# Presentation: 464840

## Atmospheric Methane Distribution, Trend, and Linkage with Surface Ozone

**Atmospheric Methane Distribution, Trend, and Linkage with Surface Ozone**

**Arlene M. Fiore****1 ****(arlene.fiore@noaa.gov), Larry W. Horowitz****1****, Ed Dlugokencky****2****, J. Jason West****3**
** ****1****NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ  ****2****NOAA Global Monitoring Division, Earth System Research Laboratory, Boulder, CO  ****3****Atmospheric and Oceanic Sciences Program and Woodrow Wilson School, Princeton University, Princeton, NJ**

**1. Introduction**

**REFERENCES****	**
- Dentener, F., *et al*. (2003), *J. Geophys. Res., 108*, 4442, doi:10.1029/2002JD002916.
- Dlugokencky, E.J., *et al*. (2003), *Geophys. Res. Lett., 30*, 1992, doi:10.1029/2003GL018126.
- Dlugokencky, E.J., *et al*. (2005), *J. Geophys. Res., 110*, D18306, doi:10.1029/2005JD006035.
- Horowitz, L.W., *et al*. (2003), *J. Geophys. Res., 108*, 4784, doi:10.1029/2002JD002853.

**What is driving observed CH****4**** trends? ****	****Does CH****4**** source location influence the O****3**** response?**** **

**Methane (CH****4****) emission controls can be a cost-effective strategy for abating both global surface ozone (O****3****) and greenhouse warming [*****West and Fiore*****, 2005; see also poster by *****West et al*****.]**
**     ******** ****previous modeling studies used fixed CH****4**** concentrations and globally uniform changes,**
**          ****but CH****4**** is observed to vary spatially and temporally **
** **
**The major sink of CH****4**** is reaction with tropospheric OH; emissions of CH****4**** are shown in Section 2**
**Surface CH****4**** rose by ~5-6 ppb yr****-1**** from 1990-1999, then leveled off (Section 3), possibly reflecting: **
**   ****(1) source changes of CH****4**** [*****e.g*****. *****Langenfelds et al*****., 2002; *****Wang et al*****., 2004] or other species that**
**         ****influence OH [*****e.g*****. *****Karlsd******ó******ttir and Isaksen*****, 2000]**
**   ****(2) meteorologically-driven changes in the CH****4**** sink [*****e.g.***** *****Warwick et al*****., 2002; *****Dentener et al*****., 2003; **
**         *****Wang et al*****., 2004]   **
**   ****(3) an approach to steady-state with constant lifetime [*****Dlugokencky et al*****., 2003]**

** ****Ozone response is largely independent of CH****4**** source location**
** ****30% decrease in global anthropogenic CH****4 ****emissions reduces JJA**
**    ****U.S. surface afternoon O****3**** by 1-4 ppbv**
** ****BASE simulation (constant emissions) captures observed rate of   **
**    ****CH****4**** increase from 1990-1997, and leveling off post-1998**
** ****ANTH emissions improve modeled CH****4**** post-1998**
** ****Wetland emissions in ANTH+BIO best match the observed CH****4****  **
**    ****seasonality, interhemispheric gradient, and global mean trend**
** ********CH4**** decreases by ~2% from 91-95 to 00-04 due to warmer    **
**    ****temperatures (35%) and higher OH (65%, resulting from a **
**    ****~10% increase in lightning NO****x ****emissions)**
**Future research should:**
** ****consider climate-driven feedbacks from fire and biogenic emissions on ********CH4**
** ****develop more physically-based parameterizations of lightning NO****x**** emissions to **
**    ****determine whether higher emissions are a robust feature of a warmer climate**

- Van Aardenne, J.A., F. Dentener, J.G.J. Olivier and J.A.H.W. Peters (2005), The EDGAR 3.2 Fast Track 2000 dataset (32FT2000).
- Wang , J.S., et al. (2004), Global Biogeochem. Cycles, 18, GB3011, doi:10.1029/2003GB002180.
- Warwick, N.J., *et al*. (2002), *Geophys. Res. Lett., 29* (20), 1947, doi:10.1029/2002GL015282
- West, J.J. and A.M. Fiore (2005), *Environ. **Sci. & Technol., 39, *4685-4691.

- Karlsdóttir, S., and I.S.A. Isaksen (2000), *Geophys. Res. Lett., 27* (1), 93-96.
- Langenfelds, R.L., et al. (2002), *Global Biogeochem. Cycles, 16*, 1048, doi:10.1029/2001GB001466.
- Olivier, J.G.J., *et al*. (1999), *Environmental Science & Policy, 2*, 241-264.
- Olivier, J.G.J. (2002) In: "CO2 emissions from fuel combustion 1971-2000", 2002 Edition, pp. III.1-III.31. International Energy Agency (IEA), Paris. ISBN 92-64-09794-5.

**3. Influence of Sources on Surface CH****4**** Distribution and Trend**

- Global mean surface CH4 concentrations as measured (or sampled in the model) at 42 Global Monitoring Division (GMD) stations [*e.g.* *Dlugokencky et al*., 2005] with an 8-year minimum record. Values are area-weighted after averaging in latitudinal bands (60-90N, 30-60N, 0-30N, 0-30S, 30-90S).

- Mean model bias and correlation with 1990-2004 monthly mean surface GMD observations

**nmol/mol = ppb in dry air**

**2. Methane in the MOZART-2 CTM**

**BASE**
**Constant emissions (1990)**

**Sensitivity simulations applying different CH****4**** emission inventories:**

**ANTH**** **
**Time-varying anthropogenic emissions**

**ANTH + BIO **
**Time-varying anthropogenic and **
**wetland emissions**

- EDGAR v3.2 1990,1995 and
-  “FAST-TRACK” 2000 anthrop.
-   emissions [*Olivier*, 2002; *van*
*  **Aardenne et al*., 2005]
- Biogenic source adjusted to
-   match BASE 1990 total

**6. Conclusions**

**OBS (GMD)     ****BASE     ****ANTH     ****ANTH+BIO**

**ANTH+BIO ****improves:**
**(1) High N latitude seasonal cycle, (2) Trend, **
**(3) Low bias at S Pole, especially post-1998**

- Surface CH4 concentrations at selected GMD stations

**nmol/mol = ppb in dry air**

**Tropospheric O****3**** response to**
**anthropogenic CH****4**** emission **
**changes is approximately linear**

**5. Ozone Response to CH****4**** Emission Controls **

** ****Stronger sensitivity in NO****x****-saturated regions (Los Angeles), partially due to local O****3**** production from CH****4**
** ****O****3**** change independent of CH****4**** source location except for <10% effects in the Asian source region**

**Latitudinal distribution of 1990 CH****4**** **
**emissions for cases shown below**

**4. Meteorologically-driven Changes in the CH****4**** Lifetime**

****** ****Meteorological drivers for trend **
** ****Not just an approach to steady-state**

**Global mean surface CH****4**** in **
**BASE simulation (constant emissions)**

**CH****4 ****Lifetime Against **
**Tropospheric OH**

** ****Mean annual CH****4**** lifetime shortens**

**Deconstruct ************ from 91-95 to 00-04 into individual contributions by varying T and OH separately**

** ****OH increases in the model by +1.4% due to a     **
**     ****0.3 Tg N yr****-1**** increase in lightning NO****x **

** ****~100 gas and aerosol species, ~200 reactions**
** ****NCEP meteorology 1990-2004**
** ****1.9****o**** latitude x 1.9****o ****longitude x 64 vertical levels**
** ****detailed description in *****Horowitz et al*****. [2003]**

**Simulations of anthropogenic CH****4**** emission reductions (relative to BASE)**

******tropospheric O****3**** (Tg)**

**Year**

****** ****surface CH****4**** (ppb)**

**Change in CH****4**** and O****3**** approaching **
**steady-state after 30 years**** **

**0        4            9          13         17         21          29**