Harmonisation of historical and future emission data for climate and air quality modelling

Climate change and air quality research are closely related research areas that have often been investigated with different objectives. However, addressing both topics as a joint approach can lead to synergies and help to avoid counteracting effects, where mitigating one may exacerbate the other. The convergence of methods and approaches is necessary to consider on the one hand the climate trend and forcing in mitigation scenarios applied by the air quality community and on the other hand to better understand and describe the impact of short-lived climate pollutants on the regional climate.

The project FOCI aims to analyse non-CO2 forcings on both climate and air quality and therefore requires a joint approach. A core task of the project is the application of regional climate and urban scale models driven by global earth system models to describe continental to urban scale air quality under present and future climate conditions. The results of these processes will be used to investigate possible mitigation and adaptation scenario options.

The present and future anthropogenic emissions required for such model investigations need to be consistent with CMIP6 historical climate reconstruction and future scenario simulations. CMIP6 has been based on CEDS emissions that are therefore the necessary reference for FOCI activities. One critical aspect is that pollutants considered in CEDS do not include particulate matter (PM2.5 and PM10), but only its black carbon (BC) and organic carbon (OC) components. This is understandable considering the objective for which CEDS has been built, but it would cause a significant underestimation of particulate matter concentrations and raises the need to define a method to estimate the non-speciated PM2.5 and PM10 emissions from the available information.

In order to derive PM emissions for CEDS we investigate a number of approaches based on the use of different proxies from the EDGAR database. In particular, we consider the feasibility of deriving PM2.5 from BC and OC as the main components of fine particulate matter. For emission sectors where BC and OC is not available in the emission inventories, we explore the possibility of using alternative proxies including NOx. By combining the different approaches we derive PM2.5 emissions for CEDS at a spatial grid resolution of 0.1 degree and compare these for each main emissions sector.

These estimated dataset of consistent CEDS and particulate matter emissions are used in the FOCI project numerical models to describe continental to urban scale air quality under present climate conditions. We also discuss the implications of employing our approach to derive consistent emissions for particulate matter in conjunction with SSP emission data for projections to ultimately evaluate the impact of key radiative forcers on climate and societal systems.