PEGASOS brings together most of the leading European research groups, with state-of the-art observational and modeling facilities to:

• Quantify the magnitude of regional to global feedbacks between atmospheric chemistry and a changing climate and to reduce the corresponding uncertainty of the major ones.
• Identify mitigation strategies and policies to improve air quality while limiting their impact on climate change.

Schematic view of the air quality-climate change system and the two core PEGASOS objectives

PEGASOS will address five Specific Scientific Questions, bridging the spatial and temporal scales that connect local surface-air pollutant exchanges, air quality and weather with global atmospheric chemistry and climate. PEGASOS major focus for air quality will be Europe including effects of changes in pollutant emissions elsewhere and the time horizon for the study will be the next 50 years.

PEGASOS will provide improved process understanding in areas of major uncertainty for better quantification of feedbacks between air quality and a changing climate. PEGASOS will conduct, for the first time, a fully integrated analysis of dynamically changing emissions and deposition, their link to tropospheric chemical reactions and interactions with climate, and emerging feedbacks between chemistry-climate and surface processes. PEGASOS will target both local and regional scales, taking into account chemistry and climate feedbacks on the global scale.

PEGASOS will include development of new climate-sensitive biogenic and anthropogenic emission models, state-of-the-science laboratory and field process studies, development and use of the most advanced models. The outcomes (scenarios, emissions, data sets, models, new knowledge and recommendations) will be disseminated to authorities, policy makers and the research community.

Specific Scientific Questions

To reach its objectives PEGASOS will address the following scientific questions:

• Q1 How has past air quality policy inadvertently affected present day climate and, the corollary, how has climate change over the last decades affected Europe’s ability to meet its air quality targets for ozone, particulate matter (PM), etc.? How will currently planned air quality regulations affect climate?
• Q2 How will emissions (including methane, biomass burning emissions, biogenic hydrocarbons, etc.) respond to a changing climate, shifts in biomes, and land cover/land use and what will be the effect of these changes on European air quality (ozone, PM, etc.) and climate.
• Q3 How will climate change affect the atmospheric self-cleansing capacity (HOx budget and cycling), atmospheric aerosol concentrations (both number and mass) and how will this in turn feed back to climate? How will climate change affect the regional accumulation of pollutants (including aerosols) and the resulting air quality and its regulation in Europe on both regional and urban scales?
• Q4 What are the main missing processes in current air quality-climate models and how can these tools be improved for the simulation of multi-scale chemistry-climate interactions including local changes?
• Q5 Which policy-relevant metrics should be used to facilitate the consideration of short-lived species in international treaties dealing with climate-relevant compound regulations and the assessment of air quality and climate policies co-benefits or other interactions?