Traffic NO2 formula (Traffic NO2 Overlay)

The calculations follow the standard rekenmethode 1 (SRM 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 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

Notes

• If the traffic amount is defined as a single value, that value is used for all defined hours. However, if the amount if an 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 calculation method is only applicable for urban environments.

See also

• Traffic NO2 Overlay

References

• The overlay calculations are based on Standard Calculation Method 1 (SRM1) as defined by the dutch government: http://wetten.overheid.nl/BWBR0022817/2013-03-22