Measurements of the Impacts of Neighborhood Scale Cool Pavement Deployments on Albedo, Temperatures, and Pedestrian Thermal Comfort in the Greater Los Angeles Area

Abstract:

Climate change is expected to exacerbate the urban heat island effect in cities around the world, increasing the risk of heat-related illnesses and mortality. Solar reflective “cool pavement” is one of several mitigation strategies that has the potential to counteract the negative effects of the urban heat island effect. An increase in pavement albedo results in less heat being absorbed by the pavement, which in turn results in reduced surface temperatures. Near surface air temperatures could also be reduced if cool pavements are deployed at sufficiently large spatial scales, though this has never been confirmed by field measurements. This field study is the first to conduct controlled measurements of the environmental consequences of neighborhood-scale cool pavement installations in the real world. We measured surface temperature, near-surface air temperature, albedo, and thermal comfort both before and after cool pavement installation. In addition, pavement albedo was measured several times after cool pavement installation to assess the extent to which it decreases due to aging. The field site (~0.7 km²) was located in Covina, California, approximately 30 km east of Downtown Los Angeles. Continuous, mobile transect measurements of air and surface temperature were taken over the target area (with cool pavement installed) and a corresponding control area (upwind with no cool pavement), every three hours between 06:00 and 21:00 Pacific Time (PT). Continuous, mobile albedo measurements were taken to assess the effect of weathering on the albedo of the cool pavement. Lastly, mean radiant temperature was measured, both on the sidewalk and over the pavement, to quantify how pedestrian thermal comfort would be impacted by the cool pavement. Preliminary results show that cool pavement reduces mean surface temperature by ~1­–5.5 Cº, with the largest reductions generally observed around 03:00 PT. Cool pavement albedo varied widely, from ~0.10 to 0.37, and we observed a clear decrease in albedo over time. Air temperature change due to cool pavement was within the range of instrument noise during midday, but a mean air temperature reduction of ~0.4 and 0.7 Cº was observed at 18:00 and 21:00 PT, respectively. Further analysis will be completed to quantify the effect of cool pavement on pedestrian thermal comfort.