Enhanced sulfur in the upper troposphere and lower stratosphere in spring 2020

Sulfur compounds in the upper troposphere and lower stratosphere (UTLS) impact the atmosphere radiation budget, either directly as particles or indirectly as precursor gas for new particle formation. In situ measurements in the UTLS are rare but are important to better understand the impact of the sulfur budget on climate. The BLUESKY mission in May and June 2020 explored an unprecedented situation. (1) The UTLS experienced extraordinary dry conditions in spring 2020 over Europe, in comparison to previous years, and (2) the first lockdown of the COVID-19 pandemic caused major emission reductions from industry, ground, and airborne transportation. With the two research aircraft HALO and Falcon, 20 flights were conducted over central Europe and the North Atlantic to investigate the atmospheric composition with respect to trace gases, aerosol, and clouds. Here, we focus on measurements of sulfur dioxide (SO$_{2}$) and particulate sulfate (SO$^{2-}$$_{4}$) in the altitude range of 8 to 14.5 km which show unexpectedly enhanced mixing ratios of SO$_{2}$ in the upper troposphere and of SO$^{2-}$$_{4}$ in the lowermost stratosphere. In the UT, we find SO$_{2}$ mixing ratios of (0.07±0.01) ppb, caused by the remaining air traffic, and reduced SO$_{2}$ sinks due to low OH and low cloud fractions and to a minor extent by uplift from boundary layer sources. Particulate sulfate showed elevated mixing ratios of up to 0.33 ppb in the LS. We suggest that the eruption of the volcano Raikoke in June 2019, which emitted about 1 Tg SO$_{2}$ into the stratosphere in northern midlatitudes, caused these enhancements, in addition to Siberian and Canadian wildfires and other minor volcanic eruptions. Our measurements can help to test models and lead to new insights in the distribution of sulfur compounds in the UTLS, their sources, and sinks. Moreover, these results can contribute to improving simulations of the radiation budget in the UTLS with respect to sulfur effects

Enhanced sulfur in the upper troposphere and lower stratosphere in spring 2020

The detection of sulfur compounds in the upper troposphere (UT) and lower stratosphere (LS) is a challenge. In-flight measurements of SO2 and sulfate aerosol were performed during the BLUESKY mission in spring 2020 under exceptional atmospheric conditions. Reduced sinks in the dry UTLS and lower but still significant air traffic influenced the enhanced SO2 in the UT and aged volcanic plumes enhanced the LS sulfate aerosol both impacting the atmospheric radiation budget and global climate

Numerical simulation of the impact of COVID-19 lockdown on tropospheric composition and aerosol radiative forcing in Europe

Aerosols influence the Earth\u27s energy balance directly by modifying the radiation transfer and indirectly by altering the cloud microphysics. Anthropogenic aerosol emissions dropped considerably when the global COVID-19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. We assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric composition with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business-as-usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May–June 2020 over Europe. The model agrees well with most of the observations, except for sulfur dioxide, particulate sulfate, and nitrate in the upper troposphere, likely due to a biased representation of stratospheric aerosol chemistry and missing information about volcanic eruptions. The comparison with a baseline scenario shows that the largest relative differences for tracers and aerosols are found in the upper troposphere, around the aircraft cruise altitude, due to the reduced aircraft emissions, while the largest absolute changes are present at the surface. We also find an increase in all-sky shortwave radiation of 0.21 ± 0.05 W m⁻² at the surface in Europe for May 2020, solely attributable to the direct aerosol effect, which is dominated by decreased aerosol scattering of sunlight, followed by reduced aerosol absorption caused by lower concentrations of inorganic and black carbon aerosols in the troposphere. A further increase in shortwave radiation from aerosol indirect effects was found to be much smaller than its variability. Impacts on ice crystal concentrations, cloud droplet number concentrations, and effective crystal radii are found to be negligible

HOx cycling during the Cyprus Photochemistry Experiment

Meeting abstract fro AOGS 2016 Beijing for an oral presentation of results from the CYPHEX 2014 measurement campaign.Abstract from attachedMax Planck Society, University of Cheste

Measurement report: Emission factors of NH3 and NHx for wildfires and agricultural fires in the United States.

Ammonia (NH3) is an important trace gas in the atmosphere and fires are among the poorly investigated sources. During the FIREX-AQ aircraft campaign in 2019, we measured gaseous ammonia and particulate ammonium (NH4+) in smoke plumes emitted from six wildfires in the Western US and 66 small agricultural fires in the Southeastern US. We herein present a comprehensive set of emission factors of NH3 and NHx, with NHx = NH3 + NH4+

Impact of reduced emissions on direct and indirect aerosol radiative forcing during COVID-19 lockdown in Europe

Aerosols influence the Earth’s energy balance through direct radiative effects and indirectly by altering the cloud microphysics. Anthropogenic aerosol emissions dropped considerably when the global COVID–19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. Here we assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric composition with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business as usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May June 2020 over Europe

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

Variability of aerosol particles in the urban atmosphere of Dresden (Germany): Effects of spatial scale and particle size

The spatial distribution of atmospheric particles in urban atmospheres is of significant concern for public health. However, the concentrations especially of ultrafine particles (diameter < 100 nm) are difficult to predict due to the presence of numerous diffuse particle sources and the generally inhomogeneous terrain in urban roughness layers. this study examines the spatial variability of sub-μm particle number size distributions (diameter range 5-800 nm) in the urban atmosphere of Dresden, Germany, using multiple site measurements between December 2009 and May 2010. A main result is that particles in the accumulation mode size range (300-800 nm) showed only minor spatial variability. These particles form a rather homogeneous regional background of aerosol that changes only slightly with time. Particle concentrations in the size range 5-300 nm, however, proved to be significantly influenced by the local urban sources and showed an increasing variability with decreasing particle size. Besides the apparently highly variable field of traffic-related particles, a photochemical source of ultrafine particles was identified that showed an unexpectedly high spatial homogeneity across the entire city. The spatial gradients of particle concentrations also depended on wind direction, wind speed, and temperature inversions. The results confirm the high relevance of spatially resolved ultrafine particle measurements for the assessment of health-related exposure and strategies for their monitoring in urban atmospheres