Search Results (34)

Understanding the differential impacts of emission sources of volatile organic compounds (VOCs) on formaldehyde (HCHO) levels is pivotal to effectively mitigating key photochemical radical precursors, thereby enhancing the regulation of atmospheric oxidation capacity (AOC) and ozone formation. This investigation systematically selected and analyzed year-long VOC measurements across three urban zones in Shenzhen, China. Photochemical age correction methods were implemented to develop the initial concentrations of VOCs before source apportionment; then Positive Matrix Factorization (PMF) modeling resolved six primary sources: solvent usage (28.6–47.9%), vehicle exhaust (24.2–31.2%), biogenic emission (13.8–18.1%), natural gas (8.5–16.3%), gasoline evaporation (3.2–8.9%), and biomass burning (0.3–2.4%). A machine learning (ML) framework incorporating Shapley Additive Explanations (SHAP) was subsequently applied to evaluate the influence of six emission sources on HCHO concentrations while accounting for reaction time adjustments. This machine learning-driven nonlinear analysis demonstrated that vehicle exhaust nearly always emerged as the primary anthropogenic contributor in diverse functional zones and different seasons, with gasoline evaporation as another key contributor, while the traditional reactivity metric method, ozone formation potential (OFP), tended to underestimate the role of the two sources. This study highlights the primacy of strengthening emission reduction of transportation sectors to mitigate HCHO pollution in megacities. 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

Over recent decades, China has achieved significant progress in reducing haze pollution, yet photochemical pollution, primarily characterized by elevated ozone (O₃) levels, has intensified, posing severe ecological and public health risks. The “holiday effect”—periodic changes in human activities during holidays such as weekends and the Spring Festival—provides a critical lens to evaluate anthropogenic influences on O₃ pollution, particularly under scenarios of reduced anthropogenic emissions driven by the carbon neutrality pledge. However, a comprehensive summary of this phenomenon remains lacking. This review systematically examines spatial–temporal variations and driving factors, including precursor emissions, atmospheric oxidation capacity (AOC), and meteorological conditions, of the holiday effects across China. Key findings reveal that reduced nitrogen monoxide during holidays weakens its titration effect on O₃. Additionally, decreased particulate matter on holidays leads to improved atmospheric visibility and a corresponding enhancement in AOC and biogenic volatile organic compound emissions, all of which boost the photochemical formation capacity of O₃. Furthermore, solar radiation and temperature positively correlate with O₃ pollution during holidays, whereas rainfall and cloud cover suppress it. This review also provides suggestions for future research regarding mechanistic studies on photochemistry, machine learning for pollution drivers, radical roles in O₃ formation, and health impact assessments. Full article

Particulate matter coexists with persistent organic pollutants (POPs) in the atmosphere, which can enter the human body by accompanying inhalable particles in the respiratory tract. Photochemical conversion further alters the chemical composition of the precursor particles and secondary products. This study investigated the effects of nanoscale iron–chlorobenzene mixtures and their photochemical conversion products on early lung development in rat pups. Using network toxicology and animal experiments, we constructed a compound toxicity–target network and developed air exposure models. This study revealed that both pollutants, before and after photochemical conversion, bound to the aryl hydrocarbon receptor (AhR), increased oxidative stress, altered lung tissue morphology, and reduce inflammatory factor expression. Rat pups were highly sensitive to pollutants during critical stages of lung development. However, no significant differences in oxidative stress or inflammation were observed between the pollutants, likely because of immature lung tissues. Once tissue damage reached a threshold, the response to increasing pollutant concentrations diminished. This study provides insights into atmospheric pollutant toxicity and scientific evidence for the risk assessment of dioxin-like nanoscale mixtures. Full article

The emissions of reactive nitrogen (Nr) from cropland links the pedosphere and atmosphere, playing a crucial role in the Earth’s nitrogen cycle while significantly impacting regional climate change, air quality, and human health. Among various Nr species, nitrogen oxide (NO) and nitrous acid (HONO) have garnered increasing attention as critical precursors to surface ozone (O₃) formation due to their participation in photochemical reactions. While most studies focus on Nr emissions from soils, the specific contributions of cropland Nr emissions considering planting activities to regional O₃ pollution remain insufficiently investigated. This study applied the enhanced process-based agroecological model (FEST-C*) coupled with the air quality (CMAQ) model to quantify cropland Nr emissions and assess their contributions to regional O₃ formation across China in June 2020. The simulated results indicated that the fertilizer-induced total Nr emission was estimated at 1.26 Tg in China, with NO emissions accounting for 0.66 Tg and HONO emissions for 0.60 Tg. North China was identified as a hotspot for cropland Nr emissions, contributing 43% of the national total. The peak emissions of cropland NO and HONO occurred in June, with emissions of 169 and 192 Gg, respectively. Cropland Nr emissions contributed approximately 8% to the national monthly mean MDA8 O₃ concentration, with localized enhancements exceeding 9% in agricultural hotspots in summer. North China experienced the largest MDA8 O₃ increase, reaching 11.71 μg m⁻³, primarily due to intensive fertilizer application and favorable climatic conditions. Conversely, reductions in nighttime hourly O₃ concentrations were observed in southern North China and northern Southeast China due to the rapid titration of O₃ via NO. In this study, the contributions of cropland Nr emissions to MDA8 O₃ concentrations across different regions of China have been further constrained. Incorporating cropland Nr emissions into the CMAQ model improved simulation accuracy and reduced mean biases in MDA8 O₃ predictions. This study offers a detailed quantification of the contribution of cropland Nr emissions in regional ozone formation across China and highlights the critical need to address cropland NO and HONO emissions in air quality management strategies. Full article

L-cysteine, a precursor of essential components for plant growth, is synthesized by the cysteine synthase complex, which includes O-acetylserine(thiol) lyase (OAS-TL) and serine acetyltransferase. In this work, we investigated how S-benzyl-L-cysteine (SBC), an OAS-TL inhibitor, affects the growth, photosynthesis, and oxidative stress of Ipomoea grandifolia plants. SBC impaired gas exchange and chlorophyll a fluorescence, indicating damage that compromised photosynthesis and reduced plant growth. Critical parameters such as the electron transport rate (J), triose phosphate utilization (TPU), light-saturation point (LSP), maximum carboxylation rate of Rubisco (V_cmax), and light-saturated net photosynthetic rate (P_Nmax) decreased by 19%, 20%, 22%, 23%, and 24%, respectively. The photochemical quenching coefficient (q_P), quantum yield of photosystem II photochemistry (ϕ_PSII), electron transport rate through PSII (ETR), and stomatal conductance (g_s) decreased by 12%, 19%, 19%, and 34%, respectively. Additionally, SBC decreased the maximum fluorescence yield (F_m), variable fluorescence (F_v), and chlorophyll (SPAD index) by 14%, 15%, and 15%, respectively, indicating possible damage to the photosynthetic apparatus. SBC triggered root oxidative stress by increasing malondialdehyde, reactive oxygen species, and conjugated dienes by 30%, 55%, and 61%, respectively. We hypothesize that dysfunctions in sulfur-containing components of the photosynthetic electron transport chain, such as the cytochrome b₆f complex, ferredoxin, and the iron–sulfur (Fe-S) centers are the cause of these effects, which ultimately reduce the efficiency of electron transport and hinder photosynthesis in I. grandifolia plants. In short, our findings suggest that targeting OAS-TL with inhibitors like SBC could be a promising strategy for the development of novel herbicides. Full article

The tropospheric production of O₃ is complex, depending on nitrogen oxides (NO_x = NO + NO₂), volatile organic compounds (VOCs), and solar radiation. We present a case study showing that the O₃ concentration is higher in a rural area, 14 km downwind from a coastal town in Central Italy, compared with the urban environment. The hypothesis is that the O₃ measured inland results from the photochemical processes occuring in air masses originating at the urban site, which is richer in NO_x emissions, during their transport inland.To demonstrate this hypothesis, a feed forward neural network (FFNN) is used to model the O₃ measured at the rural site, comparing the modeled O₃ and the measured O₃ in different scenarios, which include both input parameters related to local O₃ production by photochemistry and input parameters associated with regional transport of O₃ precursors. The simulation results show that the local NO_x concentration is not a good input to model the observed O₃ (R = 0.17); on the contrary including the wind speed and direction as input of the FFNN model, the modelled O₃ is well correlated with that measured O₃ (R = 0.82). Full article

The unprecedented reductions in anthropogenic emissions over the COVID-19 lockdowns were utilised to investigate the response of ozone (O₃) concentrations to changes in its precursors across various UK sites. Ozone, volatile organic compounds (VOCs) and NO_x (NO+NO₂) data were obtained for a 3-year period encompassing the pandemic period (January 2019–December 2021), as well as a pre-pandemic year (2017), to better understand the contribution of precursor emissions to O₃ fluctuations. Compared with pre-lockdown levels, NO and NO₂ declined by up to 63% and 42%, respectively, over the lockdown periods, with the most significant changes in pollutant concentrations recorded across the urban traffic sites. O₃ levels correspondingly increased by up to 30%, consistent with decreases in the [NO]/[NO₂] ratio for O₃ concentration response. Analysis of the response of O₃ concentrations to the NO_x reductions suggested that urban traffic, suburban background and suburban industrial sites operate under VOC-limited regimes, while urban background, urban industrial and rural background sites are NO_x-limited. This was in agreement with the [VOC]/[NO_x] ratios determined for the London Marylebone Road (LMR; urban traffic) site and the Chilbolton Observatory (CO; rural background) site, which produced values below and above 8, respectively. Conversely, [VOC]/[NO_x] ratios for the London Eltham (LE; suburban background) site indicated NO_x-sensitivity, which may suggest the [VOC]/[NO_x] ratio for O₃ concentration response may have had a slight NO_x-sensitive bias. Furthermore, O₃ concentration response with [NO]/[NO₂] and [VOC]/[NO_x] were also investigated to determine their relevance and accuracy in identifying O₃-NO_x-VOC relationships across UK sites. While the results obtained via utilisation of these metrics would suggest a shift in photochemical regime, it is likely that variation in O₃ during this period was primarily driven by shifts in oxidant (OX; NO₂ + O₃) equilibrium as a result of decreasing NO₂, with increased O₃ transported from Europe likely having some influence. Full article

An oxidizing and harmful pollutant gas, tropospheric ozone is a product of a complex set of photochemical reactions that can make it difficult to enact effective control measures. A better understanding of its precursors including volatile organic compounds (VOCs) and nitrogen oxides (NO_x) and their spatial distribution can enable policymakers to focus their control efforts. In this study we used low-cost sensors (LCSs) to increase the spatial resolution of an existing NO₂ monitoring network in addition to VOC sampling to better understand summer ozone formation in Maricopa County, Arizona, and observed that afternoon O₃ values at the downwind sites were significantly correlated, ~0.27, to the morning NO₂ × rate values at the urban sites. Additionally, we looked at the impact of wildfire smoke on ozone exceedances and compared non-smoke days to smoke days. The average O₃ on smoke days was approximately 20% higher than on non-smoke days, however, the average NO₂ concentration multiplied by estimated photolysis rate (NO₂ × rate) values were only 2% higher on smoke days. Finally, we evaluated the ozone sensitivity of the region by calculating HCHO/NO₂ ratios using three different datasets: ground, satellite, and model. Although the satellite dataset produced higher HCHO/NO₂ ratios than the other datasets, when the proper regime thresholds are applied the three datasets consistently show transition and VOC-limited O₃ production regimes over the Phoenix metro area. This suggests a need to implement more VOC emission controls in order to reach O₃ attainment in the county. Full article

Nitrogen oxides (NO_X) in the atmosphere cause oxidation reactions with photochemical radicals and volatile organic compounds, leading to the accumulation of ozone (O₃). NO_X constitutes a significant portion of the NO_y composition, with nitrous acid (HONO) and nitric acid (HNO₃) following. HONO plays a crucial role in the reaction cycle of NO_X and hydrogen oxides. The majority of HNO₃ reduction mechanisms result from aerosolization through heterogeneous reactions, having adverse effects on humans and plants by increasing secondary aerosol concentrations in the atmosphere. The investigation of the formation and conversion mechanisms of HONO and HNO₃ is important; however, research in this area is currently lacking. In this study, we observed HONO, HNO₃, and their precursor gases were observed in the atmosphere using parallel-plate diffusion scrubber-ion chromatography. A 0-D box model simulated the compositional distribution of NO_y in the atmosphere. The formation reactions and conversion mechanisms of HONO and HNO₃ were quantified using reaction equations and reaction coefficients. Among the various mechanisms, dominant mechanisms were identified, suggesting their importance. According to the calculation results, the produce of HONO was predominantly attributed to heterogeneous reactions, excluding an unknown source. The sink processes were mainly governed by photolysis during daytime and reactions with OH radicals during nighttime. HNO₃ showed dominance in its production from N₂O₅, and in its conversion mechanisms primarily involving aerosolization and deposition. Full article

12-oxo-phytodienoic acid (OPDA) is a primary precursor of jasmonates, able to trigger autonomous signaling cascades that activate and fine-tune plant defense responses, as well as growth and development. However, its mechanism of actions remains largely elusive. Here we describe a dual-function messenger of OPDA signaling, reduced glutathione (GSH), that cross-regulates photosynthesis machinery and stress protection/adaptation in concert, optimizing plant plasticity and survival potential. Under stress conditions, the rapid induction of OPDA production stimulates GSH accumulation in the chloroplasts, and in turn leads to protein S-glutathionylation in modulating the structure and function of redox-sensitive enzymes such as 2-cysteine (Cys) peroxiredoxin A (2CPA), a recycler in the water–water cycle. GSH exchanges thiol-disulfides with the resolving Cys^R₁₇₅, while donating an electron (e⁻, H⁺) to the peroxidatic Cys^P₅₃, of 2CPA, which revives its reductase activity and fosters peroxide detoxification in photosynthesis. The electron flow protects photosynthetic processes (decreased total non-photochemical quenching, NPQ_(T)) and maintains its efficiency (increased photosystem II quantum yield, Φ_II). On the other hand, GSH also prompts retrograde signaling from the chloroplasts to the nucleus in adjusting OPDA-responsive gene expressions such as Glutathione S-Transferase 6 (GST6) and GST8, and actuating defense responses against various ecological constraints such as salinity, excess oxidants and light, as well as mechanical wounding. We thus propose that OPDA regulates a unique metabolic switch that interfaces light and defense signaling, where it links cellular and environmental cues to a multitude of plant physiological, e.g., growth, development, recovery, and acclimation, processes. Full article

The problem of poor air quality in urban areas has a negative impact on the health of residents. This is especially important during periods of smog. In Poland, as in other countries, the problem of poor air quality, especially during the winter season, is associated with a high concentration of particulate pollutants in ambient air (PM₁₀, PM_2.5). Sources of particulate emissions, in addition to solid-fuel boilers, include means of transportation, especially those equipped with diesel engines. In turn, during periods of strong sunshine (spring and summer), the problem of photochemical smog, whose precursors are nitrogen oxides NO_X, arises in urban areas. Their main sources of emissions are internal combustion engines. Therefore, to improve air quality in urban areas, changes are being made in the transport sector, among which is upgrading the fleet of urban transport vehicles to low- or zero-emission vehicles, which are more environmentally friendly. In addition, measures that reduce the harmfulness of the transportation sector to air quality include the introduction of clean transportation zones, as well as park-and-ride (P&R) systems. The purpose of this article is to present the results in terms of PM₁₀, PM_2.5, and NOx emission reductions, implemented over a period of two years (2021–2022) in the area of the Rzeszow agglomeration, related to the modernization of the suburban bus fleet and the implementation of a P&R system for passenger cars. The results of the study were compared with the value of estimated emissions from coal-fired boilers used for residential heating and hot water, which also contribute to smog. Thanks to the implementation of the project, i.e., the replacement of 52 old buses with new buses of the Euro VI emission class and the construction of new P&R spaces, the total average annual reduction in emissions amounted to approximately 703.6 kg of PM₁₀, approximately 692.7 kg of PM_2.5, and a reduction of approximately 10.4 tons of NO_X. Full article

The development of new and advanced materials for various environmental and energy applications is a prerequisite for the future. In this research, the removal of hazardous moxifloxacin (MOX) is accomplished by synthesizing new hybrids of MOF-5 i.e., Ni/Mo.S₂/MOF-5/GO, Ni.S₂/MOF-5/GO, Mo.S₂/MOF-5/GO, and Ni/Mo.S₂/MOF-5 nanocomposites by using a metal-organic framework (MOF-5) and graphene oxide (GO) as a precursor. The introduction of Ni_xMo_xS₂ facilitates the unique interfacial charge transfer at the heterojunction, demonstrating a significant improvement in the separation effectiveness of the photochemical electron-hole pairs. To evaluate equilibrium adsorption capacity, time, pH, and concentration of organic pollutants were used as experimental parameters. The adsorption kinetics data reveals pseudo-first-order (R² = 0.965) kinetics when Ni/Mo.S₂/MOF-5/GO photocatalyst was irradiated under light for 90 min against MOX degradation. This led to a narrow energy band gap (2.06 eV in Ni/Mo.S₂/MOF-5/GO, compared to 2.30 eV in Ni/Mo.S₂/MOF-5), as well as excellent photocatalytic activity in the photodegradation of moxifloxacin (MOX), listed in order: Ni/Mo.S₂/MOF-5/GO (95%) > Ni.S₂/MOF-5/GO (93%) > Mo.S₂/MOF5/GO (90%) > Ni/Mo.S₂/MOF-5 (86%) in concentrations up to 2.0 mgL⁻¹, caused by the production of superoxide (O₂^•−) and hydroxide (OH^•) radicals, which encouraged the effective photocatalytic activities of the heterostructure. After five successive tests demonstrating its excellent mechanical stability, the impressive recyclability results for the Ni/Mo.S₂/MOF-5/GO revealed only a tiny variation in efficiency from 95% (for the first three runs) to 93% (in the fourth run) and 90% (in the fifth run). These findings show that the heterostructure of Ni/Mo.S₂/MOF-5/GO is an effective heterojunction photocatalyst for the quick elimination of moxifloxacin (MOX) from aqueous media. Full article

Volatile organic compounds (VOCs) are an important source of air pollution, harmful to human health and the environment, and important precursors of secondary organic aerosols, O₃ and photochemical smog. This study focused on the low-temperature catalytic oxidation and degradation of benzene, dichloroethane, methanethiol, methanol and methylamine by ozone. Benzene was used as a model compound, and a molecular sieve was selected as a catalyst carrier to prepare a series of supported active metal catalysts by impregnation. The effects of ozone on the catalytic oxidation of VOCs and catalysts’ activity were studied. Taking benzene as a model compound, low-temperature ozone catalytic oxidation was conducted to explore the influence of the catalyst carrier, the active metal and the precious metal Pt on the catalytic degradation of benzene. The optimal catalyst appeared to be 0.75%Pt–10%Fe/HZSM(200). The catalytic activity and formation of the by-products methylamine, methanethiol, methanol, dichloroethane and benzene over 0.75%Pt–10%Fe/HZSM(200) were investigated. The structure, oxygen vacancy, surface properties and surface acidity of the catalysts were investigated. XRD, TEM, XPS, H₂-TPR, EPR, CO₂-TPD, BET, C₆H₆-TPD and Py-IR were combined to establish the correlation between the surface properties of the catalysts and the degradation activity. Full article

Ground-level ozone (O₃) is a significant source of air pollution, mainly in most urban areas across the globe. Ground-level O₃ is not emitted directly into the atmosphere. It results from photo-chemical reactions between precursors and is influenced by weather factors such as temperature. This study investigated the spatial and temporal analysis of ground-level ozone and analyzed the significant anthropogenic precursors and the weather parameters associated with ground-level ozone during daytime and nighttime at three cities in peninsular Malaysia, namely, Kuala Terengganu, Perai, and Seremban from 2016 to 2020. Secondary data were acquired from the Department of Environment (DOE), Malaysia, including hourly data of O₃ with trace gases and weather parameters. The secondary data were analyzed using temporal analysis such as descriptive statistics, box plot, and diurnal plot as well as spatial analysis such as contour plot and wind rose diagram. Spearman correlation was used to identify the association of O₃ with its precursors and weather parameters. The results show that a higher concentration of O₃ during the weekend due to “ozone weekend effects” was pronounced, however, a slightly significant effect was observed in Perai. The two monsoonal seasons in Malaysia had a minimal effect on the study areas except for Kuala Terengganu due to the geographical location. The diurnal pattern of O₃ concentration indicates bimodal peaks of O₃ precursors during the peak traffic hours in the morning and evening with the highest intensity of O₃ precursors detected in Perai. Spearman correlation analysis determined that the variations in O₃ concentrations during day and nighttime generally coincide with the influence of nitrogen oxides (NO) and temperature. Lower NO concentration will increase the amount of O₃ concentration and an increasing amount of O₃ concentration is influenced by the higher temperature of its surroundings. Two predictive models, i.e., linear (multiple linear regression) and nonlinear models (artificial neural network) were developed and evaluated to predict the next day and nighttime O₃ levels. ANN resulted in better prediction for all areas with better prediction identified for daytime O₃ levels. Full article