AUTHOR=Neirynck Johan , Verstraeten Arne 

TITLE=Variability of Ozone Deposition Velocity Over a Mixed Suburban Temperate Forest

JOURNAL=Frontiers in Environmental Science

VOLUME=6

YEAR=2018

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2018.00082

DOI=10.3389/fenvs.2018.00082

ISSN=2296-665X

ABSTRACT=<p>A 10-year long dataset of half-hourly ozone (O<sub>3</sub>) fluxes was used to study the variability in deposition velocity (υ<sub>d</sub>) over a mixed temperate suburban forest. Average (median) υ<sub>d</sub> amounted to 0.70 (0.46) cm s<sup>−1</sup>, with day- and night-time average (median) of 0.98 (0.73) cm s<sup>−1</sup> and 0.46 (0.30) cm s<sup>−1</sup>, respectively. It was found that the precipitation form had a marked impact on υ<sub>d</sub> and the deposition efficiency (υ<sub>d/</sub>υ<sub>dmax</sub>), with highest values measured when the canopy was dew-wetted or covered with snow. The analysis further evidenced that traffic volume led to increased deposition due to the presence of chemical reactions between O<sub>3</sub> and nitric oxide (NO) above the canopy surface. During the working week, daytime values of υ<sub>d</sub>, υ<sub>d/</sub>υ<sub>dmax</sub> and the O<sub>3</sub> fluxes (<italic>F</italic>) were found to be significantly higher than the weekend values, especially during the winter half-year. In a next step, half hourly deposition data were aggregated into day- and night-time monthly values, for a correlative study with measured environmental variables. Monthly average night-time/daytime υ<sub>d</sub> and υ<sub>d/</sub>υ<sub>dmax</sub> were positively correlated with the relative humidity at the canopy surface (<italic>RH</italic>(z<sub>0</sub>′)) and negatively correlated with the water levels below the ground surface. During the daytime, monthly υ<sub>d</sub> and υ<sub>d/</sub>υ<sub>dmax</sub> were additionally increased during the working-week when traffic volume was high. There existed, however, substantially different weather conditions, in which unaccounted covariates with a totally different meteorological signature controlled the υ<sub>d</sub> and <italic>F</italic>. It was speculated that, among other, biogenic volatile compounds (BVOCs) could have contributed to O<sub>3</sub> quenching in some (spring) months with severe drought stress.</p>