Assessment of the total, stomatal, cuticular, and soil 2 year ozone budgets of an agricultural field with winter wheat and maize crops

This study evaluates ozone (O-3) deposition to an agricultural field over a period of 2years. A two-layer soil-vegetation-atmosphere-transfer (Surfatm-O-3) model is used to partition the O-3 flux between the soil, the cuticular, and the stomatal pathways. The comparison between measured and modeled O-3 fluxes exhibited a good agreement, independently of the canopy structure and coverage and the climatic conditions, which implicitly validates the O-3 flux partitioning. The total, soil, cuticular, and stomatal O-3 budgets are then established from the modeling. Total ecosystem O-3 deposition over the 2year period was 87.5kgha(-1). Clearly, nonstomatal deposition dominates the deposition budget, especially the soil component which represented up to 50% of the total deposition. Nevertheless, the physiological and phenological differences of maize and winter wheat induced large difference in the stomatal deposition budgets of these two crops. Then, the effect of simplified parameterizations for soil and cuticular resistances currently used in other models on the O-3 budget is tested. Independently, these simplified parameterizations cause an underestimation of the O-3 deposition ranging between 0% and 11.2%. However, the combination of all simplifications resulted in an underestimation of the total O-3 deposition by about 20%. Finally, crop yield loss was estimated to be 1.5-4.2% for the winter wheat, whereas maize was not affected by O-3

Ozone production in a maritime pine forest in water-stressed conditions

International audienceDuring two growing seasons of a maritime pine stand, in 2014 and 2015, ozone (O-3) fluxes have been determined using the eddy covariance (EC) method and compared to the outputs of a big-leaf O-3 deposition model including stomatal, cuticular and soil pathways. The model developed in this study generally allowed to properly reproduce the measured ozone deposition. Ozone fluxes showed a strong reduction during two water stressed periods in September 2014 and July 2015. The model partly explain this fall due to the reduction of stomatal deposition. Despite this stomatal closure, measured O-3 fluxes presented systematically lower negative values than the model outputs, and sometimes even positive values around midday during periods marked by strong water stress. In other words, the difference between observed and modelled O-3 fluxes (hereinafter referred to as the residual O-3 flux) is systematically positive on daytime during these water-stressed periods. This positive residual flux traduced the existence of an O-3 source below the flux measurement level, responsible for positive fluxes that counterbalance deposition fluxes. We developed an O-3 production module based on a terpene emission algorithm and an OH concentration proxy, to try to explain the observed ozone production. As this parametrisation allowed us to reproduce well the daily and inter-daily dynamics of the residual O-3 flux, it confirms that the latter actually resulted from O-3 production processes. This ozone production is here highlighted for the first time using O-3 fluxes measurements by the EC method. The chemical reactions possibly involved in O-3 production processes in this maritime pine forest have been discussed and different mechanisms are proposed, based on peroxy radicals chemistry or stress-induced BVOCs

LANDEX-Episode zero : First observations of secondary organic aerosol formation from the landes forest (France)

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LANDEX – Linking in canopy volatile organic compound reactivity to nocturnal new particle formation

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