# Presentation: 489197

## Abating Global Ozone Pollution

**Abating Global Ozone Pollution**
**with **
**Methane Emission Controls**

**EMEP Second Meeting of the Task Force on Hemispheric Transport of Air Pollution**
**Moscow, Russia**
**Arlene M. Fiore **
**J. Jason West**
**Larry W. Horowitz**
**June 7, 2006**

## Radiative Forcing of Climate, 1750-Present:Important Contributions from Methane and Ozone 

**IPCC [2001]**

**Level of scientific understanding**

## Air quality-Climate Linkage:CH4, O3 are important greenhouse gasesCH4 contributes to background O3

**CONTINENT 2 **

**OCEAN**

**Boundary layer**
**     ****(0-3 km)**

**Free Troposphere**

**CONTINENT 1 **

**Air quality-Climate Linkage:****CH****4****, O****3**** are important greenhouse gases****CH****4**** contributes to background O****3**

**O****3**

**Direct Intercontinental Transport**

**Notes:**
Time scale

## Attributed mainly to increases in methane and NOx 

**Change in 10-model mean July surface O****3 **** [*****Prather et al*****., 2003]**

**Attributed mainly to increases in methane and NO****x**** **
**[*****Wang et al*****., 1998; *****Prather et al*****., 2003]**

**Observations indicate historical increase in background ozone; IPCC scenarios project future growth**

**Ozone at European mountain sites 1870-1990  [*****Marenco et al*****., 1994]**

**2100 SRES A2 - 2000**

## Rising background O3 has implications 

**Rising background O****3**** has implications **
**for attaining air quality standards**

**20**

**40**

**60**

**80**

**100**

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

**U.S. 8-hr **
**average**

**Analyses of surface O****3**** from North American and European monitoring sites indicate increasing background in recent years**
**[*****Lin et al*****., 2000; *****Jaffe et al*****., 2003, 2005; *****Vingarzan*****, 2004; *****EMEP/CCC-Report 1/2005 *****]**

**Europe**
**seasonal**

**WHO/Europe**
**8-hr average**

**new CA**
**standard**
**8-hr avg**

##  Impacts of O3 precursor reductions on global surface O3 

**Steady-state change in 8-hr daily maximum surface O****3**** **
**averaged over 3-month “O****3**** season”**
**from 20% reductions in global anthropogenic emissions**

**NO*****x***

**NMVOC**

**CO**

**CH****4**

*West et al., submitted*

**MOZART-2 model (2.8° x 2.8°)**

**Notes:**
Time Scale

## Double dividend of methane controls:

**Double dividend of methane controls:**
** ****Improved air quality and reduced greenhouse warming**

** ****Abating O****3**** with CH****4**** controls yields largest climate benefit**

**AIR QUALITY: **
**Change in population-weighted **
**mean 8-hr daily max surface O****3**** **
**in 3-month “O****3**** season” (ppbv)**

**Steady-state results from MOZART-2**

**Notes:**
Per ppb o3 change CH4 best for climate ; Time Scale

## Impacts of O3 Precursor Reductions on 

**Impacts of O****3 ****Precursor Reductions on **
**U.S. Summer Afternoon Surface O****3**** Frequency Distributions**

*West & Fiore, ES&T, 2005*

**GEOS-Chem Model Simulations (4°x5°)**

## Contributions from precursor emissions to the tropospheric O3 burden also add linearly

**Contributions from precursor emissions to the tropospheric O****3 ****burden also add linearly**

**Decrease in global tropospheric O****3**** inventory (Tg)**
**in GEOS-Chem model (4°x5°)**
**from 50% global reductions in anthropogenic emissions**

** ****Anthropogenic emissions of NO****x ****and methane have the largest**
**impact on tropospheric O****3**

*Fiore et al., GRL, 2002*

**NO****x**

** ****CH****4**

**VOC**

**CO**

**NO****x**
**+**
**VOC**

**ALL**

**Notes:**
Ch4: 27, NOx: 21, CO, VOC, 4 each; NOX+VOC = 24; ALL = 52  ;linearity also shown in GISS model with 100% reductions [Shindell 2005]

## Global observations of atmospheric CH4 

*Frankenberg et al., Science, 2005*

**SCIAMACHY**

**Column-averaged CH****4**** **
**volume mixing ratio**
**(Aug-Nov 2003) **

**NOAA/GMD cooperative **
**network of background **
**sampling sites (1983-present)**
*e.g.* *Dlugokencky et al., 2005*

-  **Space-based observations may provide new constraints on the CH****4**** budget**

## Estimates of current CH4 emissions 

***c/o Michael Raupach, CSIRO, Australia; studies cited in IPCC TAR, AR-4***

**Estimates of current CH****4**** emissions**

**Methane sink (OH) also ~30% uncertain [*****Stevenson et al*****., 2006]**

**Total CH****4**** source ~600 Tg yr****-1****, ~60% anthropogenic [*****IPCC TAR*****]****>25% uncertainty in present-day CH****4**** sources**

**anthropogenic**

**Notes:**
Uncertainties from Prinn?

## Emission estimates for the past decade are fairly consistent with surface CH4 observations

**BASE**** (****constant emissions****):**
**captures observed rise, **
**    ****then flattening**
**meteorologically-driven **
**    ****(OH & T)**

**Emission estimates for the past decade are fairly consistent with surface CH****4 ****observations**

*Fiore et al., GRL, in press*

**OBS[*****NOAA/GMD*****]**
**BASE**
**VARY**

**VARY**** ****(****increasing EDGAR 3.2 + time-varying wetland emissions****)**** ****improves:**
**	******** ****Global mean surface concentration**
**	******** ****Interhemispheric gradient **
**	******** ****High N latitude seasonal cycle**

**Transient, full-chemistry simulations with MOZART-2 (1.9° x 1.9°) **
**driven by 1990-2004 NCEP**

**Notes:**
Global mean in dry air averaged over the msmt sites on previous slide 

## Atmosphere gradually responds to decreases in CH4 emissions  following the CH4 perturbation lifetime (~12 years)

**Does the spatial pattern of the O****3**** decrease depend on CH****4 ****source location?**

**Model approaches new steady-state **
**after 30 years of simulation**

**Change in methane and ozone in MOZART-2 model (1.9° x 1.9°)**
**when global anthrop. CH****4 ****emissions are reduced by 30%**

**Surface Methane Concentration **
**(ppb)**

**Tropospheric Ozone Burden (Tg)**

**Notes:**
92% 

## Change in global July surface O3  mainly independent of CH4 source location

**Zero anth. CH****4**** emis. from Asia **

**30% decrease in global anth. CH****4**** emis.**

**Zero Asia – global 30%**

**Change in global July surface O****3 **** ****mainly independent of CH****4**** source location**

**Results from 11****th**** year of transient simulation beginning in 1990 (met. year 2000)**

** ****Slightly larger response in ****	****source region**
** ****Stronger response in high-NO****x**** ****	****and downwelling regions **

**MOZART-2 model (1.9° x 1.9°)**

## Tropospheric O3 responds approximately linearly to anthropogenic CH4 emission changes across models

**Tropospheric O****3**** responds approximately linearly to anthropogenic CH****4**** emission changes across models**

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

## Will methane continue to increase in the future? 

**Will methane continue to increase in the future? **

*Dentener et al., ACP, 2005*

**Anthropogenic CH****4**** emissions (Tg yr****-1****)**

## Future CH4 controls complement reductions in other O3 precursors

**Future CH****4**** controls complement reductions in other O****3**** precursors**

*Dentener et al., ACP, 2005*

**Change in mean 2020-2030 surface O****3**** in TM3 model (7.5****°**** x 10°) **

**CO,NO****x****,NMVOC controls only**

**+**

** ****O****3**** changes from all precursor reductions add**
**     ****approximately linearly **

**CH****4**** controls only**

**≈**

**O****3**** change from controls on all precursors**

## Anthropogenic CH4 contributes ~5 ppb to surface O3; 
    ~50 Tg to tropospheric burden

O3 responds approximately linearly to CH4 reductions, and to combined changes in CH4 and other precursors
CH4 controls complement NOx and NMVOC controls   

CH4 source location has little influence on O3 production; heterogeneities arise from NOx distribution and transport 
Target cheapest CH4 controls worldwide 

Reducing CH4 emissions decreases surface O3 everywhere and lowers radiative forcing (decadal time scale)
 CH4 controls could offset positive forcing from NOx controls 

**    ****~50 Tg to tropospheric burden**
**O****3**** responds approximately linearly to CH****4**** reductions, and to combined changes in CH****4**** and other precursors**
**CH****4**** controls complement NO****x**** and NMVOC controls   **
**CH****4**** source location has little influence on O****3**** production; heterogeneities arise from NO****x**** distribution and transport **
**Target cheapest CH****4**** controls worldwide**** **
**Reducing CH****4**** emissions decreases surface O****3**** everywhere and lowers radiative forcing (decadal time scale)**
****** ****CH****4**** controls could offset positive forcing from NO****x ****controls **

**Conclusions: Abating O****3**** pollution with CH****4**** controls **

**Remaining challenges:**
** ****Better constraints on emissions, anthropogenic vs. natural **
** ****Role of global change on future atmospheric CH****4**

- Unpublished work funded by NOAA, NASA and Luce Foundation (with CATF)