The impacts of ozone precursor emissions on radiative forcing and background ozone Frank Raes, Frank Dentener IES, Joint Research Centre of the European Commission, Ispra, Italy

Methane and tropospheric ozone SOME FACTS CH 4 is emitted into the atmosphere and is removed by oxidation into CO and CO 2 O 3 is produced in the atmosphere from precursor gases like CH 4, NMVOC, NO X CH 4 and CO contribute to hemispheric background O 3 (~35 ppb) Recent studies find O 3 health effects at current background levels CH 4 produces the 2 nd largest radiative forcing O 3 produces the 3 rd largest radiative forcing

Tropospheric ozone and methane QUESTIONS ADRESSED CH 4 emission controls aim at reducing radiative forcing. What is their potential for reducing background O 3 ? –Effect of CC policy on conventional AQ NO x and NMVOC emisison controls aim at reducing O 3. What is their potential for reducing radiative forcing? –Effect of AQ policy on CC

Approach Global emission projections up to 2030 with GAINS model For CH 4, CO, NO x, NMVOC Four scenarios –“Current legislation”: baseline –“Maximum feasible” NOx and NMVOC reductions (AQ) –“Maximum feasible” CH4 reduction (CC) –“Maximum feasible” CH4, NOx and NMVOC reductions (combined) Compute impact of scenario’s on –Background tropospheric ozone concentrations –Methane concentrations –Radiative forcing by O3 aand CH4 With –TM3 (JRC Ispra) –STOCHEM (UK Met.Office)

EuropeNorth America Asia + OceaniaLatin America Africa + Middle EastMaximum Feasible Reduction (MFR) SRES A2 - World TotalSRES B2 - World Total COCH 4 Global emission projections CH 4 and CO [Mt/yr]

Europe Asia + Oceania Africa + Middle East North America Latin America Maximum Feasible Reduction (MFR) Source: M.Walsh, 2002 Global emission projection NO x [Mt/yr] NO x

___ Baseline ___ Max NO x +NMVOC reduction ___ Max CH 4 reduction ___ Max CH 4 +NO x +NMVOC reduction Global emission scenarios: Global emission scenarios developed by IIASA/RAINS, TM3 calculations by JRC-IES Impacts of CH 4 and NO x /VOC controls on ozone and CH 4 burden

Changes in background ozone between baseline 2020 and MFR of CH 4 +NO x +NMVOC Global emission scenarios developed by IIASA/RAINS, TM3 calculations by JRC-IES  O3 (ppb)

Change in global mean radiative forcing [W/m 2 ] The red error bars indicate the uncertainty ranges identified in IPCC TAR Baseline MFR CH4 MFR NOx+NMVOC MFR CH4+NOx+NMVOC Radiative forcing from CH4O3Total CH4+O3 CH4 O3 CH4 + O3

Conclusions Ozone precursor emissions influence background ozone and radiative forcing Baseline scenario (CLE) leads to an increase in both hemispheric ozone (+5 ppb) and O3+CH4 radiative forcing (+0.2 W/m 2 ) in next 30 years NO x and NMVOC controls would decrease ozone, but increase the lifetime of methane: effects on radiative forcing cancel out Max CH4, NO x and NMVOC controls would reduce both hemispheric ozone (- 9 ppb) and O3+CH4 radiative forcing (  0.3 W/m 2 ) compared to the baseline.