References

1. The Dynamics of Particle Deposition on Urban Oak Leaves in Syracuse, NY R. M. Upham and D. L. Johnson, Department of Chemistry SUNY ESF; D. J. Nowak, USDA Forest Service, Northeast Experiment Station, Syracuse, NY • Urban trees provide aesthetic value to the cityscape and have generally been shown to improve air quality. This project focuses on the role of urban tree leaf surfaces in modulating the temporal and spatial dynamics of atmospheric particulate matter movement within urban ecosystems. We posit that cost effective integrated environmental management plans must incorporate arboreal components. That perspective raises questions such as: • How much particulate matter do tree leaves intercept? • How long does it stay on the leaves? • Is there any physical or chemical fractionation that occurs? • Are these quantitative relationships significantly different for single trees as compared to those in stands? • How do individual tree species differ in this context? • Aren’t indoor environments subject to similar scrutiny? • We applied scanning electron microscopy to the direct characterization of aerosol particles on oak leaves (IPA, individual particle analysis) in order to begin addressing some of these questions. Particles were analyzed by SEM/EDX, IPA (Johnson, et al, 1999). IPA determines size and elemental composition of deposited particles, and computes aerosol particle mass loading per unit area of leaf. Samples were taken ~ weekly from these, and two other,oak trees during the 150 day growing season of 2001. Wind speed, direction, temperature, humidity and rainfall data were summarized hourly from a Met station < 50 m from the test trees. Observed mass loading was compared to that estimated from assumptions below. Nowak and O’Connor (2001) estimated ~100 tons of PM10 are deposited on tree leaves in Syracuse each year. With 24% urban forest cover, a leaf area index of 4, 100% retention for the particles, and a 150 day growing season, this is equivalent to approximately 60 g atmospheric particles per cm2 of leaf. Methods Conclusions Results Deposition velocity tabulations (eg., Lovett, 1994) can be used to estimate mass accumulation rates of atmospheric particles on oak leaves. The difference between such estimates and what is observed can be attributed to “resuspension”. Literature values for resuspension rates vary from 10 to 90% (Zinke, 1967) The present analyses of PM10 and PM2.5 on oak leaves show resuspension rates must be near the top end of this range; in the present case, >90%. The obvious next question is… “Where does this material go?” Note non-linear axes Geometric mean PM10 showed a small mass loading increase on the leaves over the growing season, but from a practical perspective it was remarkably constant at about 1 g cm-2. PM2.5, on the other hand, showed a progressive mass loading increase on the leaves from May to October, but the temporal variability could not be definitively correlated with any of the meteorological variables. References D.L. Johnson, D.J. Nowak and V.A. Jouraeva (1999). Characterizing individual particles on tree leaves using computer automated scanning electron microscopy. Adv. Env. Res., 2(4): 456-466. G.M. Lovett (1994) Atmospheric deposition of nutrients and pollutants in North America: an ecological perspective. Ecol. Appl. 4(4): 629-650. D.J. Nowak and P.R. O’Connor (2001). Syracuse Urban Forest Master Plan: Guiding the City’s Forest Resource into the 21st Century. USDA General Technical Report NE-278 P.J. Zinke (1967). Forest interception studies in the United States. In: Forest Hydrology, W.E. Sopper and H.W. Hull, eds., Pergamon Press, Oxford, UK pp 137-161. Portions of this work are from the MS Thesis of R.M. Upham Supported by funding from USDA Award No. 02-CA-11242343-048