidity: clearly no linear relationship. Pankow et al. reported a significant, if weak, relationship between relative humidity and sorption to urban atmospheric particles . Higher relative humidities correlated with higher vapor-phase POP concentrations and lower aerosol POP concentrations. They hypothesized that a stronger relationship might have been observed if the sample times were shorter and more samples were collected during periods of highest relative humidity. It was also not clear if the change in humidity was a function of source that would also change the atmospheric contamination distribution.

The recent work by this investigator, reproduced in Figure 3, is the first to show a linear relationship between vapor phase POP concentrations and relative humidity that cannot be due to confounding factors such as changing air mass, local sources, or seasonal variability. Unfortunately, this relationship is still not conclusive. Nor is it predictive. The effect of relative humidity in one month could not be used to predict the effect in another month. In order to construct a predictive model, relative humidity and temperature need to be examined independently and reproducibly.

Effect Of Ultra Violet Light: Other than photodegradation, which is not the focus of this study, plant exposure to light may affect vapor/plant exchange of POPs by changing the surface character of the leaf. A typical plant leaf is about four to ten cells, or a few hundred microns, thick. The surface of the leaf is covered by a single cell epidermis layer. A waxy, waterproof cuticle covers the air side of the epidermis and is interrupted by occasional stomatal pores. Through the stomata, the plant transpires by taking in CO₂ and releasing O₂ and water vapor. Stomata open (usually during the day) and close (usually during the night) according to the transpiration needs of the plant . Of course, in addition to gases that the plant naturally uses or releases, other gases are also exchanged: ozone, sulfur dioxide, and POPs. Deinum et al. presented a conceptual/mathematical model of organic chemical vapor uptake by plants and concluded that stomatal behavior should be considered when constructing predictive models. The predicted effect due to the stomatal pores included a diurnal variation in vapor phase concentrations with higher organic vapor concentrations at night. The data of Hornbuckle and Eisenreich (figure 3) is the only data set I know of that addresses diurnal POP vapor variations in a remote system and contradicts the above hypothesis. We found daytime vapor POP concentrations exceeded nighttime concentrations. This does not invalidate the stomata hypothesis, however, since the terrestrial system examined by Hornbuckle and Eisenreich was dominated by Sphagnum moss, a plant with no active stomata. Further investigation is required to determine the effect of sunlight on POP vapor exchange.

HYPOTHESIS: Temperature, relative humidity and ultra violet light control the uptake of semi-volatile organic compounds by vegetation and therefore control their atmospheric concentration. This work, when complete, will show

• how the dynamics of water vapor effects the concentrations of air-borne organic pollutants
• whether temperature effects on gas-phase concentrations are thermodynamically predictable
• how natural changes in the plant/leaf surface effect the uptake and release of POPs; and
• whether whole-leaf equilibria governs the availability of atmospheric organic compounds

APPROACH: The hypotheses will be investigated using a controlled environmental chamber. Several recent field studies have indicated the importance of vapor-surface exchange and have examined the correlation between climatic factors and vapor/particle partitioning, variation in vapor concentrations, and plant accumulation of POPs. The separate importance of temperature, relative humidity, and solar radiation is difficult to evaluate in the field, however, since all factors vary simultaneously and are often dependent. Previous laboratory investigations of vapor-surface exchange have required 1) high vapor and surface concentrations of the compounds; 2) high surface area to volume ratios; and 3) high temperatures. These chemical concentrations and surface to volume ratios exceed ambient levels by orders of magnitude while the temperature range commonly exceeds ambient temperatures by more than 20°C. It is therefore difficult to extrapolate laboratory results to natural systems. The use of a large (600m³) controlled chamber in this study allows investigation of relative humidity, temperature and light as separate components under conditions normally found in the natural environment.

Chamber Description: The Ashford test chamber used in this study was originally designed as a part of a military ordnance test facility (See photo included in appendix). Extensive modifications have been made over the past few years, converting it to a unique facility for atmospheric simulation, air pollution, cloud physics, and aerosol research studies. The heart of the test facility is a cylindrical chamber of 9 m diameter and 9 m height. The total volume is 600 m³, making it one of the largest available test chambers in the United States. The chamber was designed to minimizes wall effects and simulate actual atmospheric conditions (See photo enclosed in appendix). It is lined with a fluorinated epoxy-polyurethane copolymer, resurfaced in 1994, which coats the entire surface including a mixing fan but excluding the glass enclosures for UV lights. Absolute filters are incorporated to permit virtually complete removal of particles (<200 Aitken nuclei/cm³). Vapor phase contaminants can be removed using adsorbent resins to reduce chamber concentrations of POP to below detection limit (< .1 ng/m³ for PAHs). Humidity control is possible through cooling coils in the ductwork and a nebulizer nozzle in the chamber ceiling. The chamber is further equipped with a water (and detergent if required) flushing system for cleaning the walls. Ultra violet lamps are located around the chamber wall to permit near uniform intensity distribution within the chamber. Twenty-four individual light fixtures, each containing two special Sylvania high intensity blacklight lamps, are arranged in three horizontal rows and eight vertical columns spaced equally along the chamber wall. Each of the light source combinations is encased in a gas-tight enclosure equipped with a 15" x 96" Pyrex glass from panel. Forced air cooling (separated from the chamber air) is used to minimize temperature increase at these light source fixtures. The resulting light intensity corresponds to approximately 50% of the average mid-day solar radiation at sea level in mid-latitudes. Pressure, temperature and humidity is monitored and recorded continually in the chamber using a data logger (Campbell Scientific CR10) with calibrated thermocouples and relative humidity probe. An infrared transmissometer is available for measuring liquid water content in fog.

Although this study focuses on gas-phase dynamics, the chamber can be equipped for aerosol addition, growth and characterization. Fog conditions can be simulated in the chamber by wetting the walls using a rotating spray nozzle and then reducing the chamber pressure to about 30mb below ambient. This chamber has been used extensively for a variety of aerosol and fog related investigations requiring accurate simulation of atmospheric conditions. Dehumidifiers and a fine-control humidification system are an integral part of the chamber's support capabilities. Effects of relative humidity, particle type and concentration, and gaseous contaminants on aerosol growth rates can be reproducibly studied. Fogs can be formed on resultant aerosol to study effects of particle hydration on vapor-particle exchange of POPs. The effect of fog, particle suspension, and particle deposition on the dynamics of POP exchange with plants will be examined using this facility in future studies.

Vapor POPs are added to the chamber in two ways. Ambient concentrations may be studied by ventilating the chamber with outside air. The facility is located near rural Ashford, New York, about 55 km south of Buffalo, NY. Concentrations of PCBs and many PAHs are expected to be representative of non-urban areas in much of the United States. For compounds not detectable in ambient air, vapor POPs can be added to the chamber using a gas-generator column. The gas-generator column constructed by adding a solution of POPs in hexane to a glass column filled with glass beads. The hexane is allowed to evaporate, leaving adsorbed POPs. These POPs are then added to the chamber by introducing the generator column to the ventilation flow. The system may be completely sealed and ports accessed individually for gas addition or extraction.

Air is sampled through a sealed port modified to include an adsorbent column. Depending on the anticipated vapor concentration, 20 to 100 m³ of chamber air is removed from the system. This range of volumes represents 3 to 17% of the chamber volume. Because the system is sealed, the accompanying pressure change will be measured and included in subsequent data interpretation and modeling. A pressure change will not be important for studies performed at ambient concentrations, when the ventilation port remains open.

Operation of the chamber will be supervised by employees of Calspan Inc. who have extensive experience with the chamber. Calspan employees will therefore be involved in the characterization and optimization of the chamber for this study.

Chamber Characterization: Defining the behavior of the system before experiments begin is a critical part of this project. Interpretation of the data will require a mass balance approach in order to describe POP behavior with regard to plant sorption separately from POP sorption to the chamber walls. Characterization is expected to take up to 6 months of the two year project and will include assessment of the following:

- Pressure control. Seals on the chamber will be examined using pressure variation. Gas tight seals must be maintained.

- Humidity control. Maintenance of a constant humidity will be evaluated for the time required for the experiments. Changes in relative humidity as a function of sampling flow must also be evaluated.

- Temperature variation. Although temperature is not explicitly controlled in the chamber, UV lights, flow rates, and circulation of ambient air will allow the study to measure effects of temperature. Use of these devices as temperature controls will be evaluated.

- Activity of the coated surface. Vapor dynamics in the empty chamber will be evaluated as a control to the plant sorption work. Characterization of POP vapor behavior in the empty system is of utmost concern, as the results of this work will be used as a control when plants are added to the chamber.

Experimental Design: Experiments will be conducted with attention to isolating the parameters of study: temperature, humidity, and light. The general method that will be applied is outlined here. Adjustments to this method are expected as the system is fully characterized. Once the system is characterized, each parameter will be evaluated for its effect on vapor phase concentrations. Although this project focuses on the dynamics of gas-phase POPs, plants will be sampled and analyzed for POPs at least twice over the course of this project.

1. System is ventilated with particle-free outside air. The system is swept with ambient air until a constant POP value is reached. This is expected to require about 24 hours. The actual time will be established during the system characterization portion of the project. During all experiments, the system is well mixed by the floor fan.

2. For experiments requiring an enriched POP gas, air is fed through the POP gas generator column until a uniform concentration is reached. Again, the time required will be established during system characterization. Air is removed through the system and cleaned before discharge using a cartridge of activated carbon in the flow stream.

3. Once the system, including temperature, relative humidity, and UV intensity, is near steady state, air is sampled. Sampling time will require one to four hours, during which all parameters are held near constant and constantly monitored and recorded. Each experiment is repeated at least three times under identical conditions.

Plant Species: The plant chosen for this study, Ficus benjamina, was chosen as a surrogate for deciduous trees and shrubs common to North America. In addition, this plant, sometimes called a fig tree, is fairly resilient, easily obtainable at local nurseries and its surface area is not difficult to measure. Approximately ten large (1.5 m height) plants will be used in the study. Physical characteristics of each individual will be assessed prior and after each air sample collection (i.e. surface area, mass, height). Chemical characteristics including leaf lipid content, water content, and POP concentration will be analyzed from a set of triplicate leaf samples collected at the initiation of the work. POP concentrations at this time would be reflective of nursery or ambient air POP contamination. Another sample, in triplicate, is collected at the end of the project. Interpreting the sorption behavior is based on air samples, however, not plant samples, so numerous plant samples are not required.

Sample Analysis: Fifty to one hundred adsorbent (air) samples will be collected for this project. Each one will be analyzed either by Soxhlet solvent extraction using a 1:1 hexane/acetone mixture or by supercritical fluid extraction (SFE). Refer to Hornbuckle et al. (1995) for details on the solvent extraction method. The SFE method uses supercritical CO₂ , passing through the sample at pressures ~5000 psi and T= 90 °C. CO₂ extracts the POP from the adsorbent. The POP is removed from the CO₂ by expanding the supercritical SFE in dichloromethane. An ISCO Model 260D syringe pump and a Keystone vessel extractor will be used. Once extracted, by either method, the sample is concentrated using a rotoevaporator (Buchii) and nitrogen (N-Evap, Organomation, Inc.) and internal standards are added. Two internal standards are used for the PCB analysis; 2,4,6-trichlorobiphenyl (PCB #30) and 2,2,'3,4,4',5,6,6'-octachlorobiphenyl (PCB #204). Three internal standards are used for PAH analysis; d-8 naphthalene, d10-fluorene, d12-fluoranthene, and d12-perylene. The concentrated extracts are analyzed by gas chromatography / mass spectrometry (GC/MS, PAHs) and gas chromatography / electron capture (GC/ECD, PCBs). Sample treatment efficiency will be evaluated in part using surrogate POP addition prior to adsorbent extraction. These surrogates are d10-acenaphthene, d10- phenanthrene, d10-pyrene, d12-benzo[e]pyrene, d12-benzo[ghi]perylene, 3,5-dichlorobiphenyl, 2,3,5,6-tetrachlorobiphenyl, and 2,3,4,4,'5,6-hexachlorobiphenyl.

· Hewlett Packard 6890GC/MSD equipped with HPChemstation analytical software and an automatic sampler.

· Hewlett Packard 5890 gas chromatograph with electron capture detector and automatic sampler.

· Data logger with 10' thermocouples and relative humidity probe (Campbell Scientific) and laptop computer.

· 'Toxics' lab equipped with low UV-emitting lights, Buchi Rotovapor, and N-Evap solvent concentrator.

QUALITY ASSURANCE: The data collected for this project will be analyzed and reported in a manner that assesses precision, accuracy, representativeness, completeness, and comparability with other projects.

Precision, defined as the relative uncertainty about a given measurement, is assessed by replicate analyses. Precision will be monitored by the analysis of 10% of the air samples, collected on adsorbent resin, split into two equal fractions and each analyzed as separate samples. Duplicate air samples will be collected with every 5 samples (20% inclusion). Duplicate air samples will be collected simultaneously from different ports in the chamber. All plant samples will be collected and analyzed in duplicate.

Accuracy, defined as the absolute uncertainty about the true value, will be assessed by surrogate spike recoveries in every sample and by spike experiments with performance standards. The compounds serving as surrogates will differ for each compound class. Surrogates for air samples are added to the top of the resin cartridges prior to sampling; surrogates for vegetation are added to the samples prior to storage. All compounds will be reported on a compound-specific basis (e.g. PCB congeners).

Chamber blanks will consist of 10% of the samples collected. Air chamber blanks are adsorbent cartridges carried to the chamber and returned to the laboratory unopened. They will be opened briefly in the field to allow surrogate addition. Sample results will not be corrected for blank values; analyte concentrations in samples and blanks will be reported. These blanks relate back to the entire data set rather than to a subset of samples prepared simultaneously. Field blanks for vegetation cannot be measured as all plants retain some POP contamination due to background POP levels in air. Solvent (CO₂ or hexane/acetone) and glassware blanks will be analyzed with every sample set or about one in seven samples.

Comparability expresses the confidence with which one data set can be compared to another, either between laboratories or within a laboratory for different batches of samples. All data in this study will have internal comparability due to the use of self-consistent field and analytical procedures, and can be monitored by surrogate spike recovery performance. Comparability between these data and other investigators' data will be dependent on the similarity of the field and analytical methods used between the studies. This can be determined by comparing accuracy measures. Data will be reported in units consistent with other studies of toxics in air and vegetation.

Completeness is defined as the percentage of acceptable data needed to validate the study. It is calculated as the number of samples with concentrations above detection passing QA criteria divided by the number of samples analyzed having concentrations above detection multiplied by 100. Completeness for this study is set at 80%; sample that fail QA will not be used in the predictive model. Once collected, air and vegetation samples are tightly wrapped in precombusted foil, sealed in a plastic bag, and frozen at -10C or lower. After collection, all samples will be protected from UV light.

The facility used for this project is owned and maintained by Calspan SRL Corp. (Calspan Advanced Technology Center, PO Box 400. Buffalo, NY 14225). Commitment to this collaboration is indicated by matching funds from CUBRC (Calspan-UB Research Corp.) for the initial startup of the chamber. The principal investigator, K.C. Hornbuckle, will oversee all aspects of the project. Modification of the chamber will be conducted with the assistance of employees of Calspan and the University at Buffalo Civil Engineering machine shop. Initial startup costs for the chamber are supported by Calspan as indicated in the budget. Operation of the chamber will be supervised by Calspan staff, who will be present during all chamber activities. Actual sample collection will be conducted by the principal investigator or a graduate student from the University at Buffalo. Air samplers will be calibrated on at the chamber prior to each experiment.

A final report will be issued to the NSF Project Officer upon completion of all sample analyses and data interpretation at the end of the project period. The final report will contain the complete data set and QA/QC results. Progress on sample extraction, analytical procedures, and timeline will be prepared for the project officer every 6 months in a format designated.

FUTURE DIRECTIONS FOR COLLABORATIONS AND EXPANSION OF THIS PROJECT:

This project, which is an examination of the behavior of atmospheric pollutants at ambient levels and simulated climate, represents a new use of the Ashford environmental chamber, which has previously been used for ordance testing and high chemical concentration experiments. It is expected the results of experiments in the chamber will provide new insight to atmospheric processes that go beyond the original expectations of this proposal. Expansion of this project is expected in the area of photochemical reactivity of gas-phase and particle-bound organic compounds, nucleation of gas-phase contaminants at high gas-phase concentrations, and sorption of organics to homogeneous and/or monodispersive aerosols. These are important issues that need to be examined under the broad subject of atmospheric fate and transport of gas-phase pollutants using the Ashford chamber. In addition to use of the chamber to control climatic factors, it is expected that this project will be used to support field research. Field investigations that are expected to proceed from this include examination of the ultimate fate of contaminants absorbed to leaves, transfer of plant-sorbed contaminants to soils, the coupling of atmospheric deposition to plants and subsequent runoff of the contaminants to watersheds. Modeling or predictive efforts are the ultimate goal of this research. Future modeling efforts will include coupling of surface exchange processes for organic contaminants with long range dispersion models previously designed for atmospheric transport of nutrients and acid rain precursors, evaluation of hydrometeorologic models as components of an atmospheric transport model, and predictive models for non-point sources of POPs to watersheds, tributaries and lakes.

This work is multidisciplinary in nature and benefits from an inclusive approach with regard to science and engineering disciplines. It is fully expected and desired that this project will act as the basis for collaborations with scientists and engineers from other departments, universities, and industry. Collaboration outside of the University of Buffalo's Department of Civil Engineering is required due to the lack of colleagues pursuing air pollution issues, but such collaborations are also beneficial for long-term development of research and educational goals. Expansion of the project to include several related disciplines encourages innovation, requires a broader knowledge base from investigators, and is beneficial to students active in the project. Likely collaborators, in addition to those in civil engineering, will be solicited in disciplines such as analytical chemistry, biogeochemistry, chemical engineering, geography, ecology, geology, and physics.

TEACHING AND MENTORING ASPECTS OF THE PROJECT:

The central goal of this investigator, in pursuing any and all funding for research activities, is to train students for future work and contributions to the fields of science and engineering. Towards this goal, one or more students will be funded throughout the duration of the project and mentored to the conclusion of his/her degree program. Mentoring, at the graduate level should help students develop good problem solving skills, accomplish tasks according to an agreed upon schedule, interact with other professionals in the field, understand how the thesis project fits into a broader goal, transfer skill between applications, and communicate the ideas, conclusions, and implications of their work. It is important that students develop a feeling of 'ownership' of the project and the problem they are addressing. Students acquire this through an investment of time and energy, as well as from progressively increasing responsibilities.

I have initiated a long-term commitment to graduate and undergraduate engineering education. Towards this commitment, I have participated in several workshops and conferences intended to improve my teaching skills and increase my exposure to advances in engineering education reform. These activities include two workshops offered by the University at Buffalo; one designed as a teaching orientation for new professors, the other focused on use of case studies in teaching. In addition, I was selected to participate in the National Science Foundation's Engineering Education Scholars Workshop, organized by Clifford Davidson, Department of Civil and Environmental Engineering and Susan Ambrose, Director of the Eberly Center for Teaching (see Davidson and Ambrose for an excellent review of teaching techniques and advice for junior faculty ). An abstract has been submitted to the International Conference on Engineering Education for a paper summarizing the objectives and results of this workshop. Through these workshops, I have identified several key areas for focus:

1. Integration of graduate students in research. It is my goal to introduce graduate students into all areas of research including proposal writing, literature review, presentation of results at national meetings and through peer reviewed journals, and perhaps most importantly, through informal and regular discussion of the details and broad impacts of engineering research. The specific actions I have taken include meeting with students on a weekly (scheduled) basis, sponsoring student's registration fees at conferences (e.g.. 2 students will attend the Air and Water Management Association's Atmospheric Deposition to the Great Waters Conference, Oct. 28-30, 1996), and introducing students to academic and industrial scientists and engineers. Through long-term mentoring, I am committed to producing students who are highly skilled with regard to technical knowledge, problem solving skills, and communicating their work to a broad audience.

2. Use of active learning techniques in graduate and undergraduate courses. Active learning and teaching techniques that encourage active learning have been recognized as a important method (or set of methods) of training students for skill transfer and flexibility. In engineering, the need for active learning techniques is especially vital, as newly employed engineers are regularly asked to apply their theoretical knowledge to new problems . Active learning requires the student and the teacher to participate in the learning processes as interactive partners beyond which is required in the traditional engineering classroom. Techniques for encouraging active learning can be very simple changes in the style of lecturing, or they can be very involved and complicated activities that require significant teacher preparation time and group coordination. I have begun with adapting my lecture and intend to proceed to more advanced techniques. Simple modifications of the lecture have shown to produce greater retention of ideas and problem solving. For example, research has long indicated that students are most attentive to a lecture in the first and last ten minutes. During the interim period, student attentiveness drops off markedly . Modifications I have introduced into my lectures include conducting minute papers, think-pair-share activities, and using open-ended questions to drive the lecture. The minute papers (which students call 'pop quizzes') are used to encourage students to assimilate new ideas while still in the classroom instead of waiting until just prior to an exam. Students are presented with a conceptual problem and asked to write a strategy for solving the problem or summarize their understanding of the problem. When used in the middle of the class period, minute papers are an effective way of reminding students of what I (the instructor) thinks is important. It is also a good way to keep track of attendance and supplements other forms of assessment . Think-pair-share is another technique I use to develop higher thinking and analytical skills while students are in the classroom . Students are presented with a question that has no correct answer. They are given three to six minutes to discuss their approach with another student. After this period, students are called on to describe their approach to the problem. This technique reinforces particular concepts, promotes team problem solving, and increases student-instructor exchange - all of which are known to improve learning and retention. My long-term goal, with regard to classroom teaching, is to fully incorporate problem-based learning, in the style of Don Woods, chemical engineering professor at McMaster University. Problem based learning, as an overall teaching method, involves more open and non-traditional approach to developing student strategies for solving complex engineering problems. Aspects of this approach include skill development in: brainstorming; systematic decision-making; stress and time management; defining goals; creativity; team organizing and management; and flexibility. Although these skills are not traditional to engineering education, student success in gaining employment and advancement depends heavily on these factors.

3. Recruitment and retention of women in engineering. Although well known, the reasons for the loss of high ability women from science, mathematics, and engineering (SME) majors are not well understood. There is, however, sufficient evidence to suggest the loss is NOT due to poor preparation, lack of interest, or inherent difficulties with SME subjects. A number of researchers have concluded that the loss of women from SME majors is due to discomfort in the culture or environment offered in many SME departments (see recent work by Seymour . Some of the ways to combat this discomfort are only possible on an institutional scale (small grants for individuals or groups, establishment of resource centers and data bases, receptions and other opportunities for peer and student/faculty informal interaction) but other opportunities are available for individual faculty. Over the course of my academic career, the following initiatives are expected: (1) Use of my current position as faculty advisor of the student chapter of the Society of Women Engineers (SWE) to identify freshman and incoming transfer women potentially interested in engineering; (2) Act as a personal/professional mentor to graduate students and undergraduate students who request such a relationship; and (3) Assist SWE in building a mentor/mentoree network between senior and entering women student engineers. In addition, the use of active learning techniques, as outlined above, has been shown to improve the learning climate for women in engineering.

 

1) Simonich, S. L.; Hites, R. A. Importance of vegetation in removing polycyclic aromatic hydrocarbons from the atmosphere. Nature 1994, 370, 49-51.

2) Simonich, S. L.; Hites, R. A. Vegetation-atmosphere partitioning of polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 1994, 28, 939-943.

3) Wania, F.; Mackay, D. Tracking the distribution of persistent organic pollutants. Environ. Sci. Technol. 1996, 30, 390A-396A.

4) Wania, F.; Mackay, D. Global fractionation and cold condensation of low volatility organochlorine compounds in polar regions. Ambio 1993, 22, 10-18.

5) Hornbuckle, K. C.; Jeremiason, J. D.; Sweet, C. W.; Eisenreich, S. J. Seasonal variation in air-water exchange of polychlorinated biphenyls in Lake Superior. Environ. Sci. Technol. 1994, 28, 1491-1501.

6) Hornbuckle, K. D.; Sweet, C. W.; Pearson, R. F.; Swackhamer, D. L.; Eisenreich, S. J. Assessing annual water-air fluxes of polychlorinated biphenyls in Lake Michigan. Environ. Sci. Technol. 1995, 29, 869-877.

7) Hornbuckle, K. C.; Eisenreich, S. J. Dynamics of gaseous semi-volatile organic compounds in a terrestrial ecosystem: Effects of diurnal and seasonal climate variation. Atmos. Environ. 1996, 30, 3935-3945.

8) Hornbuckle, K. C.; Eisenreich, S. J. Bioconcentration factors for semi-volatile organic compounds in Sphagnum moss and spruce needles. Environ. Sci. Technol. in review, ,

9) Miller, S. The persistent PCB problem. Environ. Sci. Technol. 1982, 16, 98-99A.

10) Baek, S. O.; Field, R. A.; Goldstone, M. E.; Kirk, P. W.; Lester, J. N.; Perry, R. A review of atmospheric polycyclic aromatic hydrocarbons: sources, fate and behavior. Water, Air, and Soil Pollution 1991, 60, 279-300.

11) Ramdahl, T.; Alfheim, I.; Bjorseth, A.; Mobile Source Emissions including Polycyclic Organic Species, Reidel: Dordrecht, 1983, pp.277-298.

12) Paterson, S.; Mackay, D.; Tam, D.; Shiu, W. Y. Uptake of organic chemicals by plants: a review of processes, correlations and models. Chemosphere 1990, 21, 297-331.

13) Paterson, S.; Mackay, D.; Bacci, E.; Calamari, D. Correlation of the equilibrium and kinetics of leaf-air exchange of hydrophobic organic chemicals. Environ. Sci. Technol. 1991, 25, 866-871.

14) Paterson, S.; Mackay, D.; McFarlane, C. A model of organic chemical uptake by plants from soil and the atmosphere. Environ. Sci. Technol. 1994, 28, 2259-2266.

15) McLachlan, M. S.; Welsch-Pausch, K.; Tolls, J. Field validation of a model of the uptake of gaseous SOC in Lolium multiflorium (rye grass). Environ. Sci. Technol. 1995, 29, 1998-2004.

16) Tolls, J.; McLachlan, M. S. Partitioning of semivolatile organic compounds between air and Lolium Multiflorum (Welsh Ray grass). Environ. Sci. Technol. 1994, 28, 159-166.

17) Riederer, M. Estimating partitioning and transport of organic chemicals in the foliage/atmosphere system: Discussion of a fugacity-based model. Environ. Sci. Technol. 1990, 24, 829-837.

18) Sabljic, A.; Gusten, H.; Schonherr, J.; Riederer, M. Modeling plant uptake of airborne organic chemicals. 1. Plant cuticle/water partioning and molecular connectivity. Environ. Sci. Technol. 1990, 24, 1321-1326.

19) Trapp, S.; Mattries, M.; Scheunert, I.; Topp, E. Modeling the bioconcentration of organic chemicals in plants. Environ. Sci. Technol. 1990, 24, 1246-1252.

20) Ligocki, M. P.; Pankow, J. F. Measurements of the gas/particle distributions of atmospheric organic compounds. Environ. Sci. Technol. 1989, 23, 75-83.

21) Pankow, J.; Bidleman, T. F. Effects of Temperature, TSP and percent non-exchange material in determing the gas-particle partitioning of organic compounds. Atmos. Environ. 1991, 25A, 2241-2249.

22) Pankow, J. F.; Storey, J. M. E.; Yamasake, H. Effects of relative humidity on gas-particle partitioning of semivolatile organic compounds to urban particulate matter. Environ. Sci. Technol. 1993, 27, 2220-2226.

23) Deinum, G.; Baart, A. C.; Bakker, D. J.; Duyzer, J. H.; Van den Hout, K. D. The influence of uptake by leaves on atmospheric deposition of vapor phase organics. Atmos. Environ. 1995, 29, 997-1005.

24) Chiou, C. T.; Shoup, T. D. Soil sorption of organic vapors and effects of humidity on sorptive mechanism and capacity. Environ. Sci. Technol. 1985, 19, 1196-1200.

25) Rhue, R.; Rao; Smith, R. Vapor-phase adsorption of alkylbenzenes and water on soils and clays. Chemosphere 1988, 17, 727-741.

26) Rhue, R. D.; Pennell, K. D.; Rao, P. S. C.; Reve, W. H. Competitive adsorption of alkylbenzene and water vapors on predominantly mineral surfaces. Chemosphere 1989, 18, 1971-1986.

27) Ong, K. S.; Lion, L. W. Effects of soil properties and moisture on the sorption of trichloroethylene vapor. Water Research 1991, 25, 29-36.

28) Goss, K. Effects of temperature and relative humidity on the sorption of organic vapors on quartz sand. Environ. Sci. Technol. 1992, 26, 2287-2294.

29) Pennell, K. D.; Rhue, R. D.; Rao, P. S. C.; Johnston, C. T. Vapor-phase sorption of p-xylene and water on soils and clay minerals. Environ. Sci. Technol. 1992, 26, 756-763.

30) Goss, K.-U. Adsorption of organic vapors on ice and quartz sand at temperatures below 0°C. Environ. Sci. Technol. 1993, 27, 2826-30.

31) Cape, J. N. Contact angles of water droplets on needles of Scots pine (Pinus sylvestris L.) growing in polluted atmospheres. New Phytol. 1983, 93,

32) Burkhardt, J.; Eiden, R. Thin water films on coniferous needles. Atmos. Environ. 1994, 28, 2001-2017.

33) Thibodeaux, L.; Nadler, K.; Valsaraj, K.; Reible, D. The effect of moisture on volatile organic chemical gas-to-particle partitioning with atmospheric aerosols - competitive adsorption theory predictions. Atmos. Environ. 1991, 25A, 1649-1656.

34) Nobel, P. S., Physicochemical and environmental plant physiology. . Academic Press, Inc.: San Diego, CA, 1991. p.3-4.

35) Swackhamer, D. L. Quality assurance plan for the Green Bay Mass Balance Study 1. PCBs and Dieldrin. Great Lakes National Program Office of the United States Environmental Protection Agency, Chicago, IL, .

36) Hornbuckle, K. C.; Achman, D. R.; Eisenreich, S. J. Over-water and over-land polychlorinated biphenyls in Green Bay, Lake Michigan. Environ. Sci. Technol. 1993, 27, 87-98.

37) Davidson, C. I.; Ambrose, S. A., The New Professor's Handbook. . Anker Publishing Company, Inc.: Boltonm MA, 1994. p.199.

38) Hornbuckle, K. C.; van der Meulen, M. C. H. in review, ,

39) Wankat, P. C.; Oreovicz, F. S., Teaching Engineering. . McGraw-Hill, Inc.: New York, 1993. p.370.

40) Bonwell, C. C.; Eison, J. A., Active learning: creating excitement in the classroom. . School of Education and Human Development at The George Washington University: Washington, DC, 1991. p.104.

41) Penner, J. G., Why Many College Teachers Cannot Lecture. . Charles C. Thomas: Springfield, IL, 1984. .

42) Verner, C.; Dickinson, G. The lecture: an analysis and review of research. Adult Education 1967, 17, 85-100.

43) Stuart, J.; Rugtherford, R. J. D. Medical student concentration during lectures. Lancet 1978, 2, 514-516.

44) Angelo, T. A.; Cross, K. P., Classroom assessment techniques: a handbook for college teachers. . Jessey-Bass: San Francisco, 1993. .

45) Cooper, J.; Prescott, S.; Cook, L.; Smith, L.; Mueck, R. Cooperative learning and college instruction: effective use of student learning teams. The California State University Foundation, pp. 10. .

46) Seymour, E. Revisiting the "Problem Iceberg": science, mathematics, and engineering students still chilled out. Journal of College Science Teaching 1995, May,

47) Woods, D., et al., Developing problem solving skills: the McMaster problem solving program, 1996.

48) Woods, D. R. Major challenges to teaching problem solving. Annals of Engineering Education 1979, 70, 277-284.

49) Woods, D. R.; Problem solving. What Research Says to the Science Teacher - problem solving, Gabel, D., Ed.; National Science Teachers Association: Washington, D.C., 1988, .

50) Tobias, S., Overcoming Math anxiety: Revised and Expanded. . W.W. Norton and Co.: New York, 1990. .

51) Oakes, J. Opportunities, achievement and choice: Women and minority students in science and mathematics. Review of Educational Research 1990, 16, 153-222.

52) Fox, M. F.; Women, academia, and careers in scienc eand engineering. The Equity Equation Fostering the Advancement of Women in the Sciences, Mathematics and Engineering, Davis, C., Ginorio, A. B., Hollenshead, C. S., Lazarus, B. B., Ed.; Jossey-Bass Publishers: San Francisco, 1996, .

53) Seymour, E.; Hewitt, N. M., Talking about Leaving: Why Undergraduates Leave the Sciences. . Westview Press: Boulder, CO, 1996. p.265.

54) Seymour, E. The loss of women from science, mathematics, and engineering undergraduate majors: an explanatory account. Science Education 1995, 79, 437-473.

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