Volcanic eruptions are estimated to add at most 0.44 gigatons of CO2 (1 gigaton = 1 billion metric tons) to the earth's atmosphere annually. If all 0.44 gigatons of CO2 remain in the atmosphere and spread around the atmosphere evenly, what concentration in ppm would it constitute? The effective volume of the earth's atmosphere is about 4.2 billion km^3, and take the average pressure to be 550 mm Hg and the average temperature to be -10 degrees C. The molar mass of air is 29 g/mol.