Ozone and sulfur dioxide dry deposition to forests: Observations and model evaluation

Abstract

Abstract. Fluxes and deposition velocities of 03 and SO2 were measured over both a deciduous and a mixed coniferous-deciduous forest for full growing seasons. Fluxes and deposition velocities of 03 were measured over a coniferous forest for a month. Mean deposition velocities of 0.35 to 0.48 cm/s for 03 and 0.6 to 0.72 cm/s for SO2 were observed during the growing seasons of 1997 and 1998. Weekly averages of 03 deposition velocity ranged from 0.25 cm/s at the beginning and end of the season to 1.25 cm/s in late June. SO2 had a smaller seasonal variation, from 0.75 to 1.5 cm/s between the beginning and peak of the season. Because 03 concentrations are higher, the flux of 03 to forests is considerably greater than the flux of SO2. Daytime deposition velocities are very similar at each site, from 0.75 to 0.79 cm/s for 03, and from 1.01 to 1.04 cm/s for SO2. Diurnal cycles for both gases are discussed, as are the impact of some weather events. The peak time for 03 deposition velocity is in midmorning, while it is near midday for SO2. Surface wetness is usually associated with a small increase in deposition velocity, but for some rain events a major increase was noted. Minimum deposition velocities usually occur at night and increase slowly in the predawn hours before light. Comparisons are made between observations of deposition velocity and predictions made with the Meyers multilayer deposition velocity model. While the model is, on average, unbiased for 03, it tends to underpredict the higher deposition velocity values. The model is slightly biased low (underpredicts) for SO2 deposition velocity. The strengths of the model are noted, as are opportunities for improvement. IntroductionIn addition to their use in local and regional scale air quality models, deposition velocity models are integral to the inferential dry deposition monitoring networks that operate in the United States, Canada, and Europe ]. Because of the high cost and complexity of direct flux measurements, operational dry deposition networks measure concentrations of air pollutants and infer the flux of pollutants to the surface using a modeled deposition velocity (flux equal to deposition velocity times concentration).In an earlier paper [Meyers et al., 1998] we reported on the formulation of the Multilayer Model (MLM) for deposition velocity which is being used in operational dry deposition networks in the United States and the observations from three field studies which were used to evaluate and improve the MLM. Those studies were performed over agricultural fields of pasture, corn, and soybeans. Details of the model and field This work reports on three new field studies which measured fluxes of 03 and SO2 over forests, and the evaluation of the MLM with those data. The studies were conducted over a pine plantation in central North Carolina during the spring of 1996, over a deciduous forest in northwestern Pennsylvania during the growing season of 1997, and over a mixed forest in the Adirondack Mountain region of New York during the growing season...

Development of an Atmosphere-Soil-Vegetation Model for Investigation of Radioactive Materials Transport in the Terrestrial Biosphere

“…This indicates that the modeled scheme for gas absorption by stomata based on photosynthesis is reasonable and can be used to predict the gas deposition onto the crop field. Figure 3 illustrates the temporal changes of calculations and measurements 31) in CO 2 flux and deposition velocity of O 3 and SO 2 over the deciduous broad-leaved forest. While SOLVEG in general predicted the measured diurnal changes in gas fluxes, it underestimated measurements during the daytime for both O 3 and SO 2 several times.…”

Estimates of Cloud Water Deposition at Mountain Acid Deposition Program Sites in the Appalachian Mountains

“…Data from Meyers et al 48 show little overall bias with an uncertainty of Ϯ50% for estimates of the dry deposition of SO 2 and HNO 3 calculated using the MLM. Data from Finkelstein et al 49 suggest the MLM underestimates deposition velocities for SO 2 for complex, forested sites. The differences are expected to be lower for longer averaging times (i.e., monthly and seasonal periods).…”

“…Cloud deposition values at the sites for 1994 -1998 were estimated by the CLOUD model. The multilayer model (MLM) 48,49 was utilized to estimate dry depositions from filter pack concentration data for Whitetop Mountain. The MLM is used to simulate dry deposition at CASTNet sites.…”

Canopy Controls on the Forest-Atmosphere Exchange of Biogenic Ozone and Aerosol Precursors

“…For example, plants take up carbon dioxide (CO 2 ) via stomatal uptake for photosynthesis. Ozone and sulfur dioxide (SO 2 ) are widely recognized as having among the highest deposition efficiencies via plant uptake (Wesely 1989;Finkelstein et al 2000;Hogg et al 2007). Once taken up by the plant, ozone damages the leaf by oxidizing the tissue.…”