This is the basic concept of the increase (and decrease) of air temperature during the daytime, when the sun is out.

As the solar altitude increases toward noon and then decreases, the heating of the ground increases then decreases, and the heat conducted to and convected within the air increases and decreases, We figure the insolation is highest at noontime; however, observations show that the maximum temperature of the day tends to occur sometime in the middle of the afternoon. We may speculate that it is somewhat due to the fact that outdoor thermometers are located about 1.5 meters above the ground, and that it takes time for heat to be conducted to the air and then convected upward to the thermometer location, but the time factor is actually just minutes, so this can't be the full reason.