Lay summary
This proposal deals with the atmospheric composition in the Arctic. Climate change is currently proceeding fastest in the Arctic than anywhere else on the planet. One key hypothesis for this fast warming is that short-lived species (including ozone and aerosols) influence the Arctic climate in several ways either directly through radiative forcing and indirectly through clouds and snow/ice albedo. In particular, the role of light absorbing aerosols (such as black carbon) remains largely unknown. There are ample evidences that the Arctic troposphere is characterized by elevated concentrations of particles of different origins both in late winter and spring (the so-called Arctic Haze) but also in summer. The Arctic and summer haze are composed of a mix of particles of different origins and most largely result from long range transport of anthropogenic pollution from mid-latitudes and from wildfires in boreal regions. However, the pathways for the transport of pollution into the Arctic, the relative contributions of various geopolitical regions, as well as the role of biomass burning in boreal forest are not known in a quantitative manner. In this project, we propose to explore two specific questions, including (i) the pathways for long range transport of aerosol and ozone-related pollution from the northern mid-latitudes to the Arctic and (ii) the impact of the boreal wildfires on the Arctic atmospheric composition. We will address these questions using conjointly the fully coupled model of aerosol-chemistry-climate ECHAM5-HAMMOZ as well as a suite of products from various platforms (including satellite such as CALIOP, MISR, MODIS, ground-based stations in the Arctic and pan-Arctic region, and research aircrafts such as those deployed in the framework of the POLARCAT experiment). We are planning to 1) conduct a comprehensive analysis of a boreal wildfire event collected in POLARCAT and to test our model's representation of the processes related to transport of boreal biomass burning pollution; 2) develop a timeseries (annual cycle) of the CALIOP vertically-resolved attenuated backscatter at relevant locations of the northern mid-latitudes to test our model's ability to reproduce the long range transport of pollution towards the Arctic; 3) explore the factor that govern interannual variability in the Arctic composition with a focus over the period from 2006 to 2008. The proposed work will provide an improved quantitative understanding of the processes governing the Arctic composition and ultimately of the processes that govern climate change there but also globally.