Biogenic nitrogen oxide emissions from soils – impact on NO<sub>x</sub> and ozone over West Africa during AMMA (African Monsoon Multidisciplinary Experiment): modelling study

Abstract

Abstract. Nitrogen oxide biogenic emissions from soils are driven by soil and environmental parameters. The relationship between these parameters and NO fluxes is highly non linear. A new algorithm, based on a neural network calculation, is used to reproduce the NO biogenic emissions linked to precipitations in the Sahel on the 6 August 2006 during the AMMA campaign. This algorithm has been coupled in the surface scheme of a coupled chemistry dynamics model (MesoNH Chemistry) to estimate the impact of the NO emissions on NO x and O 3 formation in the lower troposphere for this particular episode. Four different simulations on the same domain and at the same period are compared: one with anthropogenic emissions only, one with soil NO emissions from a static inventory, at low time and space resolution, one with NO emissions from neural network, and one with NO from neural network plus lightning NO x . The influence of NO x from lightning is limited to the upper troposphere. The NO emission from soils calculated with neural network responds to changes in soil moisture giving enhanced emissions over the wetted soil, as observed by aircraft measurements after the passing of a convective system. The subsequent enhancement of NO x and ozone is limited to the lowest layers of the atmosphere in modelling, whereas measurements show higher concentrations above 1000 m. The neural network algorithm, applied in the Sahel region for one particular day of the wet season, allows an immediate response of fluxes to environmental parameters, unlike static emission inventories. Stewart et al. (2008) is a companion paper to this one which looks at NO x and ozone concentrations in the boundary layer as measured on a research aircraft, examinesCorrespondence to: C. Delon (claire.delon@aero.obs-mip.fr) how they vary with respect to the soil moisture, as indicated by surface temperature anomalies, and deduces NO x fluxes. In this current paper the model-derived results are compared to the observations and calculated fluxes presented by Stewart et al. (2008).

Modelling the effect of soil moisture and organic matter degradation on biogenic NO emissions from soils in Sahel rangeland (Mali)

“…In that purpose, a new approach for the calculation of biogenic NO emissions from soils has been developed by Delon et al (2007), in order to use general environmental parameters easily available as inputs. This approach was used at the regional scale to simulate pulse events in the Sahel (Delon et al, 2008) and at the yearly scale at several Sahelian sites Laouali et al, 2012). This approach has been partly inspired by the hole-in-thepipe (HIP) concept, developed by Firestone and Davidson (1989), presenting the environmental parameters which control the variation of trace-N-gases by nitrification and denitrification with different levels of regulation, from proximal (e.g.…”

“…While the STEP model was initially designed for 1-D simulations in well-documented study sites, it has also been re- cently used at the regional scale in the Gourma region to produce maps of vegetation biomass by Jarlan et al (2003), and in the Sahelian belt (12 • N-20 • N; 20 • W-35 • E) by Pierre et al (2012) and Pierre et al (2011), to estimate the amount of dust emissions in that region. The NO flux model has also been applied in the region of Niamey, Niger (Delon et al, 2008) to reproduce NO pulses at the beginning of the wet season, and their impact on ozone formation during the AMMA field campaign in 2006. Furthermore, it has been used at the regional scale in the Sahel and in West Africa to calculate NO release to the atmosphere.…”

Atmospheric nitrogen budget in Sahelian dry savannas

“…The resulting algorithm provides on line biogenic NO emissions and is developed in Delon et al (2007). It is fully coupled to the SVAT model ISBA, and has been previously tested in the 3-D coupled chemistry-dynamics model MesoNH-C (which uses surface scheme ISBA) to reproduce NO pulses after a rain event in Niger (Delon et al, 2008). • N) will be explored in this study.…”

Steps towards a mechanistic model of global soil nitric oxide emissions: implementation and space based-constraints

“…A regional non-linear regression model was created using observations over Europe relating S NO x to seven climatic and soil condition variables (Delon et al, 2007). Delon et al (2008) updated this model for use over Africa and found a continuous dependence on soil moisture was crucial to correctly represent temporal variability in S NO x .…”