Chasing pre-industrial aerosols

ended

Aerosol particles affect the climate by scattering incoming radiation and by acting as cloud condensation nuclei; however, their net effect remains of highest uncertainty, specifically when quantifying their relationship to anthropogenic greenhouse gases. It has been estimated that 45% of the variance of aerosol forcing arises from uncertainties in natural emissions. This highlight the importance of understanding pristine preindustrial-like environments, with natural aerosols only. One of the great challenges in understanding preindustrial aerosols and their sources resides in identifying the processes by which new particles form and grow from oxidized vapours. We recently presented in Science the ground-breaking observation of purely organic nucleation. The existence of this mechanism was confirmed by laboratory experiments where we show that highly oxygenated molecules are able to form new particles independent of H2SO4. This finding sheds the light into the preindustrial era where the anthropogenic emissions were almost absent and H2SO4 concentration was rather minimal. The aim of my project is to provide unprecedented data to resolve the preindustrial nucleation mechanism. I will organize intensive long-term measurements in pristine preindustrial-like environments like the Arctic and Siberia. Using state-of-the-art chemical ionization mass spectrometry, I will retrieve the chemical cluster composition and the vapours concentration. Additionally, I am planning short intensive measurements at high altitude above the oceans. Finally, these measurements will be complemented by laboratory experiments needed to probe the observed mechanism and retrieve a parametrization that can be used in global modelling. The outcome of these field campaigns combined with laboratory experiments will provide extraordinary results in understanding pre-industrial aerosol formation, which will set the baseline for estimations of the impact of present and future aerosol on climate.