<Li> The planetary boundary layer is the part of the troposphere that is closest to Earth's surface and is directly affected by it, mainly through turbulent diffusion . During the day the planetary boundary layer usually is well - mixed, whereas at night it becomes stably stratified with weak or intermittent mixing . The depth of the planetary boundary layer ranges from as little as about 100 metres (330 ft) on clear, calm nights to 3,000 m (9,800 ft) or more during the afternoon in dry regions . </Li> <P> The average temperature of the atmosphere at Earth's surface is 14 ° C (57 ° F; 287 K) or 15 ° C (59 ° F; 288 K), depending on the reference . </P> <P> The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as 101325 pascals (760.00 Torr; 14.6959 psi; 760.00 mmHg). This is sometimes referred to as a unit of standard atmospheres (atm). Total atmospheric mass is 5.1480 × 10 kg (1.135 × 10 lb), about 2.5% less than would be inferred from the average sea level pressure and Earth's area of 51007.2 megahectares, this portion being displaced by Earth's mountainous terrain . Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured . Thus air pressure varies with location and weather . </P> <P> If the entire mass of the atmosphere had a uniform density from sea level, it would terminate abruptly at an altitude of 8.50 km (27,900 ft). It actually decreases exponentially with altitude, dropping by half every 5.6 km (18,000 ft) or by a factor of 1 / e every 7.64 km (25,100 ft), the average scale height of the atmosphere below 70 km (43 mi; 230,000 ft). However, the atmosphere is more accurately modeled with a customized equation for each layer that takes gradients of temperature, molecular composition, solar radiation and gravity into account . </P>

What is the weight of the air on the earth's surface called