What causes steam to rise from a wetted asphalt surface?
Sometimes you can see steam rising from asphalt surfaces when the sun comes out after a rain or a snowfall. The black top soaks up the sun’s heat and warms the asphalt and the water on it. The cold air in close contact with the road surface is warmed, presumably to the same temperature of the water on the road. At the same time, some of the rain water or melt water from the wetted asphalt evaporates into the air. Just above the surface, the air is still relatively cold and its moisture content much lower than that of the surface. As the rising vapours from the surface cool, some of it condenses into tiny droplets that we see as wispy streamers that resemble smoke. Eventually, the rising tufts of steam fog encounter drier air and disappear. You see the same thing even more prominently on cold, crisp mornings near lakes or over rivers as cold air drifts across relatively warm open water; or in a cold bathroom when the bath is filled with hot water. Your bath water is often much hotter th
Sometimes you can see steam rising from asphalt surfaces when the sun comes out after a rain or a snowfall. The asphalt absorbs the sun’s heat and causes the top layers of the asphalt to warm. This in turn warms the moist air in close contact with the road surface. As the rising air currents of warm, moist air above the asphalt encounter the cooler surrounding air, some of the water vapour condenses into tiny droplets that we see as wispy streamers that resemble smoke. Eventually, the rising tufts of steam encounter drier air and disappear.
