Effect of increasing urban albedo on meteorology and air quality of Montreal (Canada) - Episodic simulation of heat wave in 2005

Increasing albedo is an effective strategy to mitigate urban air temperature in different climates. Using reflective urban surfaces decreases the air temperature, which potentially reduces the rate of generation of smog. However, for implementing the albedo enhancement, complicated interactions between air, moisture, aerosols, and other gaseous contaminant in the atmosphere should be considered. We used WRF-CHEM to investigate the effect of increasing albedo in Montreal, Canada, during a heat wave period (July 10th through July 12th, 2005) on air quality and urban climate. The reflectivity of roofs, walls, and roads are increased from 0.2 to 0.65, 0.6, and 0.45, respectively. Air temperature at 2-m elevation is decreased during all hours in the simulation period and the maximum reduction is about 1 °C on each day (T_max is reduced by about 0.7 °C) The concentration of two regulated pollutants -ozone (O₃) and fine particulate matters (PM_2.5) - is calculated at a height of 5-m above the ground. The maximum decrease in 8-h averaged ozone concentration is about 3% (~0.2 ppbv). 24-h averaged PM_2.5 concentration decreases by 1.8 μg/m³. This relatively small change in concentration of pollutants is related to the decrease in planetary boundary layer height caused by increasing the albedo. Additionally, the combined effect of decreased solar heat gain by building surfaces and decreased air temperature reduces the energy consumption of HVAC systems by 2% (~0.1 W/m²), which exacerbates the positive effect of the albedo enhancement on the air quality.