Modelling the Mixing of Size Resolved Traffic Induced and Background Ultrafine Particles from an Urban Street Canyon to Adjacent Backyards

Abstract

By means of numerical simulations the aims of this study are as follows: (1) to investigate the dispersion and mixing of ultrafine particles (UFP) with pre-existing size resolved UFP in a street canyon and its vicinity with the ENVI-met 3D microscale model; (2) to show the effects of boundary conditions, like wind direction and traffic emissions, on the UFP concentration in the near vicinity; and (3) to evaluate the importance of deposition and coagulation at the street scale. The decrease in UFP concentration in nucleation mode particles (diameter < 30 nm) and Aitken mode particles (diameter between 30-100 nm) downwind of the street canyon is caused by the large differences in the size distributions of the emissions and the background. Based on the wind direction and traffic emissions, the UFP concentration over the rooftop increases by 23% for the South-West wind up to 165% for the Northern wind. The background distribution for the South-West wind direction remains mono-modal, with a peak in the Aitken mode as a result of the relatively low contribution of advected particles from the street canyon. For the Northern wind the background size distribution transforms to a bi-modal distribution, with peaks in the nucleation and the Aitken modes as a result of the high UFP concentration advected from the boulevard. The overall effect of deposition and coagulation on the UFP is negligible for the cases considered in this study. Overall, deposition is more efficient and faster than coagulation in removing particles, and especially those in the nucleation mode.

Ultrafine Particles and PM2.5 at Three Urban Air Monitoring Stations in Northern Taiwan from 2011 to 2013

“…Most of the researches have shown that both local rush hour traffic emission and new particle formation (NPF) play key roles in the diurnal variation of UFPs concentrations, in which two concentration peaks in the morning and evening could be attributed to traffic emission, while one peak in the afternoon is due to NPF (Young et al, 2012;Cheung et al, 2013;Young et al, 2013;Betha et al, 2014;Nikolova et al, 2014).…”

Geospatial spreadsheets with microscale air quality visualization and synchronization for supporting multiple-scenario visual collaboration

“…One explanation for this deficiency is that the methods developed for monitoring and modelling at larger scales are inappropriate for microscale phenomena (Woo et al 2011). However, increasing numbers of MSAQ models (Bruse and Fleer 1998, Chang and Meroney 2003, Chu et al 2005 and other studies (Vos et al 2013, Nikolova et al 2014) are trying to overcome these limitations. Therefore, the present study focused on the development and validation of GS to enable comparisons in the context of MSAQ.…”

Emissions and Possible Environmental Implication of Engineered Nanomaterials (ENMs) in the Atmosphere

“…Dry deposition and coagulation of particles were identified to be the most important aerosol dynamic processes that control the evolution and removal of particles. However, CFD calculations on a street canyon for different wind directions by Nikolova et al [158] revealed that the overall effect of deposition and coagulation on the UFP is negligible for the cases considered. They conclude that overall, deposition is more efficient and faster than coagulation in removing particles, and especially those in the nucleation mode.…”