This study investigated the characteristics of the flow and dispersion of reactive pollutants in three-dimensional idealized street canyons in the presence of building-roof cooling to provide implications in how a green-roof system contributes to mitigating of pedestrian exposure to near-roadway air pollution in street canyons. The pollutant chemistry was simulated using a coupled CFD-chemistry model. In the presence of building-roof cooling, winds and temperature fields inside the building canopy of the street canyon were significantly modified. Building-roof cooling, intensified the street-canyon vortex strength (up to 26.6% in downdraft, 10.4% reverse flow, and 7.7% in updraft). Building-roof cooling also decreased air temperature in the street canyon by supplying cooler air near the building roof. The changes in the in-canopy distributions of primary pollutants (NOX, VOCs and CO) due to building-roof cooling were mainly caused by the modified mean flow rather than the chemical reactions. High concentrations of primary pollutants occurred near the upwind building because the reverse flows were dominant at street level, making this area the downwind region of emission sources. Ozone concentrations were lower than the background concentration near the ground, where NOX concentrations were high. Building-roof cooling decreased primary pollutant concentrations by approximately −2.4% compared to those under non-cooling conditions. By contrast, building-roof cooling increased O3 concentrations by about 1.1% by reducing NO concentrations in the street canyon compared to concentrations under non-cooling conditions.

Abstract We examine the effect of anthropogenic aerosol forcing on the East Asian summer monsoon (EASM) using the Community Atmosphere Model version 5.1.1. One control and two sensitivity model experiments were conducted in order to diagnose the separate roles played by sea surface temperature (SST) variations and anthropogenic sulfate aerosol forcing changes in East Asia. We find that the SST variation has been a major driver for the observed weakening of the EASM, whereas the effect of the anthropogenic aerosol forcing has been opposite and has slightly intensified the EASM over the recent decades. The reinforcement of the EASM results from radiative cooling by the sulfate aerosol forcing, which decelerates the jet stream around the jet's exit region. Subsequently, the secondary circulation induced by such a change in the jet stream leads to the increase in precipitation around 18–23°N. This result indicates that the increase in anthropogenic emissions over East Asia may play a role in compensating for the weakening of the EASM caused by the SST forcing.

This study investigated the characteristics of the flow and dispersion of reactive pollutants in three-dimensional idealized street canyons in the presence of building-roof cooling to provide implications in how a green-roof system contributes to mitigating of pedestrian exposure to near-roadway air pollution in street canyons. The pollutant chemistry was simulated using a coupled CFD-chemistry model. In the presence of building-roof cooling, winds and temperature fields inside the building canopy of the street canyon were significantly modified. Building-roof cooling, intensified the street-canyon vortex strength (up to 26.6% in downdraft, 10.4% reverse flow, and 7.7% in updraft). Building-roof cooling also decreased air temperature in the street canyon by supplying cooler air near the building roof. The changes in the in-canopy distributions of primary pollutants (NOX, VOCs and CO) due to building-roof cooling were mainly caused by the modified mean flow rather than the chemical reactions. High concentrations of primary pollutants occurred near the upwind building because the reverse flows were dominant at street level, making this area the downwind region of emission sources. Ozone concentrations were lower than the background concentration near the ground, where NOX concentrations were high. Building-roof cooling decreased primary pollutant concentrations by approximately −2.4% compared to those under non-cooling conditions. By contrast, building-roof cooling increased O3 concentrations by about 1.1% by reducing NO concentrations in the street canyon compared to concentrations under non-cooling conditions.

Abstract We examine the effect of anthropogenic aerosol forcing on the East Asian summer monsoon (EASM) using the Community Atmosphere Model version 5.1.1. One control and two sensitivity model experiments were conducted in order to diagnose the separate roles played by sea surface temperature (SST) variations and anthropogenic sulfate aerosol forcing changes in East Asia. We find that the SST variation has been a major driver for the observed weakening of the EASM, whereas the effect of the anthropogenic aerosol forcing has been opposite and has slightly intensified the EASM over the recent decades. The reinforcement of the EASM results from radiative cooling by the sulfate aerosol forcing, which decelerates the jet stream around the jet's exit region. Subsequently, the secondary circulation induced by such a change in the jet stream leads to the increase in precipitation around 18–23°N. This result indicates that the increase in anthropogenic emissions over East Asia may play a role in compensating for the weakening of the EASM caused by the SST forcing.

Vehicular emissions are major sources of gaseous and particulate matter pollutants in urban atmospheres. Stringent environmental regulations on vehicular emissions have been consistently implemented, leading to a substantial decrease in exhaust emissions. In contrast, non-exhaust emissions are increasing with the growing share of electric vehicles. Non-exhaust particulate matter emissions account for approximately 90% of total vehicular emissions. However, standardized guidelines for non-exhaust emissions have not been established, largely due to the challenges in estimating ambient concentrations from non-exhaust particulate matter sources. In this study, we performed a particulate matter simulation to investigate the quantitative impact of non-exhaust emissions in Seoul, using a coupled atmospheric chemistry–CFD model (CFD-Chem). We evaluated the model using various emission factors and determined the most accurate emission factor by comparing it with observed PM concentrations at the pedestrian level. Our simulated PM concentrations follow the diurnal variation of traffic volume, indicating a significant contribution of non-vehicular emissions to PM concentration at ground level. We observed that the impact of non-exhaust sources on pedestrians is higher in alleys than on main streets. Our results suggest that precise simulations are essential for establishing accurate and standardized guidelines for non-exhaust emissions.