Y. L. Yung, R. L. ShiaY. L. Yung, R. L. ShiaDivisions of Geological and Planetary Sciecnes, California Institute of TechnologyDivisions of Geological and Planetary Sciecnes, California Institute of Technology

Mao-Chang LiangMao-Chang LiangResearch Center for Environmental Changes, Academia SinicaResearch Center for Environmental Changes, Academia Sinica

Improved Nitrous Oxide Budget from Analysis of Recent Isotopologue DataImproved Nitrous Oxide Budget from Analysis of Recent Isotopologue Data

ReferencesReferences

IPCC 2007 (AR4); Rahn and Wahlen (2000); Morgan et al. (2004); Roeckmann et al. (2003; 2006); Roeckmann and Levin (2005).

AbstractAbstractWe develop a simple box model for nitrous oxide (N2O) that is based on laboratory kinetics measurements and constrained to reproduce the age of air in the stratosphere from the Caltech/JPL two-dimensional model of the terrestrial atmosphere. We study three types of models. The Baseline Model assumes that the primary sources of N2O are the land, the ocean and agriculture, and the primary sink is destruction in the stratosphere. The Standard Model includes additional N2O sources from rivers, estuaries and coastal zones as well as fossil fuel combustion and industrial processes, as recommended by the assessment of IPCC [2007]. Extended Models explores the consequences of a climate-related acceleration of cross-tropopause air exchange processes that transport N2O from the troposphere to the stratosphere and projections of future concentrations of N2O. The model includes all the commonly studied isotopologues and isotopomers of N2O and can account for most of known observations. These observations include the abundances and trends of the isotopologues and isotopomers of N2O since the Pre-Industrial Era. The data suggest that the negative trends in the isotopic fractionations appear to slow down in recent decades, a result that can be explained by the Standard Model but not the Baseline Model. We also discuss more speculative results on future projections of N2O.

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

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+ AD 3.6 6.5 5.1 5.5

FF+ BB+ RE 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

Table 1. Sources of NTable 1. Sources of N22O from modelsO from models

• 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 uncertainties.

Troposphere

Focean Fland Fanthro

Fsink

Measurements include

1. N2O trend

2. 18O

3. 15N

(1) Ocean source with 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.

Method – A Simple Box ModelMethod – A Simple Box Model

Future WorkFuture Work

ConclusionConclusion

Model Result: NModel Result: N22O Time SeriesO Time Series

ocean

land

2003

1970

1700

FF+BB+RE

Figure 1. Comparison of N2O concentrations from 1700 to the present between the Baseline Model (solid line) and data. Crosses: Machida et al. [1995]. Khalil and Rasmussen [1992]. NOAA/CMDL.

Figure 2. Sources and Sinks for N2O from 1700 to the present. OC = ocean; LD = land; AN = anthropogenic; Total = OC + LD + AN. SK = sink. TD = trend = dN2O/dt. Units are in Tg N yr-1.

Figure 3a. Comparison of specific isotopic change for 15N(N2O) between the Baseline Model (black line), Standard Model (red line) and Extended model (green line) and data (cross ; Bernard et al. 2006) from 1700 to 2003 A.D.

Figure 3b.Comparison of specific isotopic change for 15N(N2O) between the Baseline Model (black line), Standard Model (red line) and Extended model (green line) and data (Roeckmann and Levin 2005) from 1990 to 2002 A.D.

Figure 3c. Same as Figure 3a except for 18O(N2O) Figure 3d. Same as Figure 3b except for 18O(N2O).

Sources of NSources of N22O O (IPCC AR4 vs. Model)(IPCC AR4 vs. Model)

Figure 5: Summary of model results and IPCC recommended values. AG: Agriculture. HE: Human excreta. AD: Atmospheric deposition. FF: Fossil fuel combustion & industrial processes. BB: Biomass and biofuel burning. RE: Rivers, estuaries, coastal zones.

Isotopic composition provides useful constraints for the budget of N2O. The results are consistent with and refines those of IPCC 2007 (AR4) (see Table 1 and Figure 5).

Figure 4. Isotopic signature of the sources of N2O for 18O(N2O) and 15N(N2O) in the model. Cross: Ocean; Asterisk: Land; Triangle: 1700 A.D.; Square: 1970; Circle: 2003. Dot: Combustion + Runoff (see Table.1).

Sources and sinksSources and sinks