To examine the diurnal variation of albedo, the solar reflectivity was continuously monitored over time on one clear day on a concrete pavement (C2) and on another clear day on an asphalt pavement (B2) and is plotted in Fig. 6. Measured albedo changes over time during day: it is high in the early morning and then low and relatively constant around the middle of the day (9:00–15:00 h) and then low again in the late afternoon when there is a low incident angle of solar radiation as in the early morning. The diurnal variation of solar reflectivity of an asphalt pavement (B2) in three days is plotted in Fig. 7. The same trend was observed for the concrete pavement results. This implies that the albedo should be measured in the middle of the day (9:00–15:00) to obtain a constant and conservative value. Otherwise, if the albedo is measured in the early morning and late afternoon, the value obtained will tend to be larger than that measured in the middle of the day.