Wei Xu

Ozone (O ₃ ) pollution in coastal China exhibits a widespread increasing trend in autumn, coinciding with the active period of typhoons. Yet, the role of typhoons in autumn O ₃ variations remains unclear. Here, we analyze autumn O ₃ evolution during 63 typhoon episodes over 2014–2023, and illustrate diverse impacts of typhoons on O ₃ variations over different coastal regions. We find that sideswiping typhoons, which move northward along the coasts, are more likely to trigger O ₃ pollution, enhancing surface O ₃ by 14.6∼39.5%. Model simulations show that O ₃ enhancements over northern coastal regions are primarily resulted from chemical production and vertical transport (VTRA), while horizontal transport becomes the dominant factor responsible for elevated O ₃ in southern regions during Typhoon “Muifa.” Impacts of typhoons on autumn O ₃ under global warming are further investigated using a pseudo‐global‐warming simulation technique. If the typhoon occurred under a warmer background, substantial O ₃ increases during typhoon days would be found, particularly in the northern regions, driven by stronger chemical processes and VTRA. Sensitivity simulations suggest that counteracting this warming‐induced O ₃ amplification would require a joint reduction of NO x and VOCs emissions by 30%–75%. This study offers new insights on autumn O ₃ variations impacted by typhoons based on observations and model projections, providing a scientific basis for surface O ₃ formation and possible control strategy in the warming future.

Secondary organic aerosol (SOA) formation in coastal regions, where a substantial world population resides, remains poorly understood, hindering estimation of its effects on air quality and human health. Here, SOA formation from coastal air oxidation was investigated using a field-deployed oxidation flow reactor at Tanxu Island in the Yangtze River Delta, China. High-humidity conditions with relative humidity (RH) >90% resulted in maximum SOA production of 3.7 μg m^-3, more than three times that under RH -3). This discrepancy could be attributed to an enhanced contribution of aqueous-phase processing, together with the supply of anthropogenic precursors from continental outflow. In turn, when humid coastal air was transported to nearby cities such as Shanghai, SOA production could increase, as indicated by the organic aerosol loading effect. Closure analysis indicated that the gas-phase OH oxidation of measured gaseous organics explained 57% of the measured SOA production at equivalent photochemical ages <3 days and RH <80%, with the overlooked contributions from oxygenated aromatics (18%) and furans (6%) highlighted. By isolating air mass origins, we found that SOA production with continental air masses was more than three times that in marine air masses at RH <90%; the unexplained fraction for SOA production in continental air masses (49%) was also higher than that in marine air masses (35%), suggesting unidentified anthropogenic precursors such as volatile chemical products. These results provide quantitative constraints on SOA formation in coastal air, with implications for understanding SOA pollution in downwind coastal cities.

Secondary organic aerosol (SOA) formation in coastal regions, where a substantial world population resides, remains poorly understood, hindering estimation of its effects on air quality and human health. Here, SOA formation from coastal air oxidation was investigated using a field-deployed oxidation flow reactor at Tanxu Island in the Yangtze River Delta, China. High-humidity conditions with relative humidity (RH) >90% resulted in maximum SOA production of 3.7 μg m-3, more than three times that under RH <90% (1.2 μg m-3). This discrepancy could be attributed to an enhanced contribution of aqueous-phase processing, together with the supply of anthropogenic precursors from continental outflow. In turn, when humid coastal air was transported to nearby cities such as Shanghai, SOA production could increase, as indicated by the organic aerosol loading effect. Closure analysis indicated that the gas-phase OH oxidation of measured gaseous organics explained 57% of the measured SOA production at equivalent photochemical ages <3 days and RH <80%, with the overlooked contributions from oxygenated aromatics (18%) and furans (6%) highlighted. By isolating air mass origins, we found that SOA production with continental air masses was more than three times that in marine air masses at RH <90%; the unexplained fraction for SOA production in continental air masses (49%) was also higher than that in marine air masses (35%), suggesting unidentified anthropogenic precursors such as volatile chemical products. These results provide quantitative constraints on SOA formation in coastal air, with implications for understanding SOA pollution in downwind coastal cities.

Earth system models exhibit persistent biases in simulating cloud condensation nuclei (CCN) over the Southern Ocean and Antarctica, largely due to inadequate representation of aerosol sources. Here, we present year‐round (January 2023–February 2024) measurements of aerosol hygroscopicity (HTDMA), particle number size distribution (SMPS), and CCN concentration from King Sejong Station (KSJ), Antarctica, to constrain CCN sources in this pristine environment. Size‐resolved hygroscopicity‐based source apportionment shows that sea salt aerosol (SSA) contributes 43%–54% of CCN at cloud‐relevant supersaturations (Sc = 0.2%–1.0%). Compared against the Copernicus Atmosphere Monitoring Service reanalysis (CAMSRA), our observations demonstrate that models underestimate SSA‐derived CCN at KSJ by a factor of 30 at Sc = 0.2%, providing critical constraints for aerosol–cloud interactions.

Marine primary organic aerosols (mPOAs) play a key role in ocean–atmosphere–climate interactions. Yet their effects on cloud formation remain uncertain because mPOA number size distribution measurements are lacking, obscuring its parameterizations for climate models. The mPOA number size distribution is resolved by combining long-term hygroscopicity, size, number and composition measurements in pristine marine air. The resulting bimodal distribution shows strong Aitken (∼60 nm) and accumulation (∼150 nm) modes, unlike the parameterization in widely used models. Total mPOA number is probably underestimated by a factor of three (observed/parameterized ≈ 3.1), doubling mPOA-originated cloud condensation nuclei across realistic marine supersaturations. An observation-guided sensitivity analysis indicates a potential first aerosol indirect effect of –0.03 to –0.04 W/m2 over the global ocean, reaching –0.1 to –0.2 W/m2 over biologically active waters when mPOA surface tension reduction is considered, underscoring the need for trustworthy mPOA representation to reduce the uncertainties in aerosol–cloud interactions.

Organosulfates (OSs) are important components of secondary organic aerosol, yet their molecular composition and formation processes in mountain atmospheres remain poorly constrained. In this study, PM2.5 samples collected during summer and winter at a high-altitude background site at Wuyi Mountain, southeastern China, were analyzed using high-performance liquid chromatography coupled with orbitrap mass spectrometry (HPLC-Orbitrap MS) to examine how seasonal changes in precursor availability and atmospheric processing influence OS molecular composition. Clear seasonal differences were observed in the molecular composition and structural characteristics. Summer OSs were enriched in more highly oxygenated species (with OSc >-1 accounting for 72 % of the total OS signal abundance), whereas winter OSs were characterized by larger (C5–C23), less oxygenated (O4–O7), and more unsaturated molecules, reflecting more diverse precursor influences. Among 35 structurally identified OSs, isoprene- and monoterpene-derived species were enriched in summer, while aliphatic-like OSs and monoterpene-derived nitrooxy-OSs were more abundant in winter, indicating seasonal variations in precursor availability and the relative importance of atmospheric processing. Mechanistic analysis suggested that summer OS formation was more closely associated with sulfate-rich and highly acidic conditions favorable for multiphase processing, whereas wintertime OS formation reflected greater influences from elevated atmospheric oxidants and nitrogen-related chemistry. Regional transport further contributed to wintertime OS composition by increasing anthropogenic precursor inputs and promoting atmospheric aging. These findings demonstrate that seasonal OS variability in mountain environments reflects the interplay between precursor availability and atmospheric processing, providing field-based molecular evidence for the coupling of biogenic and anthropogenic influences in secondary organic aerosol formation and evolution.

Marine organic aerosols remain a major source of uncertainty in aerosol cloud–climate interactions, in part because marine ecosystem structure and biological drivers are often represented in overly simplified terms, typically reduced to bulk chlorophyll‑a. Here, a full year of high-resolution aerosol mass spectrometry measurements at Mace Head (west coast of Ireland) is combined with HYSPLIT air-masses exposure metrics and gap-free phytoplankton functional type (PFT) fields to explore influences on primary marine organic aerosol (PMOA) and methane sulphonic acid (MSA). During the spring-summer diatom climax, PMOA correlates with dominant bloom taxa (R=0.65-0.70) and micronekton (R=0.55), with rapid 1-3 day responses and secondary maxima at ~25 days, consistent with early labile release and later lysis/grazing. During that same phase, MSA also showed a lagged responses to both PFT and micronekton reflecting delayed DMS production and oxidation. However, comparable phytoplankton air-mass exposure in the late summer of that same year (i.e. early depletion phase) did not reproduce such high correlations, with time-scale analyses indicating weakened coupling at warmer sea-surface temperatures despite moderately stronger winds. These results imply that structured ecosystem composition and physical forcing both contribute to cross-basin seasonal differences in marine organic aerosols formation. This motivates future research vessel campaigns and mesocosm experiments to explicitly manipulate PFT interactions and air-sea physics.