Traffic NO2 Overlay

What is the Traffic NO2 overlay?

Active Traffic NO2 air polution overlay

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

Traffic NO2 air polution overlay colors

File:Traffic NO2-Overlay Legend.jpg

Traffic NO2 overlay colors

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 depending 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