Some endurance athletes (such as cyclists and long distance runners) use a hypobaric chamber to enhance their ability to use oxygen. A hypobaric chamber mimics the effect of being at a high altitude, where the amount of oxygen available to the lungs is less than at sea level. A typical hypobaric chamber simulates the environment at an altitude of 9000 ft above sea level, where the air pressure is approximately 7 × 10⁴ Pa. What is the amount of oxygen available at this altitude compared with that at sea level? Express your answer as a fraction (without units).