The correct answer is option 3: "is warmed by terrestrial radiation." Airmass near the earth`s surface is warmer because it absorbs heat that is radiated back by the earth`s surface. This process is known as terrestrial radiation. The earth`s surface is warmed by the sun during the day, and it emits radiation in the form of heat. The airmass near the surface absorbs this heat, causing it to warm up. Option 1, "radiates heat," is incorrect because airmass near the surface does not radiate heat, but rather absorbs it. Option 2, "contains dust particles," is not directly related to the warming of the airmass. Option 4, "is far from the sun," is also incorrect because the distance from the sun does not determine the temperature of the airmass near the earth`s surface.