Measurements of particle emissions and contrail ice particle properties behind a large passenger aircraft burning 100% sustainable aviation fuel in cruise

The use of sustainable aviation fuels (SAF) derived from biomass and waste materials can provide one approach to partially decarbonize air traffic relatively quickly and offers a pathway to mitigate the non-CO2 climate impacts from long-lived contrails on short time scales. Many SAFs naturally contain no or only low amounts of aromatic compounds which act as soot precursors during combustion. As soot particles serve as primary nucleus for contrail ice, lower soot emissions should result in lower contrail ice particle numbers. In the joint project ECLIF3 (Emissions and Climate Impact of alternative Fuels), DLR, Airbus, Rolls-Royce, Neste and other participants aimed to characterize emissions and contrail properties behind a modern passenger aircraft burning both conventional Jet A-1 fuel and HEFA-SPK (Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene) and a blend of HEFA-SPK and Jet A-1 on both engines on the ground and in flight. For the first time, flight tests in cruise using 100% HEFA-SPK on all engines were feasible in this framework. In two field campaigns in 2021 an Airbus A350-900 equipped with Rolls Royce Trent XWB-84 engines served as source aircraft. With the DLR Falcon 20E5 research aircraft we probed trace gases, volatile and non-volatile particles, and ice particle properties. The independent fuel tanks of the A350 permitted us to sample emissions from reference Jet A-1 and HEFA-SPK in similar meteorological conditions. Measurements of the exhaust closely behind the engine exit and up to several minutes behind the lead aircraft allowed us to characterize both, direct engine emissions depending on engine thrust conditions and the effects on contrail formation and properties. With respect to the Jet A-1 used here, we find a significant reduction in non-volatile particle emissions when burning HEFA-SPK; similar trends are seen in the ice particle numbers in the contrails. The results outline the importance of fuel composition (e.g. sulfur and aromatics content) on particle emissions and contrail formation. The analysis also shows the complexity of the contrail formation process and its dependence on fuel composition, engine thrust and meteorological conditions in the ambient atmosphere

Few basepairing-independent motifs in the apical half of the avian HBV ε RNA stem-loop determine site-specific initiation of protein-priming.

Hepadnaviruses, including human hepatitis B virus (HBV), replicate their tiny DNA genomes by protein-primed reverse transcription of a pregenomic (pg) RNA. Replication initiation as well as pgRNA encapsidation depend on the interaction of the viral polymerase, P protein, with the ε RNA element, featuring a lower and an upper stem, a central bulge, and an apical loop. The bulge, somehow assisted by the loop, acts as template for a P protein-linked DNA oligo that primes full-length minus-strand DNA synthesis. Phylogenetic conservation and earlier mutational studies suggested the highly based-paired ε structure as crucial for productive interaction with P protein. Using the tractable duck HBV (DHBV) model we here interrogated the entire apical DHBV ε (Dε) half for sequence- and structure-dependent determinants of in vitro priming activity, replication, and, in part, in vivo infectivity. This revealed single-strandedness of the bulge, a following G residue plus the loop subsequence GUUGU as the few key determinants for priming and initiation site selection; unexpectedly, they functioned independently of a specific structure context. These data provide new mechanistic insights into avihepadnaviral replication initiation, and they imply a new concept towards a feasible in vitro priming system for human HBV

Cleaner Skies during the COVID-19 Lockdown

During spring 2020, the COVID-19 pandemic caused massive reductions in emissions from industry and ground and airborne transportation. To explore the resulting atmospheric composition changes, we conducted the BLUESKY campaign with two research aircraft and measured trace gases, aerosols, and cloud properties from the boundary layer to the lower stratosphere. From 16 May to 9 June 2020, we performed 20 flights in the early COVID-19 lockdown phase over Europe and the Atlantic Ocean. We found up to 50% reductions in boundary layer nitrogen dioxide concentrations in urban areas from GOME-2B satellite data, along with carbon monoxide reductions in the pollution hot spots. We measured 20%–70% reductions in total reactive nitrogen, carbon monoxide, and fine mode aerosol concentration in profiles over German cities compared to a 10-yr dataset from passenger aircraft. The total aerosol mass was significantly reduced below 5 km altitude, and the organic aerosol fraction also aloft, indicative of decreased organic precursor gas emissions. The reduced aerosol optical thickness caused a perceptible shift in sky color toward the blue part of the spectrum (hence BLUESKY) and increased shortwave radiation at the surface. We find that the 80% decline in air traffic led to substantial reductions in nitrogen oxides at cruise altitudes, in contrail cover, and in resulting radiative forcing. The light extinction and depolarization by cirrus were also reduced in regions with substantially decreased air traffic. General circulation–chemistry model simulations indicate good agreement with the measurements when applying a reduced emission scenario. The comprehensive BLUESKY dataset documents the major impact of anthropogenic emissions on the atmospheric composition

Cleaner Skies during the COVID-19 Lockdown

During spring 2020, the COVID-19 pandemic caused massive reductions in emissions from industry and ground and airborne transportation. To explore the resulting atmospheric composition changes, we conducted the BLUESKY campaign with two research aircraft and measured trace gases, aerosols, and cloud properties from the boundary layer to the lower stratosphere. From 16 May to 9 June 2020, we performed 20 flights in the early COVID-19 lockdown phase over Europe and the Atlantic Ocean. We found up to 50% reductions in boundary layer nitrogen dioxide concentrations in urban areas from GOME-2B satellite data, along with carbon monoxide reductions in the pollution hot spots. We measured 20%–70% reductions in total reactive nitrogen, carbon monoxide, and fine mode aerosol concentration in profiles over German cities compared to a 10-yr dataset from passenger aircraft. The total aerosol mass was significantly reduced below 5 km altitude, and the organic aerosol fraction also aloft, indicative of decreased organic precursor gas emissions. The reduced aerosol optical thickness caused a perceptible shift in sky color toward the blue part of the spectrum (hence BLUESKY) and increased shortwave radiation at the surface. We find that the 80% decline in air traffic led to substantial reductions in nitrogen oxides at cruise altitudes, in contrail cover, and in resulting radiative forcing. The light extinction and depolarization by cirrus were also reduced in regions with substantially decreased air traffic. General circulation–chemistry model simulations indicate good agreement with the measurements when applying a reduced emission scenario. The comprehensive BLUESKY dataset documents the major impact of anthropogenic emissions on the atmospheric composition