# Traffic NO2 formula (Traffic NO2 Overlay)

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

$Cjm[NO_{2}]=Ca,jm[NO_{2}]+Cb,jm[NO_{2}]$ where:

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

#### Contribution NO2

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

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

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

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

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

The computation of the dilution factor, $\theta$ , is split into two situations. 

For surrounding cells within a distance of 30m:

$\theta =a\cdot S^{2}+b\cdot S+c$ And for cells within a distance of 30-60m (for road-type 1 only):

$\theta =\alpha \cdot S^{p}$ where:

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

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

$fNO_{2}={\frac {ENO_{2}}{ENO_{x}}}$ where:

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

#### Tree Factor

The tree factor is calculated as followed:

$A_{t}=\pi \cdot {\frac {d^{2}}{A_{c}}}$ $F_{b}=1+{\frac {t}{2\cdot A_{t}}}$ where:

$A_{c}$ = Grid cell area in square meters.
$d$ = Search distance of trees, currently set on 30 meters,
$A_{t}$ = Search area measured in amount of cells,
$t$ = Amount of tree cells within the search distance,
$F_{b}$ = 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:

$E_{drive}=(1.0-j_{c})\cdot n_{c}\cdot E_{c,d}+(1.0-j_{v})\cdot n_{v}\cdot E_{v,d}+(1.0-j_{t})\cdot n_{t}\cdot E_{t,d}+(1.0-j_{b})\cdot n_{b}\cdot E_{b,d}$ $E_{jam}=j_{c}\cdot n_{c}\cdot E_{c,j}+j_{v}\cdot n_{v}\cdot E_{v,j}+j_{t}\cdot n_{t}\cdot E_{t,j}+j_{b}\cdot b_{t}\cdot E_{b,j}$ $E=(E_{drive}+E_{jam})\cdot {\frac {1000}{(24\cdot 3600)}}$ where:

$E$ = Calculated emission of either NOx or NO2
$E_{drive}$ = Calculated emission of driving traffic of either NOx or NO2.
$E_{jam}$ = Calculated emission of jammed traffic of either NOx or NO2.
$E_{c,d}$ = 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.
$E_{v,d}$ = 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.
$E_{t,d}$ = 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.
$E_{b,d}$ = 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.
$E_{c,j}$ = 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.
$E_{v,j}$ = 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.
$E_{t,j}$ = 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.
$E_{b,j}$ = 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.
$n_{c}$ = number of car traffic, hourly or daily value. Configured in roads using Function Value NUM_CARS or as grid prequel.
$n_{v}$ = number of van traffic, hourly or daily value. Configured in roads using Function Value NUM_VANS or as grid prequel.
$n_{t}$ = number of truck traffic, hourly or daily value. Configured in roads using Function Value NUM_TRUCKS or as grid prequel.
$n_{b}$ = number of bus traffic, hourly or daily value. Configured in roads using Function Value NUM_BUSES or as grid prequel.
$j_{c}$ = fraction of car traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_CARS.
$j_{v}$ = fraction of van traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_VANS.
$j_{t}$ = fraction of truck traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_TRUCKS.
$j_{b}$ = fraction of bus traffic in traffic jams. Configured in roads using Function Value JAM_FACTOR_BUSES.