For some reason, a skier decides to ski from the summit of a mountain near Park City UT (elevation = 9970 ft, T= -10 degrees C, Patm = 623 mmHg) to the base of the mountain (elevation = 6920 ft, T = -5 degrees C, and Patm = 688 mmHg) with a balloon tied to each of her ski poles. If each balloon is filled to a volume of 2.00 L at the summit, what is the volume of each balloon at the base?