As cities seek solutions to combat urban heat islands, reflective pavements are increasingly recognized as a key urban cooling strategy. As part of the GAF Cool Community Project, more than 700,000 square feet of dark asphalt surfaces in Pacoima, California—one of the hottest areas in the San Fernando Valley—were treated with GAF’s DuraShield-SR in June and July of 2022.
This water-based epoxy pavement coating is designed to reflect solar radiation, preventing pavement from absorbing excessive heat and lowering surface temperatures. By cooling the surrounding air, the coating helps mitigate the urban heat island effect and reduces heat-related health risks throughout the day. The treated areas included streets, basketball courts, playgrounds, and parking lots, providing broad coverage to maximize the cooling benefits for the community.
While research generally agrees on the benefits of cool pavements at larger scales, their impact at the pedestrian level remains debated, with concerns about glare, increased radiant temperature, and UV reflection.
A recent study, led by Altostratus Inc., the creator of California’s Urban Heat Island Index, and published in Environmental Research Communications, evaluated the effectiveness of Pacoima’s cool pavement coatings in lowering surface and air temperatures while enhancing pedestrian thermal comfort.
Altostratus specializes in climate modeling at meso- to micro-scales. It provides fine-scale meteorological forecasting for urban environments, addressing factors such as heat islands, emissions, air quality, and building energy consumption.
Lead researcher Haider Taha emphasized the study’s multi-scale, multi-platform approach, stating, “We analyzed a wide range of data over the course of a year, assessing impacts at both the community and individual levels—including the surface, pedestrian level, and urban canopy layer—to better understand potential effects. Our research bridges a critical gap between scientific understanding and practical solutions for urban heat challenges.”
Equipment for Evaluating Cool Pavements
Two adjacent, similar community sections were selected as test and reference areas to compare surface and near-surface micrometeorology before and after applying reflective coatings. These areas shared comparable weather, airflow patterns, tree cover, street orientation, sky-view factors, building heights, urban morphology, and pavement types to ensure that any observed micrometeorological differences post-installation were due to albedo modifications.
To assess the effects of DuraShield-SR at the surface, pedestrian, and atmospheric levels, the study employed the following instrumentation:
Reflectometer: The Solar-i Reflectometer, manufactured by Surface Optics, was used for spot, in situ measurements prior to and after reflective coatings were installed.
Satellites: MODIS for 500-m albedo, Landsat-9 for 30-m albedo, ECOSTRESS for 70-m land-surface temperature, and Sentinel-2 for 10-m albedo.
Aircraft: NASA/JPL HyTES data was obtained for several flyovers in the project area—they provide snapshot thermal imagery and temperature data.
Drone: GAF provided drones for visible and thermal imagery.
Automated weather stations: Two weather stations (ATMOS 41) were installed in test and reference areas on City of LA street lighting poles. The purpose was to capture above-canopy background conditions over the test and reference areas and ensure that any thermal environmental changes within the urban canopy were not caused by some changes in background conditions.
Mobile platform: An electric golf cart was instrumented and used as the main observational platform in extensive mobile transects through the test and reference communities. An electric cart was selected to avoid the effects of tailpipe exhaust heat on temperature readings and continuously cover the entire project area while at low speeds to better capture of cool-pavements’ effects.
Field Solar Reflectance Measurements
The 410-Solar-i Reflectometer is a highly portable and field-deployable instrument that played a crucial role in this study by enabling on-site measurements of surface reflectance before and after the application of DuraShield-SR. Its compact design allows for easy transport and rapid data collection across various locations, making it an ideal tool for testing cool pavements in real-world conditions. Reflectance was measured at several locations in the project area, shown with red circles in Figure 1.
Figure 1. Mobile-transect route and reflectometer sampling points. The two black circles are locations of the project’s weather stations.
Establishing Pre-Coating Broadband Albedo
Broadband albedo was computed from 410-Solar-i reflectometer field measurements, using a spectral weighting function of 1.5 atmospheres, verifying that there was practically no difference in the total albedo of streets between these two communities prior to coating. The medians for albedo were 0.0550 and 0.0535, and the means were 0.0544 and 0.0536.
VIS Reflectance & Glare
The 410-Solar-i Reflectometer measures reflectance across multiple spectral bands, including UV, visible (VIS), and near-infrared (NIR). A key focus of this study was assessing the potential glare effects of cool pavements. VIS reflectance measurements with the 410-Solar-i confirmed that glare is not a concern with DuraShield-SR.
A comparison of visible spectrum (VIS) reflectance between the existing parking lot surface and the newly applied reflective coating showed only a modest increase. The original pavement had a VIS reflectance of 0.08–0.10, while the DuraShield-SR coating measured between 0.12 and 0.15—a small enough change to avoid visual or glare discomfort.
NIR Reflectance
Measurements from the 410-Solar-i Reflectometer showed a substantial increase in NIR reflectance for the DuraShield-SR coating compared to uncoated pavement (Fig. 2). The rise in albedo was primarily due to enhanced NIR reflectance, rather than changes in the visible (VIS) spectrum. As a result, glare and visual comfort remain unaffected, while the cooling benefits are significant. Specifically, the NIR reflectance of the original parking lot material ranged from 0.1 to 0.15, whereas the reflective coating increased this to 0.4–0.5, representing a major improvement in heat mitigation.
Reflectance in the near-infrared (NIR) ranges: comparison between existing parking-lot material (p1, p3, p4) and the DuraShield-SR coating (p6, p5, p7). Wavelengths presented in this figure are 0.70–1.10 μm, 1.00–1.70 μm, and 1.70–2.50 μm. Each location is in triplicate as 3 samples were taken at nearby points.
UV Reflectance
While cool pavements primarily alter VIS and NIR albedo, concerns have been raised about potential air quality impacts due to changes in UV reflectance, as UV radiation drives key photodissociation reactions affecting ozone (O₃), nitrogen dioxide (NO₂), and peroxyacetyl nitrate (PAN). The critical UV range for surface albedo modifications is 0.3 to 0.37 μm, which aligns with the first reflectance band of the 410-Solar-i Reflectometer. Measurements in this case show that DuraShield-SR coatings do not significantly change—or may even reduce—UV albedo, confirming that certain reflective materials can effectively enhance VIS and NIR reflectance without negatively affecting UV reflectance.
Results
The Altostratus Inc. study revealed reductions of ambient air temperatures by as much as 3.5°F during extreme heat events and a 25-50% reduction in the local census-tract urban heat island effect during temperature peaks, without negative urban air quality or glare effects. The results reinforce the efficacy of cool pavement technology as one strategy to help cities tackle extreme heat.
To read the full publication see:
Taha, Haider. “Micrometeorological Effects and Thermal-Environmental Benefits of Cool Pavements: Findings from a Detailed Observational Field Study in Pacoima, California.” Environmental Research Communications, vol. 6, no. 3, 2024, p. 035016, https://doi.org/10.1088/2515-7620/ad2a8e.