Thesis of Alejandra Velazquez-Garcia

Defense of thesis of Alejandra Velazquez-Garcia - Laboratory LOA

Abstract :
The link between fine aerosol optical properties and their chemical composition is not yet well
understood, and was investigated using long-term in situ observations performed at the
“ATmospheric Observations in liLLe” platform from 2016 to 2020 using a combination of
aerosol mass spectrometer, aethalometer, and nephelometer. Highly absorbing aerosols and a
marked seasonality of the mass contribution of ammonium nitrate (AN) in spring were
observed. We evidence that AN (35%) and carbonaceous aerosols (51%) are predominant
regarding light extinction at 525 nm. Besides, a novel approach combining these in situ
measurements to backtrajectories and emission inventories identifies a Brown Carbon (BrC)
decrease within 24 hours after emission even during wintertime, pointing at a likely systematic
underestimation of the contribution of residential heating (identified by the presence of BrC) to
the aerosol absorption in the region.

Keywords : Atmospheric pollution, climate impact, in situ observations, PM1, extinction coefficient,
aerosol origins