Assume that the global average concentration of sulfur dioxide (SO_2) is 1.5 ppb. If globally averaged dry and wet deposition rates for SO_2 are 1.0kg/ha/yr and 5.0kg/ha/yr, respectively, then what is the lifetime of SO_2 due to the combined processes of wet and dry deposition? Assume temperature and pressure are 20*C and 1atm, respectively. Also assume that the volume of the troposphere is 4.25x10^9 km^3.