Nonlinear changes in urban heat island intensity, urban breeze intensity, and urban air pollutant concentration with roof albedo

Abstract

Abstract This study systematically examines how the urban heat island (UHI) and urban breeze circulation (UBC) respond to an increase in roof albedo (α r) and its influence on urban air pollutant dispersion. For this, idealized ensemble simulations are performed using the Weather Research and Forecasting (WRF) model. The increase in α r from 0.20 to 0.65 decreases the UHI intensity, UBC intensity, and urban planetary boundary layer (PBL) height in the daytime (from 1200 to 1700 LST) by 47%, 36%, and 6%, respectively. As both UBC intensity and urban PBL height decrease, the daytime urban near-surface passive tracer concentration increases by 115%. The daytime UHI intensity, UBC intensity, and urban tracer concentration nonlinearly change with α r: For 0.10 ≤ α r < 0.80, the rates of changes in the UHI intensity, UBC intensity, and urban tracer concentration with α r overall increase as α r increases. For α r ≥ 0.80, the daytime roof surface temperature is notably lower than the daytime urban near-surface air temperature, the UHI intensity, UBC intensity, and urban tracer concentration very slightly changing with α r. This study provides insights into the associations between changes in roof surface temperature and roof surface energy fluxes with α r and those in UHI intensity.

Keywords

• Roof albedo
• Urban heat island
• Urban breeze circulation
• Pollutant dispersion
• Urban air quality
• Cool roof