OsloCTM2  3D global chemical transport model  Standard tropospheric chemistry/stratospheric chemistry or both. Gas phase chemistry + essential heteorogenous reactions  Modules optional to include. -Carbonaceous aerosols -Sea salt -Mineral dust -Nitrate aerosols -Organic aerosols from VOCs Ongoing work on integration of these module with gas phase chemistry.

Coarse grid Standard grid High resolution Figures made by M. Gauss 2006

19 or 40 layers 60 layers

CTM studies of changes in hydroxyl distribution and its impact on methane and Stig B. Dalsøren and Ivar S. A. Isaksen, Department of geosciences, University of Oslo, Norway

CTM studies, effect of surface emission changes  Tropospheric version, 12 years continuous run  Model resoloution: T42 ( 2.8° x 2.8°), 40 vertical layers up to 10 hpa.  Year 2000 meteorology from ECMWF IFS model.  53 chemical species. 102 gas phase reactions, 2 aeorosol reactions.  POET: Monthly averaged methane concentration based on surface observations set in lowest model layer.  Emissions of CO, NOx, NMVOCs from POET project. - Anthropogenic: Interannual variation - Biomass burning, natural month to month variation

Have anthropogenic emissions of CO, NOx, hydrocarbons changed the oxidizing capacity of the atmosphere? ….. NO   increase in OH CO   decrease in OH troposphere OH HO 2 h, H 2 O NO O3O3 CO, hydrocarbons

OH

General increase in global averaged OHGeneral increase in global averaged OH OH reduced in years with much biomass burning. Biomass burning, inefficient combustion → high CO/NOx emission ratio → reduce global averaged OH (Dalsøren 2001)OH reduced in years with much biomass burning. Biomass burning, inefficient combustion → high CO/NOx emission ratio → reduce global averaged OH (Dalsøren 2001) Could OH be predicted from simple linear relation ?:Could OH be predicted from simple linear relation ?:

What about regional changes? Can a simple realtion be found on regional scales? For a more detailed regional discussion see Dalsøren and Isaksen 2006 (under reveiw GRL) Numb er RegionChange CO emissions % energy, industry,transp ort Change NO x emissions % energy, industry,transp ort OH change %/yr CH4 loss (k x OH x CH4) change %/yr Correaltion coefficient r 1Northern America Latin America Southern America Northern Europe <0 5Southern Europe + Mediterranean Northern Africa Southern Africa <0 8Middle East <0 9Southeast Asia + islands Australia <0 Global

Sensitivity study southeast Asia Motivation:  Methane loss particularly sensitive to abundance and changes of OH at low latitudes.  The Middle East and Southeastern Asia contribute almost 20 % (2.8 % and 15.9 % respectively) to the total loss in  What would be the effects of an expected continuing emission increase in these regions with a shift towards a lower CO/NOx emission ratio, representative of fossil fuel combustion sources. Setup: 2001 emissions unchanged except the anthropogenic emission of CO and NOx in Southeast Asia which were allowed to increase by the same relative amount as in the period (14.83% and 61.31% respectively (previous table). Major findings:  OH concentration in Southeast Asia % and the methane loss in the region %.  Global changes: 0.84 % for OH and 1.33% for methane loss. Southeast Asia’s contributionl global methane loss ~ +1 %.

Summary impact on methane global averages  Trend methane: %/ yr, slowdown recent years.  Trend methane loss (k x OH x CH 4 ) : % / yr  Trend methane loss ”due to OH” (k x OH) : 0.16 % /yr. - Sensitive to temperature, i.e. changes in tropical regions. and changes in OH near surface and changes in OH near surface Trend OH surface = %/yr OH troposphere = % / yr  1/3 of increase in methane loss due to OH changes from emissions affecting species in the troposphere. 2/3 of increase in methane loss due to increases in methane itself

Conclusions   Emission changes in the period caused a global average increase in OH of 0.08 %/yr. The global increase in OH is driven by changes in the Northern Hemisphere. Deviations from the trend were found in years with much biomass burning.   A simple statistically significant linear relation for global OH with the CO/NOx emission ratio was found.   Large regional differences in emission trends and different lifetimes of decisive components result in regional differences in OH changes. The OH abundance within a region is not only dependent on the in-situ emissions but also long range transport of CO, NOx-reservoirs and ozone from other regions. The regions where we found a linear relation were characterized by relative large emissions and not so much influence from transboundary pollutant transport and nonlinear chemistry. The CO/NOx emission ratios in regions where linear relations with CO/NOx emis ratio were found span a certain but quite wide range of Tg(CO)/Tg(N).   Global averaged methane loss increases with 0.5%/yr. 2/3 is explained by the increase in methane and that 1/3 is due to enhancing OH levels related to changed emissions of CO, NOx and NMVOCs.   Even if it is not a straightforward task, anthropogenic emissions are one of the factors influencing the OH budget that is possible to control. Even over the time frame of a decade emission changes and regulations have significant effects on the OH and methane budget, both globally and regionally. We believe that our findings have further policy implications as the derived relation of OH with the CO/NOx emission ratio in some regions could be used as a predicator of OH changes due to emission changes and measures taking place in the coming decade.