Search Results (211)

Ammonia (NH₃), as a vital component of the nitrogen cycle, exerts significant influence on the biosphere, air quality, and climate by contributing to secondary aerosol formation through its reactions with sulfur dioxide (SO₂) and nitrogen oxides (NO_x). Despite its critical environmental role, NH₃’s transient atmospheric lifetime and the variability in spatial and temporal distributions pose challenges for effective global monitoring and comprehensive impact assessment. Recognizing the inadequacies in current in situ measurement capabilities, this study embarked on an extensive analysis of NH₃’s temporal and spatial characteristics over East Asia, using the Infrared Atmospheric Sounding Interferometer (IASI) onboard the MetOp-B satellite from 2013 to 2024. The atmospheric NH₃ concentrations exhibit clear seasonality, beginning to rise in spring, peaking in summer, and then decreasing in winter. Overall, atmospheric NH₃ shows an annual increasing trend, with significant increases particularly evident in Eastern China, especially in June. The regional NH₃ trends within China have varied, with steady increases across most regions, while the Northeastern China Plain remained stable until a recent rapid rise. South Korea continues to show consistent and accelerating growth. East Asia demonstrates similar NH₃ emission characteristics, driven by farmland and livestock. The spatial and temporal inconsistencies between satellite data and global chemical transport models underscore the importance of establishing accurate NH₃ emission inventories in East Asia. Full article

This study investigates the emission characteristics and environmental impacts of pollutants from bagasse-fired biomass boilers through the integrated field monitoring of two sugarcane processing plants in Guangxi, China. Comprehensive analyses of flue gas components, including PM_2.5, NOx, CO, heavy metals, VOCs, HCl, and HF, revealed distinct physicochemical and emission profiles. Bagasse exhibited lower C, H, and S content but higher moisture (47~53%) and O (24~30%) levels compared to coal, reducing the calorific values (8.93~11.89 MJ/kg). Particulate matter removal efficiency exceeded 98% (water film dust collector) and 95% (bag filter), while NOx removal varied (10~56%) due to water solubility differences. Heavy metals (Cu, Cr, Ni, Pb) in fuel migrated to fly ash and flue gas, with Hg and Mn showing notable volatility. VOC speciation identified oxygenated compounds (OVOCs, 87%) as dominant in small boilers, while aromatics (60%) and alkenes (34%) prevailed in larger systems. Ozone formation potential (OFP: 3.34~4.39 mg/m³) and secondary organic aerosol formation potential (SOAFP: 0.33~1.9 mg/m³) highlighted aromatic hydrocarbons (e.g., benzene, xylene) as critical contributors to secondary pollution. Despite compliance with current emission standards (e.g., PM < 20 mg/m³), elevated CO (>1000 mg/m³) in large boilers indicated incomplete combustion. This work underscores the necessity of tailored control strategies for OVOCs, aromatics, and heavy metals, advocating for stricter fuel quality and clear emission standards to align biomass energy utilization with environmental sustainability goals. Full article

This perspective explores the use of biochar, a carbon-rich material derived from biomass, as a sustainable solution for mitigating volatile organic compounds (VOCs) emitted during asphalt production and use. VOCs from asphalt contribute to ozone formation and harmful secondary organic aerosols (SOAs), which negatively impact air quality and public health. Biochar, with its high surface area and capacity to adsorb VOCs, provides an effective means of addressing these challenges. By tailoring biochar’s surface chemistry, it can efficiently capture VOCs, while also offering long-term carbon sequestration benefits. Additionally, biochar enhances the durability of asphalt, extending road lifespan and reducing maintenance needs, making it a promising material for sustainable infrastructure. Despite these promising benefits, several challenges remain. Variations in biochar properties, driven by differences in feedstock and production methods, can affect its performance in asphalt. Moreover, the integration of biochar into existing plant operations requires the further development of methods to streamline the process and ensure consistency in biochar’s quality and cost-effectiveness. Standardizing production methods and addressing logistical hurdles will be crucial for biochar’s widespread adoption. Research into improving its long-term stability in asphalt is also needed to ensure sustained efficacy over time. Overcoming these challenges will be essential for fully realizing biochar’s potential in sustainable infrastructure development Full article

Medellín, a densely populated city in the Colombian Andes, faces significant health and environmental risks due to poor air quality. This is linked to the atmospheric dynamics of the valley in which it is located (Aburrá Valley). The region is characterized by a narrow valley and one of the most polluted areas in South America. This is a comparative study of the chemical composition of PM_2.5 (particles with diameter less than 2.5 µm) in Medellín between two periods (2014–2015 and 2018–2019) in which temporal trends and emission sources were evaluated. PM_2.5 samples were collected from urban, suburban, and rural stations following standardized protocols and compositional analyses of metals (ICP-MS), ions (ion chromatography), and carbonaceous species (organic carbon (OC) and elemental carbon (EC) by thermo-optical methods) were performed. The results show a reduction in average PM_2.5 concentrations for the two periods (from 26.74 µg/m³ to 20.10 µg/m³ in urban areas), although levels are still above WHO guidelines. Urban stations showed higher PM_2.5 levels, with predominance of carbonaceous aerosols (Total Carbon—TC = OC + EC = 35–50% of PM_2.5 mass) and secondary ions (sulfate > nitrate, 13–14% of PM_2.5 mass). Rural areas showed lower PM_2.5 concentrations but elevated OC/EC ratios, suggesting the influence of biomass burning as a major emission source. Metals were found to occupy fractions of less than 10% of the PM_2.5 mass; however, they included important toxic species associated with respiratory and cardiovascular risks. This study highlights progress in reducing PM_2.5 levels in the region, which has been impacted by local policies but emphasizes current and future challenges related mainly to secondary aerosol formation and carbonaceous aerosol emissions. Full article

In this study, the chemical compositions of PM_2.5 (particulate matter < 2.5 μm) and the molecular compositions of methanol-soluble organic carbon (MSOC) in suburban Shanghai during summer were measured to investigate the molecular characteristics of organic aerosol (OA) under high humidity. Diurnal variation analysis reveals the influence of relative humidity (RH) on secondary organic aerosol (SOA) components. Organosulfates (OSs), particularly nitrooxy-OSs, exhibit a positive correlation with increasing humidity rather than atmospheric oxidants in this high-humidity site. This suggests that high RH can promote the formation of OSs, possibly through enhancing particle surface area and volume, and creating a favorable environment for aqueous-phase or heterogeneous reactions in the particle phase. A considerable proportion of CHOS compounds may be derived from anthropogenic aliphatic hydrocarbon derivatives. These compounds exhibit slightly elevated daytime concentrations due to increased emissions of long-chain aliphatics from sources such as diesel combustion, as well as photochemically enhanced oxidation to OSs. In contrast, CHONS compounds increased at night, driven by high-humidity liquid-phase oxidation. Terpenoid derivatives accounted for 13.4% of MSOC and contributed over 40% to nighttime CHONS. These findings highlight humidity’s important role in driving daytime and nighttime processing of anthropogenic and biogenic precursors to form SOA, even under low SO₂ and NO_x conditions. Full article

Atmospheric aqueous-phase reactions have been recognized as an important source of secondary organic aerosols (SOAs). However, the unclear reaction kinetics and mechanics hinder the in-depth understanding of the SOA sources and formation processes. This study selected ten different substituted phenolic compounds (termed as PhCs) emitted from biomass burning as precursors, to investigate the kinetics using OH oxidation reactions under simulated sunlight. The factors influencing reaction rates were examined, and the contribution of reactive oxygen species (ROS) was evaluated through quenching and kinetic analysis experiments. The results showed that the pseudo-first-order rate constants (k_obs) for the OH oxidation of phenolic compounds ranged from 1.03 × 10⁻⁴ to 7.85 × 10⁻⁴ s⁻¹ under simulated sunlight irradiation with an initial H₂O₂ concentration of 3 mM. Precursors with electron-donating groups (-OH, -OCH₃, -CH₃, etc.) exhibited higher electrophilic radical reactivity due to the enhanced electron density of the benzene ring, leading to higher reaction rates than those with electron-withdrawing groups (-NO₂, -CHO, -COOH). At pH 2, the second-order reaction rate (k_{PhCs, OH}) was lower than at pH 5. However, the k_obs did not show dependence on pH. The presence of O₂ facilitated substituted phenols’ photodecay. Inorganic salts and transition metal ions exhibited varying effects on reaction rates. Specifically, NO₃⁻ and Cu²⁺ promoted k_{PhCs, OH}, Cl⁻ significantly enhanced the reaction at pH 2, while SO₄²⁻ inhibited the reaction. The k_{PhCs, OH} were determined to be in the range of 10⁹~10¹⁰ L mol⁻¹ s⁻¹ via the bimolecular rate method, and a modest relationship with their oxidation potential was found. Additionally, multiple substituents can suppress the reactivity of phenolic compounds toward •OH based on Hammett plots. Quenching experiments revealed that •OH played a dominant role in phenolic compound degradation (exceeding 65%). Electron paramagnetic resonance confirmed the generation of singlet oxygen (¹O₂) in the system, and probe-based quantification further explored the concentrations of •OH and ¹O₂ in the system. Based on reaction rates and concentrations, the atmospheric aqueous-phase lifetimes of phenolic compounds were estimated, providing valuable insights for expanding atmospheric kinetic databases and understanding the chemical transformation and persistence of phenolic substances in the atmosphere. Full article

Volatile organic compound (VOC) emissions have become a critical environmental concern due to their contributions to photochemical smog formation, secondary organic aerosol generation, and adverse human health impacts in the context of accelerated industrialization and urbanization. Catalytic oxidation over perovskite-type catalysts is an attractive technological approach for efficient VOC abatement. This review systematically evaluates the advancements in perovskite-based catalysts for VOC oxidation, focusing on their crystal structure–activity relationships, electronic properties, synthetic methodologies, and nanostructure engineering. Emphasis is placed on metal ion doping strategies and supported catalyst configurations, which have been demonstrated to optimize catalytic performance through synergistic effects. The applications of perovskite catalysts in diverse oxidation systems, including photocatalysis, thermal catalysis, electrocatalysis, and plasma-assisted catalysis, are comprehensively discussed with critical analysis of their respective advantages and limitations. It summarizes the existing challenges, such as catalyst deactivation caused by carbon deposition, sulfur/chlorine poisoning, and thermal sintering, as well as issues like low energy utilization efficiency and the generation of secondary pollutants. By consolidating current knowledge and highlighting future research directions, this review provides a solid foundation for the rational design of next-generation perovskite catalysts for sustainable VOC management. Full article

Atmospheric intermediate volatile organic compounds (IVOCs) are important precursors of secondary organic aerosols (SOAs), and in-depth research on them is crucial for atmospheric pollution control. This review systematically synthesizes global advancements in understanding IVOC sources, emissions characterization, compositional characteristics, ambient concentrations, SOA contributions, and health risk assessments. IVOCs include long-chain alkanes (C₁₂~C₂₂), sesquiterpenes, polycyclic aromatic hydrocarbons, monocyclic aromatic hydrocarbons, phenolic compounds, ketones, esters, organic acids, and heterocyclic compounds, which originate from primary emissions and secondary formation. Primary emissions include direct emissions from anthropogenic and biogenic sources, while secondary formation mainly results from radical reactions or particulate surface reactions. Recently, the total IVOC emissions have decreased in some countries, while emissions from certain sources, such as volatile chemical products, have increased. Ambient IVOC concentrations are generally higher in urban rather than in rural areas, higher indoors than outdoors, and on land rather than over oceans. IVOCs primarily generate SOAs via oxidation reactions with hydroxyl radicals, nitrate radicals, the ozone, and chlorine atoms, which contribute more to SOAs than traditional VOCs, with higher SOA yields. SOA tracers for IVOC species like naphthalene and β-caryophyllene have been identified. Integrating IVOC emissions into regional air quality models could significantly improve SOA simulation accuracy. The carcinogenic risk posed by naphthalene should be prioritized, while benzo[a]pyrene requires a combined risk assessment and hierarchical management. Future research should focus on developing high-resolution online detection technologies for IVOCs, clarifying the multiphase reaction mechanisms involved and SOA tracers, and conducting comprehensive human health risk assessments. Full article

The interaction of nitrate radicals (NO₃) with the air–water interface is a critical aspect of atmospheric chemistry, influencing processes such as secondary organic aerosol (SOA) formation, pollutant transformation, and nighttime oxidation. This study investigates the behavior of NO₃ radicals at the air–water interface and in bulk water environments through ab initio molecular dynamics simulations, directly comparing them with Cl and ClO radicals. Three distinct configurations of NO₃ in water droplets were analyzed: surface-parallel, surface-perpendicular, and bulk-phase. The results reveal environment-dependent dynamics, with surface-localized NO₃ radicals exhibiting fewer but more flexible hydrogen bonds compared to bulk-solvated radicals. Analysis of radial distribution functions, coordination numbers, and population distributions demonstrates that NO₃ radicals maintain distinct interfacial and bulk-phase preferences, with rapid equilibration in both environments. Electronic structure analysis shows significant modulation of spin density and molecular orbital distributions between surface and bulk environments. The comparative analysis with Cl and ClO radicals highlights how the unique planar geometry and delocalized π-system of NO₃ influence its hydration patterns and interfacial activity. These results offer fundamental molecular-level insights into NO₃ radical behavior at the air–water interface and in aqueous environments, enhancing our understanding of their role in heterogeneous atmospheric processes and nocturnal chemistry. Full article

Oligomerization of glyoxal (GL) and methylglyoxal (MG) plays a vital role in secondary organic aerosol (SOA) formation in aqueous aerosols. However, the influence of emerging contaminants on the oligomerization of GL and MG remains unclear. Therefore, using quantum chemical and kinetic calculations, we investigated the oligomerization of GL and MG in the presence of phthalate esters (PAEs), including dimethyl phthalate (DMP), diethyl phthalate (DEP), dipropyl phthalate (DPP), and dibutyl phthalate (DBP), and the role of PAEs in the oligomerization. Our findings indicate that the direct PAE-mediated oligomerization of GL and MG is hindered due to the lack of reactive sites. However, the oligomerization of GL and MG is readily mediated by the hydrolysates of PAEs, which are the preferred forms of PAEs in weakly acidic aerosols, attributable to the additional -OH groups. The mechanisms show that the indirect PAE-mediated oligomerization proceeds via three-step reactions, including nucleophilic attack on carbenium ions, hydration, and deprotonation, which are thermodynamically and kinetically favorable. Our results reveal that the role of PAEs in the GL/MG oligomerization needs to be emphasized, particularly in conditions with a pH value approaching neutrality. Full article

This study explores the transport mechanisms and pollutant dynamics influencing particulate matter concentrations at the Pomigliano d’Arco monitoring site, situated in a densely urbanized and industrialized region near Naples, Southern Italy, where daily PM₁₀ averages consistently exceed EU thresholds. Exploiting an innovative residence time analysis, based on backward-trajectory analysis with the HYSPLIT model, we investigated air mass histories from 2018 to 2023 to identify predominant pollutant transport pathways and their temporal dynamics. Seven distinct airflow clusters were identified, with the most frequent originating from the western and northeastern directions, influenced by local circulation and long-range transport from the central Mediterranean and northern Africa. Seasonal variations revealed elevated PM₁₀ levels during winter months, attributed to increased residential heating and temperature inversions, as well as summer peaks linked to Saharan dust transport and secondary aerosol formation. The residence time analysis highlighted regions within the central Mediterranean and northern Africa as significant contributors to high PM₁₀ concentrations at the monitoring site, emphasizing the role of both local emissions and transboundary pollution. These findings provide critical insights for policymakers and air quality managers to develop targeted mitigation strategies aimed at reducing PM pollution in urban and industrialized areas, thereby enhancing public health and environmental sustainability. Full article

Ammonia (NH₃) is an important precursor to airborne fine particulate matter (PM_2.5) which causes significant health issues and can significantly impact terrestrial and aquatic ecosystems through deposition. The largest source of NH₃ emissions in the UK is agriculture, including animal husbandry and NH₃-based fertilizer applications. This study investigates the impact of mitigation measures targeting UK NH₃ emissions from farming activities, focusing on their implications for air quality and nitrogen deposition in 2030. A series of mitigation scenarios—low2030, medium2030, and high2030—were developed through engagement with stakeholders, including farmers, advisers, and researchers, and their impact was modelled using the CMAQ air quality model. These scenarios represent varying levels of the uptake of mitigation measures compared to a baseline (base2030). The results indicate that reductions in total NH₃ emissions across the UK could reach up to 13% under the high2030 scenario (but reaching nearly 20% for some regions). These reductions can lead to significant decreases in NH₃ concentrations in some parts of the UK (up to 22%, ~1.2 µg/m³) but with a mean reduction of 8% across the UK. However, the reductions have a limited effect on fine ammonium particulate (${\mathrm{N}\mathrm{H}}_4^{+}$) concentrations, achieving only modest reductions of up to 4%, with mean reductions of 1.6–1.9% due to a NH₃-rich atmosphere. Consequently, the mitigation measures have minimal impact on secondary inorganic aerosol formation and PM_2.5 concentrations, aligning with findings from other studies in Europe and beyond. These results suggest that addressing the primary sources of PM_2.5 or other PM_2.5 precursors, either alone or in combination with NH₃, may be necessary for more substantial air quality improvements. In terms of nitrogen (N) deposition, reductions in NH₃ emissions primarily affect NH₃ dry deposition, which constitutes approximately two-thirds of reduced nitrogen deposition. Total N deposition declines by 15–18% in source regions depending on the scenario, but national average reductions remain modest (~4%). While the study emphasizes annual estimates, further analyses focusing on finer temporal scales (e.g., daily or seasonal) could provide additional insights into exposure impacts. This research highlights the need for integrated mitigation strategies addressing multiple pollutants to achieve meaningful reductions in air pollution and nitrogen deposition. Full article

In contemporary times, wastewater treatment plants (WWTPs) were recognized as substantial sources of odorous emissions, potentially impacting nearby communities’ sensory experience. This study investigates the half-lives (T½) of odorous compounds emitted from WWTPs and their degradation due to atmospheric hydroxyl radicals (•OH) in different environmental settings. The calculated half-lives of specific odorants in rural areas ranged from 31.36 min to 517.33 days, in urban areas from 42.50 min to 1550 days, and in the marine boundary layer from 42.50 min to 129,861 days. These results show that compounds with high reactivity and short T½, such as methanethiol and ethanethiol, degrade rapidly and are less likely to contribute to long-term odor nuisances. In contrast, compounds with longer half-lives, such as carbonyl sulfide and ammonia, persist longer in the atmosphere, with higher potential for sustained odor issues. The findings suggest that •OH plays a significant role in degrading odorous compounds. These insights into odorant–oxidant kinetics may aid in predicting atmospheric half-lives and their contribution to secondary aerosol formation, thus informing regulatory and mitigation strategies to improve air quality. Full article

This study investigates the atomization process in Respimat^® Soft Mist^TM Inhalers (SMIs) using a validated Volume of Fluid (VOF)-to-Discrete Phase Model (DPM) to simulate the transition from colliding liquid jets to aerosolized droplets. Key parameters, including colliding jet inlet velocity, surface tension, and liquid viscosity, were systematically varied to analyze their impact on the atomization, i.e., aerosolized droplet size distributions. The VOF-to-DPM simulation results indicate that higher jet inlet velocities enhance ligament fragmentation, producing finer and more uniform droplets while reducing total atomized droplet mass. The relationship between surface tension and atomization performance in colliding jet atomization is not monotonic. Reducing surface tension plays a complex dual role in the atomization process. On the one hand, lower surface tension enhances the likelihood of liquid jet breakup into a liquid sheet, leading to the formation of smaller ligaments under the same airflow conditions and shear forces. This increases the probability of generating more secondary droplets. On the other hand, reduced surface tension also destabilizes the liquid surface shape, decreasing the formation of fine, high-sphericity droplets in regimes where surface tension is a dominant force. Viscosity also influences atomization through complex mechanisms, i.e., lower viscosity reduces resistance to ligament breakup but promotes droplet interactions and coalescence, while higher viscosity suppresses ligament fragmentation, generating larger droplets and reducing atomization efficiency. The validated VOF-to-DPM framework provides critical insights for enhancing the performance and efficiency of inhalation therapies. Future work will incorporate nozzle geometry, jet impingement angles, and surfactant effects to better understand and optimize the atomization process in SMIs, focusing on achieving preferred droplet size distributions and emitted doses for enhanced drug delivery efficiency in human respiratory systems. Full article

Black carbon (BC) aerosols emitted from biomass, fossil fuel, and waste combustion contribute to the radiation budget imbalance and are transported over extensive distances in the Earth’s atmosphere. These aerosols undergo physical and chemical modifications with co-existing aerosols (e.g., nitrate, sulfate, ammonium) through aging processes during long-range transport and are primarily removed from the troposphere by wet deposition. Using precipitation samples collected in North America between 26 October and 1 December 2020 by the National Atmospheric Deposition Program (NADP), we investigated the relationships between BC and both water-soluble ions and water-soluble organic carbon (WSOC) using Spearman’s rank coefficients. We then attempted to identify the sources of BC in the wet deposition using factor analysis (FA) and satellite data of fire smoke. BC showed a very strong correlation with nitrate (ρ = 0.83). Strong correlations were also found with WSOC, ammonium, calcium, and sulfate ions (ρ = 0.78, 0.74, 0.74, and 0.67, respectively). FA showed that BC was in the same factor as nitrate, ammonium, sulfate, and WSOC, indicating that BC could originate from secondary aerosol formation and biomass burning. Supported by satellite data of fire and smoke, BC and other correlated pollutants were believed to be associated with wildfire outbreaks in several states in the United States (US) during November 2020. Full article