The study found that the amount of carbon dioxide in the air in Tokyo has been increasing faster than expected, reaching up to 550 ppm. This increase is linked to higher levels of bicarbonate and pH in the urine of medical students in the city. When students took a car trip with closed windows, the levels of carbon dioxide inside the car reached about 5000 ppm, leading to even higher levels of bicarbonate and pH in their urine. These findings suggest that the rising atmospheric carbon dioxide levels are affecting the health of people in Tokyo.