Nonstationary modeling of NO<sub>2</sub>, NO and NO<sub><i>x</i></sub> in Paris using the Street-in-Grid model: coupling local and regional scales with a two-way dynamic approach

Abstract

<jats:p>Abstract. Regional-scale chemistry-transport models have coarse spatial resolution (coarser than 1 km ×1 km) and can thus only simulate background concentrations. They fail to simulate the high concentrations observed close to roads and in streets, where a large part of the urban population lives. Local-scale models may be used to simulate concentrations in streets. They often assume that background concentrations are constant and/or use simplified chemistry. Recently developed, the multi-scale model Street-in-Grid (SinG) estimates gaseous pollutant concentrations simultaneously at local and regional scales by coupling them dynamically. This coupling combines the regional-scale chemistry-transport model Polair3D and a street-network model, the Model of Urban Network of Intersecting Canyons and Highway (MUNICH), with a two-way feedback. MUNICH explicitly models street canyons and intersections, and it is coupled to the first vertical level of the chemical-transport model, enabling the transfer of pollutant mass between the street-canyon roof and the atmosphere. The original versions of SinG and MUNICH adopt a stationary hypothesis to estimate pollutant concentrations in streets. Although the computation of the NOx concentration is numerically stable with the stationary approach, the partitioning between NO and NO2 is highly dependent on the time step of coupling between transport and chemistry processes. In this study, a new nonstationary approach is presented with a fine coupling between transport and chemistry, leading to numerically stable partitioning between NO and NO2. Simulations of NO, NO2 and NOx concentrations over Paris with SinG, MUNICH and Polair3D are compared to observations at traffic and urban stations to estimate the added value of multi-scale modeling with a two-way dynamical coupling between the regional and local scales. As expected, the regional chemical-transport model underestimates NO and NO2 concentrations in the streets. However, there is good agreement between the measurements and the concentrations simulated with MUNICH and SinG. The two-way dynamic coupling between the local and regional scales tends to be important for streets with an intermediate aspect ratio and with high traffic emissions. </jats:p>

Black carbon modelling in urban areas: investigating the influence of resuspension and non-exhaust emissions in streets using the Street-in-Grid (SinG) model

“…As detailed in Lugon et al (2020), this dynamic coupling between local and regional scales allows a direct interaction between concentrations in the street network and those in the urban background: the mass transfer between the street and the background concentrations influence both the street and the background concentrations. Furthermore, SinG uses consistent chemical and physical parameterizations, such as the same chemical module and meteorological data, at both local and regional scales.…”

“…Furthermore, SinG uses consistent chemical and physical parameterizations, such as the same chemical module and meteorological data, at both local and regional scales. SinG and MUNICH are described in Lugon et al (2020) and Kim et al (2018), and Polair3D is presented by Boutahar et al 2004; Sartelet et al (2007), all available in the Polyphemus platform (Mallet et al, 2007). The size distribution of BC is modeled with a sectional approach, with diameters ranging typically from 10 −3 µm and 10 µm.…”

“…This two-way coupling between the streets and the background can be especially important for BC, as the concentrations observed in streets are considerably larger than BC concentrations in the urban background. Previous studies regarding gas-phase pollutants observed an important effect of the two-way coupling on NO 2 , NO and NO x concentrations in the streets, which may reach 60% in streets with high traffic emissions (Lugon et al, 2020;Kim et al, 2018).…”

“…Although the vertical mass transfer between the streets and the background influenced the concentrations in the streets, its influence on the background concentrations is often neglected. The multi-scale model Street-in-Grid (SinG) combines the Model of Urban Network of Intersecting Canyons and Highways (MUNICH) (Lugon et al, 2020;Kim et al, 2018) for modelling street concentrations and Polaid3D for modelling background concentrations (Sartelet et al, 2007), allowing to simulate local and regional scale simultaneously. SinG performs a two-way coupling between regional and local scales, taking into account at each iteration the influence of the vertical mass transfer between the background and the streets on both the background and the street concentrations.…”

Simulation of O&lt;sub&gt;3&lt;/sub&gt; and NO&lt;sub&gt;X&lt;/sub&gt; in Sao Paulo street urban canyons with VEIN (v0.2.2) and MUNICH (v1.0)

“…It solves pollutant reactions using a chemical mechanism, so it can also simulate the production of ozone inside the urban canyons. MUNICH has been used to simulate ozone (O 3 ) and nitrogen oxides (NO x ) by Wu et al (2020) in Tianhe District of Guangzhou city, and NO x as part of Street in Grid (SinG) model in Kim et al (2018), Thouron et al (2019) and Lugon et al (2020) in the Paris region.…”