Atmospheric dry deposition is a crucial process influencing the fate of polycyclic aromatic hydrocarbons (PAHs) and their derivatives. Seasonal variations in deposition reflect changes in the environmental behaviour and sources of these compounds over time. This study investigated the occurrence and dry deposition fluxes of PAH and their derivatives in atmospheric particulate samples collected on Beihuangcheng Island (BHC) in the central Bohai Sea in August and October 2019 and February and May 2020. The study focused on 16 priority PAHs designated by the United States Environmental Protection Agency (Σ16PAHs), 12 alky-PAHs (Σ12A-PAHs), and 25 nitro-PAHs (Σ25N-PAHs). We calculated the dry deposition velocities of PAHs and their derivatives using an improved Slinn model, which accounted for the significant variations among particles of different sizes. The results revealed that the annual average concentrations of Σ16PAHs, Σ12A-PAHs, and Σ25N-PAHs were 2.5 ± 2.4 ng m−3, 0.4 ± 0.2 ng m−3, and 0.09 ± 0.08 ng m−3, respectively. In summer, 2- and 3-ring compounds dominated Σ16PAHs, Σ12A-PAHs, and Σ25N-PAHs. In contrast, 4-, 5-, and 6-ring compounds were more prevalent in winter. Oil combustion was identified as the main source of PAHs and their derivatives in the atmosphere at BHC. These compounds were mainly associated with fine particles in the <0.65 μm and 0.65–1.1 μm size ranges. The dry deposition fluxes of PAHs and their derivatives were estimated using the observational data and a typical dry deposition model. The annual average dry deposition fluxes of Σ16PAHs, Σ12A-PAHs, and Σ25N-PAHs were 75.37 ± 45.08 μg m−2 yr−1, 20.88 ± 8.29 μg m−2 yr−1, and 3.58 ± 1.61 μg m−2 yr−1, respectively. This study provides new insights into the environmental fate of PAHs and their derivatives and valuable guidance for developing effective measures to protect marine ecosystem health.
Coastal fog efficiently scavenges atmospheric particles and provides a pathway for transferring dissolved elements to terrestrial and aquatic ecosystems, yet their short-term variability within individual fog events remains poorly resolved. This study presents a time-resolved characterization of dissolved elements in four coastal fog events sampled at Casitas Pass, Southern California. Twenty-one elements were targeted in filtered fogwater by inductively coupled plasma-mass spectrometry, of which nineteen were quantified. Temporal variability was evaluated using liquid water content (LWC), air-equivalent element concentrations, enrichment factors relative to upper continental crust and locally collected sea spray, source contribution estimates, air-mass back trajectories, and Spearman correlation analysis. Na, Ca, Mg, and K accounted for approximately 94-98% of the total dissolved element concentration, confirming a strong marine influence. Total dissolved elemental concentrations tended to decrease with increasing LWC (Spearman’s ρ = -0.44, p = 0.057), consistent with an aqueous dilution effect, whereas this relationship was substantially attenuated when concentrations were expressed on an air-equivalent basis (ρ = 0.24, p = 0.318). This indicates that LWC contributed to concentration variability but was not the sole controlling factor. Time-resolved profiles further showed substantial within- and between-event variability associated with changes in aerosol loading, fog microphysics, particle scavenging and removal, and air-mass history. Source contribution estimates indicated that Mg was predominantly marine, whereas Fe and Cr showed substantial crustal contributions. In contrast, Zn, Cu, Mo, Cd, Pb, V, Ni, Ba, and W were largely associated with non-sea-spray and non-crustal fractions, consistent with mixed anthropogenic influences including traffic, combustion, shipping, oil-related activities, and regional industrial emissions. The results demonstrate that coastal fog integrates marine, crustal, and anthropogenically influenced aerosol sources, while rapid changes in LWC, atmospheric element burden, and air-mass origin can substantially modify dissolved element composition over the course of individual fog events.
We use global atmospheric chemistry models (GACMs) to understand the extent to which NOx emissions from ships affect the surface ozone concentration and its seasonal cycle over continental regions. Here we use three different attribution approaches: NOx-tagged, combined-tagged and perturbation; implemented in three different GACMs, for understanding the qualitative and quantitative differences in employing these approaches for attributing surface ozone to NOx emitted from ships sailing over various marine regions. Using the NOx-tagged method, we attribute ∼10 % contribution of ship NOx emissions to the simulated surface ozone over the receptor regions considered in our study. The summer peak in this contribution (eg. Over NW Europe) was mainly from NOx emissions over nearby marine regions (such as Baltic and North Seas). During the non-summer months, we simulate large contributions to surface ozone from remote marine regions (such as North Pacific). The combined-tagged approach attributes only ∼7.7 % relative contribution from ship-tagged component, which is a smaller relative contribution compared to the NOx-tagged approach, due to the attribution considering an equally weighted small contribution of reactive carbon emitted from ships. Perturbation approach simulates the impact of changing NOx emissions on surface ozone concentration, which in our study is ∼2.3 % of the ozone in the unperturbed simulation. This impact simulated using the perturbation approach is smaller compared to the contributions simulated using the tagging approaches discussed above. We explore the reason for the smaller impact simulated using the perturbation approach compared to the tagged contributions, by simulating NOx-tagged and combined-tagged perturbations in ship NOx emissions and quantify the role of both perturbed and unperturbed tagged emission sources in contributing to the response to perturbation. The non-tagged surface ozone response to ship-NOx perturbation is ∼2.5-5 times smaller than the response from the ship-tagged ozone component, because of compensating negative responses due to reduction in ozone production from other contributing tagged-components such as land-based natural and anthropogenic ozone precursor NOx sources.
Aerosols strongly influence climate by regulating cloud vertical structure and precipitation efficiency. Using nearly seven years of ground-based, in situ, and satellite observations over Gadanki (13.50N, 79.20E), a tropical station in India, this study investigates meteorological and aerosol interactions in warm (below the 00C level) and mixed-phase clouds (within the -200C to -400C level), with a particular focus on identifying phase-dependent aerosol-cloud interaction pathways and their vertical structure within clouds. Random Forest and Extreme Gradient Boosting models are employed to relate cloud optical depth (COD) to aerosol optical depth (AOD) and meteorological conditions. By analyzing COD sub-layers above the cloud base, this study distinguishes how aerosol, thermodynamics and dynamical controls on cloud optical properties vary with cloud-phase and vertical position inside the cloud. In warm clouds, COD near the cloud base shows a strong association with AOD, exerting a dominant positive influence across all liquid water path regimes, consistent with patterns expected from cloud condensation nuclei (CCN) limited activation and saturation at high aerosol loading. This AOD association weakens with height and is replaced by wind speed, indicating the increasing role of entrainment-driven turbulent mixing. Cloud base temperature emerges as an additional predictor for most of the liquid water path regimes, consistent with increased CCN growth at lower temperatures. In contrast, mixed-phase clouds column-integrated COD has the strongest association with temperature, consistent with the cloud conditions associated with ice formation and liquid depletion. Near cloud base, AOD emerged as secondary predictor, with higher COD preferentially associated with lower AOD, consistent with conditions associated with more efficient CCN activation under relatively cleaner conditions and a reduced role of AOD relative to thermodynamics and ice-phase processes. Meanwhile, wind direction emerges as a dominant modulator for sublayers, reflecting the influence of air –mass origin on glaciation and the persistence of supercooled liquid water. These results demonstrate that aerosol impacts on COD are strongly phase- and height-dependent, underscoring the need for phase-aware representations of aerosol–cloud–meteorology coupling in climate models.
The long-term increase of ozone (O3) concentration in China has attracted growing attention in recent years, particularly during the pre-pandemic periods of 2014-2019, when the ambient PM2.5 is remarkably reduced. However, the variation of relatively higher nocturnal O3 value (HNOV) and the influencing factors on an annual time scale and a national scale are still unclear. Here, we have focused on analysis of the 5-year (2015–2019) summer field observation dataset with the GeoDetector model. The study is with the aim to investigate the spatiotemporal patterns and influencing mechanisms of the frequency of nocturnal O3 exceeding 80 μg/m3 (FNO80), a provisional metric to characterize the HNOV. We found a significant nationwide increasing trend in summer FNO80 during 2015–2019, rising from 18 ± 15% in 2015 to 25 ± 18% in 2019, with high-FNO80 sites widely distributed in northern China (e.g., Northern Coastal Area and Middle Reaches of the Yellow River Area). GeoDetector analysis revealed that intensifying daytime O3 pollution was the key influencing factor (with a contribution of 39%) of the nationwide long-term increasing trend in FNO80, while precipitation and relative humidity were with contributions of 20% and 19% respectively, showing the primary role in mitigating high nocturnal O3 levels. Focusing on five megacities (Beijing, Xi’an, Guangzhou, Shanghai, and Chengdu), the 5-year average FNO80 was the highest in urban Beijing (36 ± 6%) and the lowest in urban Guangzhou (4 ± 2%). The urban-suburban differences of FNO80 (ΔSuburban-UrbanFNO80) were distinct across cities, and the daytime O3 was still the most correlated influencing factor. Notably, Xi’an exhibited a fast increase of FNO80 and a prominent urban-suburban FNO80 difference, which linked to the deteriorated daytime O3 pollution and large daytime urban-suburban O3 gap. In these megacities, nocturnal PM2.5 and NO2 concentrations also exerted important impacts on FNO80. This study quantified the effects of multiple factors on nocturnal O3 across China against the backdrop of a significant improvement in PM2.5 pollution, providing support for policy-making to mitigate O3 pollution.
Coal-to-gas (CTG) has triggered long- and short-term energy evolutions, and urban-rural disparities in VOC sources, reactivity, toxicity, and O3 sensitivity. Scant research hindered targeted policy improvement. In winter 2024 pre-heating/heating seasons (PHS/HS), we measured 116 VOCs at urban/rural sites, and pioneered their quantifications of residential natural gas combustion (NGC) and pinpointing of NGC emission impacts. Together, we established Hebei provincial residential/industrial biomass/coal/NG emission inventories covering pre-/ongoing/post-CTG stages. From pre- to post-CTG (2012–2022), NG surged, coal diminished, and biomass rebounded (VOC emissions: +252.8%/–42.1%/+60.7%). NGC yielded lower emission factor of 64.1 μg/m3 NG consumed and alkane/alkene fractions than coal/biomass. Long-term combustion emissions (CE) declined stepwise within the “2+26” cities, with sporadic resurgence in coal-reliant urban and biomass-rebound rural areas. NG/LPG-usage contributions to VOCs and reactivity rose, and eventually isolated as an independent source in this study. Urban VOCs/ozone formation potential (OFP)/secondary organic aerosol potential (SOAP)/OH loss rate (LOH)/toxicity increased in HS compared to PHS driven mainly by heating coal combustion (CC) from thermal plants, while rural levels decreased regardless of resurgent biomass burning (BB). Increased urban CC, rural BB and decreased rural CC tracers in HS corroborated the foregoing findings. NGC dominated HS’s VOCs/OFP/SOAP/LOH, particularly in urban site, but not to toxicity. Arising mainly from CTG-related NOx declines, urban O3 shifted from VOC-limited (PHS) to VOC-NOx-limited (HS), while rural site transitioned from co-limited to NOx-limited. We clarified CTG effects on spatiotemporal disparities in energy and VOC emissions, delineating priority targets for region-specific control.
Amino acids, as important constituents of atmospheric organic nitrogen, play significant roles in global biogeochemical cycles. Their atmospheric fate has traditionally been attributed to photochemical processes, whereas the role of the unique chemistry in microdroplet, characterized by spontaneous OH radical generation, remains poorly understood. Here, we used a microdroplet generation apparatus coupled with online electrospray ionization mass spectrometry to study the spontaneous transformation of three representative amino acids (tryptophan, serine, and cysteine). By systematically varying reaction time, initial concentration and sheath gas pressure, we confirmed that these reactions occur specifically in microdroplets. Products analysis by a triple quadrupole mass spectrometer revealed spontaneously generated OH radicals as the primary driver, yielding distinct products such as hydroxylated monomers and dimers, that differs from that of bulk-phase oxidation. Quantitative assessment further revealed that high salinity, acidic pH, and oxidative atmospheres significantly accelerate the reactions, with notable compound-specific effects. High salinity most prominently enhanced serine transformation (∼7%), acidic condition (pH 3.0) maximally promoted tryptophan conversion (∼11%), and O2 primarily accelerated oxidation pathway of cysteine (∼17%). These findings reveal that the spontaneous transformation of amino acids in microdroplets, modulated by salinity, acidity, and oxygen availability, represents a previously unrecognized pathway for organic nitrogen conversion in the atmosphere. This work provides experimental evidence for integrating such processes into atmospheric chemistry models to reassess the cycling and lifetime of organic nitrogen.
Historically, anthropogenic combustion activities have emitted black carbon (BC) and organic aerosols into the atmosphere, contributing to global pollution and to the Earth’s radiative balance. Detailed analyses of ice-core archives are important for improving our understanding of past aerosol emissions and their implications for climate. For this study, using a nebulizer system combined with water dialysis in addition to BC measurements with a Single Particle Soot Photometer (SP2), we conducted observations of transmission electron microscopy (TEM) samples of sub micrometer water-insoluble (WI) particles in an ice core from Southeast Greenland. We analyzed samples of 1910, a period when BC concentrations were high, and of 2013, when the model indicated large biomass-burning effects in summer but anthropogenic effects in the other seasons. A large proportion of WI particles were carbonaceous, including aggregates and spheres, with morphological features typical of combustion particles. Their mass deposition flux values (Fx) were estimated from TEM analysis results and BC concentrations. For 70–1000 nm WI particles, the Fx values of BC and organic-rich particles were 0.05–0.8 mg m-2 season-1 and 0.3–0.8 mg m-2 season-1 for 2013, and 0.5–1.7 mg m-2 season-1 and 0.5–1.2 mg m-2 season-1 for 1910. The Fx values of carbonaceous aggregates were higher in 1910 than in 2013, except in summer. Aggregates comprising mainly organics, which were almost absent from 2013 samples, were found in 1910 samples, along with soot-containing aggregates, implying contributions from wood combustion. These results suggest that anthropogenic combustion activities during the pollution period approximately 100 years ago emitted substantial amounts of submicrometer WI organic particles into the atmosphere along with BC. The combination of BC measurement and TEM analysis is expected to be useful for estimating the amounts of morphologically and compositionally categorized organic and trace metals when applied to various clean accumulated samples.
Aerosol optical depth (AOD) is widely used to estimate surface fine particulate matter (PM2.5), defined as particles with an aerodynamic diameter smaller than 2.5 μm, particularly in regions where ground monitoring is sparse. However, their seasonal correspondence over Europe remains poorly understood. Using integrated surface observations, satellite retrievals, and reanalysis data, we examine the relationship between column AOD and surface PM2.5 across Europe during 2013–2021. A robust seasonal contrast is evident: column AOD peaks in summer and is lowest in winter, whereas surface PM2.5 exhibits the opposite seasonal feature. This mismatch is closely linked to vertical aerosol structure, with a transition height at approximately 0.88 km where the seasonal ranking of aerosol extinction reverses. Below this height, aerosol extinction is highest in winter and lowest in summer, while above it, extinction is enhanced in spring and summer. Aerosol extinction profiles from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) show that sulfate aerosols make an important contribution to aerosol extinction over Europe, while elevated dust extinction in spring and summer and enhanced near-surface sea-salt extinction in winter further modulate the seasonal vertical structure. The summed extinction from five major aerosol components reproduces the vertical extinction structure observed by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). These findings provide an explanation for the seasonal AOD–PM2.5 decoupling over Europe and offer insights for improving AOD-based PM2.5 estimation in air-quality applications.
Climate change and tropospheric ozone pollution present interconnected challenges to China's environmental and public health. To quantify the climatic impacts on ozone, we employed a Transformer model trained on multi-source data including a multi-model ensemble from the Coupled Model Intercomparison Project Phase 6 (CMIP6). This model projected China's ozone trends for 2024–2100 under four Shared Socioeconomic Pathways (SSPs: SSP1-2.6 to SSP5-8.5) and quantified the health risks attributable to long-term ozone exposure. Historical validation confirmed the high accuracy of the ozone Transformer model (R2=0.91), with SHapley Additive exPlanations (SHAP) analysis pinpointing temperature and surface solar radiation as the dominant meteorological drivers. Results showed a clear upward trend in annual mean near-surface ozone, with the national average under SSP5-8.5 reaching 92.66 μg/m3 by 2100. Regionally, the near-surface ozone increased by 1%–5% over the Northeast (NE), Eastern China (EC), and the Northwest (NW), with the NE showing the largest increases and the highest scenario sensitivity. Climate forcing intensified seasonal contrasts, lengthening the ozone season and amplifying the winter-spring increases. A health risk assessment showed that the population-weighted excess ozone concentration (ExC) above the WHO Long-term Air Quality Guideline increased by up to 11.0% under SSP2-4.5. Although the national premature mortality declined by 10%–42% across the four scenarios due to the population reduction, an LMDI decomposition revealed that the climate-driven component is positive, with the largest climate-driven increase of +106.5 thousand persons occurring under SSP2-4.5 rather than under SSP5-8.5These findings indicate the climate-driven amplification of ozone pollution and support-coordinated mitigation to advance China’s dual-carbon goals.
