ACS ES&T Air最新文献

{"title":"Unique Microphysical Structures of Ultrafine Particles Emitted from Turbofan Jet Engines","authors":"Akihiro Fushimi*,&nbsp;Yuji Fujitani,&nbsp;Lukas Durdina,&nbsp;Julien G. Anet,&nbsp;Curdin Spirig,&nbsp;Jacinta Edebeli,&nbsp;Hiromu Sakurai,&nbsp;Yoshiko Murashima,&nbsp;Katsumi Saitoh and Nobuyuki Takegawa,&nbsp;","doi":"10.1021/acsestair.4c0030910.1021/acsestair.4c00309","DOIUrl":"https://doi.org/10.1021/acsestair.4c00309https://doi.org/10.1021/acsestair.4c00309","url":null,"abstract":"<p >The impact of aircraft exhaust particles on human health and climate are raising concerns globally. Particle number concentrations in exhaust plumes of turbofan jet engines, which are commonly used in civil aviation, are generally dominated by volatile particles (sulfates or organics) rather than nonvolatile particles (mostly soot). However, the mechanism of emission and formation of volatile particles are unclear. Here, we evaluated the exhaust particles from turbofan engines at the engine exit and downstream. In downstream samples, the number of soot particles with scattering-layered graphene-like structures, typically generated by combustion, was &lt;1% of the total number of particles analyzed. The remaining fraction predominantly contained trace amorphous, amorphous, and onion-like particles that partially contain graphene-like circular layers. The microphysical structures of these three types of particles in aircraft exhaust plumes were newly identified. They were mainly single spherical particles with diameters of ∼10–20 nm, suggesting that they were formed via nucleation and partial pyrolysis and were not significantly affected by coagulation with preexisting soot particles. The unique internal structures of these particles may affect their physicochemical properties, including volatility, surface reactivity, and solubility, and potentially impact their interaction with the human respiratory tract.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 5","pages":"847–856 847–856"},"PeriodicalIF":0.0,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143921215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Machine Learning Approach for Predicting the Pure-Component Surface Tension of Atmospherically Relevant Organic Compounds","authors":"Ryan Schmedding,&nbsp;Mees Franssen and Andreas Zuend*,&nbsp;","doi":"10.1021/acsestair.4c0029110.1021/acsestair.4c00291","DOIUrl":"https://doi.org/10.1021/acsestair.4c00291https://doi.org/10.1021/acsestair.4c00291","url":null,"abstract":"<p >Atmospheric aerosols are complex mixtures of highly functionalized organic compounds, water, inorganic electrolytes, metals, and carbonaceous species. The surface properties of atmospheric aerosol particles can influence several of their chemical and physical impacts, including their hygroscopic growth, aerosol–cloud interactions, and heterogeneous chemical reactions. The effects of the various compounds within a particle on its surface tension depend in part on the pure-component surface tensions. For many of the myriad of organic compounds of interest, experimental pure-component surface tension data at tropospheric temperatures are lacking, thus, requiring the development and application of property estimation methods. In this work, a compiled database of experimental pure-component surface tension data, covering a wide range of organic compound classes and temperatures, is used to train four different types of machine learning models to predict the temperature-dependent pure-component surface tensions of atmospherically relevant organic compounds. The trained models process input information about the temperature and the molecular structure of an organic compound, initially in the form of a Simplified Molecular Input Line Entry System (SMILES) string, to enable predictions. Our quantitative model assessment shows that extreme gradient-boosted descent along with Molecular ACCess System (MACCS) key descriptors of molecular structure provided the best balance of derived input complexity and model performance, resulting in a root-mean-square error (RMSE) of ∼1 mJ m^–2 in pure-component surface tension. Additionally, a simplified model based on molar mass, elemental ratios, and temperature as inputs was developed for use in applications for which molecular structure information is incomplete (RMSE of ∼2 mJ m^–2). We demonstrate that including predicted pure-component surface tension values in thermodynamically rigorous bulk–surface partitioning calculations may substantially modify the critical supersaturations necessary for aerosol activation into cloud droplets.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 5","pages":"808–823 808–823"},"PeriodicalIF":0.0,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143921209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Selective Ocean–Atmosphere Bacterial Flux Through the Pacific Sea Surface Microlayer","authors":"Ariel C. Tastassa,&nbsp;Yael Dubowski,&nbsp;Or Argaman Meirovich,&nbsp;Irina Kuzmenkov and Naama Lang-Yona*,&nbsp;","doi":"10.1021/acsestair.4c0030210.1021/acsestair.4c00302","DOIUrl":"https://doi.org/10.1021/acsestair.4c00302https://doi.org/10.1021/acsestair.4c00302","url":null,"abstract":"<p >Marine–atmosphere microbial exchange is essential for nutrient cycling and ecosystem dynamics, though mechanisms are poorly understood. The role of the sea surface microlayer (SML) in mediating these exchanges was investigated. Samples were collected across a latitude gradient in the Pacific Ocean, and 16S rRNA gene and transcript sequences from surface seawater (SW), SML, and atmospheric samples were analyzed. The genomic signature varied diurnally and spatially, with the SW community being the most consistent and the air community the most variable. The SML displayed genomic characteristics intermediate between SW and air. The 16S rRNA transcript signature, a proxy for active microbial communities, showed tight clustering in the air and SML, suggesting selective control compared to SW. The transcriptional community composition in the air clustered between the SML and SW, pointing to viable non-SML-mediated exchange. Furthermore, taxa from air- and marine-associated communities showed a gradient of presence through all three environments, suggesting an exchange of key species through the SML. Additionally, certain volatile organic compounds in the atmosphere demonstrated a noteworthy relationship with specific bacterial taxa in the SML. This study improves our understanding of the role of the SML in ocean–atmosphere exchanges of marine bacteria and highlights how microbial communities travel and best utilize their environment.</p><p >Ocean−atmosphere microbial transport mechanisms are not well understood. Here, we investigate bacterial exchange processes through the sea surface microlayer using genomic and transcriptomic approaches. Our findings reveal distinct patterns between genomic presence and transcriptional activity, providing new perspectives on microbial transport across this critical interface.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 5","pages":"837–846 837–846"},"PeriodicalIF":0.0,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acsestair.4c00302","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143921216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Four Decades of Atmospheric Mercury Records at Mt. Everest Reveals Significant Reduction in Anthropogenic Mercury Emissions Over the Past Decade","authors":"Ruoyu Sun,&nbsp;Rui Zhang,&nbsp;Yuchen Yang,&nbsp;Yi Liu,&nbsp;Wang Zheng,&nbsp;Qianggong Zhang,&nbsp;Huiming Lin,&nbsp;Yindong Tong*,&nbsp;Yanxu Zhang,&nbsp;James Schauer,&nbsp;Xuejun Wang and Jiubin Chen,&nbsp;","doi":"10.1021/acsestair.4c0029610.1021/acsestair.4c00296","DOIUrl":"https://doi.org/10.1021/acsestair.4c00296https://doi.org/10.1021/acsestair.4c00296","url":null,"abstract":"<p >Mercury (Hg) is a highly toxic metal of global concern, with its anthropogenic emissions strictly controlled by the Minamata Convention on Mercury. The effectiveness of this convention is evaluated by global atmospheric Hg monitoring among other indicators. However, it is uncertain to directly link anthropogenic Hg emissions to atmospheric Hg concentrations mainly due to legacy Hg re-emissions. Here, we reconstructed the past atmospheric Hg concentrations and isotope compositions using the annually resolved (1982–2020) leaves of <i>Androsace tapete</i> at Mt. Everest, Tibetan Plateau. Our reconstruction indicates that the atmospheric Hg concentrations increased from the early 1980s to 2002 (3.31 ng m^–3), followed by a large (∼70%) decline until 2020 (0.90 ng m^–3). The declining trend of atmospheric Hg concentrations resembles those observed at North Hemisphere background sites, particularly in Chinese rural areas. Notably, there has been an increasing enrichment of light isotopes in atmospheric Hg over the past decade. Using an isotope mixing model based on δ²⁰²Hg, we show that the atmospheric Hg has declined over the past decade that is mainly driven by reduced anthropogenic emissions. The contributions of the terrestrial legacy re-emissions are rather stable, but their atmospheric fractions increased from ∼44% in 2010 to ∼62% in 2020. Given the importance of legacy Hg, the current strategies should prioritize assessing legacy Hg remobilization.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 5","pages":"824–836 824–836"},"PeriodicalIF":0.0,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143921211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Changes in Light Absorption and Chemical Properties for Biomass Burning Organic Aerosol over Long Time Scales","authors":"Rachel O’Brien*,&nbsp;Hongmin Yu,&nbsp;Natalie Warren,&nbsp;Claire Robinson,&nbsp;Christopher Y. Lim,&nbsp;Carolyn E. Jordan,&nbsp;Bruce E. Anderson,&nbsp;Jesse H. Kroll and Christopher D. Cappa,&nbsp;","doi":"10.1021/acsestair.4c0027010.1021/acsestair.4c00270","DOIUrl":"https://doi.org/10.1021/acsestair.4c00270https://doi.org/10.1021/acsestair.4c00270","url":null,"abstract":"<p >Photolysis driven fragmentation is known to decrease the light absorbing properties of brown carbon (BrC) molecules in organic aerosol particles, but chemical changes and the lifetimes for the more photorecalcitrant fraction are not well understood. In this study, we probe the photoaging behavior of biomass burning organic aerosol (BBOA) particles collected on filters during the two Fire Influence on Regional and Global Environments Experiment (FIREX) campaigns in 2016 and 2019. We evaluate changes in the chemical properties during direct photolysis on the filters and probe the photobleaching rates over extended time periods in dilute aqueous solutions. We find that most of the laboratory burns (FIREX 2016) increase the average carbon oxidation state of the BBOA over 1–3 days of photolysis. We also introduce a new characterization method called Solar Flux-Weighted Mass Absorption Cross-section (SFW-MAC) that describes the full absorption properties of the mixture. We find that estimates from our photolysis rates are in the same range as ambient lifetimes. Our results show that longer term aging studies of more than 4 days are needed to fully capture the bleaching rate of atmospheric BrC aerosols, especially for photorecalcitrant BrC that will play a larger role farther away from the original emission source.</p><p >When brown carbon containing aerosol particles are irradiated, they can lose color, which is a process termed photobleaching. This study shows that the photobleaching rate is variable but generally has a lifetime of about 20 h and that a large change in the oxidation state of the mixture occurs during the photolysis. This laboratory rate is longer than most other laboratory measurements and more in agreement with ambient results. Longer-term experiments enabled these improvements in the rate estimates.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 5","pages":"773–785 773–785"},"PeriodicalIF":0.0,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143921213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gas-Phase Oxidation of Guaiacol by NO3 Radicals: Kinetic Measurements and Implications","authors":"Xiangyu Zhang,&nbsp;Hongxia Liu,&nbsp;Jianlin Cheng,&nbsp;Wei Song,&nbsp;Haichao Wang,&nbsp;Yanli Zhang and Xinming Wang*,&nbsp;","doi":"10.1021/acsestair.4c0035310.1021/acsestair.4c00353","DOIUrl":"https://doi.org/10.1021/acsestair.4c00353https://doi.org/10.1021/acsestair.4c00353","url":null,"abstract":"<p >Methoxyphenols, critical tracers of biomass burning emissions, are emitted in large quantities during lignin pyrolysis. Gas-phase reaction of methoxyphenols with nitrate radicals (NO₃) yields to important secondary products like nitrophenols, yet their atmospheric kinetics are far from adequate and consistent. This study investigates the gas-phase reaction kinetics of guaiacol, a key representative methoxyphenol, with NO₃ by using a controlled 30 m³ indoor chamber. Both relative rate and absolute rate methods were employed, yielding rate constants of (3.1 ± 0.2) × 10^–11 and (2.43 ± 0.19) × 10^–11 cm³ molecule^–1 s^–1, respectively, at 298 ± 2 K under dry conditions. The rate constant decreased with an increase in humidity, highlighting the inhibitory effect of water vapor on NO₃-initiated reactions. The calculated nocturnal atmospheric lifetime of guaiacol due to NO₃ reactions is less than 2 min at typical nocturnal NO₃ levels, underscoring the significance of this pathway in the budget of methoxyphenols during nighttime or within a 24 h cycle. To the best of our knowledge, this study represents the first determination of the NO₃-guaiacol rate constant using the absolute rate method and provides insights into the role of relative humidity in methoxyphenol oxidation. These findings offer critical data for understanding the atmospheric fate of biomass burning emissions and their contributions to nighttime chemistry and air quality.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 5","pages":"903–910 903–910"},"PeriodicalIF":0.0,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143921518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Co-Occurring Extremes of PM2.5 and Ozone in Warm Seasons of the Yangtze River Delta of China: Insights from Explainable Machine Learning","authors":"Yan Lyu*,&nbsp;Danni Wu,&nbsp;Fuliang Han,&nbsp;Huiying Zhang,&nbsp;Fengmao Lv,&nbsp;Azhen Kang,&nbsp;Yijia Hu and Xiaobing Pang,&nbsp;","doi":"10.1021/acsestair.4c0031410.1021/acsestair.4c00314","DOIUrl":"https://doi.org/10.1021/acsestair.4c00314https://doi.org/10.1021/acsestair.4c00314","url":null,"abstract":"<p >Recently, summertime PM_2.5 and ozone extremes were reported to frequently co-occur in southern China. In this study, we further demonstrate that their co-occurring extremes can spread into warm seasons in the Yangtze River Delta (YRD) region of China. The annual co-occurrence frequency ranged from 26% to 50% in the YRD from 2015 to 2022, with higher frequencies observed in coastal cities. Notably, the co-occurrence frequency was higher during the COVID-19 pandemic, implying that such co-occurrence may be more spatially widespread with continuous PM_2.5 reduction in China. Taking the pandemic period as an example, we leveraged a machine learning algorithm (i.e., Random Forest) coupled with SHapley Additive ExPlanation (SHAP) to identify higher relative importance of solar radiation-related variables (e.g., surface net solar radiation) during co-occurrence periods compared to non-co-occurrence periods in the YRD. Additionally, incorporating volatile organic compounds (VOCs) measurements, we further showed the higher relative importance of VOCs to the extremes of ozone and PM_2.5 through a case study at Shaoxing (a typical city in the YRD). Overall, the findings highlight the increasing potentials for co-occurring extremes with ongoing PM_2.5 reductions in the YRD and suggest that reducing VOCs (e.g., halocarbons) may help mitigate these extremes in the future.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 4","pages":"578–588 578–588"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ultrafine Particle Growth Rate During Biogenic Secondary Organic Matter Formation as a Function of Particle Composition, Size, and Phase","authors":"Michael S. Taylor Jr.,&nbsp;Devon N. Higgins,&nbsp;Justin M. Krasnomowitz and Murray V. Johnston*,&nbsp;","doi":"10.1021/acsestair.4c0033910.1021/acsestair.4c00339","DOIUrl":"https://doi.org/10.1021/acsestair.4c00339https://doi.org/10.1021/acsestair.4c00339","url":null,"abstract":"<p >The growth rate of ultrafine seed particles by uptake of secondary organic matter (SOM) is studied with a flow tube reactor to elucidate key factors that can enhance or inhibit the rate. Through application of a time-dependent kinetic model, the molecular growth factor (GF) associated with SOM formation is determined. GF is defined as the fraction of the oxidation products from a biogenic precursor that contribute to seed particle growth. Two seed particle compositions (ammonium sulfate and ammonium bisulfate) are studied under two phase states (effloresced and deliquesced at either 10% or 60% relative humidity) for growth by two different biogenic precursors (isoprene and α-pinene). The results show: (1) ammonium sulfate seed particles give higher GFs than ammonium bisulfate seed particles, (2) increasing the water content of the seed particle increases the GF, and (3) isoprene and α-pinene show the same dependencies of GF on seed particle composition and water content. These dependencies suggest that physicochemical processes in the aqueous layer at or near the air–particle interface enhance the growth rate of particles in the 40 to 80 nm size range, which is relevant to the formation of cloud condensation nuclei.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 4","pages":"615–624 615–624"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High Abundance of Atmospheric Sulfonates Derived from Light-Duty Gasoline Vehicles","authors":"Shuang Chen,&nbsp;Huixia Han,&nbsp;Lihong Ren,&nbsp;Yisheng Xu*,&nbsp;Libin Wu,&nbsp;Yuanguan Gao,&nbsp;Yuanbi Yi,&nbsp;Xinping Yang,&nbsp;Mingliang Fu,&nbsp;Hang Yin,&nbsp;Yan Ding and Pingqing Fu*,&nbsp;","doi":"10.1021/acsestair.4c0033410.1021/acsestair.4c00334","DOIUrl":"https://doi.org/10.1021/acsestair.4c00334https://doi.org/10.1021/acsestair.4c00334","url":null,"abstract":"<p >Particulate matter (PM) emissions from light-duty gasoline vehicles (LDGV) pose a threat to both air quality and human health. However, the molecular compositions and chemical properties of these complex mixtures are poorly understood. In this study, we performed a detailed characterization of exhaust PM from LDGV at various speed phases at the molecular level by employing ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry. We found that with increasing speed, the number of organic compounds increased significantly, especially organic nitrogen-containing and sulfur-containing compounds. Moreover, the increase of speed leads to high temperature and high pressure in the cylinder, which in turn leads to a series of thermal cracking–polymerization–cyclization reactions, resulting in new particulate matter with more aromatic structures. In addition, considerable intermediate volatility organic compounds and semivolatile organic compounds were identified in the exhaust PM. Notably, we observed the presence of sulfonates in tailpipe particulate matter during low- or high-speed phases, which highlights a previously negligible source of organic sulfonates in the atmosphere.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 4","pages":"607–614 607–614"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemical Imaging of Atmospheric Biomass Burning Particles from North American Wildfires","authors":"Felipe A. Rivera-Adorno,&nbsp;Jay M. Tomlin,&nbsp;Nurun Nahar Lata,&nbsp;Lisa Azzarello,&nbsp;Michael A. Robinson,&nbsp;Rebecca A. Washenfelder,&nbsp;Alessandro Franchin,&nbsp;Ann M. Middlebrook,&nbsp;Swarup China,&nbsp;Steven S. Brown,&nbsp;Cora J. Young,&nbsp;Matthew Fraund,&nbsp;Ryan C. Moffet and Alexander Laskin*,&nbsp;","doi":"10.1021/acsestair.4c0024210.1021/acsestair.4c00242","DOIUrl":"https://doi.org/10.1021/acsestair.4c00242https://doi.org/10.1021/acsestair.4c00242","url":null,"abstract":"&lt;p &gt;The effects of biomass burning aerosols (BBA) on radiative forcing and cloud formation depend on chemical composition and the internal structures of individual particles within smoke plumes. To improve our understanding of the chemical and physical properties of BBA emitted at different times of the day and their evolution during atmospheric aging, we conducted a study as a part of the Fire Influence on Regional to Global Environments and Air Quality field campaign. Particle samples were collected onboard a research aircraft from smoke plumes from a wildfire in eastern Oregon during late afternoon and nighttime flights on August 28, 2019. A time-resolved aerosol collector was used to collect samples on substrates for offline spectromicroscopic imaging to investigate the single-particle characteristics of BBA particles. Approximately 20,400 individual particles from 10 selected samples were analyzed using computer-controlled scanning electron microscopy coupled with energy-dispersive X-ray microanalysis, revealing their elemental composition, morphology, and viscosity. Elemental microanalysis indicated that aged potassium is likely found in the form of K&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;, KNO&lt;sub&gt;3&lt;/sub&gt;, and possible K-organic salts. Further chemical speciation and carbon bonding mapping within individual particles were conducted using synchrotron-based scanning transmission X-ray microscopy (STXM) coupled with near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Real-time, water-soluble light absorption measurements were acquired using a particle-into-liquid sampler instrument coupled to a liquid waveguide capillary cell and total organic analyzer. In the late afternoon samples, 65% of the total particle number population consisted entirely of organic components, compared to 46% in the nighttime particles. These differences were attributed to discrepancies in composition at the time of emission and to the daytime condensation and accumulation of photochemically formed secondary organic material on existing BBA particles, a process that halts at night. Microscopy images indicated that particle viscosity was lower in the nighttime particles (&lt;10&lt;sup&gt;1&lt;/sup&gt; Pa·s), likely due to increased relative humidity and a higher contribution from hygroscopic inorganic components. The chemical heterogeneity of individual particles was quantified using STXM-derived mixing state parameters. The nature of carbon bonding within individual particles was inferred from the extent of carbon sp&lt;sup&gt;2&lt;/sup&gt; hybridization derived from NEXAFS spectra. Average percentages of sp&lt;sup&gt;2&lt;/sup&gt; hybridization range between 40% and 60%, with no noticeable differences between late afternoon and nighttime flights. These findings were compared with the online optical properties of both late afternoon and nighttime smoke plumes, providing valuable insights into the complex relationship between chemical composition and optical properties of BBA particles at different times","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"2 4","pages":"508–521 508–521"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814423","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}