cooling and warming effects of a grass covered area and adjacent asphalt area in a hot day

knowledge of the warming or cooling effects induced by asphalt or grass covered areas, may improve our understanding of how thermal stress or thermal comfort is created for workers who have to work outdoors for long hours in warm seasons. for this purpose a field measurements were carried out to know the cooling and warming effects of two adjacent areas, one covered with grass and the other with asphalt. these two adjacent coverages were located in an open area, in zanjan, a city in the north west of iran. a calm and sunny day in june was selected to perform measurements. the temperature and relative humidity, on the grass and asphalt surfaces and also at a heights of 1.2 m above them were measured at 2 hours interval from 6 a.m. to 12 p.m. results showed that in the measurement day, the grass surface temperature was less than asphalt surface temperature in the afternoon and in the before noon there was no significant difference between temperatures. whereas, the temperature measurements at the height of 1.2 m above asphalt and grass, showed that the air temperature above grass was less than the air above asphalt during the measurements period, but in the afternoon, the difference between these temperatures was less than that of before noon. both grass and asphalt surfaces, showed the cooling and warming effects, which are impressed on the air above them, due to thermal convection.