1.                      Dry deposition

The dry deposition in LOTOS-EUROS is parameterised following the well known resistance approach:

 

 

Ra : aerodynamic resistance

Rb : viscous sub-layer resistance

Rc : surface resistance.

 

The deposition speed is described as the reciprocal sum of three resistances: the aerodynamic resistance, the viscous sub- layer resistance and the surface resistance. The aerodynamic resistance is dependent on atmospheric stability and is calculated with the stability part of the model. The method used to describe this resistance can be found in Chapter 7 on Meteorology. The viscous sub-layer resistance and the surface resistances for acidifying components and particles are described following the EDACS system developed at ECN. The description of this system is incorporated in Annex C. EDACS includes parameterisations for SO2, NH3, NO, NO2, HNO3 and fine and coarse mode aerosol.

The EDACS system does not parameterise surface resistances for ozone deposition, which we describe below. Further, we present how we estimate the concentrations at measuring height.

1.1                   Surface resistance of ozone

For the surface resistance of ozone we have adopted the same structure as for the acidifying components in EDACS (see Annex C, and Fig 5.1). Hence the Rc value is parameterised as follows:

 

vegetative surface:

                                                                                 

water surfaces:

Rc=Rwat                                                                                                                                                                                                              

bare soil:         

Rc=Rsoil                                                                                                                                         

snow cover:    

Rc=Rsnow                                                                                                                                       

 

 

Figure 5.1:        Resistance analogy approach in dry deposition models.

Table 5.1 shows the surface resistance values for soil surfaces (Rsoil), snow-covered surfaces (Rsnow) and water surfaces (Rwat). The formulation of all other resistances is discussed in Annex C.

Table 5.1 Ozone surface resistance values (s m-1) for soil surfaces (Rsoil), snow-covered surfaces (Rsnow) and water surfaces (Rwater).

Resistance type

Resistance(s m-1)

Rsoil

200

Rwater

2000

Rsnow

2000

 

1.2                   Concentrations at measureing height

The LOTOS-EUROS system contains the option to diagnose the concentration (cg) at measuring height (zg). To diagnose the concentration at measuring height we use that the deposition flux is constant over height. It follows that:

 

 

The aerodynamic resistance from measuring height (zref) to the height (z) for which the dry deposition speed is calculated in the stability module of LOTOS-EUROS. The abovementioned approach is used for all components except Ozone and NOx.

For O3 and NOx we assume a photochemical steady state within the profile. We asess the Ox and NOx concentratrion at measuring height using the Ox and NOx deposition speeds:

 

[NO2] * k1 = [NO] * [O3] * k3

 

The reaction rates k1 and k2 are given in Annex A and B. Solving this equation by using NO=NOx-NO2 and O3 = Ox-NO2 gives the equilibriated ground level concentrations.