# Presentation: 324912

## A21E-0863 Connecting Climate and Air Quality: Tropospheric Ozone Response to Methane Emission Controls

**A21E-0863 Connecting Climate and Air Quality: Tropospheric Ozone Response to Methane Emission Controls**

**Arlene M. Fiore****1 ****(arlene.fiore@noaa.gov), Larry W. Horowitz****1****, J. Jason West****2**
** ****1****NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ    ****2****Atmospheric and Oceanic Sciences Program and Woodrow Wilson School, Princeton University, Princeton, NJ**

** ****Methane source location has little influence on the surface (or tropospheric) O****3**** distribution**
**(<10% globally except for localized effect in Asian source region) **
** ****Larger ozone response in downwelling regions and locations with NO****x****-saturated chemistry**
** ****Largest % decreases occur in lower troposphere (due to T dependent k****OH-CH4****)**

** ****Characterize the O****3**** response to CH****4 ****control**
** ****Quantify the climate and air quality benefits from CH****4**** controls**
** ****Evaluate CH****4**** controls in future emission scenarios where emissions of other O****3 ****precursors are also changing**** **

**1. Introduction **

- Methane (CH4) oxidation in the presence of nitrogen oxides (NOx) contributes to tropospheric ozone (O3), raising baseline levels of ozone pollution in surface air globally. Since methane is also a potent greenhouse gas, controls on methane offer a strategy for jointly addressing air pollution and climate goals [*e.g*., *Fiore et al*., 2002; *Dentener et al*., 2005; *West and Fiore*, 2005; *EMEP*, 2005].

**Objectives**

**3. Ozone Response to Methane Controls in Idealized Scenarios**

**Simulations with global anthropogenic CH****4**** emissions decreased by 30%, either: **
**(1) uniformly worldwide, or (2) entirely from Asia**

**2. Transient Methane Simulations with MOZART-2**

** **global 3D model of tropospheric chemistry
-  ~100 gas and aerosol species, ~200 reactions
-  1.9o latitude x 1.9o longitude x 28 vertical levels
-   multi-decadal, full-chemistry simulations
-  **Idealized scenarios**: Emissions representative of early 1990s, as described in *Horowitz et al*. [2003] except for wetland emissions which we increased by 58 Tg yr-1 to match recent estimates; 1990-2004 NCEP meteorology recycled after 15 years
** ****Future scenarios**: Current Legislation Emissions (CLE) 2000 to 2030 [*Dentener et al*., 2005]; biomass burning GFED v.1 [*van der Werf et al*., 2003]; wetland distribution from *Wang et al*. [2004]; 2000-2004 NCEP meteorology recycled every 5 years

**Acknowledgments**
- Funding from Luce Foundation via Clean Air Task Force; Ellen Baum (CATF), Joe Chaisson (CATF), Chip Levy (GFDL), Vaishali Naik (Princeton), and Dan Schwarzkopf (GFDL) for insightful conversations; Frank Dentener (JRC-IES) for providing the baseline CLE emissions.

**References**
- Dentener, F., *et al*. (2005) *Atmos. Chem. Phys. 5*, 1731-1755.
- Fiore, A.M., *et al*. (2002) *Geophys. Res. Lett., 29*, 1919.
- Friedenreich, S.M. and V. Ramaswamy (1999) *J. Geophys. Res., 104*, 31389-31409.
- GFDL GAMDT (2004), *J. Climate, 17*, 4641-4673.

**CLE increases surface CH****4**** by 240 ppbv; tropospheric O****3**** by 15 Tg; surface O****3**** by 1.4 ppbv (2026-30 mean – 2005-9 mean).**
****** ****Scenario C decreases CH****4**** by 540 ppb relative to CLE 2030, by 260 ppb relative to CLE 2005, and roughly stabilizes surface O****3**** despite 5 Tg N yr****-1**** increase in anthropogenic NO****x**** emissions.**

**4. Future Methane Control Scenarios**

**Methane emissions in MOZART-2**

**SPATIAL DISTRIBUTION**

**     ****Anthropogenic CH****4**** contributes:**
**     ****~50 Tg (~15%) to tropospheric**
**        ****O****3**** burden**
**     ****~5 ppbv to surface O****3**

**LINEARITY**

|  | Standard (1990s) | CLE (2005) | CLE (2030) |
| --- | --- | --- | --- |
| Simulations | Idealized | Future |  |
| Anthrop. | 261 | 332 | 428 |
| Biogenic* | 214 | 222 | 222 |
| Biomass Burning | 72 | 23 | 23 |
| Total | 547 | 577 | 673 |

***Biogenic includes wetlands, oceans, and termites**

**5. Conclusions**

**Radiative forcing from**** ****2005 to 2030**

- We calculate CH4 forcing from an analytical expression [*Ramaswamy et al*., 2001] and O3 forcing with the GFDL AM2 radiative transfer model [*Freidenreich and Ramswamy*, 1999; *Schwarzkopf and Ramaswamy*, 1999; *GFDL GAMDT*, 2004]

- Annual Mean Daily Max 8-hr Ozone (ppbv)

**Global anthropogenic CH****4**** emissions decreased uniformly by 30%**

**Simulation (1) - Base**

**TIME SCALE**

**Nearing a new steady-state**
**             ****after 30 years**

- Anthrop. NOx increases
-    by 5.3 Tg N yr-1 (+19%)
- Anthrop. CO decreases
-    by 44 Tg CO yr-1 (-10%)
- Anthrop. NMVOC increase
-   by 3 Tg C yr-1 (+3%)

**EMISSIONS**

** ****GLOBAL ANNUAL MEAN RESULTS **

** ****IMPACTS ON CLIMATE**

** ****IMPACTS ON AIR QUALITY**

- Percentage of model grid box-days where daily max 8-hour O3 exceeds 70 ppbv by season and region

- Change in daily max 8-hour O3 (scenario B – CLE) in the season with max occurrences above 70 ppbv

** ****Spatial pattern of O****3**** response is largely independent of CH****4**** source location, but depends strongly on NO****x**** distribution**
** ****Magnitude of the O****3**** response is approximately linear with reductions in anthropogenic CH****4**** emissions **
**   ****(~0.1 Tg tropospheric O****3**** per Tg yr****-1**** anthropogenic CH****4**** reduced) **
** ****O****3**** decrease from CH****4**** controls is typically maximum near the middle of the total O****3**** distribution, (*****e.g.***** 40-70 ppbv total O****3****), but also extends to the high end of the distribution in NO****x****-saturated conditions (Los Angeles, Houston)**
** **
** ****Future CH****4 ****controls relative to the CLE baseline (scenarios B or C) would offset the projected positive climate forcing and reduce the incidence of high-O****3**** events in all regions, even improving air quality in Europe relative to 2005.**

- CLE 2030 daily max 8-hr average O3 (ppbv)

- Each point represents one daily maximum 8-hour average O3 value in one model grid cell
- from Jun 1 to Aug 31

**Surface O****3**** (ppbv)**

**Tropospheric O****3**** **
**Burden (Tg)**

**Surface NO****x**** emissions **
**2030:2005 ratio**

**Difference: Scenario B 2030 – CLE 2030**

- Increased incidence of
- O3 > 70 ppbv in CLE from 2005 to 2030 occurs in all regions and seasons

**Max CH****4**** impact at ~40-70 ppbv total O****3****, plus some high-O****3**** events**

**Aggressive CH****4**** reductions (scenarios B and C)  offset the positive forcing predicted under the CLE baseline**

- EMEP (2005), EMEP/CCC-Report 1/2005, Norwegian Institute for Air Research, Norway.
- Horowitz, L.W. *et al*. (2003), *J. Geophys. Res., 108*, 4784.
- Prather, M.J. *et al*. (2001) in Climate Change 2001, *ed*. J.T. Houghton *et al*., pp. 239-287, Cambridge University Press.
- Ramaswamy, V. et al. (2001) in Climate Change 2001, *ed*. J.T. Houghton *et al*., pp. 349-416, Cambridge University Press.
- Schwarzkopf, M.D. and V. Ramaswamy (1999) *J. Geophys. Res., 104*, 9467-9488.

- Shindell *et al*. (2005) *Geophys. Res. Lett., 32*, L040803.
- Wang, J.S. *et al.* (2004) *Global Biogeochem. Cycles, 18*, GB3011.
- West and Fiore (2005) *Environ. Sci. Technol, 39*, 4685-4691.
- West *et al*. (2006) *Proc Natl Acad. Sci., 103*, 3988-3993.
- van der Werf, G.R. *et al*. (2003) *Global Change Biol., 9*, 547-562.