Spatial Measurements of Ultrafine Particles Using an Engine Exhaust Particle Sizer^TM within a Local Community Downwind of a Major International Trade Bridge in Buffalo, New York

Abstract

Ultrafine particles (UFP) can be defined as having at least one dimension that is less than 100 nanometers. Because of their dimensions, they exhibit unique properties that affect atmospheric transport, exposures, and possibly health endpoints. Freshly generated Diesel particulate matter (DPM) is predominantly in the ultrafine particle size range size range, which in practice is defined by the detection characteristics of the sampling instrument. During two seasons, an Engine Exhaust Particle Sizer^TM (TSI, St. Paul, MN) detects particles over a range of 5.6–560 nm was used to continuously measure real-time particle size distributions along several streets that extend from the Peace Bridge (PB), a major international trade bridge, into a the nearby adjacent neighborhood that has reported a high prevalence rate of asthma (Lwebuga-Mukasa 2000). The Peace Bridge connects Buffalo, NY, USA to Fort Erie, ON, Canada. During summer 2004, one minute average particle number concentrations were continuously monitored along neighborhood streets near the Peace Bridge Complex (PBC) plaza out to about 2 km. Ultrafine particle counts as a function of bridge traffic showed downwind UFP levels at 300 m ranging from 60,000–70,000 p/cm³. Upwind background UFP levels at the shore line of Lake Erie were typically 8,000–10,000 p/cm³ under similar traffic and meteorological conditions. During winter 2006, additional measurements were conducted in front of several homes that were part of a separate indoor-outdoor exposure study (McAuley et al. 2010). Sampling at the homes was done during the weekdays when heavy diesel truck traffic was highest. Results showed that most of the UFP number concentrations fell between 10–20 nm in front of homes with UFP levels ranging from 59,000 p/cm³ at couple hundred m downwind to 81,000 p/cm³ several hundred m directly downwind of the Peace Bridge under similar diesel trucks traffic and meteorological conditions.

INTRODUCTION

Emissions from motor vehicles are known to be an important source of air pollution in urban areas (Fenger 1999; Sharma and Khare 2001; Bogo et al. 2001; Perrino et al. 2002). Exposure in populated communities near major international trade bridges in North America has become an increasing concern since the implementation of the North American Free Trade Agreement (NAFTA) in 1994 that resulted in increased truck traffic. A number of North American international border crossings are located in populated areas with similar issues of heavy diesel truck traffic and automobile emissions. There have been reports of associated health effects for populations living near the bridges. For example, elevations in PM₁₀ (particles with an aerodynamic diameter of less than 10 micrometers) and ozone from heavy diesel truck traffic across a US–Mexico border between El Paso, Texas, and Juarez, Mexico were found to result in elevated respiratory effects in children living in Juarez, Mexico (Romieu et al. 2003). A study at the Windsor Ambassador Bridge found that, after NAFTA, diesel particle concentrations were higher than what was previously recorded (Diamond et al. 2004).

Recently, ultrafine particles (UFP) have attracted considerable attention as a potential health concern. Although epidemiological evidence links increases in particulate matter (PM) to increases in mortality and morbidity (Vedal 1997; Dockery 1993), further investigation is still needed to assess whether it is the mass (Osunsanya et al. 2001), number concentration (Peters et al. 1999; Yue et al. 2007), and/or other particle characteristics (e.g., surface area and composition) that are associated with the adverse health effects of exposure to PM.

In general, ultrafine particles traverse the air-stream lines during respiration and can deposit throughout the airways. Respiratory effort and the size of ultrafine particles significantly affect local respiratory deposition patterns, with the surface dose increasingly favoring the upper airways for smaller size particles (e.g., 40 nm) (Kim and Jaques 2000, 2004). The ability of ultrafine particles to also deposit in lower airways may lead to elevated alveolar inflammation and exacerbated lung disease (Seaton et al. 1995). Others have provided evidence that ultrafine particles may be able to pass into systemic and peripheral circulation (Nemmer et al. 2002). Exposures to excessively high levels of ultrafine particles compared to a high surface load may decrease alveolar macrophage clearance (Oberdorster et al. 1992), ultimately leading to increased penetration into the epithelial layer, producing inflammation (Donaldson 2001). Direct human exposures to elevated levels of ultrafine particles may be associated with cardiac arrhythmia and myocardial ischemia within a few hours after exposures (Peters et al. 2001; Yue et al. 2007).

Ultrafine particles in the nuclei-mode are typically formed as a result of gas-to-particle formation and vapor phase reactions upon the particles exiting the tailpipe (Kittleson 2001). Studies have shown that the freshly emitted combustion diesel particles (<10 nm) quickly form agglomerated soot particles ranging from 30–50 nm. Typically, as the exhaust cools and dilutes, new nuclei mode particles are generated (Kittleson 1998). In general, ultrafine particles are assumed to be spatially inhomogeneous as the number concentration is thought to be strongly dependent on local contributions and proximity to sources. Recent studies have shown that ultrafine particle number concentrations typically decrease with increased distances downwind from major highway sources (Zhu et al. 2002,a,b; McAuley et al. 2010).

The objective of this study is to examine the relative concentrations of ultrafine particles in a residential neighborhood downwind of the Peace Bridge, which has previously been identified as an area having a high prevalence rate of asthma in children (Lwebuga-Mukasa and Dunn-Georgiou 2000). Because of extended periods impacted by idling or stop-and-go heavy diesel truck and automobile traffic, it had been thought that local source emissions may be related to these health issues.

FIG. 1 Map of WPs of the subject's homes downwind of the PBC along with the location of the upwind site at the Great Lakes Center (GLC).

EXPERIMENTAL METHODS

Direct size-speciated particle measurements were made using a mobile air pollution lab (MAPL) as a fixed site monitor: (1) close to the PBC; (2) along several trajectories originating at the PBC and continuing into the neighborhood; and (3) at several homes in the neighborhood adjacent to the PBC.

The study area was about 4 km² directly east of the Peace Bridge and Niagara River, which runs to the north. Within the study boundary is an interstate highway that runs along the Niagara River and a matrix of residential and business roads to the east (Figure 1). An upwind/background site was located at the University of Buffalo's Great Lakes Center (GLC) located on the shore of Lake Erie. The downwind sites were to the northeast of the Peace Bridge along the prevailing southwesterly wind direction. Sites were geo-coded by both the physical address, and global coordinate waypoints acquired by satellite signals using a global positioning system (GPS) (Model Street Pilot III; Garmin International Inc., Olathe, KS), and were plotted using mapping software (Mapsource, Version 2; Garmin International Inc). Precision was within 3–5 m.

Sampling Sites

To assess possible seasonal variations in meteorology, traffic conditions and pollutant concentrations, we conducted both a summer and winter field intensive. The summer study was conducted from June 19 through June 24, 2004. The winter field intensive was conducted from January 7 to 16, 2006.

Summer 2004

During the summer 2004 and winter 2006 roadside ultrafine particles measured throughout the nearby streets throughout the lower west side of Buffalo, New York adjacent to the Peace Bridge during two different seasons. Summer 2004 roadside measurements were compared to a study conducted by Zhu and colleagues (2002a) investigating various pollutant including downwind ultrafine particle concentrations at various distances.

In June 2004, the Clarkson MAPL was stationary at several sites for periods of one or two minutes to several hours to capture high spatial and temporal ultrafine particle counts throughout the lower west side of Buffalo, NY. Measurements conducted on June 24, 2004 were made on a number of local streets and intersections in the neighborhood adjacent to the Peace Bridge Complex and immediately downwind of the PBC at distances from 69 m (distance from US toll plaza to chapel) to several hundred m. Typical distances between intersections in this neighborhood were approximately 100 m east to west and 200 m north to south. The chapel area was designated as the immediate downwind fixed site based on it accessibility. The chapel provided easy access for monitoring and comparing the east-to-west and west-to-east traffic patterns and for comparing particle size and number concentration across different seasons as described in the sections that follow.

Winter 2006

The winter field-intensive study included upwind and downwind fixed site monitoring, and it included several hours staying near eight homes on different days during similar time periods as shown (Table 1). Based on the spatial analysis of the June 2004 data, four homes were selected within the different “hotspot” areas as identified during that summer's sampling campaign

TABLE 1 Summary of Winter 2006 sampling sites at several locations and distances adjacent to the Peace Bridge in the lower west side of Buffalo, NY

Distance to PBC (m)	Latitude [degrees]	Longitude [degrees]	Waypoint	Sampling date	Sampling time total sampling	Outdoor temp.^a [deg. C]	Outdoor RH^a [%]	Wind speed^a [m/s]	Wind direction^a [degrees]	Total truck [Hourly]	Total auto traffic [Hourly]	Nanoparticle number concentration^b [p/cm^3+/−SD]
69	W78 53.952	N42 54.277	*134	1/8–1/92006	6:00 AM–6:00 AM	2.2 ± 2.0	71 ± 9	4 ± 3	170 ± 74 (S)	45	456	24,000 ± 800
235	W78 53.981	N42 54.402	2	1/9/2006	3:41 PM–8:18 PM	2.0 ± 0.2	84 ± 6	14 ± 3	265 ± 17 (W)	110	805	59,000 ± 2,500
381	W78 53.690	N42 54.349	8	1/16/2006	3:21 PM–6:21 PM	–4.3 ± 0.3	44 ± 1	6 ± 3	65 ± 12 (NE)	105	723	45,000 ± 23,000
412	W78 53.929	N42 54.499	6	1/13/2006	3:58 PM–9:12 PM	12 ± 0.7	55 ± 3	2 ± 4	249 ± 70 (SW)	53	730	47,000 ± 23,000
528	W78 53.941	N42 54.562	5	1/12/2006	3:46 PM–8:54 PM	5.7 ± 0.9	71 ± 5	2 ± 3	172 ± 10 (S)	250	673	81,000 ± 43,500
^aValues are mean ± standard deviation of 1 min data for each sampling period collected from 10 m meteorological station at the GLC.
^bNumber concentrations +/−SD measured within several m in front of the homes.
*Downwind fixed site station located on the corner of Busti and Rhode Island as measured from US toll plaza to chapel.

All the homes were located at distances ranging from 235 m to 528 m. All measurements were conducted by parking the MAPL in front of each house during evening hours ranging from 3:30 PM–8:30 PM.

Table 1 provides detailed information about meteorological data, truck and automobile traffic counts during the time that household measurements were being conducted, and ultrafine particle concentrations during each sampling campaign at the households and from collocated measurements performed at the downwind fixed site, the church, designated here as waypoint 134. It is important to note that at each location, except at waypoint 8, wind direction was south-southwest. At waypoint 8 home, wind direction was northeast. Therefore, waypoint 8 was an upwind site during the sampling period near the plaza, but the ultrafine particle concentrations were only slightly lower than at the other homes, possibly a result of its location on Route 266, a busy four-lane business route. Waypoint 2, waypoint 5, and waypoint 6 are also located close to busy roadways, including Route 66, Busti Avenue, and Interstate 190, which may also have contributed to their moderately high UFP concentrations. We were not able to obtain automobile or truck traffic data on local roadways during either the 2004 or the 2006 field-intensive studies to determine the relative impacts of this source within the downwind areas of the lower west side.

FIG. 2 Truck and automobile traffic counts east to west and west to east across the Peace Bridge. (a) Summer 2004; (b) Winter 2006.

FIG. 3 MAPL monitoring sites tracking ultrafine particles along NE wind trajectory. GPS waypoints are numbered in sequence for the consecutive sites visited during June 24, tracking the MAPL route along an approximate dispersion pattern originating from the general Peace Bridge plaza area. Measurements made with the mobile lab were between 2 and 60 min per site.

Figure 2 shows the typical diurnal truck and automobile traffic for east and westbound traffic across the Peace Bridge. Figure 3 is a map that shows the various routes where ultrafine particles were monitored during the sampling campaigns throughout the lower west side of Buffalo, NY.

Figure 4 provides the size and number concentrations and distributions at the chapel site 69 m downwind of the PBC. The data show a typical diurnal pattern of particle number and size distribution based on total truck traffic emissions in the morning, afternoon, and evening at the downwind fixed site during the household UFP measurements that were taken in January 2006 under similar meteorological conditions and diesel truck traffic counts (Table 1).

Mobile Lab

Multiple separate roadside ultrafine particle measurements were conducted in the summer and winter studies using an Engine Exhaust Particle Sizer^TM (EEPS) (TSI Incorporated, St Paul, MN) housed inside the Clarkson University Mobile Air Pollution Lab (MAPL). The EEPS was connected to a stainless steel inlet manifold. The manifold was installed on the roof of the MAPL 3.5 m above ground to effectively sample ambient air. A series of instruments connected to the manifold provided their own air supply, totaling about 16 lpm and including 10 LPM drawn by the EEPS. Flow checks were performed each day prior to monitoring to ensure that there were no leaks. The EEPS was internally calibrated and zeroed daily to ensure proper functioning.

FIG. 4 Total number concentration at church for single day 69 m east of the PBC.

The EEPS is a 32 channel particle size spectrometer that can measure particle sizes from 5.6 to 560 nm at a resolution of 0.1 second. The principle of the EEPS measurement of particles and its effectiveness for rapidly measuring size distributions is a derivation of the electrical particle spectrometer (Mirme et al. 1984; Tammet et al. 2002) and was described in detail by Johnson et al. (2004) and Liu et al. (2005). The EEPS uses the same electrical-mobility principle as the Scanning Mobility Particle Sizer (SMPS; TSI Inc., MN), but with a different detection system that allows for simultaneous measurement of all particle sizes providing rapid measure of size distributions, which is useful for transient emission sources. The EEPS uses a corona charger to charge the particles that pass near the center of an “inside-out differential mobility analyzer” column. An electric field inside the column repels the particles outward, where they are detected and counted using an array of precision electrometers connected to electrodes on the outside wall of the column. Recently, the University of Minnesota's Mobile Emissions Laboratory evaluated and compared the relative accuracy of the EEPS and SMPS for Dioctyl Sebacate (DOS) particles between 5 and 550 nm, and showed small deviations between 5 nm and 100 nm (Caldow et al. 2004). Zervas and Dorlhene (2006) compared EEPS particle number measurements to those made with condensation particle counters (CPCs) and an electrical low pressure impactor (ELPI) and found the results were comparable as long as the particle numbers were in excess of the EEPS limits of detection.

Wind Speed and Direction (Summer 2004 and Winter 2006)

Wind speed, direction, and temperature were continuously measured and recorded every 15 min during the summer of 2004 and winter of 2006 using a portable meteorological system (Davis Met Station, Davis, CA, USA) mounted on the roof of the MAPL at a height of 5 m above the ground. The Davis meteorological weather station data was validated by comparing weather data from the rooftop of the MAPL to the upwind 10 m Buffalo State Great Lakes Center (GLC) meteorological weather station located on the shore line of Lake Erie 600 meters southwest from the PBC plaza. Good agreement was found between the two meteorological stations when they were collocated, which provided confidence in the accuracy and reliability of downwind meteorological measurements, but, due to large gaps in meteorological data resulting from times when data was not collected in summer 2004 and not collected at all during winter 2006 resulting from limitations of staff and time, we used the data collected at the GLC to assess weather patterns during summer 2004 and winter 2006. Overall, in June 2004 the wind speed had a diurnal pattern of 6–10 m/s during mid-afternoon downwind measurements compared to wind speeds of 1.8–2.0 m/s during late evening measurements. Winter 2006 wind directions were typically from the west with wind speeds of 4–5 m/s during the early afternoon to late evening household measurements.

Traffic Data

Hourly traffic counts along the Peace Bridge were obtained from the Peace Bridge Authority. All traffic counts included cars, buses, and trucks traveling eastbound and westbound across the bridge. Because there were relatively few buses crossing the bridge, they were treated as trucks. Figure 4a represents the number of trucks and automobiles traveling east and westbound across the bridge for several days in June 2004, including the shaded area representing the day the several roadside measurements were conducted. In summer 2004 the hourly diesel truck traffic counts averaged 162 and automobiles 726 (Figure 4a) with traffic density for all vehicles increasing and decreasing between morning and night. In winter 2006, the hourly truck traffic (Figure 4b) averaged 147 trucks while automobiles averaged 444 vehicles per hour, with shaded areas representing days of actual household measurements during evening hours. During each sampling campaign, truck traffic counts showed similar numbers, but automobile counts were nearly 50% less during the winter 2006 study months.

FIG. 5 Normalized EEPS UFP concentrations at varying distances downwind of the Peace Bridge Plaza.

RESULTS AND DISCUSSION

Distance and Roadside Measurements Downwind of the Peace Bridge (Summer 2004)

Figure 5 shows the variation in particle number concentrations as a function of downwind distance from the PBC, and the data is compared with similar measurements by Zhu and colleagues, which were conducted downwind of a major Los Angeles highway that restricts heavy diesel trucks (2002a). To compare results, collected ultrafine particle data were normalized as a function of truck and automobile counts. This normalization allows an estimate of the relative contribution of ultrafine particle concentrations downwind from the Peace Bridge traffic versus levels of downwind ultrafine particle concentrations believed to be derived from local traffic sources. The normalized data exhibited an exponential decrease as a function of distance downwind of the Peace Bridge (r ²= 0.8) with an approximate 50% drop in ultrafine particle concentration ranging between 700–800 m in comparison to UFP concentrations 69 m downwind. The formula used for normalizing the data as a function of vehicle counts is described in the supplemental material.

Figure 5 shows some differences when directly comparing downwind ultrafine particle concentrations between the lower west side of Buffalo, NY and the LA freeway study. The LA freeway study showed that at ∼300 m ultrafine particle concentrations were approximately 75% less as compared to near highway concentrations and were similar to ultrafine particle concentrations several hundred m upwind of the freeway. The results of Zhu and colleagues, shown in Figure 5, demonstrate that there is a more rapid rate of decay from the source road, and our results showed less pronounced exponential decay from the source road. Our results also showed that at distances greater than 300 m downwind ultrafine particle concentrations were approximately one order of magnitude higher ranging from 60,000–70,000 p/cm³ as compared to the background site located several hundred m upwind where ultrafine particle concentrations under similar meteorological conditions were typically 8,000–10,000 p/cm³.

FIG. 6 Multiple ultrafine size and number concentration outside 4 homes central to area “hotspots” at varying distances from the Peace Bridge Complex during January 2006. (a) 381 m downwind, Waypoint 8; (b) 235 m downwind, Waypoint 2; (c) 412 m downwind, Waypoint 6; and (d) 528 m downwind, Waypoint 5.

Harvard University had conducted mobile (i.e., field staff walking) measurements of roadside ultrafine particle (D_p < 100 nm) concentrations along several streets throughout the lower west side of Buffalo, NY in the summer and winter of 2006 to characterize pollutant concentrations across a 10-block residential neighborhood adjacent to the Peace Bridge Plaza. Mobile ultrafine particle data collections in the adjacent neighborhood were conducted during the morning, midday and evening times using a TSI (St. Paul, MN) P-Trak CPC to examine differences in pollutant concentrations. Mobile UFP measurements across the two sampling campaigns showed a similar pattern across the seasons where mean winter ultrafine particle concentrations in the morning (23,000 p/cm³) and afternoon (22,000 p/cm³) were higher than mean summer morning ultrafine particle concentrations (12,000 p/cm³) and afternoon (12,200 p/cm³) measurements. These results are similar to findings from our study despite the lower concentrations, which may be because the P-Trak does not have the same particle size and time resolution as the EEPS. Therefore, direct comparisons of total particle counts will be underreported by size and time resolution limitations of the P-Trak when used in close proximity to combustion sources. Most importantly the results of both sampling campaigns provide similar insight into daily and seasonal patterns of ultrafine particle roadside concentrations (Spengler HEI Report 2009).

The LA freeway studies are important for understanding particle concentrations downwind of a major source, but do not provide results that can be used uniformly in areas with other local sources. The results of the 2004 summer campaign of multiple neighborhood locations allowed the determination of areas that may be “hot spots” and the assessment of the Peace Bridge source contribution vs. local source impacts on community exposures to ultrafine particles.

Area “Hotspot” Roadside Ultrafine particle Measurements and Concentrations (January 2006)

In January 2006, a study was performed to examine the size of ultrafine particle distribution and number concentrations at several homes in areas in the lower west side of Buffalo. The selection of these homes was based on the roadside ultrafine particle measurements conducted during the summer of 2004 under similar truck traffic and meteorological conditions. The results of these UFP roadside counts permitted identification of “hotspot” areas and were used to select homes for additional UFP measurements. The temperatures during the winter sampling period were significantly lower than during the summer campaign. From Figures 6a–d it is apparent that the majority of the number concentration resides in the 10–20 nm mode at all distances downwind that were sampled. Ultrafine particle number concentrations at the homes ranged from 58,900 p/cm³ 235 m downwind to 81,000 p/cm³ 528 m downwind. The data from Figure 6 shows that ultrafine particle counts measured at each home are highly variable, which is a result of fluctuation in the numbers of consistent automobile and light duty truck traffic at and around these homes, which are located on busy intersections and street corners in the lower west side. Additional ultrafine particle measurements were conducted at three different fixed site locations in winter 2006 (January 9–10, 15–17, 2006). Overall, winter 2006 air mass trajectory analysis showed that when winds were from the west or southwest as seen on January 9 and 10 ultrafine particle concentrations were low at the GLC, reached 20,000 to 30,000 p/cm³ at the school site, and ranged from 40,000 to greater than 80,000 p/cm³ at the chapel. These observations suggest that typical urban air values might be 15,000 to 20,000 p/cm³, but local sources of traffic (automobiles and light duty trucks) can double the levels as measured by the P-Trak. Applying the P-Trak to CPC adjustment reported by Zhu et al. (2006), the actual local number counts for particles of 10 nm and smaller may be three to four times higher (Spengler HEI Report 2009).

A study conducted by Ogulei et al. (2007a) in Rochester, NY showed that household heating and exhaust can be a source of ambient ultrafine particles. They reported that the particle size distribution of the heating source has a mode of 90–100 nm, with only a small percentage less than 50 nm. Comparison of the current roadside measurements in the lower west side of Buffalo, NY to results found in Rochester, NY a dominant mode of 90–100 nm relating to UFP generated from household heating in Rochester, NY does not agree with the findings in the current study and therefore, household heating does not seem to have an impact on ambient ultrafine particle counts in the lower west side as a dominant mode at all homes was found to between 10–20 nm.

Winter 2006 evening ultrafine particle measurements at the homes were conducted with outside temperatures between 2 and 12°C. Higher concentrations may be more pronounced as a result of stronger atmospheric stability and slightly lower wind speeds as during the summer months as described by Hu et al. (2009). Hu and colleagues showed that although during pre-sunrise hours traffic volumes are lower, ultrafine particle concentrations were higher downwind near roadways measured along a 3600 m transect to a major Los Angeles freeway. This pre-sunrise phenomenon was attributed to strong atmospheric stability, lower wind speeds, cooler temperatures, and high humidity that facilitated longer lifetimes and slower transport of UFP before dilution and dispersion.

In addition, several studies have shown that cooler temperatures may yield a higher number of particles as a result of partitioning between the semi-volatiles of the combustion-generated ultrafine particles during the afternoon and evening phase (Sakurai et al. 2003; Jeong et al. 2004). Higher ultrafine particle concentrations at lower temperatures are likely due to a combination of lower mixing heights and the potential for increased particle formation as suggested by Jeong et al. (2004). Comparing Jeong et al. (2004) to this study, an increase in particle concentrations was observed in the winter, but it is not clear if there is an increase in the number of particles being formed.

It is very likely that the influence of downwind particle concentrations for both local and PBC truck-generated emissions depends on several factors, including persistence and proximity of each source and local meteorology. Therefore, in evaluating the previous studies that have suggested traffic emissions from the Peace Bridge may have caused substantial community exposures to particulate matter, impacting the local high asthma prevalence rates in Buffalo's lower west side (Lwebuga-Mukasa et al. 2000, 2004), it is important to also consider that under typical meteorological conditions and traffic patterns, local sources may have as much or more influence on downwind ultrafine particle concentrations, but that cooler temperature may result in greater persistence and decreased dilution as a function of temperature as describe above.

CONCLUSIONS

Two sampling campaigns were conducted in the summer of 2004 and winter 2006 to assess the level of impact that traffic on the Peace Bridge, a major international trade bridge, may have on elevated ultrafine particle concentrations downwind of the PBC. Although the impact of the bridge traffic on ultrafine particle number concentration is clearly evident immediately downwind of the bridge (i.e., at the chapel), normalized ultrafine particles data measured at various distances downwind of the PBC provide some insight that local traffic sources may have a strong impact on ultrafine particle concentrations at other locations in the neighborhood. This study demonstrates that under real world conditions distance over which a “hotspot” is experienced is influenced by local sources such as neighborhood small light truck and automobile traffic and that local sources need to be considered along with other contributing sources when assessing exposures to increased particle concentrations near a large highway and at varying distances downwind.

This work was financially supported by the Health Effects Institute (HEI), Agreement 04-4, and supplemental support for the MAPL and supplies from Clarkson University's Biology Department. Additionally, Stephen J. Vermette, Ph.D., and the late John J. Freidhoff of Buffalo State University at SUNY, are acknowledged for their major contributions in providing space and facilities at the Great Lakes Center.