Good Agreement Between Modeled and Measured Sulfur and Nitrogen Deposition in Europe, in Spite of Marked Differences in Some Sites

Aldo Marchetto,Anne Thimonier,Karin Hansen,Tanja G M Sanders,Svetlana Tsyro,Wim De Vries,Gunilla Pihl-Karlsson,Walter Seidling,Hilde Fagerli,Michela Rogora,Andreas Schmitz,Wenche Aas,David Simpson,Per Erik Karlsson,Peter Waldner

doi:10.3389/fenvs.2021.734556

Abstract

Atmospheric nitrogen and sulfur deposition is an important effect of atmospheric pollution and may affect forest ecosystems positively, for example enhancing tree growth, or negatively, for example causing acidification, eutrophication, cation depletion in soil or nutritional imbalances in trees. To assess and design measures to reduce the negative impacts of deposition, a good estimate of the deposition amount is needed, either by direct measurement or by modeling. In order to evaluate the precision of both approaches and to identify possible improvements, we compared the deposition estimates obtained using an Eulerian model with the measurements performed by two large independent networks covering most of Europe. The results are in good agreement (bias &lt;25%) for sulfate and nitrate open field deposition, while larger differences are more evident for ammonium deposition, likely due to the greater influence of local ammonia sources. Modeled sulfur total deposition compares well with throughfall deposition measured in forest plots, while the estimate of nitrogen deposition is affected by the tree canopy. The geographical distribution of pollutant deposition and of outlier sites where model and measurements show larger differences are discussed.

Highlights

Sulfur (S) dioxide, nitrogen (N) oxides and ammonia are the atmospheric pollutants that are deposited in larger quantities, that play an important role in the chemistry of the atmosphere and that affect ecosystem condition, structure and productivity
Considering bulk open field deposition, the average values measured in the International Co-operative Programmes (ICPs) Forests network are higher than those measured in the EMEP network, on average by 12%, at least in part because most ICP Forests samplers are located in central Europe, in areas with high S emission (Figure 1)
As for SO4*, the average values measured in the ICP Forests network are higher than those measured in the EMEP network, on average by 20% for wet deposition and 44% for bulk open field deposition

Summary

Introduction

Sulfur (S) dioxide, nitrogen (N) oxides and ammonia are the atmospheric pollutants that are deposited in larger quantities, that play an important role in the chemistry of the atmosphere and that affect ecosystem condition, structure and productivity. Sulfur dioxide and N oxides may be produced by natural sources, such as volcanic activities and lightning, but they are emitted in much larger quantities by combustion processes related to human activities, such as power generation, traffic, industry, agriculture. In agriculture-rich areas, there is an excess of ammonia, and reduced N will be deposited closer to the emission source than S and N oxides (Asman et al, 1998)

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Conclusion