Acetone photolysis, via production of acetyl (CH 3 C(O)) radical, is a source of hydroxyl and hydroperoxyl radicals in the upper troposphere and peroxy acetyl nitrate in the troposphere. Still, only a...
Per- and polyfluoroalkyl substances (PFAS) are persistent, emerging environmental contaminants with diverse chemical properties and widespread industrial and consumer uses. They are used as key components in products like surfactants, lubricants, fire-fighting foams, non-stick cookware, and water-repellent coatings. Additionally, their volatility and stability enable global transport, often reaching pristine environments across various regions. This review thoroughly examines the global literature on atmospheric PFAS, focusing on their distribution in polar, midlatitude, and tropical areas, the role and mechanisms of wet deposition in their atmospheric behavior, and their chemical transformation and phase partitioning in the atmosphere. While midlatitude industrial and consumer activities are primary sources, PFAS are transported globally. Moreover, wet deposition acts as a sink for atmospheric PFAS, with snow and sea spray especially effective at scavenging long-chain PFAS. Although secondary emissions through re-volatilization could occur, the main factors governing the fate of atmospheric PFAS are precursor transformations and phase partitioning. Volatile PFAS degrade in the atmosphere into more persistent and less volatile forms via oxidative and photochemical processes. The partitioning of PFAS between gas and particulate phases depends on functionalization and chain length, with some studies also emphasizing the role of meteorological conditions. Although this review covers a broad range of regions and environments, the existing literature remains limited, especially in areas such as the Antarctic Peninsula, the Middle East, Africa, and Latin America, where data gaps persist. Future research should focus on monitoring PFAS levels in these underrepresented regions and on enhancing the fundamental and mechanistic understanding of PFAS transformation pathways. Meanwhile, policymakers should prioritize implementing stricter emission controls, reforming regulations on legacy and precursor PFAS, and harmonizing PFAS regulations worldwide.
Oxygenated volatile organic compounds (OVOCs) from volatile chemical products are emerging contributors to urban secondary organic aerosol (SOA) and ozone. Structural differences among OVOCS alter oxidation mechanisms and complicate our ability to predict air quality impacts. We examine the impact of alkyl substitution (branching) on OVOC fate during OH-initiated oxidation of two branched and two linear glycol diethers. Despite similar size and structural features, our observations show suppressed SOA yields from branched species relative to their linear counterparts, and reduced yields of lower volatility oxygenated gas-phase products. We use existing structure–activity relationships (SAR) in a simple kinetic model to examine how alkyl substitution alters the kinetics and mechanism of glycol diether oxidation. We find that peroxy radical (RO2) fate is a major control on product distributions from both branched and linear glycol diethers. Carbon-retaining hydroperoxy carbonyl products form through RO2 + HO2 reactions and RO2 H-shifts that are promoted by glycol diether functional groups. Alkyl substitution can decrease RO2 H-shift probability for both early and later generation RO2, leading to increased prevalence of bimolecular RO2 + NO pathways that promote alkoxy radical (RO) decomposition and suppress SOA formation. The governing role of functionalized RO2 fate on glycol diether oxidation, and resulting SOA production, likely applies to other classes of linear and branched OVOCs.
This study demonstrates how HCHO surface and tropospheric column behavior vary based on prevailing meteorology in the greater Boston area. Long-range transport is identified as the main driver of enhanced HCHO.
Here we report a notable slowdown in the methane growth rate observed by Total Carbon Column Observing Network (TCCON) sites in the Southern Hemisphere in 2024.
Correction for ‘Seven years of measurements of equivalent black carbon at the Capo Granitola WMO-GAW station: influence of local vegetation fires’ by Salvatore Sodano et al. , Environ. Sci.: Atmos. , 2026, 6 , 724–735, https://doi.org/10.1039/D5EA00128E.
Atmospheric aerosols play a crucial role in large-scale precipitation, global climate change, and Earth's radiative balance, with new particle formation (NPF) constituting a major source of aerosol particles. NPF is a gas-to-particle phase transition process that involves both the formation of critical clusters—commonly referred to as nucleation—and the subsequent growth of these clusters into larger particles. Theoretical and computational approaches, including quantum chemistry calculations and molecular dynamics simulations, enable investigations of NPF at the microscopic molecular level and provide fundamental insights into the mechanisms governing cluster formation. When combined with cluster dynamics models, these methods further allow quantitative assessments of the atmospheric relevance of proposed nucleation mechanisms. In recent years, machine learning techniques have also emerged as powerful tools for accelerating and optimizing these workflows. In this review, we summarize recent theoretical and computational studies on aerosol nucleation mechanisms from the perspective of molecular clusters. Particular emphasis is placed on classical and representative applications of theoretical methods in nucleation research, including configurational sampling, thermodynamics, and cluster dynamics. We aim for this review to provide a comprehensive overview of the current progress in theoretical and computational nucleation studies, while also highlighting emerging challenges and future research directions in the field.
Atmospheric microplastic (AMP) has recently emerged as a potential vector in the global carbon cycle, and a novel factor influencing the climate system. Previous studies on microplastics primarily focused on terrestrial and aquatic ecosystems, while research on AMP remains insufficient. Given the unique mobility of AMP and its function as a vector linking land, ocean, and atmosphere, this review provides a comprehensive synthesis of current knowledge on AMPs, with a focus on their sources, spatiotemporal distribution, transport and deposition processes, and detection and quantification techniques. Previous literature indicates that AMP originates from diverse sources, and its atmospheric distribution exhibits pronounced spatial heterogeneity, with transmission and deposition processes driven by meteorological conditions, particle properties, and surface–atmosphere interactions. However, substantial knowledge gaps remain regarding standardized monitoring methods, long-range transport mechanisms, and the implications of AMPs for atmospheric processes and climate forcing. In particular, limitations in detection and quantification techniques hinder accurate assessment of AMP in the atmosphere. Here, this review provides theoretical support for a comprehensive understanding of the global cycle of AMP, which offers a scientific basis for relevant environmental risk assessment and climate management decisions.
Atmospheric new particle formation has an important effect on both air quality and climate. Therefore, it is crucial to understand the potential of forming new particles, neutral or charged, in different environments. In this study, we investigated the relationship between 3–7 nm and 7–25 nm total particle concentration (N) and formation rate (J) with the concentration and formation rate of negative 2–2.3 nm charged particles (ions), which in recent studies have been found to indicate local particle formation. Data from SMEAR II station in Hyytiälä, Finland and AHL/BUCT station in Beijing, China was used. We confirmed the strong relationship between N2–2.3,– and N3–7 or N7–25 to also be valid in Beijing. We showed that this relationship also extends to J2,− and J3 or J7. The Spearman correlation coefficients were around 0.5 for daily and around 0.7 for monthly median J. We also showed that the overall relationship of J3 with J2,− was improved, when the concentration of sub-2 nm ions, from which the 2–2.3 nm ions were growing from, was accounted for. Based on this, a preliminary model to estimate J3 based on J2,− was presented. These results show that ion data can be used to evaluate also the total particle production. We argue that the concentration of sub-2 nm ions should be accounted for to get insight into the comparative particle production using ion concentrations from different locations.
Air pollution is one of the most significant environmental challenges of recent years, and monitoring it through accessible, cost-effective methods is crucial to protecting public health. This study presents a comprehensive bibliometric analysis of the scientific literature at the intersection of citizen science, low-cost sensor technologies, and air quality monitoring, during the period 1996–2026. The study aims to systematically map the intellectual structure, thematic evolution, collaboration patterns, and future trends of this interdisciplinary field. A total of 2571 scientific publications from the Web of Science Core Collection and Scopus databases were analyzed using the bibliometrix package in R and VOSviewer software. Performance analysis, science mapping, co-citation networks, keyword co-occurrence analysis, and thematic evolution mapping were conducted. The field is rapidly developing with an annual growth rate of 15.27%. A total of 9642 authors and 978 scientific sources were identified. The USA is the most prolific country with 519 publications. The most frequently used keywords were LCS (559), air quality (432), and air pollution (349). The keyword clustering identified four main thematic clusters: sensor technologies and monitoring infrastructure; measurement and calibration; particulate matter (PM) characterization using machine learning; and citizen engagement and environmental equity. The international collaboration rate is 22.29%, and this rate is lower in developing countries and regions, such as Africa and South America, which remain significantly underrepresented. Community-based, low-cost air quality monitoring is one of the most dynamic subfields of environmental health research. Sensor calibration and data quality standardization remain the most critical research issues in the field. Capacity building in developing countries, strengthening the environmental justice dimension, and developing AI-assisted calibration methods are suggested as priority topics for future research.
Peroxyacetyl nitrate (PAN) is a secondary pollutant formed through the photochemical oxidation of volatile organic compounds (VOCs) in the presence of nitrogen dioxide (NO2). Since its identification in 1956, PAN has been recognized as a major reservoir for nitrogen (NOx) and a component of photochemical smog and NOy. Its thermal instability makes PAN lifetimes highly temperature dependent, with lifetimes ranging from minutes in the warm boundary layer to months in the upper troposphere. This behavior allows PAN to transport NOx efficiently over regional and intercontinental scales, influencing downwind ozone (O3) formation, oxidant cycling, and nitrogen deposition far from emission sources. PAN is lost primarily through thermal decomposition, with slower removal via photolysis, heterogeneous uptake, and minor reactions with OH and Cl. It correlates strongly with O3, responds nonlinearly to precursor changes, and its formation is often VOC-limited in urban regions. While PAN decomposition can enhance downwind O3 formation, PAN is also toxic in its own right, functioning as a potent lachrymator and phytotoxin that directly impacts human health and vegetation. Biomass burning, haze chemistry, and free-tropospheric transport further modulate PAN abundance and seasonality. This review synthesizes the current understanding of PAN chemistry, sources, and loss pathways; evaluates historical and modern measurement techniques; and examines PAN's role in photochemical smog, air quality, vegetation injury, and regional background O3. Key uncertainties, including heterogeneous processing, indoor chemistry, and climate-driven shifts in PAN formation, are highlighted as priorities for future research. A general analysis of the literature and future research directions is discussed.
Methanesulfonic acid (MSA; CH3SO3H), produced by oxidation of dimethylsulfide (DMS; CH3SCH3), is a key precursor for aerosols in the marine boundary layer and free troposphere. Laboratory experiments show that MSA contributes to both particle nucleation and subsequent growth, often together with sulfuric acid (H2SO4) and base vapours such as ammonia (NH3). However, the influence of relative humidity (RH) on MSA condensation to particles remains uncertain. Here, in experiments conducted under low NH3 conditions (<4 parts per trillion by volume, pptv) at the CERN Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we find that RH critically regulates the participation of MSA in the initial growth of newly formed particles. Between +10 °C and -10 °C, MSA drives rapid particle growth at high RH (>50%), whereas its contribution at low RH (<16%) is negligible. When comparing with aerosol process models such as the Model for Acid-Base Chemistry in Nanoparticle Growth (MABNAG), we find that the model fails to match our laboratory results. In particular, our measurements show that MSA drives rapid particle growth at substantially warmer temperatures and lower relative humidities than predicted by the Extended Aerosol Inorganic Model (E-AIM). This highlights the importance of further experiments to fully quantify the effect of RH on MSA particle growth and evaporation, and incorporating these measurements in aerosol models. This will be essential for accurately representing the important role of MSA in marine aerosols in global models, particularly in cold, low-NH3 environments like polar regions and the free troposphere.
The formation and radiative properties of clouds in the marine boundary layer are highly sensitive to the number of cloud condensation nuclei (CCN), which largely originate from new particle formation. At present, most climate models only consider new particle formation from sulfuric acid (SA), in pristine marine regions produced via oxidation of dimethyl sulfide (DMS) emitted by phytoplankton. However, DMS oxidation also yields methanesulfonic acid (MSA) - often in higher amounts than SA under cool conditions (<10 °C) - yet MSA's role in NPF remains elusive. Here, we present results from the CERN CLOUD chamber at temperatures of -10 °C and +5 °C, demonstrating NPF from MSA and amines (dimethylamine, DMA, and trimethylamine, TMA). We isolated effects of MSA from SA by generating MSA from an evaporator at concentrations between 105 and 108 cm-3. We find MSA and DMA form particles at +5 °C but nucleation rates (J 1.7) are slow, reaching about 1 cm-3 s-1 at MSA concentrations of 5 × 107 cm-3. However, in the presence of low concentrations of SA (below 106 cm-3) and 2-15 pptv DMA, MSA at few 107 cm-3 strongly enhances SA-DMA nucleation, reaching up to 80 cm-3 s-1. Our measurements confirm MSA together with SA and DMA molecules in initial molecular clusters during nucleation. We find TMA less effective than DMA for new particle formation, likely resulting from steric hindrance of the additional methyl group. Our findings show that MSA can boost NPF rates by 1-2 orders of magnitude in pristine marine environments and should be incorporated in climate models.
This study presents a computational investigation into the role of nitrogen oxides (NO x ) in modulating gas-phase cyclohexene oxidation by ozone (O3) and hydroxyl radical (OH) through their reactions with peroxy radicals (RO2) formed during the oxidation sequence. While NO2 suppresses further oxidation by forming peroxynitrates (RO2-NO2), NO can either enhance autoxidation through the formation of reactive alkoxy radicals (RO) or terminate the radical chain via organic nitrate (RO-NO2) formation. In this work, we evaluate the binding affinities of NO x toward RO2 molecules formed at different oxidation stages at DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97X-D/aug-cc-pVTZ level of theory. This is followed by dissociation rate coefficient calculations using detailed balance and master equation simulations, indicating the lifetime and fragmentation pathways of the covalently bound RO2-NO x molecules. The results suggest a tendency toward stronger RO2-NO x stabilization with increasing oxidation stage, with a strong influence from molecular structure. This study also explores the rarely studied dissociation of RO2-NO2 into RO and NO3. Furthermore, by computing the binding enthalpies of NO3 - and with RO2-NO x , this work assesses the detectability of these N-containing oxidation products by the nitrate ion based chemical ionization mass spectrometer (NO3 --CIMS). The results are benchmarked against nitrophenol compounds known to form stable nitrate adducts. This analysis highlights potential detection biases associated with measuring nitrate-functionalized compounds using NO3 --CIMS as variations in molecular structure and clustering tendency influence signal intensities. Overall, these results highlight the regulatory roles of NO and NO2 in hydrocarbon oxidation and offer insights to improve interpretation of these oxygenated organic nitrates in atmospheric CIMS measurements.
Open biomass burning (BB) is a major global source of atmospheric particulate matter, yet laboratory studies often report divergent aerosol aging outcomes that are difficult to compare across experiments. While this variability is frequently attributed to fuel properties or oxidation conditions, the influence of the laboratory facility architecture and smoke-conditioning design has not been systematically evaluated. To address this gap, this review develops a structured framework for comparing laboratory BB aerosol facilities, informed by an analysis of 39 facilities reported in the literature. This framework integrates a nine-category structural classification with a concise encoding of consistently reported smoke-conditioning features, and it is complemented by a working hierarchy to evaluate the relative importance of facility-conditioning factors. Organic aerosol mass enhancement is employed as a representative and widely reported outcome metric to evaluate and illustrate the interpretive value of the framework, using a combination of qualitative synthesis and semi-quantitative trend analysis. The analysis indicates that facility design choices, particularly those governing smoke handling and conditioning prior to the first measurement, which define the initial smoke state, systematically influence the reported OA mass enhancement and can, in many cases, exert a stronger effect than the aging environment itself. Beyond OA mass enhancement, the framework clarifies key design trade-offs among existing laboratory configurations, improves the cross-study comparability, and provides practical guidance for the design and interpretation of future BB aerosol experiments.
The study measured air quality near metal recycling factories (MRFs), revealing elevated toxic elements (Pb, Cr, Cu, Mo, Ni, Zn) in PM10 and PM 2.5 . Lead (Pb) levels near MRFs may pose future health risks for children.
The extremely high complexity in composition of PM2.5 poses a major challenge in assessment of its environmental health risks. Laboratory-based toxicological studies are often limited by the scarcity of real environmental PM2.5 samples, which are essential for various analyses. Most conventional sampling procedures yield insufficient amounts of PM2.5 to meet the demands for physicochemical characterization, toxicological evaluation, and replication of findings. Current synthetic models typically consist of single or limited components, lacking the multi-component realism essential for accurate toxicity assessment. Here, we present a novel, facile, and scalable spray-drying method to fabricate multi-component model PM2.5 particles with tunable chemical compositions, closely mimicking real ambient PM2.5 in morphology, size distribution, and elemental profile. At the optimized temperature of 130 degrees C, over 70% of the synthesized particles were below 2.5 & micro;m, with recovery rates of representative inorganic ions exceeding 97%. We also tested the biological toxicity response of these synthetic particles in vitro. This work provides a robust, reproducible, and accessible tool for particulate toxicology and broader airborne particle research to overcome critical supply and standardization barriers, thus enabling systematic investigation of component interactions, synergistic effects, and source-specific toxicity for advancing environmental health research and risk assessment of PM2.5.
