PM13 Watershed/Airshed Science and Regulation
Exhibit Hall
8:00 AM - Monday, 10 November 2003
(PM199) Quantifying the Deposition of Semi-volatile Organic Compounds to a Deciduous Forest Canopy in Canada.
Su, Y1, 2, Gevao, B1, Harner, T3, Wania, F1, 2, 1 Department of Physical and Environmental Sciences, University of Toronto at Scarborough, Toronto, ON, Canada2 Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, Canada3 Meteorological Service of Canada, Environment Canada, Toronto, ON, Canada
ABSTRACT- Forest canopies effectively filter many semi-volatile organic compounds (SOCs) from the atmosphere, thereby reducing air concentrations and increasing contaminant deposition to the forest floor. So far, the number of field measurements quantifying this effect is very limited, and the magnitude, variability and mechanisms of this process are not well characterized. An indirect technique relying on the measurement of bulk deposition and air concentration under the canopy and a nearby clearing was used to quantify long term average deposition velocities to a deciduous forest canopy in Southern Ontario, Canada. From October 2001 to November 2002, ambient air was sampled every 12 days using a high volume air sampler equipped with two glass fiber filters (GFF) to collect the particulate phase and two polyurethane foam plugs (PUF) to trap gaseous phase compounds. 24-hour samples were collected to ensure that the sample is representative for that day since POPs are subject to diurnal variations in atmospheric concentrations. During the same one year time period, bulk deposition in the forest and in the clearing was sampled using 16 four litre glass jars mounted 2-m above the ground and set up on a square grid at 5-m intervals. The dry deposition velocities for particle-bound chemicals are derived from the measured concentration on particles and the dry bulk flux of substances, which occur only in the atmospheric particle phase. Dry gaseous deposition velocities are further obtained by dividing the excess deposition by the gaseous air concentration. In this study, the deposition velocity is quantified for a series of SOCs, including PCBs, PBDEs and PAHs.
Key words: deposition velocity, forest canopy, SOCs