26 Development and Implementation of an Online Chemistry Module …
167
26.3 Case Study for an City Quarter of Berlin, Germany
A 9 h long test simulation starting on 21st of July at 5:00 UTC was carried out for
a model domain with 96 × 96 grid points and 10 m grid width. In the vertical the
domain extends up to 1500 m. The domain covered a small area of Berlin around the
Ernst-Reuter-Platz, a junction with some high buildings and heavy car traffic. Only
gas-phase chemistry was switched on for the simulation shown here. The chosen
chemistry option SIMPLE includes the following reactions:
NO 2 + hv → NO + O 3
(26.1)
O 3 + hv → 2OH + O 2
(26.2)
NO + O 3 → NO 2
(26.3)
RH + OH → RO 2 + H 2 O
(26.4)
RO 2 + NO → NO 2 + RCHO + HO 2
(26.5)
HO 2 + NO → NO 2 + OH
(26.6)
NO 2 + OH → HNO 3
(26.7)
Since detailed emission data are not available yet, only traffic emissions, which
were parameterized depending on the street type classes from OpenStreetMap were
considered (for main roads the following emission rates were assumed: NO =
65.93 µg m
−2 s
−1 ; NO 2 = 28.26 µg m
−2 s
−1 ; RH = 21.05 µg m
−2 s
−1 ).
Selected results of the simulation are presented in Fig. 26.1. The figure shows
surface concentrations of nitrogen dioxide (NO 2 ) and ozone (O 3 ) and matching vertical cross sections along the indicated line (in Fig. 26.1a) at 13:30 UTC. The vertical
cross sections also include the vertical velocity as contours.
Both, NO 2 and O 3 vary in space and time due to the chemical transformation of the
atmospheric trace gases and advection by turbulent motions. The near surface, concentrations of NO 2 are high due to the direct emission from traffic and conversion of
nitrogen monoxide (NO) to NO 2 . The daytime O 3 , nitrogen oxides (NO x ) and VOCs
(volatile organic compounds) relation is driven by a complex non-linear photochemistry. Figure 26.1 shows the typical VOC-sensitive regime where O 3 concentrations
are depressed by NO x titration.
The presented vertical profiles in Fig. 26.1c, f show that the chemical components
are mixed upwards with the gradual increase of the boundary layer from simulation
start towards the early afternoon.
167
26.3 Case Study for an City Quarter of Berlin, Germany
A 9 h long test simulation starting on 21st of July at 5:00 UTC was carried out for
a model domain with 96 × 96 grid points and 10 m grid width. In the vertical the
domain extends up to 1500 m. The domain covered a small area of Berlin around the
Ernst-Reuter-Platz, a junction with some high buildings and heavy car traffic. Only
gas-phase chemistry was switched on for the simulation shown here. The chosen
chemistry option SIMPLE includes the following reactions:
NO 2 + hv → NO + O 3
(26.1)
O 3 + hv → 2OH + O 2
(26.2)
NO + O 3 → NO 2
(26.3)
RH + OH → RO 2 + H 2 O
(26.4)
RO 2 + NO → NO 2 + RCHO + HO 2
(26.5)
HO 2 + NO → NO 2 + OH
(26.6)
NO 2 + OH → HNO 3
(26.7)
Since detailed emission data are not available yet, only traffic emissions, which
were parameterized depending on the street type classes from OpenStreetMap were
considered (for main roads the following emission rates were assumed: NO =
65.93 µg m
−2 s
−1 ; NO 2 = 28.26 µg m
−2 s
−1 ; RH = 21.05 µg m
−2 s
−1 ).
Selected results of the simulation are presented in Fig. 26.1. The figure shows
surface concentrations of nitrogen dioxide (NO 2 ) and ozone (O 3 ) and matching vertical cross sections along the indicated line (in Fig. 26.1a) at 13:30 UTC. The vertical
cross sections also include the vertical velocity as contours.
Both, NO 2 and O 3 vary in space and time due to the chemical transformation of the
atmospheric trace gases and advection by turbulent motions. The near surface, concentrations of NO 2 are high due to the direct emission from traffic and conversion of
nitrogen monoxide (NO) to NO 2 . The daytime O 3 , nitrogen oxides (NO x ) and VOCs
(volatile organic compounds) relation is driven by a complex non-linear photochemistry. Figure 26.1 shows the typical VOC-sensitive regime where O 3 concentrations
are depressed by NO x titration.
The presented vertical profiles in Fig. 26.1c, f show that the chemical components
are mixed upwards with the gradual increase of the boundary layer from simulation
start towards the early afternoon.