Journal of Geophysical Research: Atmospheres最新文献

Aerosol liquid water content (ALWC) and pH significantly influence secondary inorganic aerosol (SIA) formation. However, the spatiotemporal variations in ALWC and aerosol pH, along with their impacts on SIA formation, remain poorly understood. Based on a-year-long field observations of aerosol chemical components, ALWC and aerosol pH for Lanzhou and Beijing were calculated using ISORROPIA II. Aerosol liquid water content in Lanzhou was highest in winter and lowest in summer (17.2 vs. 3.30 μg m⁻³), opposite to that of Beijing (10.6 vs. 22.9 μg m⁻³). Aerosol pH in both cities was highest in winter and lowest in summer (4.68 vs. 2.96 in Lanzhou, 5.34 vs. 2.88 in Beijing). Machine learning identified TNH₃ (NH₄⁺ + NH₃), SO₄²⁻, NO₃⁻, relative humidity (RH), and temperature as crucial factors influencing ALWC and aerosol pH in both cities, while Mg²⁺ and Cl⁻ were unique factors influencing pH in Lanzhou during summer and winter, respectively. During pollution periods, the effect of ALWC on enhancing heterogeneous and aqueous-phase reactions for SIA formation was more pronounced in Beijing than in Lanzhou, as elevated ALWC levels provided more reaction medium and facilitated solid-to-liquid phase transitions. Additionally, elevated pH notably enhanced aqueous-phase sulfate production via the O₃ oxidation pathway in winter in both cities and via the H₂O₂ oxidation pathway in summer in Beijing. This study highlights the heterogeneity of ALWC and pH, along with their distinct impacts on SIA formation, which should be considered in atmospheric models to improve predictions of secondary aerosol formation and better assess the associated environmental and climatic effects.

Land restoration projects are implemented across Africa to combat land degradation and climate change. By changing the vegetation cover, these projects can potentially impact cloud formation through changes in energy and water partitioning between the Earth's surface and the atmosphere. In West Africa, satellite observations have shown an increase in cloud formation over restored areas. However, even though the spatial arrangement of restored areas differs between regreening approaches, such as farmer-managed natural regeneration, area protection or reforestation, it is unknown how the spatial pattern of restoration projects impacts cloud formation. In this study, we use the Weather Research and Forecasting (WRF) mesoscale atmospheric model to determine how land restoration affects cloud formation for a case study at the border of the transnational W-Arly-Pendjari national park complex, with a sharp boundary between forest and grassland. First, we carry out a sensitivity analysis to determine the underlying mechanisms of cloud formation over forest regions, after which we run 27 land restoration scenarios with low (21%), intermediate (43%), and high (85%) forest cover and varying spatial clustering to assess the impact of land restoration patterns on cloud formation. The results highlight that an intermediate forest cover with higher clustering increases cloud formation due to stronger mesoscale circulation. A small scale heterogeneity in forest cover or a high forest cover, on the other hand, inhibits cloud formation. Because clouds play an important role in the Earth's water and energy balance, these results provide important insight into how projects can be designed to increase their climate benefits.

Studying aerosol liquid water content (ALWC) in high-humidity, high-organic-aerosol atmospheric environments is critically important for understanding how organic matter regulates climatic and environmental effects. Here, using field observations and model simulations, we explored ALWC at a subtropical coastal site in Shenzhen. We employed a multipath ALWC calculation framework for a comprehensive closure study of ALWC and quantified the contribution of organic matter to ALWC. Results showed average ALWC during the observation period was 8.8 μg m⁻³ nearly equivalent to the dry aerosol mass. Unexpectedly, organics—accounting for over 70% of the total mass concentration of PM_2.5—contributed an average of 42% ± 15% to ALWC, representing the highest contribution reported to date in similar studies. This demonstrated that neglecting the organic compounds significantly underestimate ALWC, as was further revealed consequently reducing aerosol extinction capacity by approximately 17.2%. Unlike previous assumptions, we found that organic contribution highly depends on their hygroscopicity (κ_org) not mass fraction or ambient humidity. Our study highlights the significant role of organics in regulating aerosols liquid water content urging their inclusion in air quality and climate simulation models with the implementation of carbon reduction strategies.

Aerosols over the Tibetan Plateau (TP) strongly influence regional climate and hydrological cycles. Here we investigate the size-resolved microphysical and optical properties of aerosols in an urban area of the northern TP using a tandem system of a differential mobility analyzer, a condensation particle counter, and a single particle soot photometer. Under the 2021 summer conditions, the average particle number size distribution follows a lognormal pattern, peaking at ∼70 nm. Refractory black carbon (rBC) aerosols constitute 17.7% of the total particle population in the 100–750 nm mobility diameter (D_mob) range, with their proportion rising to over 50% for D_mob > 500 nm. Most rBC particles are externally mixed, while only 12.2% are thickly coated with non-refractory materials. Externally mixed rBC particles show strong non-sphericity, with a dynamic shape factor increasing from 1.8 at 115 nm to 2.8 at 750 nm, consistent with aggregate structures. In contrast, thickly coated rBC particles are nearly spherical, with coating thickness increasing with size. The total rBC mass estimated from size-resolved measurements closely matches bulk rBC mass directly measured. rBC-free particles exhibit slight non-sphericity, with shape factor positively correlated with refractive index, likely due to dust contributions. Bulk scattering coefficients derived from size-resolved data match those estimated under the well-mixed spherical assumption. However, the later scheme—lacking observational constraints on morphology and mixing state—overestimates absorption by over a factor of three, thereby underestimating the single-scattering albedo. These results provide key constraints for improving aerosol radiative forcing estimates and advancing understanding of aerosol–climate interactions over the TP.

The Mediterranean Sea is a weak sink for the atmospheric CO₂ with the October-March extended winter season characterized by the occurrence of high CO₂ sink events. Here, we analyzed state-of-the-art ocean and atmospheric reanalyses and observational data sets to investigate the variability of the winter sink and its relation with synoptic atmospheric features crossing the region in the period 1999–2020. High CO₂ sink events are identified using classical extreme event approach with fixed threshold (95p) based on the CO₂ daily flux distribution. First, we showed that these events are driven by large-scale atmospheric configurations that produce stronger-than-average wind speed and colder-than-average 2 m and sea surface temperature patterns in the region. Second, a co-location analysis was applied to assess the probability to detect an extra-tropical cyclone at a fixed distance from the location of the events showing that the larger the event's magnitude, the higher the probability. In most of the cases, these cyclones originate within the Mediterranean region and are usually deeper, bigger in terms of size and characterized by a stronger circulation with respect to the systems that usually cross the region. By establishing a statistical relationship between high CO₂ sink events and synoptic atmospheric activity, we emphasize the potential influence of the cyclone activity on the carbon budget of the Mediterranean Sea.

Aerosol trace element (TE) transport serves as a critical driver of marine TE biogeochemical cycles and climate feedback systems. In the rapidly warming Arctic Ocean (AO), however, the contemporary distribution patterns and decadal variability of aerosol TE deposition remain poorly constrained, representing a critical gap in our understanding of current and future Arctic environmental changes. Here, we present extensive shipboard observations of 13 aerosol TEs across the AO during summer 2024. TE concentrations and the enrichment levels of these anthropogenic TEs rank among the lowest globally observed in the AO. The comparable or even elevated mineral- dominated TE concentrations and deposition fluxes (Al, Fe) in the Central AO than Peripheral AO challenge current dust models, potential influenced by sea ice/snow resuspension. Coal combustion (As, Se), non-exhaust vehicular emissions (Ni, Cr), and metallurgical activities (Zn) emerged as primary anthropogenic sources, with detectable anthropogenic imprint even in mineral-dominated TEs (e.g., Fe, Mn). Decadal comparisons with historical records revealed a near ten-fold reduction in Pb and Cd enrichment, contrasting with a near-doubling of V enrichment driven by intensified Arctic shipping. Moreover, the distinct aerosol Fe/Al fractionation between this study and historical observations likely arises from mixing inputs of anthropogenic Fe-rich particles and permafrost-derived Fe-depleted weathering products, which amplify uncertainties in Fe flux estimations derived from dust proxy approaches. This study provides advance understanding of aerosol TE dynamics in the warming Arctic and provide critical constraints for polar biogeochemical cycles.

The characteristics of Pekeris modes as well as Lamb modes are investigated using the new reanalysis data set JAWARA, which spans over 19 years and covers the entire middle atmosphere. Pekeris modes are a class of global normal modes whose energy is trapped in two height regions that is, around the stratopause and the surface, while the energy of Lamb mode is trapped only at the surface. Statistically significant spectral peaks corresponding to both Pekeris and Lamb modes are detected for seven normal modes. The vertical structures closely match theoretical expectations for most modes. Notably, the geopotential height amplitudes of the Pekeris modes are comparable to or greater than those of the Lamb modes in the mesosphere and lower thermosphere, suggesting an important role for Pekeris modes in the dynamics of this region. On the other hand, the Lamb modes are dominant in the stratosphere.

Organic aerosols (OAs) exhibit non-ideal behaviors that challenge conventional models assuming ideal equilibrium partitioning. This study integrates a unified kinetic framework into WRF-Chem model to handle non-ideal evolution of OAs with considering kinetic mass transfer process with multidirectional interactions (particle surface area, volume, molecular weight) governed by Fick's second law. Simulations in winter of the North China Plain (NCP) reveal that non-ideal treatment enhances condensation of organics species and water vapor, amplifies interactions between OA, aerosol liquid water content (ALWC), and secondary inorganic aerosols (SIA, pSO₄²⁻, pNO₃⁻ and pNH₄⁺). The revised framework reduces mean bias in OA and SIA predictions from normalized mean bias (NMB) of −18.4% to −2.9%, −33.4% to −23.0%, −2.0% to −0.3%, and −35.4% to −30.2%, respectively, achieves better performance in reproducing ALWC with better correlation (from 0.81 to 0.88), and improves PM_2.5 modeling accuracy (NMB from −18.0% to −9.5%) in “2 + 26” city cluster among the NCP. The framework enhances predictions without modifying chemical mechanisms and suggests a potential reductions in direct radiative forcing estimation (−0.77 W/m² among the NCP). The findings advocate urgent integrating non-ideal behavior of OA into air quality models to advance aerosol prediction.

Representation of aerosol-cloud interactions (ACI) remains one of the largest uncertainties in climate models and our understanding of climate change. Using multisource cloud, aerosol, and meteorology data during summer of 2015–2024, this study investigates ACI from the perspective of aerosol size (denoted by Ångström exponent, AE) over the ocean and land in eastern China. Our findings reveal that at a fixed cloud water path, the cloud droplet effective radius (CER) increases with the aerosol index (AI) under high-AE conditions (fine-mode aerosols), while CER decreases with increasing AI when AE is below 1.4 (coarse-mode aerosols) in both regions. We interpret the opposite correlations as arising from aerosol size-dependent regulation of cloud-nucleating ability, which leads to distinct dominant cloud microphysical processes. Over land, smaller aerosols with lower cloud-nucleating ability lead to weaker competition for water vapor and the collision-coalescence process becomes dominant due to the enhanced turbulence as aerosols increase. Conversely, activation efficiency is significantly stronger for coarse-mode aerosols over the ocean and the competition effect becomes the dominant process. In addition, the dominant aerosol size decreases as cloud top pressure increases over land, leading to a transition in the CER-AI relationships from negative to positive. The link between lower cloud tops and finer aerosols is consistent with the enhanced radiative stabilization induced by a higher proportion of fine aerosols (often light-absorbing). In contrast, AE values over the ocean remain consistently low, resulting in persistent negative correlations. Despite variations in meteorological conditions, the opposite correlations under dominant coarse- and fine-mode aerosol conditions still exist.

The Arctic atmosphere in the winter months of the Northern Hemisphere is influenced by a stratospheric polar vortex, characterized by strong westerly circumpolar winds and extremely low temperatures. These vortices impact surface weather in various ways, and their dynamics may be affected by recent anthropogenic climate change. However, key aspects of these dynamics, such as the processes of energy and helicity cascading, remain unclear. In this study, we propose a novel approach to studying polar vortex dynamics that considers kinetic helicity. Mainly using ERA5 reanalysis data but also Aeolus Level 2C wind data, we examine the evolution of kinetic helicity in the stratosphere over the Arctic region during winter 2022/23. Our focus is on the formation and stability of the polar vortex, as well as sudden stratospheric warmings (SSWs). We find that the polar vortex is strongly helical, with the sign of kinetic helicity depending on the evolutionary stage of the vortex. Our analysis of the kinetic energy and kinetic helicity spectra reveals the presence of dual cascades during vortex formation. The spectral properties of the stratosphere over the Arctic change seasonally and as a function of the magnitude of the kinetic energy and helicity, with spectra being steeper during polar vortex activity. Similar correlations are absent for the spectra in the troposphere. Finally, we found that the evolution of kinetic enstrophy and helicity can predict the occurrence of SSWs with an accuracy of approximately 8 days.