Hemispheric Transport of Air Pollution (HTAP) : specification of the HTAP2 experiments : ensuring harmonized modelling

In 2012, the Hemispheric Transport of Air Pollution (HTAP) Task Force launched a cooperative multi-model experiments and analysis (HTAP Phase 2) that is intended to inform the Convention on Long-range Transboundary Air Pollution (LRTAP) and other multi-lateral cooperative efforts, as well as national governments on actions to decrease air pollution and its impacts. The HTAP Phase 2 modelling experiments have been designed to provide: - relative contributions of regional and extra-regional sources of air pollution in different regions of the world that will help refine the source/receptor relationships derived from the previous HTAP Phase 1 simulations. - a basis for model evaluation and process studies to characterize the uncertainty in the estimates of regional and extra-regional contributions and to understand the differences between models. - input to assessments of the impacts of control strategies on the contribution of regional and extra-regional emissions sources to the exceedance of air quality standards and to impacts on human health, ecosystems, and climate. The purpose of this report is to gather in a single document the guidance and technical specifications provided from 2012 to end of 2015 by the Joint Research Center (European Commission) to the global modelers participating to HTAP Phase 2, which are currently only partly accessible through the HTAP WIKI pages (Annex 1). It also includes some information on the input to the AQMEII (Air Quality Model Evaluation International Initiative) and MICS (Model Inter-comparison Study for Asia) regional simulations performed in the frame of HTAP2, as well as additional information with respect to the HTAP_v2.2 global emission inventory. This report provides detailed background information to a technical overview paper (Galmarini et al., 2016) in the special issue of the Atmospheric Chemistry and Physics journal, entitled 'Global and regional assessment of intercontinental transport of air pollution: results from HTAP, AQMEII and MICS.