Nitrous Oxide: Stratospheric Isotopic Nitrous Oxide: Stratospheric Isotopic Composition and Tropospheric Impact Composition and Tropospheric Impact

Y. L. Yung, J. Weibel* and R. L. ShiaDivisions of Geological and Planetary Sciences

California Institute of Technology, CA*Chemistry Department, Shenandoah University,

Winchester, VA

N N+ O-

nitrous oxide

14N14N16O (446) _ 14N15N16O (456) -- N 15N14N16O (546) -- N

14N14N18O (448) --18O(δ15N = ½ [δN + δN])

# Source: natural -- land -- ocean anthropogenic -- agriculture, fossil fuels & industry, biomass burning,… # Sink: (stratosphere) -- photolysis and chemistry (~160-220 nm)

N2O continues to increase in the atmosphere. However, contribution of each source is not well-quantified.

Kim and Craig 1993

Liang and Yung 2007 JGR112(D13): D13307

Source of N2O (IPCC vs. Model)

Natural sources Soils (natural vegetation)

Oceans

Atmospheric chemistry

Anthropogenic sources AG+ HE+ ADa

FF+ BB+ RE b

0 1 2 3 4 5 6 7 8 9 10 (Tg N yr-1)

a. AG: Agriculture. HE: Human excreta. AD: Atmospheric deposition.b.FF: Fossil fuel combustion & industrial processes. BB: Biomass and biofuel burning. RE: Rivers, estuaries, coastal zones.

IPCC2007 AR4 IPCC2007 AR4 range Model result

(1) Ocean source = prescribed isotopic composition. (2) The isotopic composition of anthropogenic source = land source(3) Solve the mean isotopic composition of land for PRE. (4) Magnitude of the natural and anthropogenic sources are deduced. (5) The strength of STE does not vary.(6) The lifetimes do not vary with time.

Troposphere

F_ocean F_land F_anthro.

F_sink

ISI 2008 Liang and Yung, Isotopic Constraints on the Global Budget and Trend of Atmospheric Nitrous Oxide

Available measurements:

1. N2O trend

2. 18O

3. 15N ( and )

x: Machida et al. [1995] +: Bernard et al. [2006]

x: Sower et al. [2002]

Time evolution of δ18O(N2O) and δ15N (N2O)

Sources and sinks

OC -- oceanLD -- landAN -- anthropogenicTotal = OC+LD+ANSK -- sinkTD -- trend

ocean

land

2003

19701700

FF+BB+RE

Secular changes

= [(t1) - (t2)] / [N2O(t1) - N2O(t2)]

1700-2003 A.D.Bernard et a 2006

1970-2003 A.D.Bernard et al. 2006

1990-2003 A.D.Rockmann and Levin 2005

Models

Source of N2O (in Tg N year-1) †

AR4 Baseline Model Standard Model Extended Model (E1)

Natural sources Soils under natural vegetation 6.6 5.2 5.2 5.2 Oceans 3.8 5 5 5 Atmospheric chemistry 0.6 0 0 0 Natural total 11 10.2 10.2 10.2 Anthropogenic sources

AG+ HE+ ADa 3.6 6.5 5.1 5.5

FF+ BB+ RE b 3.1 0 1.4 3.2 Anthropogenic total 6.7 6.5 6.5 8.7 Total sources 17.7 16.7 16.7 18.9

• Use the Caltech/JPL 2-D and MOZART/CAM-CHEM 3-D models for better estimates.

Better measurements are needed as present data have large errors.

Source of N2O (IPCC vs. Model)

Natural sources Soils (natural vegetation)

Oceans

Atmospheric chemistry

Anthropogenic sources AG+ HE+ ADa

FF+ BB+ RE b

0 1 2 3 4 5 6 7 8 9 10 (Tg N yr-1)

a. AG: Agriculture. HE: Human excreta. AD: Atmospheric deposition.b.FF: Fossil fuel combustion & industrial processes. BB: Biomass and biofuel burning. RE: Rivers, estuaries, coastal zones.

IPCC2007 AR4 IPCC2007 AR4 range Model result