VL-oferUriii xvl-B— / 335 Comparison of Chemical Schemes Used in Photochemical Modelling — Swedish Conditions Karin PleijelJohannaAltenstedt and Yvonne Andersson-Skold DmsmmoH of this document is unlimited Goteborg, October 1996 B 1235 IVL SWEDISH ENVIRONMENTAL RESEARCH INSTITUTE________________ Organisation/Organization RAPPORTSAMMANFATTNING Institute! for Vatten- och Luftvardsforskning Report Summary Adress/Address Projekttitel/Project title Box 47086 Forenklad kemisk modeliering for halter av ozon 402 58 GOTEBORG och PAN i Sverige. Telefonnr/Telephone 031-46 00 80 Anslagsgivare for projektet/Project sponsor Naturvardsverket Rapportforfattare, author Karin Pleijel, Johanna Altenstedt and Yvonne Andersson-Skold Rapportens titel och undertitel/Title and subtitle of the report Comparison of Chemical Schemes Used in Photochemical Modelling - Swedish Conditions Sammanfattning/Summary The compressed chemical description used in three internationally well-known models, i.e. the EMEP, CBM-IV and RADM-II models were set up in a model frame being representative for Swedish conditions. The results from the use of these compressed chemical schemes were compared with the results when an explicit scheme with a high level of detail i.e. the IVL model in the 1995 version, was used in the same model set-up. In addition, a new approach to compressed chemical modelling was presented, based on the Photochemical Ozone Creation Potential (POCP), and the results were compared with the results from the well established compressed schemes. The compressed scheme used in the EMEP model (1993 version), including some minor modifications in order to make the models strictly comparable, was seen to be in good to excellent agreement with the results from the IVL model for most of the studied scenarios. For two-day simulations the CBM-IV scheme also gave results very close to the IVL model. For scenarios describing very NOx limited conditions including high VOC conditions, the POCP and the CBM-IV schemes were in closer agreement with the IVL model results than the EMEP model was. The 50% VOC Swedish emission reduction scenarios gave peak ozone reductions of 3-4 ppb (6-7 %) as simulated by the IVL model for summer conditions. The corresponding PAN reduction was 0.2-0.3 ppb (ca 40%). The 50 % NOx emission reduction gave 5-6 ppb (ca 10%) ozone reductions and 0.1-0.2 (ca 20%) PAN reductions. A combined reduction of 50% VOC and 50% NOx emissions gave 7-9 ppb (ca 15 %) ozone reductions and 0.3-0.4 (45-50%) PAN reductions. Nyckelord samt ev. anknytning till geografiskt omrade, naringsgren eller vattendrag/Keywords Atmosphere, EMEP, CBM-IV, model, ozone, oxidant, PAN, POCP, RADM-II, Sweden Bibliografiska uppgifter/Bibliographic data IVL Rapport B1235 Bestallningsadress for rapporten/Ordering address IVL, Biblioteket, Box 21060, S-100 31 Stockholm, Sweden DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Comparison of Chemical Schemes Used in Photochemical Modelling - Swedish Conditions Karin Pleijel, Johanna Altenstedt and Yvonne Andersson-Skold* * Current address: Melica Miljokonsulter, Fjallgatan 3E, 413 17 Gdteborg IVL Gdteborg, October 1996 B 1235 Abstract The compressed chemical description used in three internationally well-known models, i.e. the EMEP, CBM-IV and RADM-II models were set up in a model frame being representative for Swedish conditions. The results from the use of these compressed chemical schemes were compared with the results from an explicit scheme with a high level of detail i.e. the IVL model in the 1995 version, used in the same model set-up. In addition, a new approach to compressed chemical modelling was presented, based on the Photochemical Ozone Creation Potential (POCP), and the results were compared with the results from the well established compressed chemical schemes. The compressed scheme used in the EMEP model (1993 version), including some minor modifications in order to make the models strictly comparable, was seen to be in good to excellent agreement with the results from the IVL model for most of the studied scenarios. For two-day simulations the CBM-IV scheme also gave results very close to the IVL model. For scenarios describing very NOx limited conditions including high VOC conditions, the POCP and the CBM-IV schemes were in closer agreement with the IVL model results than the EMEP model was. The 50% VOC emission reduction scenarios gave maximum ozone reductions of 3-4 ppb (6-7 %) as simulated by the IVL model for summer conditions. The corresponding PAN reduction was 0.2-0.3 ppb (ca 40%). The 50 % NOx emission reduction gave 5-6 ppb (ca 10%) ozone reductions and 0.1-0.2 (ca 20%) PAN reductions. A combined reduction of 50% VOC and 50% NOx emissions gave 7-9 ppb (ca 15 %) ozone reductions and 0.3-0.4 (45-50%) PAN reductions. 1 Table of contents Abstract........................................................................................................................... 1 Table of contents .............................................................................................................2 1 Introduction ........................................................................................................ 3 2 Description of the chemical schemes.......................................................................... 4 2.1 The IVL chemical scheme.............................................................................. 4 2.2 The EMEP chemical scheme................................................................. 4 2.3 The CBM-IV chemical scheme.......................................................................5 2.4 The RADM-II chemical scheme.....................................................................5 2.5 The POCP chemical scheme...........................................................................5 2.6 Alternative schemes........................................................................................7 3 Model set-up and simulations ......................................................................................8 3.1 Chemical modifications ...................................................................................9 3.2 Dry deposition .................................................................................................9 3.3 Initial concentrations .....................................................................................10 3.4 Emissions ...................................................................................................... 11 3.5 Meteorology..................................................................................................12 3.6 Simulation scenarios .....................................................................................12 4 Results and discussion of the comparisons ................................................................14 4.1 Results from the IVL model ..........................................................................14 4.2 Results from the EMEP model ..................................................................... 21 4.3 Results from the CBM-IV model ................................................................. 22 4.4 Results from the RADM-II model ............................................................... 23 4.5 Results from the POCP model ..................................................................... 23 4.6 The alternative schemes under NOx limited conditions .............................. 24 5 Conclusions .............................................................................................................. 27 References.................................................................................................................... 28 Acknowledgements...................................................................................................... 28 Appendix 1 Description of the POCP chemical scheme 2 Conversion of chemical species between chemical schemes 2 1 Introduction Ozone formation from emissions ofNOx and VOC is today an environmental problem of great concern. In the design of European ozone abatement strategies, photochemical modelling comprises a necessary part. The photochemical models in use today either describe the meteorology in a detailed and complex manner or include a detailed description of the chemical processes. As abatement strategies for ozone and other oxidants have to consider effects on continental and global scales, the need for a detailed description of the transport processes often dominates over the need for a detailed chemical description, thus the chemical processes have to be described in a compressed way. For many potential model users, compressed chemical models are necessary, since computer capacity still is one of the limiting factors, even though this parameter is substantially improved with time. In order to investigate the reliability of simulated results they must be compared both to measured data and among the models. In the work presented here, three compressed chemical schemes used in European abatement strategy models, i.e. the EMEP MSC-W (Simpson et al., 1993 ), the CBM-IV (Gery et al., 1989) and the RADM-II (Stockwell et al., 1990) models, have been compared with the explicit chemical scheme used in the IVL photochemical model (Andersson-Skold, 1995), under Swedish conditions (Pleijel and Andersson- Skold, 1992; Janhall and Andersson-Skold, 1995). The major difference among the compared chemical