3. A recent estimate of the prehistoric global rate of denitrification is about 1.61011 kg(N) /year, and about half the N-atoms that are denitrified are in the form of N2O. Thus the inflow of N to the troposphere in the form of N2O from denitrification was 0.81011 kg(N) /year. The concentration of N2O in the troposphere was, prehistorically, about 280 ppb(v) a. Assuming steady state, and that the only input flow of N2O to the troposphere is that of denitrification from the Earth's surface, what was the residence time, in years, of N2O in the troposphere? (15 pts.) b. The N2O concentration in the troposphere is no longer in steady state because agriculture and fossil fuel burning has led to an increase in the flow of N2O to the atmosphere. The inflow of N2O to the atmosphere has now doubled to 1.61011 kg(N)/y. If that inflow rate remains constant into the future, when a new steady state is reached would you expect that your estimate in part a. is an underestimate, an overestimate, or a reasonable estimate, of the eventual new steady-state residence time? Why? Hint: consider the equation dM/dt=abM. (5 pts.)