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1)      Brief description 

The principal objective of the Volt'Air model is to simulate ammonia volatilisation fluxes after the application of organic (slurry, farm yard manure, effluents…) or mineral (ammonium nitrate, urea, N solutions) fertiliser to bare soil as well as the volatilisation of crop protection products (pesticides) and, if needed, soil cultivation and irrigation. Volt’Air is used to (i) improve the accuracy in taking into account agro-environmental factors in national emissions inventories, (ii) evaluate strategies and techniques to reduce ammonia loss through volatilisation and (iii) generate simple models or functions that may be integrated into environmental assessments and decision making tools, using meta-modelling for example.

2)      Model technical data

1. Detailed model description

The model describes two distinct compartments: the soil and the atmosphere. The processes taking place in the soil (the equilibrium between the various chemical forms of the compound of interest, transfers in the soil, sources and sinks) permit the calculation of gas phase ammonia or pesticide concentration at the soil-atmosphere interface and the mechanisms taking place in the atmosphere use this concentration to calculate the volatilisation flux. The different processes involved are described modularly (see the figure below). Volt’Air takes the main factors into account.

Figure :the various processes and parameters taken into account in the Volt’Air model

The spatial scale is an agricultural parcel and the temporal scale varies from several days to several weeks, with a time step that can be set to less than one hour, to an hour or to several hours. It is a one dimensional model. The soil compartment is divided into several horizontal layers that extend down to about one meter's depth.

The different equations of the model are solved explicitly following an iterative scheme whose time step is adapted according to the meteorological input data.

The model has the following strengths:

• Its input data include variables that are easily available
• It describes various techniques for fertiliser and pesticide application, soil cultivation and irrigation
• Various types of fertiliser can be studied separately
• Multiple types of pesticides can be applied at the same time
• Two types of experimental conditions can be reproduced:  real agricultural field or semi-controlled wind tunnel conditions

2. Development laboratory

INRA, AgroParisTech, UMR 1402, EcoSys

3. Parameters and input variables

Parameters :

• Physico-chemical properties of compounds (nitrogen containing compounds and pesticides)
• Hydraulic properties of the organic products

Input data :

• Soil - all data relative to the soil (texture, analytical properties, hydraulic characteristics) and initial water content
• Cultural techniques - all information concerning agricultural practices (application, incorporation, irrigation)
• Parcel configuration - latitude, size, albedo, roughness length
• Variables measured using a classic meteorological station

4. Principal output variables (diagnostic)

Instantaneous volatilisation flux and cumulated loss (ammonia, pesticides)

Energy balance and surface soil temperature, turbulence parameters

Temperature, water content, ammonia, nitrate and urea nitrogen content, as well as pesticide content in each soil layer

5.Technical characteristics

Language: Volt’Air is programmed in C and compiled using Visual C/C++

OS: Windows, Linux

User guide: under construction

6.Who are the users?

The program is used by various researchers in different countries (France, Canada, the Netherlands, Switzerland...) and for instruction purposes (Master AgroParisTech, Winter School Eclaire 2014).

7. Coupling

With FIDES (off- line):  Volt’Air generates emissions of compounds and turbulence data that is used by FIDES to calculate atmospheric dispersion as well as gaseous deposition of these compounds downstream of the emitting parcel at a distance specified by the user (<1km). FIDES generates atmospheric concentrations and fluxes of the deposited material

With CHIMERE (on-libe): a new module was developed for CHIMERE to estimate ammonia emissions coming from mineral fertilisation of agricultural soils. These emissions were calculated using Volt’Air coupled with spatial data concerning agricultural practices, soil properties and meteorological data

With SurfAtm (on-line): currently under development in order to take cover crop into account è Volt’Air-Veg