The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) provides the first spaceborne Doppler radar measurements. We construct a tropical cyclone (TC) dataset by collocating 16 months of EarthCARE observations with the International Best Track Archive for Climate Stewardship, comprising 96 intercepts of 27 TCs. The inner-core region exhibits enhanced reflectivity, stronger and more variable upward air motion, and a broader Doppler velocity distribution. Two independent inner-core intercepts show consistent Doppler and air velocity structures. In the rainband region, the Doppler velocity distribution shifts toward more negative values, accompanied by more negative particle terminal velocities and a bright band near the melting level. Particle classifications show small ice dominates the upper troposphere, whereas snow extends toward more negative Doppler velocities between 5 and 12 km. These results show that radial variations in Doppler velocity reflect differences in both air motion and particle sedimentation. We conduct a preliminary single-case comparison for Hurricane Humberto using the Nonhydrostatic Icosahedral Atmospheric Model with two common microphysical configurations. Both configurations underestimate TC intensity and produce narrower distributions than observed. Compared with the Kodama et al. (2021) configuration, the Takasuka et al. (2024) configuration more closely reproduces upper-level structure, with more gradual reflectivity and Doppler velocity changes and a broader cloud ice distribution. Because the comparison is limited to one case, it demonstrates sensitivity to the microphysical configurations rather than a general evaluation of model performance. Overall, EarthCARE provides complementary constraints on vertical air motion, condensate properties, and particle sedimentation for evaluating TC microphysics.
Large uncertainty exists in the role that the ocean plays as a net source for atmospheric volatile organic carbon (VOC) compounds, in part because of poorly quantified processes near the air–sea interface. Laboratory studies imply that heterogeneous reactions of ozone at the ocean surface may be a key source of VOCs to the marine atmosphere, but the representativeness of such experiments for the chemically complex surface ocean waters is unclear due to limited field evidence. Here, we determined the production ratios of select VOCs formed during ozonolysis of fresh, natural seawater from laboratory experiments under turbulent conditions using a proton-transfer-reaction quadrupole mass spectrometer (PTR-MS). To quantify seasonal variability, near-surface water samples were collected from a temperate marine station during different seasons and measured for ozone-driven VOC production ratios. In all experiments, out of the VOCs monitored the dominant products of ozonolysis were m/z 69 (C5H9+), followed by m/z 59 (acetone/propanal) and m/z 45 (acetaldehyde). Clear seasonal differences in VOC production imply that marine biogeochemistry likely drives the availability and composition of VOC precursors. Further ozonolysis experiments using diluted VOC precursors (senescent algal culture, fatty acids, certified natural organic matter (NOM)) resulted in different VOC production compared to those using natural seawater. Our results show that ocean biogeochemical cycling is a key driver of variability in ozone-driven VOC production at the sea surface.
This study elucidates the mechanisms of selected transformation pathways of 2,4-dinitrophenol (2,4-DNP) using an integrated computational framework. In the gas phase, the calculated initial reactions with hydroxyl radicals (⚫OH) and ozone (O3) are kinetically more favorable than the direct reaction with nitrogen dioxide radical (⚫NO2), which is kinetically hindered. In the aqueous phase, solvation substantially modifies the calculated reaction kinetics, and the cumulative electron-withdrawing effect of the two nitro substituents lowers the O3 reaction rate coefficient by approximately three orders of magnitude relative to mononitrocatechol. For the key radical intermediate generated by ⚫OH addition, hydrogen atom abstraction (HAA) by O2 is kinetically favored over the competing ⚫NO2 pathway based on the calculated barriers and an illustrative comparison of effective rates under representative atmospheric concentrations. At the gas-aqueous interface, molecular dynamics (MD) simulations show a non-monotonic dependence of 2,4-DNP adsorption on hydration in the idealized C60/water system, with adsorption strengthening at moderate hydration and weakening at high hydration. Finally, QSAR calculations predict that certain ozonolysis products exhibit higher predicted Ames mutagenicity and developmental toxicity indicators than the parent compound, indicating product-specific changes in predicted toxicity profiles during oxidation. These screening-level predictions require experimental validation. These findings provide molecular-level mechanistic insights into selected transformation pathways and interfacial interactions involving 2,4-DNP and motivate further experimental investigation of its transformation products and their toxicological properties.
Nocturnal ozone (O3) increase (NOI) has become common worldwide, raising the risk of O3 pollution. While weather types serve as critical drivers of NOI, their specific dynamic influences remain poorly understood. Using ground observations and reanalysis datasets, this study identified the relationship between weather types and NOI days in a representative city in the North China Plain, and revealed the meteorological characteristics and physical mechanisms driving these events. During 2021–2023, 370–444 NOI days were observed, with the occurrence predominantly concentrated between 00:00 and 06:00 local time (69.53 %). After screening, a total of 171 representative NOI days were finally identified to characterize the overall occurrence of local NOI events. Based on the Lamb-Jenkinson method, the representative NOI days were classified into four primary weather types: A-type (57.89 %), S-type (19.88 %), WNE-type (14.04 %), and C-type (8.19 %). A-type was dominated by high-pressure anticyclones with calm conditions, whereas C-type was controlled by low-pressure systems and influenced by moist airflows. S-type was located in the transition zone between high and low pressure, influenced by southern geostrophic winds, and WNE-type was characterized by high-pressure systems with W-N-E geostrophic flows. Distinct mechanical triggers for NOI were further resolved for different types: A-type is dominated by high-pressure subsidence; C-type is driven by cold-pool downdrafts and convective motions; whereas both S-type and WNE-type are primarily controlled by synoptically-driven intense wind shear. This study elucidates the diverse dynamical pathways of weather-driven NOI, providing mechanistic insights for improving O3 forecasting and mitigation strategies in urban environments.
The 2022 Hunga Tonga (HT) eruption injected an unprecedented amount of water vapour (WV) into the stratosphere and mesosphere, emerging as a potential multi-year driver of variability in those layers and associated climate feedbacks. Using satellite and reanalysis datasets, and ensemble simulations with the SOCOLv4 model, with and without the HT forcing, we diagnose the chain of processes linking the eruption to the exceptionally strong Northern Hemisphere stratospheric polar vortex (SPV) observed in winter 2024/2025. Satellite data show “tongues” of enhanced WV descending from the mesosphere into the polar stratosphere, collocated with ozone reductions and persistent cold anomalies, alongside a record-strong SPV. Our model with the HT forcing can reproduce the main structure of the descending plume, its effects on chemistry, and the SPV strengthening, albeit with underestimated magnitudes and an earlier onset than observed. Offline radiative transfer calculations indicate that the WV and ozone anomalies drive net radiative cooling over the polar stratosphere, which steepens meridional temperature gradients and thereby intensifies the Arctic polar vortex. The observed 2024/2025 winter thus represents a plausible manifestation of HT-induced vortex variability. Our simulations also predicted the observed shift towards more favorable conditions for sudden stratospheric warmings in the winter 2025/2026 as the WV forcing declines.
