What is the diameter of a weather balloon (in meters) filled with He at 15,000 m? On the ground the balloon was filled with He at 18 °C at 0.96 atm to a volume of 7.3 L. At 15,000 m the atmospheric pressure is 10.8 kPa and the temperature is -79 °C. Recall the volume of a sphere equals (4/3)pr 3 and that one liter is 1 dm3. What is the volume and the diameter?