Satellite-derived leaf area index and roughness length information for surface–atmosphere exchange modelling: a case study for reactive nitrogen deposition in north-western Europe using LOTOS-EUROS v2.0

Abstract

Abstract. The nitrogen cycle has been continuously disrupted by human activity over the past century, resulting in almost a tripling of the total reactive nitrogen fixation in Europe. Consequently, excessive amounts of reactive nitrogen (Nr) have manifested in the environment, leading to a cascade of adverse effects, such as acidification and eutrophication of terrestrial and aquatic ecosystems, and particulate matter formation. Chemistry transport models (CTMs) are frequently used as tools to simulate the complex chain of processes that determine atmospheric Nr flows. In these models, the parameterization of the atmosphere–biosphere exchange of Nr is largely based on few surface exchange measurement and is therefore known to be highly uncertain. In addition to this, the input parameters that are used here are often fixed values, only linked to specific land use classes. In an attempt to improve this, a combination of multiple satellite products is used to derive updated, time-variant leaf area index (LAI) and roughness length (z0) input maps. As LAI, we use the Moderate Resolution Imaging Spectroradiometer (MODIS) MCD15A2H product. The monthly z0 input maps presented in this paper are a function of satellite-derived normalized difference vegetation index (NDVI) values (MYD13A3 product) for short vegetation types (such as grass and arable land) and a combination of satellite-derived forest canopy height and LAI for forests. The use of these growth-dependent satellite products allows us to represent the growing season more realistically. For urban areas, the z0 values are updated, too, and linked to a population density map. The approach to derive these dynamic z0 estimates can be linked to any land use map and is as such transferable to other models. We evaluated the sensitivity of the modelled Nr deposition fields in LOng Term Ozone Simulation – EURopean Operational Smog (LOTOS-EUROS) v2.0 to the abovementioned changes in LAI and z0 inputs, focusing on Germany, the Netherlands and Belgium. We computed z0 values from FLUXNET sites and compared these to the default and updated z0 values in LOTOS-EUROS. The root mean square difference (RMSD) for both short vegetation and forest sites improved. Comparing all sites, the RMSD decreased from 0.76 (default z0) to 0.60 (updated z0). The implementation of these updated LAI and z0 input maps led to local changes in the total Nr deposition of up to ∼30 % and a general shift from wet to dry deposition. The most distinct changes are observed in land-use-specific deposition fluxes. These fluxes may show relatively large deviations, locally affecting estimated critical load exceedances for specific natural ecosystems.

A Multifaceted Exploration of Atmospheric Turbulence and Its Impact on Optical Systems: Structure Constant Profiles and Astronomical Seeing

“…considering the standard gravitational acceleration of the Earth's surface, denoted as g 0 = 9.8065 m/s 2 , along with the average potential temperature θ in kelvin and the term k h in (33). Another crucial parameter for determining the gradient of the refractive index, as outlined in (26), is the Monin-Obukhov length (L) [22],…”

Improving the spatial and temporal variability of ammonia emissions from agriculture in Western Europe

“…Dry deposition is a mass transfer process where ammonia is first transported to the surface by turbulent and molecular diffusion and then removed by adsorption or absorption by vegetation, soil, or other surfaces (Swart et al, 2023;van der Graaf et al, 2018). The process is governed by 1) the concentration in air, 2) turbulent transport processes in the boundary layer, 3) the chemical and physical nature of the depositing species, and 4) the efficiency of the surface to capture or absorb gases and particles (Chamberlain and Spence, 1997).…”

“…Dry deposition may comprise a large part of the total deposition (Zhang Introduction | 23 et al, 2009). Earlier modeling studies showed that dry deposition of NH x constitutes over 60 % of the total N deposition in Western Europe (van der Graaf et al, 2018).…”

“…However, because of the requirements for expensive instrumentation and the technical difficulties of measuring highly reactive gases, the availability of dry deposition monitoring networks across Europe is minimal (Erisman et al, 1998). Consequently, large-scale assessment of NH 3 dry deposition is hindered by the extremely limited number of deposition observation sites (van der Graaf et al, 2018). Measurements of NH 3 dry deposition fluxes largely remain experimental and are limited to campaigns of short durations (Zöll et al, 2016).…”

“…The LOTOS-EUROS uses a set of temporal factors to break down annual total emissions into hourly emissions. The model is regularly used to address reactive nitrogen budgets (Banzhaf et al, 2015;Hendriks et al, 2016;van der Graaf et al, 2020van der Graaf et al, , 2018, and we refer to these publications for a detailed model description.…”