Ozone deposition impact assessments for forest canopies require accurate ozone flux partitioning on diurnal timescales

Dry deposition is an important sink of tropospheric ozone that affects surface concentrations, and impacts land carbon sink. Dry deposition pathways include plant uptake via stomata and nonstomatal removal by soils, leaf surface and chemical reactions. In this study, we explore the importance of stomatal and non-stomatal uptake processes in driving ozone dry deposition variability, using observations at two ozone flux measurement sites (Ispra and Hyytiälä), as well as a commonly applied ’big leaf’ parameterization (BL) and a multi-layer model (MLC-CHEM) applied in atmospheric models. We find that BL cannot reproduce the diurnal cycle in ozone deposition at our sites, while MLC-CHEM accurately reproduces the different sink pathways. Evaluation of non-stomatal uptake further corroborates the roles of wet leaf uptake in the morning under humid conditions, and soil uptake during warm conditions. The misrepresentation of stomatal versus non-stomatal uptake in BL results in an overestimation of growing-season cumulative ozone uptake (CUO), by 18% (Ispra) and 28% (Hyytiälä), while MLC-CHEM reproduces CUO within 6% of the observed values. Our results indicate the need to accurately describe the partitioning of the ozone atmosphere-biosphere flux over the in-canopy stomatal and nonstomatal loss pathways to provide more confidence in atmospheric model of surface ozone mixing ratios, deposition fluxes and vegetation ozone impact assessments.

VISSER Auke;  GANZEVELD Laurens;  GODED BALLARIN Ignacio;  KROL Maarten;  MAMMARELLA Ivan;  MANCA Giovanni;  BOERSMA K. F.; 

2022-01-18

COPERNICUS GESELLSCHAFT MBH

JRC125846

1680-7316 (online),   

https://acp.copernicus.org/articles/21/18393/2021/,    https://publications.jrc.ec.europa.eu/repository/handle/JRC125846,   

10.5194/acp-21-18393-2021 (online),