1. A. R. Ravishankara, John S. Daniel, Robert W. Portmann (2009)
Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
A. R. Ravishankara, John S. Daniel, Robert W. Portmann (2009)

2. ODS: ozone-depleting substances ODP: ozone depletion potential
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
Abbreviations:
ODS: ozone-depleting substances
ODP: ozone depletion potential
GWP: 100-year global warming potential
Similarities between CFCs and N2O:
both are very stable in the troposphere, where they are emitted
both are transported to the stratosphere, where they release active chemicals destroying ozone
both have substantial anthropogenic sources, but N2O also has natural sources in addition
↔ despite this similarities, N2O remains unregulated by the Montreal Protocol
N2O’s reactions in the stratosphere:
90%
4.4%
5.6%
N2O + hv  N2 + O
N2O + O(1D)
N2 + O2
2NO

3. ODPX = mCFC−11 ∙ ∆μCFC−11 ∙ τX ∙ ∆O3 X mX ∙ ∆μX ∙ τCFC−11∙ ∆O3 CFC−11
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
NO catalytically destroys Ozone as shown by Crutzen and Johnston:
NO + O3  NO2 + O2
O + NO2  NO + O2
O + O3  2 O2
The paper’s authors quantify the ozone destruction of N2O by determing the ODP for N2O:
ODPX = mCFC−11 ∙ ∆μCFC−11 ∙ τX ∙ ∆O3 X mX ∙ ∆μX ∙ τCFC−11∙ ∆O3 CFC−11
m: molecular weight of the ODS
Δμ: change in the mixing ratio boundary condition
τ: atmospheric lifetime
ΔO3: change in globally averaged column ozone computed by the model

4. Comparison of different ODPs: Factors that influence N2O‘s ODP:
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
Comparison of different ODPs:
Factors that influence N2O‘s ODP:
N2O contribute most to depletion where ozone concentrations are the largest
Conversion rate of N2O to NOX
levels of odd hydrogen, bromine and methan
stratospheric volcanic sulfate aerosols decrease the ODP by sequestering NOX to HNO3
Cly – concentrations due to the formation of ClONO2 and conversion of ClO to Cl by NO
ODPCFCl = 1
ODPHCF-225cb = 0.033
regulated by the
Montreal Protocol
ODPHCF-225ca = 0.025
ODPHCF = 0.022
ODPHCF = 0.020
ODPN2O = 0.017

5. Comparison of ODP-weighted N2O emissions with other ODS
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
Comparison of ODP-weighted N2O emissions with other ODS
Anthropogenic emissions of 10 million tons N2O per year make up for its smaller ODP
The emissions of all CFCs together in 1987 were around one ton per year.
The uncertainties come from uncertainties in the emission estimates, not from the ODP
anthropogenic N2O emissions are the single most important of the anthropogenic ODS emissions today

6. Looking into the future
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
Looking into the future
In any case N2O emissions are unlikely to be lower than they are today
For all scenarios, N2O is expected to remain the largest ODS emission throughout the rest of this century.
The authors regard the regulation of N2O as largest option for protection of the ozone layer
N2O is important for both the future ozone layer and climate
→ „Limiting future emissions would enhance the recovery
of the ozone layer from its depleted state and would also
reduce the anthropogenic forcing of the climate system,
representing a win-win for both ozone and climate.“

7. ODPX = mCFC−11 ∙ ∆μCFC−11 ∙ τX ∙ ∆O3 X mX ∙ ∆μX∙ τCFC−11∙ ∆O3 CFC−11
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
Follow-up papers and how ODPN2O might change
ODPX = mCFC−11 ∙ ∆μCFC−11 ∙ τX ∙ ∆O3 X mX ∙ ∆μX∙ τCFC−11∙ ∆O3 CFC−11
Ravell et al. (2015): The changing ozone depletion potential of N2O in a future climate
GHG
Tstr
cat. NOx - cylcle
Brewer-Dobson circ.
time
N2O -> NOx
N2Ostr
UVstr
N2O
CH4
HOx
NO2
Cly
ClO
OH + NO2 + M  HNO3 + M
ClO + NO2 + M  ClONO2 + M

8. Follow-up papers and how ODPN2O might change
Ravishankara et al. (2009): Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
Follow-up papers and how ODPN2O might change
Ravishankara et al. (2009): now: : % calculating with 1959 Cly concentrations;
Flemming et al. (2011): now: : % one medium WMO scenario; 2D-model
Ravell et al. (2015): now: : % % 9 simulations of a medium-high scenario; 3D-model
Ravell et al. (2015) Figure 1