Correction to: Scientific Data https://doi.org/10.1038/s41597-022-01900-7, published online 29 December 2022.Several of the units in the original version were published in metres, rather than μm; ...several ± signs were omitted from numerical values; and Table 2 was incorrectly formatted to cause certain rows and columns to mis-align. These have been corrected in the pdf and HTML versions of the article.
A comprehensive investigation of polar stratospheric clouds was performed on 25 January 2000 with instruments onboard a balloon gondola flown from Kiruna, Sweden. Cloud layers were repeatedly ...encountered at altitudes between 20 and 24 kilometers over a wide range of atmospheric temperatures (185 to 197 kelvin). Particle composition analysis showed that a large fraction of the cloud layers was composed of nitric acid trihydrate (NAT) particles, containing water and nitric acid at a molar ratio of 3:1; this confirmed that these long-sought solid crystals exist well above ice formation temperatures. The presence of NAT particles enhances the potential for chlorine activation with subsequent ozone destruction in polar regions, particularly in early and late winter.
This study investigates the sensitivity of two brightness temperature differences (BTDs) in the infrared (IR) window of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) to various cloud ...parameters in order to understand their information content, with a focus on cloud thermodynamic phase. To this end, this study presents radiative transfer calculations, providing an overview of the relative importance of all radiatively relevant cloud parameters, including thermodynamic phase, cloud-top temperature (CTT), optical thickness (τ), effective radius (Reff), and ice crystal habit. By disentangling the roles of cloud absorption and scattering, we are able to explain the relationships of the BTDs to the cloud parameters through spectral differences in the cloud optical properties. In addition, an effect due to the nonlinear transformation from radiances to brightness temperatures contributes to the specific characteristics of the BTDs and their dependence on τ and CTT. We find that the dependence of the BTDs on phase is more complex than sometimes assumed. Although both BTDs are directly sensitive to phase, this sensitivity is comparatively small in contrast to other cloud parameters. Instead, the primary link between phase and the BTDs lies in their sensitivity to CTT (or more generally the surface–cloud temperature contrast), which is associated with phase. One consequence is that distinguishing high ice clouds from low liquid clouds is straightforward, but distinguishing mid-level ice clouds from mid-level liquid clouds is challenging. These findings help to better understand and improve the working principles of phase retrieval algorithms.
Aviation contributes to anthropogenic climate change mainly by contrails, CO2 and NOx emissions, whereof contrails are considered the largest single contributor to the radiative forcing from ...aviation. Powering aircraft with kerosene containing fewer or no-aromatics, i.e., “Sustainable Aviation Fuels” (SAF) or hydroprocessed, fossil-based kerosene, can significantly reduce contrail climate forcing. However, such kerosene is currently scarcely available. Moreover, less than 10 % of the flights worldwide cause more than 80 % of the contrail climate forcing. Hence, this study investigates a targeted allocation of paraffinic, i.e., aromatics-free kerosene to flights and flight segments with the highest contrail climate forcing, by calculating the resulting contrail energy forcing (in J) on 844 364 flight trajectories worldwide departing from five large European airports in 2019.
The contrail radiative forcing integrated over contrail evolution (i.e., contrail energy forcing J) is simulated for a reference fleet powered with conventional kerosene of 14.1 m - % hydrogen content. 5 % of overall kerosene demand assumed to be paraffinic kerosene with 15.3 m - % hydrogen content is allocated via a uniform, a flight-specific and a segment-specific approach. The uniform allocation assumes that all flights receive the same blend of 5 % paraffinic kerosene. The other cases target 100 % paraffinic kerosene either to flights or segments with highest contrail energy forcing. Compared to the reference, the results indicate a reduction on contrail energy forcing by 4 %, 36 % and 55 %, respectively. For market shares of paraffinic kerosene up to 30 %, a segment specific allocation appears advantageous compared to a flight specific allocation. However, they might require airport and aircraft modifications. Uncertainties in contrail climate benefits can be reduced by providing additional information on kerosene properties and accurate meteorological data. Overall, this study highlights robust potentials of paraffinic kerosene to significantly reduce the climate forcing from aviation.
•This study investigates flight-, segment or uniform paraffinic kerosene supply.•Paraffinic kerosene reduces contrail climate forcing.•Targeted use of paraffinic kerosene increases contrail climate benefits.
Sustainable aviation fuel (SAF) can reduce aviation’s CO2 and non-CO2 impacts. We quantify the change in contrail properties and climate forcing in the North Atlantic resulting from different ...blending ratios of SAF and demonstrate that intelligently allocating the limited SAF supply could multiply its overall climate benefit by factors of 9–15. A fleetwide adoption of 100% SAF increases contrail occurrence (+5%), but lower nonvolatile particle emissions (−52%) reduce the annual mean contrail net radiative forcing (−44%), adding to climate gains from reduced life cycle CO2 emissions. However, in the short term, SAF supply will be constrained. SAF blended at a 1% ratio and uniformly distributed to all transatlantic flights would reduce both the annual contrail energy forcing (EFcontrail) and the total energy forcing (EFtotal, contrails + change in CO2 life cycle emissions) by ∼0.6%. Instead, targeting the same quantity of SAF at a 50% blend ratio to ∼2% of flights responsible for the most highly warming contrails reduces EFcontrail and EFtotal by ∼10 and ∼6%, respectively. Acknowledging forecasting uncertainties, SAF blended at lower ratios (10%) and distributed to more flights (∼9%) still reduces EFcontrail (∼5%) and EFtotal (∼3%). Both strategies deploy SAF on flights with engine particle emissions exceeding 1012 m–1, at night-time, and in winter.
Aviation-related aerosol emissions contribute to the formation of contrail cirrus clouds that can alter upper tropospheric radiation and water budgets, and therefore climate. The magnitude of ...air-traffic-related aerosol-cloud interactions and the ways in which these interactions might change in the future remain uncertain. Modelling studies of the present and future effects of aviation on climate require detailed information about the number of aerosol particles emitted per kilogram of fuel burned and the microphysical properties of those aerosols that are relevant for cloud formation. However, previous observational data at cruise altitudes are sparse for engines burning conventional fuels, and no data have previously been reported for biofuel use in-flight. Here we report observations from research aircraft that sampled the exhaust of engines onboard a NASA DC-8 aircraft as they burned conventional Jet A fuel and a 50:50 (by volume) blend of Jet A fuel and a biofuel derived from Camelina oil. We show that, compared to using conventional fuels, biofuel blending reduces particle number and mass emissions immediately behind the aircraft by 50 to 70 per cent. Our observations quantify the impact of biofuel blending on aerosol emissions at cruise conditions and provide key microphysical parameters, which will be useful to assess the potential of biofuel use in aviation as a viable strategy to mitigate climate change.
A comprehensive understanding of the cloud thermodynamic phase is crucial for assessing the cloud radiative effect and is a prerequisite for remote sensing retrievals of microphysical cloud ...properties. While previous algorithms mainly detected ice and liquid phases, there is now a growing awareness for the need to further distinguish between warm liquid, supercooled and mixed-phase clouds. To address this need, we introduce a novel method named ProPS (PRObabilistic cloud top Phase retrieval for SEVIRI), which enables cloud detection and the determination of cloud-top phase using SEVIRI (Spinning Enhanced Visible and Infrared Imager), the geostationary passive imager aboard Meteosat Second Generation. ProPS discriminates between clear sky, optically thin ice (TI) cloud, optically thick ice (IC) cloud, mixed-phase (MP) cloud, supercooled liquid (SC) cloud and warm liquid (LQ) cloud. Our method uses a Bayesian approach based on the cloud mask and cloud phase from the lidar–radar cloud product DARDAR (liDAR/raDAR). The validation of ProPS using 6 months of independent DARDAR data shows promising results: the daytime algorithm successfully detects 93 % of clouds and 86 % of clear-sky pixels. In addition, for phase determination, ProPS accurately classifies 91 % of IC, 78 % of TI, 52 % of MP, 58 % of SC and 86 % of LQ clouds, providing a significant improvement in accurate cloud-top phase discrimination compared to traditional retrieval methods.
Measurements of gaseous (NO, NOy, SO2, HONO) and ice particle concentrations in young contrails in primary and secondary wakes of aircraft of different sizes (B737, A319, A340, A380) are used to ...investigate ice particle formation behind aircraft. The gas concentrations are largest in the primary wake and decrease with increasing altitude in the secondary wake, as expected for passive trace gases and aircraft‐dependent dilution. In contrast, the measured ice particle concentrations were found larger in the secondary wake than in the primary wake. The contrails contain more ice particles than expected for previous black carbon (soot) estimates. The ice concentrations may result from soot‐induced ice nucleation for a soot number emission index of 1015 kg−1. For a doubled ice particle concentration in young contrails, a contrail cirrus model computes about 60% increases of global radiative forcing by contrail cirrus because of simultaneous increases in optical depth, age, and cover.
Key Points
Gaseous and ice particle concentrations were measured within aircraft wakes
Contrails contain more ice particles than expected for previous BC estimates
Ice particle concentration in contrails is important for aviation climate impact
Around 5 % of anthropogenic radiative forcing (RF) is
attributed to aviation CO2 and non-CO2 impacts. This paper
quantifies aviation emissions and contrail climate forcing in the North
Atlantic, one ...of the world's busiest air traffic corridors, over 5 years.
Between 2016 and 2019, growth in CO2 (+3.13 % yr−1) and
nitrogen oxide emissions (+4.5 % yr−1) outpaced increases in flight
distance (+3.05 % yr−1). Over the same period, the annual mean contrail
cirrus net RF (204–280 mW m−2) showed significant inter-annual
variability caused by variations in meteorology. Responses to COVID-19
caused significant reductions in flight distance travelled (−66 %),
CO2 emissions (−71 %) and the contrail net RF (−66 %) compared with
the prior 1-year period. Around 12 % of all flights in this region cause
80 % of the annual contrail energy forcing, and the factors associated
with strongly warming/cooling contrails include seasonal changes in
meteorology and radiation, time of day, background cloud fields, and
engine-specific non-volatile particulate matter (nvPM) emissions. Strongly
warming contrails in this region are generally formed in wintertime, close
to the tropopause, between 15:00 and 04:00 UTC, and above low-level clouds.
The most strongly cooling contrails occur in the spring, in the upper
troposphere, between 06:00 and 15:00 UTC, and without lower-level clouds.
Uncertainty in the contrail cirrus net RF (216–238 mW m−2) arising
from meteorology in 2019 is smaller than the inter-annual variability. The
contrail RF estimates are most sensitive to the humidity fields, followed by
nvPM emissions and aircraft mass assumptions. This longitudinal evaluation
of aviation contrail impacts contributes a quantified understanding of
inter-annual variability and informs strategies for contrail mitigation.
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