# Traffic NO2 formula (Traffic NO2 Overlay)

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

${\displaystyle Cjm[NO_{2}]=Ca,jm[NO_{2}]+Cb,jm[NO_{2}]}$

where:

${\displaystyle Cjm[NO_{2}]}$ = the calculated annual average concentration [μg/m3],
${\displaystyle Ca,jm[NO_{2}]}$ = the provided annual average background-concentration (default = 0 [μg/m3]). Configured using model attribute BASE_NO2.
${\displaystyle Cb,jm[NO_{2}]}$ = the calculated annual average traffic contribution to NO2 concentration [μg/m3].

#### Contribution NO2

To compute the annual average traffic contribution to NO2, ${\displaystyle Cb,jm[NO_{2}]}$ [μg/m3], the following formula from SRM1 is applied:

${\displaystyle Cb,jm[NO_{2}]=fNO_{2}\cdot Cb,jm[NO_{x}]+{\frac {B\cdot Ca,jm[O_{3}]\cdot Cb,jm[NO_{x}]\cdot (1-fNO_{2})}{K+Cb,jm[NO_{x}]\cdot (1-fNO_{2})}}}$

where:

${\displaystyle Cb,jm[NO_{x}]}$ = the calculated annual average traffic contribution to NOx concentration [μg/m3],
${\displaystyle Ca,jm[O_{3}]}$ = the provided annual average concentration ozon [μg/m3] (default = 42),
${\displaystyle fNO_{2}}$ = weighted fraction direct emitted NO2 [-],
${\displaystyle B}$ = parameter (default 0.6),
${\displaystyle K}$ = 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:

${\displaystyle Cb,jm[NO_{x}]=F_{k}\cdot ENO_{x}\cdot \theta \cdot F_{b}\cdot F_{meteo}}$

where:

${\displaystyle F_{k}}$ = calibration factor [-] (default = 0.62]
${\displaystyle ENO_{x}}$ = emission number NOx [μg/m/s]
${\displaystyle \theta }$ = dilution factor [-]
${\displaystyle F_{b}}$ = tree factor (default = 1)
${\displaystyle F_{meteo}}$ = 5/windspeed. Default value for windspeed is 5 m/s

The computation of the dilution factor, ${\displaystyle \theta }$, is split into two situations. [1]

For surrounding cells within a distance of 30m:

${\displaystyle \theta =a\cdot S^{2}+b\cdot S+c}$

And for cells within a distance of 30-60m (for road-type 1 only):

${\displaystyle \theta =\alpha \cdot S^{p}}$

where:

${\displaystyle S}$ = the calculation distance
${\displaystyle a}$ = configurable using model attribute: ROAD1_30M_A
${\displaystyle b}$ = configurable using model attribute: ROAD1_30M_B
${\displaystyle c}$ = configurable using model attribute: ROAD1_30M_C
${\displaystyle \alpha }$ = configurable using model attribute: ROAD1_60M_ALPHA
${\displaystyle p}$ = configurable using model attribute: ROAD1_60M_POWER

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

${\displaystyle fNO_{2}={\frac {ENO_{2}}{ENO_{x}}}}$

where:

${\displaystyle ENO_{2}}$ = emission number NOs [μg/m/s]

#### Tree Factor

The tree factor is calculated as followed:

${\displaystyle A_{t}=\pi \cdot {\frac {d^{2}}{A_{c}}}}$

${\displaystyle F_{b}=1+{\frac {t}{2\cdot A_{t}}}}$

where:

${\displaystyle A_{c}}$ = Grid cell area in square meters.
${\displaystyle d}$ = Search distance of trees, currently set on 30 meters,
${\displaystyle A_{t}}$ = Search area measured in amount of cells,
${\displaystyle t}$ = Amount of tree cells within the search distance,
${\displaystyle F_{b}}$ = Tree factor, value between 1 and 1.5.

Note that this way of calculating the tree factor is more detailed than the suggested calculation of the tree factor: 1, 1.25 or 1.5 and nothing in between.

#### Emission numbers

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

${\displaystyle E_{drive}=(1.0-j_{c})\cdot n_{c}\cdot E_{c,d}+(1.0-j_{v})\cdot n_{v}\cdot E_{v,d}+(1.0-j_{t})\cdot n_{t}\cdot E_{t,d}+(1.0-j_{b})\cdot n_{b}\cdot E_{b,d}}$

${\displaystyle E_{jam}=j_{c}\cdot n_{c}\cdot E_{c,j}+j_{v}\cdot n_{v}\cdot E_{v,j}+j_{t}\cdot n_{t}\cdot E_{t,j}+j_{b}\cdot b_{t}\cdot E_{b,j}}$

${\displaystyle E=(E_{drive}+E_{jam})\cdot {\frac {1000}{(24\cdot 3600)}}}$

where:

${\displaystyle E}$ = Calculated emission of either NOx or NO2
${\displaystyle E_{drive}}$ = Calculated emission of driving traffic of either NOx or NO2.
${\displaystyle E_{jam}}$ = Calculated emission of jammed traffic of either NOx or NO2.
${\displaystyle E_{c,d}}$ = Calculated emission of driving cars, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_CAR_NOX or EMISSION_CAR_NO2 respectively.
${\displaystyle E_{v,d}}$ = Calculated emission of driving vans, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_VAN_NOX or EMISSION_VAN_NO2 respectively.
${\displaystyle E_{t,d}}$ = Calculated emission of driving trucks, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_TRUCK_NOX or EMISSION_TRUCK_NO2 respectively.
${\displaystyle E_{b,d}}$ = Calculated emission of driving buses, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_BUS_NOX or EMISSION_BUS_NO2 respectively.
${\displaystyle E_{c,j}}$ = Calculated emission of jammed cars, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_JAM_CAR_NOX or EMISSION_JAM_CAR_NO2 respectively.
${\displaystyle E_{v,j}}$ = Calculated emission of jammed vans, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_JAM_VAN_NOX or EMISSION_JAM_VAN_NO2 respectively.
${\displaystyle E_{t,j}}$ = Calculated emission of jammed trucks, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_JAM_TRUCK_NOX or EMISSION_JAM_TRUCK_NO2 respectively.
${\displaystyle E_{b,j}}$ = Calculated emission of jammed buses, hourly or daily, of either NOx or NO2. Configured using Model attribute EMISSION_JAM_BUS_NOX or EMISSION_JAM_BUS_NO2 respectively.
${\displaystyle n_{c}}$ = number of car traffic, hourly or daily value. Configured in roads using Function Value NUM_CARS or as grid prequel.
${\displaystyle n_{v}}$ = number of van traffic, hourly or daily value. Configured in roads using Function Value NUM_VANS or as grid prequel.
${\displaystyle n_{t}}$ = number of truck traffic, hourly or daily value. Configured in roads using Function Value NUM_TRUCKS or as grid prequel.
${\displaystyle n_{b}}$ = number of bus traffic, hourly or daily value. Configured in roads using Function Value NUM_BUSES or as grid prequel.
${\displaystyle j_{c}}$ = fraction of car traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_CARS.
${\displaystyle j_{v}}$ = fraction of van traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_VANS.
${\displaystyle j_{t}}$ = fraction of truck traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_TRUCKS.
${\displaystyle j_{b}}$ = fraction of bus traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_BUSES.

## 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[2] calculation method is only applicable for urban environments.

## References

1. K. van Velze and J. Wesseling, Technische beschrijving van standaardrekenmethode 1 (SRM-1), paragraph 3.5, RIVM Briefrapport 2014-0127, https://www.rivm.nl/bibliotheek/rapporten/2014-0127.pdf
2. SRM1 ∙ Regeling beoordeling luchtkwaliteit 2007, Bijlage I ∙ Found at: http://wetten.overheid.nl/BWBR0022817/2013-01-01#Bijlage1 ∙ (last visited: 16-02-2022)