View source for Traffic NO2 formula (Traffic NO2 Overlay)

The calculations follow the standard rekenmethode 1 (SRM 1).

<math>Cjm[NO_2] = Ca,jm[NO_2] + Cb,jm[NO_2]</math>

where:
:<math>Cjm[NO_2]</math> = annual average concentration [μg/m3],
:<math>Ca,jm[NO_2]</math> = annual average background-concentration (default = 0 [μg/m3], can be adjusted via the overlay attributes),
:<math>Cb,jm[NO_2]</math> = annual average traffic contribution to NO2 concentration [μg/m3].

====Contribution NO2====
To compute the annual average traffic contribution to NO2, <math>Cb,jm[NO_2]</math> [μg/m3], the following formula from SRM1 is applied:

<math>Cb,jm[NO_2]= fNO_2 \cdot Cb,jm[NO_x] + \frac{B \cdot Ca,jm[O_3] \cdot Cb,jm[NO_x] \cdot (1-fNO_2)}{Cb,jm[NO_x] \cdot (1-Fno2)+K}</math>

where:
:<math> Cb,jm[NO_x]</math> = annual average traffic contribution to NOx concentration [μg/m3],
:<math> Cb,jm[O_3]</math> = annual average concentration ozon [μg/m3] (default = 42),
:<math> fNO_2</math> = weighted fraction direct emitted NO2 [-],
:<math> B</math> = parameter (default 0.6),
:<math> K</math> = parameter for conversion NO to NO2 (default = 100 μg/m3).

====Contribution NOX====
To compute the annual average traffic contribution to NOX, Cb,jm[NOX] [μg/m3], the following formula from SRM1 is applied:

<math>Cb,jm[NO_x] = Fk \cdot ENO_x \cdot \theta \cdot Fb \cdot Fmeteo</math>

where:
:<math>Fk</math> = calibration factor [-] (default = 0.62]
:<math>ENO_x</math> = emission number NOx [μg/m/s]
:<math>\theta</math> = dilution factor [-]
:<math>Fb</math> = tree factor (default = 1)
:<math>Fmeteo</math> = 5/windspeed. Default value for windspeed is 5 m/s

The dilution factor, <math>\theta</math>, is computed till a distance of 30m with:

<math>\theta = a \cdot S^2 + b \cdot S + c</math>

And from 30-60m (for road-type 1 and 4 only):

<math>\theta = \alpha \cdot S^{-0.747}</math>

where:
: <math>S</math> = the calculation distance
: <math>a</math>, <math>b</math>, <math>c</math> and <math>\alpha</math> = parameters depend on road-type:

[[File:NO2_overlay_02.PNG]]

The weighted fraction of direct emitted NO2 [-] is computed as:

<math>fNO_2 = \frac{ENO_2}{ENO_x}</math>

where:
: <math> ENO_2</math> = emission number NOs [μg/m/s]

====Tree Factor====
The tree factor is calculated as followed:
<math>Fb = 1 + \frac{t}{ 2 \cdot A_t}</math>

<math>A_t = \pi \cdot frac{d_t^2}{c_m^2}</math>

where:
: <mathFb</math> = Tree factor, value between 1 and 1.5
: <math>t</math> = Amount of tree cells within the search distance.
: <math>A_t</math> = Search area measured in amount of cells 
: <math>d_t</math> = Search distance of trees, currently set on 30 meters.
: <math>c_m</math> = Cell size in meters

====Emission numbers====
The emission numbers (E) for both NOx and NO2 are computed as:

<math>E = N \cdot [(1-FS)\cdot((1-(fm+fz+fb))\cdot El + fm \cdot Em + fz \cdot Ez + fb \cdot Eb) + FS \cdot ((1-(fm + fz + fb)) \cdot El,d + Fm \cdot Em,d + fz \cdot Ez,d+fb*Eb,d)] \cdot \frac{1000}{(24 \cdot 3600)}</math>

where:
* N = traffic intensity [units per day]
* fm = fraction vans [-]
* fz = fraction trucks [-]
* fb = fraction buses [-] 
* El = emission value cars [g/km]
* Em = emission value vans [g/km]
* Ez = emission value trucks [g/km]
* Eb = emission value buses [g/km]
* FS = fraction congested traffic [-]
* E*,d = emission factor per class (cars, vans, trucks or buses) if congested

{{article end
|notes=
* If the traffic amount is defined as a single value, that value is used for all defined [[Hours (Traffic Density Overlay)|hours]]. However, if the amount if an [[Attribute array|array of values]], each of the 24 indexes of that array are assumed to correspond to the hour denoted by those indexes, and as such that specific value from the array is used.
* The SRM1{{ref|srm1}} calculation method is only applicable for urban environments.
|seealso=
* [[Traffic NO2 Overlay]]
|references=
  <references>
    {{ref|srm1
      |name=SRM1
      |author=
      |page=
      |source=Regeling beoordeling luchtkwaliteit 2007, Bijlage I
      |link=http://wetten.overheid.nl/BWBR0022817/2013-01-01#Bijlage1
      |lastvisit=16-02-2022
    }}
  </references>
}}