Connecting Climate and Air Quality: The Contribution of Methane to Hemispheric Ozone Pollution

Transcription

1 Connecting Climate and Air Quality: The Contribution of Methane to Hemispheric Ozone Pollution Arlene M. Fiore Acknowledgments: Larry Horowitz, Chip Levy (NOAA/GFDL) Jason West, Vaishali Naik (Princeton University) Ellen Baum, Joe Chaisson (Clean Air Task Force) Frank Dentener, Kees Cuvelier (JRC, Italy) The TF HTAP Modeling Team Funding from Luce Foundation via Clean Air Task Force Center for Atmosphere Ocean Science, New York University March 28, 2007

2 The U.S. ozone smog problem is spatially widespread, affecting >100 million people Nonattainment Areas ( data) 4 th highest daily max 8-hr mean O 3 > 84 ppbv U.S. EPA, 2006

3 Radiative forcing of climate (1750 to present): Important contributions from methane and ozone IPCC, 2007

4 Air quality-climate Linkage: CH 4, O 3 are greenhouse gases CH 4 contributes to background O 3 in surface air Stratospheric O 3 Stratosphere ~12 km hν O 3 Free Troposphere NO 2 NO Hemispheric Pollution OH HO 2 VOC, CH 4, CO NO x VOC O 3 Direct Intercontinental Transport air pollution (smog) NO x VOC Boundary layer (0-3 km) air pollution (smog) O 3 CONTINENT 1 OCEAN CONTINENT 2

5 IPCC [2001] scenarios project future growth Projections of future CH 4 emissions (Tg CH 4 ) to 2100 Change in 10-model mean surface O SRES A Attributed mainly to increases in methane and NO x [Prather et al., 2003]

6 Rising background O 3 has implications for attaining air quality standards Recent observational analyses suggest that surface O 3 background is rising [e.g. Lin et al., 2000; Jaffe et al., 2003, 2005; Vingarzan, 2004; EMEP/CCC-Report 1/2005 ] Pre-industrial background Europe seasonal WHO/Europe 8-hr average U.S. 8-hr average Current background Future background? O 3 (ppbv)

7 Methane (and CO) emission control is an effective way of simultaneously meeting air quality standards and abating global warming --- EMEP/CCC-Report 1/2005 Ozone abatement strategies evolve as our understanding of the ozone problem advances O 3 smog recognized as an URBAN problem: Los Angeles, Haagen-Smit identifies chemical mechanism Smog as REGIONAL problem; role of NO x and biogenic VOCs recognized A GLOBAL perspective: role of intercontinental transport, background 1950s 1980s Present Abatement Strategy: NMVOCs + NO x + CH 4??

8 Double dividend of Methane Controls: Decreased greenhouse warming and improved air quality Radiative Forcing* (W m -2 ) 50% anth. VOC 50% anth. CH 4 50% anth. NO x 2030 A B % (base) anth. VOC GEOS-Chem Model (4 x5 ) Number of U.S. summer gridsquare days with O 3 > 80 ppbv 50% 50% 2030 anth. anth. A1 CH 4 NO x 2030 B1 IPCC scenario Anthrop. NO x emissions (2030 vs. present) Global U.S. Methane emissions (2030 vs. present) A1 +80% -20% +30% B1-5% -50% +12% CH 4 links air quality & climate via background O 3 Fiore et al., GRL, 2002

9 Impacts of O 3 precursor reductions on U.S. summer afternoon surface O 3 frequency distributions GEOS-Chem Model Simulations (4 x5 ) NO x controls strongly decrease the highest O 3 (regional pollution episodes) CH 4 controls affect the entire O 3 distribution similarly (background) Results add linearly when both methane and NO x are reduced Fiore et al., 2002; West & Fiore, ES&T, 2005

10 Methane trends and linkages with chemistry, climate, and ozone pollution 1) Climate and air quality benefits from CH 4 controls Characterize the ozone response to CH 4 control Incorporate methane controls into a future emission scenario 2) Recent methane trends (1990 to 2004) Are emission inventories consistent with observed CH 4 trends? Role of changing sources vs. sinks? Research Tool: MOZART-2 Global Chemical Transport Model [Horowitz et al., 2003] NCEP, 1.9 x1.9, 28 vertical levels Fully represent methane-oh relationship Test directly with observations 3D model structure

11 More than half of global methane emissions are influenced by human activities ~300 Tg CH 4 yr -1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005] ~200 Tg CH 4 yr -1 Biogenic sources [Wang et al., 2004] >25% uncertainty in total emissions Clathrates? Melting permafrost? PLANTS? Keppler et al., Sanderson et al., Kirschbaum et al., Ferretti et al., 2006 GLOBAL METHANE SOURCES (Tg CH 4 yr -1 ) WETLANDS 180 BIOMASS BURNING + BIOFUEL 30 TERMITES 20 RICE 40 ANIMALS 90 COAL 30 LANDFILLS + WASTEWATER 50 GAS + OIL 60

12 Characterizing the methane-ozone relationship with idealized model simulations Reduce global anthropogenic CH 4 emissions by 30% 0 0 Surface Methane Abundance (ppb) Tropospheric O 3 Burden (Tg) Simulation Year -12 Model approaches a new steady-state after 30 years of simulation Is the O 3 response sensitive to the location of CH 4 emission controls?

13 Change in July surface O 3 from 30% decrease in anthropogenic CH 4 emissions Globally uniform emission reduction Emission reduction in Asia Percentage Difference: Asia uniform Asia Enhanced effect in source region <10% other NH source regions < 5% rest of NH <1% most of SH Target cheapest controls worldwide

14 Decrease in summertime U.S. surface ozone from 30% reductions in anthrop. CH 4 emissions MAXIMUM DIFFERENCE (Composite max daily afternoon mean ozone JJA) NO ASIAN ANTH. CH 4 Largest decreases in NO x -saturated regions

15 Tropospheric O 3 responds approximately linearly to anthropogenic CH 4 emission changes across models X MOZART-2 [West et al., PNAS 2006; this work] TM3 [Dentener et al., ACP, 2005] GISS [Shindell et al., GRL, 2005] GEOS-CHEM [Fiore et al., GRL, 2002] IPCC TAR [Prather et al., 2001] Anthropogenic CH 4 contributes ~50 Tg (~15%) to tropospheric O 3 burden ~5 ppbv to global surface O 3

16 Multi-model study shows similar surface ozone decreases over NH continents when global methane is reduced ANNUAL MEAN OZONE DECREASE FROM 20% DECREASE IN GLOBAL METHANE 2 ppbv Full range of 12 individual models 0 EUROPE N. AMER. NA S. SA ASIA E. EA ASIA Receptor region >1 ppbv O 3 decrease over all NH receptor regions Consistent with prior studies TF HTAP 2007 Interim report draft available at

17 How much methane can be reduced? Ozone reduction (ppb) Cost-saving reductions 0.7 North America Rest of Annex I Rest of World (industrialized nations) <$10 / ton CO 2 eq. 1.4 All identified reductions 10% of anth. emissions 20% of anth. emissions Methane reduction potential (Mton CH CH 4 yr -1 ) 4 yr -1 ) IEA [2003] for 5 industrial sectors Comparison: Clean Air Interstate Rule (proposed NO x control) reduces 0.86 ppb over the eastern US, at $0.88 billion yr West & Fiore, ES&T, 2005

18 Will methane emissions increase in the future? Anthropogenic CH 4 emissions (Tg yr -1 ) Dentener et al., ACP, 2005 A2 B2 MFR Current Legislation (CLE) Scenario PHOTOCOMP for IPCC AR-4 used CLE, MFR, A2 scenarios for all O 3 precursors [Dentener et al., 2006ab; Stevenson et al., 2006; van Noije et al., 2006; Shindell et al., 2006] Our approach: use CLE as a baseline scenario & apply methane controls

19 Emission Trajectories in Future Scenarios (2005 to 2030) Anthropogenic CH 4 Emissions (Tg yr -1 ) Surface NO x Emissions 2030:2005 ratio CLE Baseline A B C Control scenarios reduce 2030 CH 4 emissions relative to CLE by: A) -75 Tg (18%) cost-effective now B) -125 Tg (29%) possible with current technologies C) -180 Tg (42%) requires new technologies Additional 2030 simulation where CH 4 = 700 ppbv ( zero-out anthrop. CH 4 )

20 Reducing tropospheric ozone via methane controls decreases radiative forcing ( ) Net Forcing (W m -2 ) OZONE METHANE CLE A B C CH 4 =700 ppb Methane Control Scenario More aggressive CH 4 control scenarios offset baseline CLE forcing

21 Future air quality improvements from CH 4 emission controls CLE2005 CLE2030 A2030 B2030 C2030 CH4_700 Percentage of model grid-cell days where surface ozone > 70 ppbv USA DJF MAM JJA SON Europe DJF MAM JJA SON Controls on global CH 4 reduce incidence of O 3 > 70 ppbv Cost-effective controls prevent increased occurrence of O 3 > 70 ppbv in 2030 relative to European high-o 3 events under CLE emissions scenario show stronger sensitivity to CH 4 than in USA

22 Summary: Connecting climate and air quality via O 3 & CH 4 Cost-saving reductions <$10 / ton CO 2 eq. All identified reductions Tg yr -1 North America Rest of Annex I Rest of World Methane reduction potential (Mton CH 4 yr -1 ) Anthrop. CH 4 emissions CLE A B C CLIMATE AND AIR QUALITY BENEFITS FROM CH 4 CONTROL Independent of reduction location (but depends on NO x ) Target cheapest controls worldwide Robust response over NH continents across models ~1 ppbv surface O 3 for a 20% decrease in anthrop. CH 4 Complementary to NO x, NMVOC controls Decreases hemispheric background O 3 Opportunity for international air quality management How well do we understand recent trends in atmospheric methane? How will future changes in emissions interact with a changing climate?

23 Can the model capture the observed trend (and be used for attribution)? Observed trend in surface CH 4 (ppb) Global Mean CH 4 (ppb) NOAA GMD Network Hypotheses for leveling off discussed in the literature: 1. Approach to steady-state 2. Source Changes Anthropogenic Wetlands/plants (Biomass burning) 3. (Transport) Data from 42 GMD stations with 8-yr minimum record is area-weighted, after averaging in bands 60-90N, 30-60N, 0-30N, 0-30S, 30-90S 4. Sink (CH 4 +OH) Humidity Temperature OH precursor emissions overhead O 3 columns

24 Bias and correlation vs. observed surface CH 4 : BASE simulation EDGAR 2.0 emissions held constant Global Mean Surface Methane (ppb) OBSERVED MOZART-2 Mean Bias (ppb) Overestimates interhemispheric gradient Overestimates but matches trend Captures flattening post but underestimates abundance r 2 Correlates poorly at high N latitudes S Latitude N

25 Estimates for changing methane sources in the 1990s Tg CH 4 yr -1 Biogenic Wastewater Biomass Burning Landfills Ruminants Energy Rice Biogenic adjusted to maintain constant total source v v v v3.2 BASE ANTH EDGAR anthropogenic inventory Inter-annually varying wetland emissions from Wang et al. [2004] (Tg CH 4 yr -1 ); different distribution ANTH + BIO Apply climatological mean (224 Tg yr -1 ) post-1998

26 Bias & Correlation vs. GMD CH4 observations: Global Mean Surface Methane (ppb) OBS BASE ANTH ANTH+BIO Mean Bias (ppb) ANTH+BIO simulation with timevarying EDGAR wetland emissions improves: Global mean surface conc. Interhemispheric gradient Correlation at high N latitudes r 2 Fiore et al., GRL, 2006 S Latitude N

27 How does meteorology influence methane abundances? Why does BASE run with constant emissions level off post-1998? Examine sink τ = [CH 4] k[oh][ch 4 ] CH 4 Lifetime (τ) against Tropospheric OH τ Temperature (88% of CH 4 loss is below 500 hpa ) Humidity Photolysis Lightning NO x τ = 0.17 yr = 1.6%) What drives the change in methane lifetime in the model?

28 Small increases in temperature and OH shorten the methane lifetime against tropospheric OH Deconstruct τ (-0.17 years) from to into individual contributions by varying OH and temperature separately τ OH + = Global Lightning NO x (TgN yr -1 ) 0 T(+0.3K) OH(+1.2%) BASE climt climoh BASE 3 LNOx (TgN/y) Year An increase in lightning NO x drives the OH increase in the model But lightning NO x is highly parameterized how robust is this result?

29 Additional evidence for a global lightning NO x increase? Estimate lightning NO x changes using options available in the GFDL Atmospheric General Circulation Model: Convection schemes (RAS vs. Donner-deep) Meteorology (free-running vs. nudged to NCEP reanalysis) Lightning NO x % change (91-95 to 00-04) 20% MOZART RAS Donner 18% 16% 14% More physically-based lightning NO x scheme [Petersen et al., 2005] Evidence from observations? % change 12% 10% 8% 6% LIS/OTD Flash counts 4% 2% 0% NCEP(nudged) Lightning NO x increase robust; magnitude depends on meteorology c/o L.W. Horowitz free-running GCM Magnetic field variations in the lower ELF range [e.g. Williams, 1992; Füllekrug and Fraser- Smith, 1997; Price, 2000] Negev Desert Station, Israel

30 Summary: Connecting climate and air quality via O 3 & CH 4 Cost-saving reductions <$10 / ton CO 2 eq. All identified reductions Tg yr Methane (ppb) τ OH to = North America Rest of Annex I Rest of World Methane reduction potential (Mton CH 4 yr -1 ) Anthrop. CH 4 emissions CLE A B C OBS BASE ANTH ANTH+BIO climt T climoh OH BASE BASE CLIMATE AND AIR QUALITY BENEFITS FROM CH 4 CONTROL Independent of reduction location (but depends on NO x ) Target cheapest controls worldwide Robust response over NH continents across models ~1 ppbv surface O 3 for a 20% decrease in anthrop. CH 4 Complementary to NO x, NMVOC controls Decreases hemispheric background O 3 Opportunity for international air quality management METHANE TRENDS FROM 1990 TO 2004 Simulation with time-varying emissions and meteorology best captures observed CH 4 distribution Model trend driven by increasing T, OH Trends in global lightning activity? Potential for climate feedbacks (on sources and sinks)