Abstract
Abstract. This paper describes a large-eddy simulation based chemical transport model, developed under the OpenFOAM framework, implemented to simulate dispersion and chemical transformation of nitrogen oxides from traffic sources in an idealized street canyon. The dynamics of the model, in terms of mean velocity and turbulent fluctuation, are evaluated using available stationary measurements. A transient model run using a photostationary reaction mechanism for nitrogen oxides and ozone subsequently follows, where non-stationary conditions for meteorology, background concentrations, and traffic emissions are applied over a 24 h period, using regional model data and measurements obtained for the city of Berlin in July 2014. Diurnal variations of pollutant concentrations indicate dependence on emission levels, background concentrations, and solar state. Comparison of vertical and horizontal profiles with corresponding stationary model runs at select times show that while there are only slight differences in velocity magnitude, visible changes in primary and secondary flow structures can be observed. In addition, temporal variations in diurnal profile and cumulative species concentration result in significant deviations in computed pollutant concentrations between transient and stationary model runs.
Highlights
The study of dispersion and chemical transformation of pollutants at urban scales is of immediate scientific and engineering interest, but it is an indispensable exercise for socioeconomists and policy makers seeking to quantify their decisions
While the Reynolds-averaged Navier–Stokes (RANS) approach has been shown to adequately represent mean flow behaviors in some cases (Baik and Kim, 1998; Kwak and Baik, 2014), in the presence of large-scale unsteady mixing, such as vortex shedding from building surfaces, mean dynamics is not always sufficient, as these motions are not universal according to the Kolmogorov hypothesis (Pope, 2000), seen in part by large discrepancies observed in simulated pollutant concentrations for dispersion scenarios in comparison with measurement data (Tominaga and Stathopoulos, 2009)
A weakly compressible, reactive finite-volume large-eddy simulation (LES) solver, based on the OpenFOAM computational continuum mechanics framework (Weller et al, 1998), has been developed for modeling chemical transport of gas-phase pollutant species in an idealized street canyon under conditions where meteorology, background pollutant concentrations, and traffic emissions vary with time
Summary
The study of dispersion and chemical transformation of pollutants at urban scales (less than 200 m; Britter and Hanna, 2003) is of immediate scientific and engineering interest, but it is an indispensable exercise for socioeconomists and policy makers seeking to quantify their decisions At this scale, the local population is in close proximity with the pollutant sources, such as nitrogen oxides (NOx) from traffic sources. While the RANS approach has been shown to adequately represent mean flow behaviors in some cases (Baik and Kim, 1998; Kwak and Baik, 2014), in the presence of large-scale unsteady mixing, such as vortex shedding from building surfaces, mean dynamics is not always sufficient, as these motions are not universal according to the Kolmogorov hypothesis (Pope, 2000), seen in part by large discrepancies observed in simulated pollutant concentrations for dispersion scenarios in comparison with measurement data (Tominaga and Stathopoulos, 2009). Using the idealized street canyon as a starting point, the chemical transport model can be further conceived and developed to simulate more realistic urban environments using detailed chemical kinetics, coupled with meteorological conditions and background concentrations extracted from measurements or regional models
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
