Mini-DOAS measurements during the HALO Southtrac mission in fall 2019

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The present proposal aims to support the participation of the mini-DOAS instrument in the Southtrac campaign in fall 2019, as well as to support the retrieval, interpretation and dissemination of the thereby measured data. The mini-DOAS instrument is a passive remote sensing instrument for simultaneous measurements of Nadir and Limb scattered skylight in the UV/vis/NIR spectral ranges from aboard the research aircraft HALO. The measurements support the sensitive detection of in-situ concentrations, vertical profiles and total atmospheric column amounts of atmospheric trace gases not measurable (BrO, OClO, IO, C2H2O2, and C3H4O2), or hardly measurable by other means (NO2, HONO, und CH2O). In addition, the measurements on the NIR provides means to simultaneously detect all three phases of H2O (liquid water and ice water path), some radiative properties of the atmosphere (e.g. relative radiances, and photon path length, …) and to collect information on the microphysical properties of aerosols and clouds. During Southtrac, the mini-DOAS measurements will contribute to three scientific objectives (CHEM-1_Q1, CHEM-1_Q2 and CHEM-2_Q1), as outlined in the envelope proposal. In particular, our measurements of (a) BrO (and IO) and photochemical calculations of the Bry (and Iy) partitioning will complete the respective halogen budgets (CHEM-1_Q), and the measurements of (b) BrO and OClO will constrain the ozone loss in the upper troposphere/lowermost stratosphere UTLS (CHEM-1_Q2). Finally, (c) the measurements of NO2, HONO and in particular of CH2O und C2H2O2 will assist to identify biomass burning affected air masses (CHEM-2_Q1).