# Traffic NO2(Overlay)

After reading this page:

- you've learned what the Traffic NO2 overlay is.
- you've learned which information is displayed on the Traffic NO2 overlay.
- you've learned how to add or remove the Traffic NO2 overlay.

## What is the Traffic NO2 Overlay?

The Traffic NO2 overlay is an overlay which displays the impact of traffic air polution (in μg/m³ NO2) in different colors for the project area. These colors indicate traffic air polution of a location based on traffic flow and distance.

## Adding and removing

To add a traffic NO2 overlay go to the Overlays menu in the GEO DATA ribbon and select Add Traffic NO2. To remove the overlay, press Remove below the overlays list.

## Calculations

The calculations follow the standard rekenmethode 1 (SRM 1), as described on [1]:

**Cjm[NO2] = Ca,jm[NO2] + Cb,jm[NO2]**

where:

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

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

**Cb,jm[NO2]= fNO2 * Cb,jm[NOx] + (B*Ca,jm[O3]*Cb,jm[NOx]*(1-fNO2))/(Cb,jm[NOx]*(1-Fno2)+K)**

where:

- Cb,jm[NOX] = annual average traffic contribution to NOx concentration [μg/m3]
- Cb,jm[O3] = annual average concentration ozon [μg/m3] (default = 42)
- fNO2 = weighted fraction direct emitted NO2 [-]
- B = parameter (default 0.6)
- K = parameter for conversion NO to NO2 (default = 100 μg/m3)

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

**Cb,jm[NOx] = Fk * ENOx * θ * Fb * Fmeteo**

where:

- Fk = calibration factor [-] (default = 0.62]
- ENOx = emission number NOx [μg/m/s]
- θ = delution factor [-]
- Fb = tree factor (default = XX)
- Fmeteo = 5/windspeed. Default value for windspeed is 5 m/s

The delution factor, θ, is computed till a distance of 30m with:

**θ = a * S^2 + b * S + c**

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

**θ = alpha * S^-0.747**

where:

- S is the calculation distance
- a, b, c and alpha are parameters depend on road-type:

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

**fNO2 = ENO2/ENOx**

where:

- ENO2 = emission number NOs [μg/m/s]

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

**E = N * [(1-FS)*((1-(fm+fz+fb))*El + fm * Em + fz * Ez + fb * Eb) + FS * ((1-(fm + fz + fb)) * El,d + Fm * Em,d + fz * Ez,d+fb*Eb,d)]*1000/(24*3600)**

where:

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

## References

The overlay calculations are based on Standard Calculation Method 1 (SRM1) as defined by the dutch government: wetten.overheid.nl