Photochemical Production Research Articles

Mixing-layer-height-referenced ozone vertical distribution in the lower troposphere of Chinese megacities: stratification, classification, and meteorological and photochemical mechanisms

Abstract. Traditional tropospheric ozone (O3) climatology uses a simple average substantially smoothed stratification structure in individual O3 profiles, limiting our ability to properly describe and understand how O3 is vertically distributed at the interface between the mixing layer (ML) and free troposphere (FT). In this study, we collected 1897 ozonesonde profiles from two Chinese megacities (Beijing and Hong Kong) over the period 2000–2022 to investigate the climatological vertical heterogeneity of the lower-tropospheric O3 distribution with a mixing-layer-height-referenced (h-referenced) vertical coordinate system. The mixing-layer height (h) was first estimated following an integral method that integrates the information of temperature, humidity, and cloud. After that, a so-called h-referenced vertical distribution of O3 was determined by averaging all individual profiles expressed as a function of z/h rather than z (where z is altitude). We found that the vertical stratification of O3 is distributed heterogeneously in the lower troposphere, with stronger vertical gradients at the surface layer and ML–FT interface. There are low vertical autocorrelations of O3 between the ML and FT but high autocorrelations within each of the two atmospheric compartments. These results suggest that the ML–FT interface acts as a geophysical “barrier” separating air masses of distinct O3 loadings. This barrier effect varies with season and city, with an ML–FT detrainment barrier in summer (autumn) and an FT–ML entrainment barrier in other seasons in Beijing (Hong Kong). Based on a Student's t test, daily h-referenced O3 profiles were further classified into three typical patterns: MLO3-dominated, FTO3-dominated, and uniform distribution. Although the FTO3-dominated pattern occurs most frequently during the whole study period (69 % and 54 % of days in Beijing and Hong Kong, respectively), the MLO3-dominated pattern prevails in the photochemically active season, accounting for 47 % of summer days in Beijing and 54 % of autumn days in Hong Kong. These occurrences of the MLO3-dominated pattern are significantly more frequent than in previously reported results at northern mid-latitudes, indicating intensive photochemical MLO3 production under the high-emission background of a Chinese megacity. From a FTO3-dominated to MLO3-dominated pattern, the O3 precursor CH2O (NO2) experiences a substantial increase (decrease) in Beijing but a slight change in Hong Kong. Vertically, the increment of CH2O is larger in the upper ML, and the decrement of NO2 is larger in the lower ML. Such vertical changes in O3 precursors push O3 production sensitivity away from the VOC-limited regime and facilitate high-efficiency production of O3 via photochemical reactions, particularly in the upper ML of Beijing.

CS2 Cycling in Seawater: Dark Production and UV Light Driven Consumption

AbstractCarbon disulfide (CS2) has recently gained attention as an important precursor for the atmospheric trace gas carbonyl sulfide (OCS), which delivers sulfur to the stratospheric sulfur layer and impacts the radiative budget of the Earth. CS2 is naturally produced in the ocean and emitted to the atmosphere. However, the magnitude of its marine emissions is only poorly constrained due to lacking understanding of its production and consumption processes. Here, we present incubation experiments with and without UV light treatment and provide evidence for a previously not considered UV‐light‐driven degradation process of CS2 in seawater, following first‐order kinetics. In addition to its already known photochemical production process, CS2 production is found in the dark, depending on the amount of dissolved organic sulfur present in seawater. We provide novel production and consumption rates of CS2 in seawater that pave the way toward mechanistically quantifying marine emissions of this important trace gas.

Influence of Wind Flows on Surface O3 Variation over a Coastal Province in Southeast China

Surface ozone (O3) is influenced not only by anthropogenic emissions but also by meteorological factors, with wind direction being one of the most overlooked factors. Here, we combine the observational data of both O3 and wind flow to compare the variation in surface O3 with wind direction between coastal and inland regions of Fujian, a province in the southeast coast of China with complicated topography. We further conduct a numerical simulation using a global chemical transport model, GEOS-Chem, to interpret the observational results, explore the linkages between these O3 variations and wind flows, and identify the dominant processes for the occurrence of high O3 that varies with wind flows. The results from the observations over 2015–2021 suggest that, over coastal regions, surface O3 concentrations show a strong dependence on wind flow changes. On average, during the daytime, when southeasterly winds prevail, the mean of O3 concentrations reaches 83.5 μg/m3, which is 5.0 μg/m3 higher than its baseline values (the mean O3 concentrations), while the northwesterly winds tend to reduce surface O3 by 6.4 μg/m3. The positive O3 anomalies with southeasterly wind are higher in the autumn and summer than in the spring and winter. During the nighttime, the onshore northeasterly winds are associated with enhanced O3 levels, likely due to the airmass containing less NO2, alleviating the titration effects. Over inland regions, however, surface O3 variations are less sensitive to wind flow changes. The GEOS-Chem simulations show that the prevailing southeasterly and southwesterly winds lead to the positive anomaly of chemical reactions of O3 over coastal regions, suggesting enhanced photochemical production rates. Furthermore, southeasterly winds also aid in transporting more O3 from the outer regions into the coastal regions of Fujian, which jointly results in elevated surface O3 when southeasterly winds dominates. When affected by wind flows in different directions, the chemical reaction and transport in the inland regions do not exhibit significant differences regarding their impact on O3. This could be one of the reasons for the difference in O3 distribution between coastal and inland regions. This study could help to deepen our understanding of O3 pollution and aid in providing an effective warning of high-O3 episodes.

Photochemical Mechanism and Control Strategy Optimization for Summertime Ozone Pollution in Yining City

To explore the formation mechanism of the ozone （O3） and emission reduction strategy in a northwestern city， an extensive field campaign was conducted in summertime in 2021 in Yining City， in which the 0-D box model incorporating the latest explicit chemical mechanism （MCMv3.3.1） was applied for the first time to quantify the O3-NOx-VOCs sensitivity and formulate a precise O3 control strategy in this city. The results showed that： ① the three indicators ［i.e.， O3 formation potential （OFP）， ·OH reaction rate （k·OH）， and relative incremental reactivity （RIR）］ jointly indicated that alkenes， oxygenated volatile organic compounds （OVOCs）， and aromatics were the highest contributors among anthropogenic volatile organic compounds （AVOC） to O3 formation， and the contribution of biogenic volatile organic compounds （BVOC） also could not be ignored. Additionally， the results based on RIR calculation implied that that the acetaldehyde， ethylene， and propylene were the most sensitive individual VOCs species in Yining City. ② The in-situ photochemical O3 variations were primarily influenced by the local photochemical production and export process horizontally to downwind areas or vertically to the upper layer， and the reaction pathways of HO2·+ NO and ·OH + NO2 contributed the most to the gross Ox photochemical production （60%） and photochemical destruction production （53%）， respectively. Hence， the reduction in local emissions for O3 precursors was more essential to alleviate O3 pollution in this city. ③ The outcome based on RIR（NOx） / RIR（AVOC） and EKMA jointly suggested that the photochemical regime in this city can be considered a transitional regime that was also nearly a VOCs-limited regime. Detailed mechanism modeling based on multiple scenarios further suggested that the NOx and VOCs synergic emission reduction strategies was helpful to alleviate O3 pollution. These results are useful to provide policy-related guidance for other cities facing similar O3 pollution in northwest China.

What caused large ozone variabilities in three megacity clusters in eastern China during 2015–2020?

Abstract. Due to a robust emission control policy, significant reductions in major air pollutants, such as PM2.5, SO2, NO2, and CO, were observed in China between 2015 and 2020. On the other hand, during the same period, there was a notable increase in ozone (O3) concentrations, making it a prominent air pollutant in eastern China. The annual mean concentration of maximum daily 8 h average (MDA8) O3 exhibited alarming linear increases of 2.4, 1.1, and 2.0 ppb yr−1 (ppb is for parts per billion) in three megacity clusters: Beijing–Tianjin–Hebei (BTH), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD), respectively. Meanwhile, there was a significant 3-fold increase in the number of O3-exceeding days, defined as MDA8 O3 > 75 ppb. Our analysis indicated that the upward increases in the annual mean concentration of MDA8 were primarily driven by the rise in consecutive O3-exceeding days. There were expansions of high O3 in urban centers to rural areas accompanied by a saturation effect so that MDA8 O3 concentrations at the high-O3 stations in 2015 remained nearly constant at 100 ppb. Last, we found a close association between O3 episodes with 4 or more consecutive O3-exceeding days and the position and strength of tropical cyclones (TCs) in the northwest Pacific and the West Pacific subtropical high (WPSH). The TC and WPSH contributed to meteorological conditions characterized by clear skies, subsiding air motion, high vertical stability in the lower troposphere, increased solar radiation, and a positive temperature anomaly at the surface. These favorable meteorological conditions greatly facilitated the formation of O3. Thus, we propose that the worsening O3 increases observed in the BTH, YRD, and PRD regions from 2015 to 2020 can be mostly attributed to enhanced photochemical O3 production resulting from an increased occurrence of meteorological conditions with high solar radiation and positive temperature anomalies under the influence of the WPSH and TCs.

Overlooked role of aqueous chromate (VI) as a photosensitizer in enhancing the photochemical reactivity of ferrihydrite and production of hydroxyl radical

The reactive oxygen species (ROS) photochemically generated from natural iron minerals have gained significant attention. Amidst the previous studies on the impact of heavy metal ions on ROS generation, our study addresses the role of the anion Cr(VI), with its intrinsic photoactivity, in influencing ROS photochemical generation with the co-presence of minerals. We investigated the transformation of inorganic/organic pollutants (Cr(VI) and benzoic acid) at the ferrihydrite interface, considering sunlight-mediated conversion processes (300–1000 nm). Increased photochemical reactivity of ferrihydrite was observed in the presence of aqueous Cr(VI), acting as a photosensitizer. Meanwhile, a positive correlation between hydroxyl radical (•OH) production and concentrations of aqueous Cr(VI) was observed, with a 650% increase of •OH generation at 50 mg L−1 Cr(VI) compared to systems without Cr(VI). Our photochemical batch experiments elucidated three potential pathways for •OH photochemical production under varying wet chemistry conditions: (1) ferrihydrite hole-mediated pathway, (2) chromium intermediate O-I-mediated pathway, and (3) chromium intermediates CrIV/V-mediated pathway. Notably, even in the visible region (> 425 nm), the promotion of aqueous Cr(VI) on •OH accumulation was observed in the presence of ferrihydrite and TiO2 suspensions, attributed to Cr(VI) photosensitization at the mineral interface. This study sheds light on the overlooked role of aqueous Cr(VI) in the photochemical reactivity of minerals, thereby enhancing our understanding of pollutant fate in acid mining-impacted environments.

Energy yields for acetylenotrophy on Enceladus and Titan

Saturn's moons Titan and Enceladus appear to satisfy three key criteria for life: presence of liquid water, nutrient availability, and metabolic energy sources. Consequently, these ocean worlds are the focus of astrobiology research investigations that aim to assess the potential for life beyond Earth. One plausible source of metabolic energy on these moons is acetylene (C2H2), a simple organic compound that is the second most abundant photochemical product in Titan's atmosphere and has been identified as a likely constituent of Enceladus' ocean. Acetylenotrophy, or the microbial fermentation of acetylene, is utilized by microbes on Earth in a number of environments. Here, we have calculated the energy yield of acetylenotrophy to be 69–78 kJ/mol C within the oceans of Titan and Enceladus, greater than the widely considered, hydrogenotrophic methanogenesis, at 25–65 kJ/mol C. Therefore, we propose acetylenotrophy as a potential metabolism on these moons that should be considered in future astrobiology studies on worlds with abundant acetylene.

Spatial and seasonal variability in volatile organic sulfur compounds in seawater and the overlying atmosphere of the Bohai and Yellow seas

Abstract. Volatile organic sulfur compounds (VSCs), including carbon disulfide (CS2), dimethyl sulfide (DMS), and carbonyl sulfide (COS), were surveyed in the seawater of the Bohai and Yellow seas and the overlying atmosphere during spring and summer of 2018 to understand the production and loss of VSCs and their influence factors. The concentration ranges of COS, DMS, and CS2 in the surface seawater were 0.14–0.42, 0.41–7.74, and 0.01–0.18 nmol L−1 during spring and 0.32–0.61, 1.31–18.12, and 0.01–0.65 nmol L−1 during summer, respectively. The COS concentrations exhibited positive correlation with dissolved organic carbon (DOC) concentrations in seawater during summer, which verified the photochemical production of COS from chromophoric dissolved organic matter (CDOM). High DMS concentrations occurred near the Yellow River, Laizhou Bay, and Yangtze River estuary, coinciding with high nitrate and chlorophyll (Chl) a concentrations due to river discharge during summer. The COS, DMS, and CS2 concentrations were the highest in the surface seawater and decreased with the depth. The mixing ratios of COS, DMS, and CS2 in the atmosphere were 255.9–620.2, 1.3–191.2, and 5.2–698.8 pptv during spring and 394.6–850.1, 10.3–464.3, and 15.3–672.7 pptv in summer, respectively. The ratios of mean oceanic concentrations and atmospheric mixing ratios for summer to spring in COS, DMS, and CS2 were 1.8, 3.1, 3.7 and 1.6, 4.6, 1.5, respectively. The ratios of the mean sea-to-air fluxes for summer to spring in COS, DMS, and CS2 were 1.2, 2.1, and 4.3. The sea-to-air fluxes of VSCs indicated that the marginal seas are important sources of VSCs in the atmosphere. The results support a better understanding of the contribution of VSCs in marginal seas.

Photochemical on-demand production of hydrogen peroxide in a modular flow reactor

Hydrogen peroxide (H2O2) is a valuable green oxidant with a wide range of applications. Furthermore, it is recognized as a possible future energy carrier achieving safer operation, storage and transportation....

Iron oxide-promoted photochemical oxygen reduction to hydrogen peroxide (H2O2).

Hydrogen peroxide (H2O2) is a valuable green oxidant with a wide range of applications. Furthermore, it is recognized as a possible future energy carrier achieving safe operation, storage and transportation. The photochemical production of H2O2 serves as a promising alternative to the waste- and energy-intensive anthraquinone process. Following the 12 principles of Green Chemistry, we demonstrate a facile and general approach to sustainable catalyst development utilizing earth-abundant iron and biobased sources only. We developed several iron oxide (FeOx) nanoparticles (NPs) for successful photochemical oxygen reduction to H2O2 under visible light illumination (445 nm). Achieving a selectivity for H2O2 of >99%, the catalyst material could be recycled for up to four consecutive rounds. An apparent quantum yield (AQY) of 0.11% was achieved for the photochemical oxygen reduction to H2O2 with visible light (445 nm) at ambient temperatures and pressures (9.4-14.8 mmol g-1 L-1). Reaching productivities of H2O2 of at least 1.7 ± 0.3 mmol g-1 L-1 h-1, production of H2O2 was further possible via sunlight irradiation and in seawater. Finally, a detailed mechanism has been proposed on the basis of experimental investigation of the catalyst's properties and computational results.

Status of atmospheric air pollution in Ukraine prior to the full-scale russian invasion. Part 2: Pollutants total content according to the satellite data

The paper describes the main features of pollutant total content distribution over Ukraine that can be used as baseline air quality data observed before the full-scale russian invasion in Ukraine. The study is based on the data derived from the TROPOspheric Monitoring Instrument (TROPOMI) onboard of the Sentinel-5 Precursor (5P) satellite that indicates nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO) and formaldehyde (CH2O) levels. We defined the characteristics of pollutants spatial distribution with full coverage of Ukrainian territory. Despite the increasing role of automotive emissions, the most polluted air in Ukraine was still observed over large industrial cities and smaller settlements having the biggest thermal power plants (TPP). The high level of pollutants content over these locations negatively affects air quality in suburban and rural areas by the prevailing wind. They form relatively stable polluted spots over larger areas. Hence, main polluted areas include: Donetsk Region; territories in the central part of Ukraine along the Dnipro River and near the destroyed Kakhovka reservoir; Kharkiv and Zmiiv TPPs; Kyiv and Trypillia TPPs; and the territories in the western part, including Lviv, Dobrotvir and Burshtyn TPPs. The polluted air from these territories determines the air quality depending on a prevailing wind. In case of high wind speeds polluted air can be distributed from urban areas towards relatively clean territories such as Carpathian and Crimean Mountains, northern Polissia, and the Medobory National Park of Podillia. We determined quantitative parameters of wind speed and direction for every pollutant that causes higher total content over relatively clean territories. Pollutants dispersion in the atmosphere varies depending on a boundary layer height (BLH). It was found that NO2, CO and SO2 content significantly increased when the BLH was below 500 m over both urban areas and clean territories with no emission sources available. The inverse dependence on the BLH was identified for CH2O. This can be explained by a more intense photochemical production at higher altitudes. The detected baseline air pollution conditions can be used in order to assess the impact of the war on air quality in Ukraine and come up with relevant post-war development measures.

Modelling the seasonal cycle of Uranus’s colour and magnitude, and comparison with Neptune

ABSTRACT We present a quantitative analysis of the seasonal record of Uranus’s disc-averaged colour and photometric magnitude in Strömgren b and y filters (centred at 467 and 551 nm, respectively), recorded at the Lowell Observatory from 1950 to 2016, and supplemented with HST/WFC3 observations from 2016 to 2022. We find that the seasonal variations of magnitude can be explained by the lower abundance of methane at polar latitudes combined with a time-dependent increase of the reflectivity of the aerosol particles in layer near the methane condensation level at 1 – 2 bar. This increase in reflectivity is consistent with the addition of conservatively scattering particles to this layer, for which the modelled background haze particles are strongly absorbing at both blue and red wavelengths. We suggest that this additional component may come from a higher proportion of methane ice particles. We suggest that the increase in reflectivity of Uranus in both filters between the equinoxes in 1966 and 2007, noted by previous authors, might be related to Uranus’s distance from the Sun and the production rate of dark photochemical haze products. Finally, we find that although the visible colour of Uranus is less blue than Neptune, due to the increased aerosol thickness on Uranus, and this difference is greatest at Uranus’s solstices, it is much less significant than is commonly believed due to a long-standing misperception of Neptune’s ‘true’ colour. We describe how filter-imaging observations, such as those from Voyager-2/ISS and HST/WFC3, should be processed to yield accurate true colour representations.

Observational Evidence of Unknown NOx Source and Its Perturbation of Oxidative Capacity in Bermuda's Marine Boundary Layer

AbstractNitrogen oxides (NOx) are key intermediates in the atmospheric cycling of reactive nitrogen, the spatiotemporal distribution of which modulates ozone (O3) production. Field campaigns were conducted at the Tudor Hill Marine Atmospheric Observatory, Bermuda, in the spring and summer of 2019 to explore atmospheric cycling of NOx and its modulation of photochemical O3 production in the marine boundary layer. In aged, clean marine air, an atypical NO2 diel profile with a solar noon peak of 69 ± 5 pptv was recorded, challenging the classic U‐shaped diel profile with a solar noon valley characterized by fast photolysis and oxidation consumption in the daytime. This result indicated an unknown daytime NOx source excluded from the current near‐explicit chemical model, which underestimated the solar noon NOx level by 20–56 pptv and source rate by 9.7–33.5 pptv hr−1, considering the upper and lower limits of total OH reactivity and halogen photochemistry in the marine boundary layer. The observed HONO level accounted for ∼56% of the unknown NOx source, implying an unknown NOx regeneration pathway with HONO as an intermediate. The photochemical nature of the unknown NOx source maximized perturbation of photochemical OH and O3 production. The O3 abundance and production rate were underestimated by 2–4 ppbv and 28%–80%, respectively, and the OH abundance and source rate were 7%–55% and 21%–57% lower than the estimated levels with the constraint of NOx, respectively. The unknown NOx source requires urgent revision of the current understanding of reactive nitrogen cycling and the oxidative capacity of the clean marine atmosphere.

Interpretable Machine Learning and Reactomics Assisted Isotopically Labeled FT-ICR-MS for Exploring the Reactivity and Transformation of Natural Organic Matter during Ultraviolet Photolysis.

Isotopically labeled FT-ICR-MS combined with multiple post-analyses, including interpretable machine learning (IML) and a paired mass distance (PMD) network, was employed to unravel the reactivity and transformation of natural organic matter (NOM) during ultraviolet (UV) irradiation. FT-ICR-MS analysis was used to assign formulas, which were classified on the basis of their molecular compositions and structural categories. Isotope (deuterium, D) labeling was utilized to unequivocally determine the photochemical products and examine the development of OD radical-mediated NOM transformation. With regard to the reactive molecular formulas, CHOS formulas exhibited the highest reactivity (86.5% of precursors disappeared) followed by CHON (53.4%) and CHO (24.6%) formulas. With regard to structural categories, the degree of reactivity decreased in the following order: tannins > condensed aromatics > lignin/CRAMs. The IML algorithm demonstrated that the crucial features governing the reactivity of formulas were the molecular weight, DBE-O, NOSC, and the presence of heteroatoms (i.e., N and S), suggesting that the large and unsaturated compounds containing S and N are more prone to photodegradation. The reactomics approach using the PMD network further indicated that 11 specific molecular formulas in the CHOS and CHO class served as hubs, implying a higher photoreactivity and participation in a range of transformations. The isotope labeling analyses also found that, among the reactions observed, hydroxylation (i.e., +OD) is dominant for lignin/CRAMs and condensed aromatics, and formulas containing ≤10 D atoms were developed. Overall, this study, by adopting rigorous and interpretable techniques, could provide in-depth insights into the molecular-level dynamics of NOM under UV irradiation.

Life cycle assessment of biofuel production from waste date stones using conventional and microwave pyrolysis

Date palm trees play a crucial role in the provision of essential nutrition by producing date fruits and are widely cultivated in Qatar. The processing of date fruits generates substantial quantities of carbon-rich date stone possessing remarkable energy potential. This inherent energy can be harnessed by applying pyrolysis techniques, which facilitate the production of many products with commercial value. Despite being a novice process, microwave (MW) pyrolysis has emerged as a promising avenue for converting biomass waste into eco-friendly biofuels. Nonetheless, the adoption of this new approach necessitates a comprehensive exploration of its ecological implications, warranting a meticulous life-cycle analysis (LCA) to ascertain its environmental footprint. As a result, using GaBi software, this study compares the life-cycle environmental impact of conventional and microwave-aided pyrolysis processes of date stone waste. The study also assesses the techno-economic analysis of the two processes. The physical and thermal analyses of the date stone waste indicated that the biomass is a high-energy source (Net calorific value-15.6 MJ/kg). While the life-cycle assessment indicated that MW pyrolysis has a greater implication on climate change (14.94 % more), ozone depletion (14.29 % more), ionizing radiation (14.36 % more), and photochemical ozone production (14.44 % more) than conventional pyrolysis. This demonstrates that conventional pyrolysis is less harmful to the environment than MW pyrolysis. The techno-economic analysis infers that conventional pyrolysis mode is superior to MW pyrolysis for the valorisation of date stone waste in terms of profitability, financial stability, and overall success.

Day–Night Transport-induced Chemistry and Clouds on WASP-39b: Gas-phase Composition

JWST has recently detected the first robust photochemical product on an exoplanet: sulfur dioxide (SO2) on WASP-39b. The data from the NIRISS instrument also reveal signs of partial coverage of clouds. Most of the previous studies have focused on interpreting spectral data with 1D models. To explore how the chemical species and cloud particles are altered by global circulation, we applied a 2D photochemical model and a 2D microphysical cloud model separately to postprocess the thermal and dynamical structures simulated by a 3D general circulation model of WASP-39b. We found that SO2 produced by photochemistry on the dayside can be transported to the nightside owing to the efficient replenishment of horizontal transport. The morning–evening limb differences in methane (CH4) abundances predicted by the 1D models disappeared after horizontal transport is included. Similarly, the inclusion of horizontal transport also reduced the limb differences in SO2. Our modeling results suggest that the fast zonal wind results in minimal or negligible limb asymmetry in composition. Based on the synthetic spectra generated by our 2D atmosphere simulations, we propose that observing SO2 absorption in the emission spectra of WASP-39b at different phases may offer opportunities to probe the horizontal quenching process of photochemical products. We will focus on the gas-phase chemistry in this paper and leave the results regarding clouds in the subsequent paper as part of the series.

Hydrogen-Mediated Photoelectrocatalysis with Nickel-Modified Poly(Heptazine Imides)

Polymeric carbon nitrides (C3N4) are photochemically active organic semiconductors that can be produced in a wide range of structural types. Here, a poly-(heptazine imide) containing nickel single atoms (Ni-PHI) is employed for photochemical hydrogen production and is compared to the non-nickel-doped semiconductor. Film deposits are formed on a platinum disk electrode (to detect hydrogen) and a coating of the molecularly rigid polymer of intrinsic microporosity PIM-1 is applied to (i) mechanically stabilize the photo-catalyst film without impeding photocatalysis and (ii) assist in the interfacial hydrogen capture/oxygen suppression process. In the presence of hole quenchers such as methanol or ethanol, anodic photocurrents linked to hydrogen production/oxidation are observed. A comparison with an experiment on glassy carbon confirms the formation of interfacial hydrogen as a mediator. The effects of hole quencher concentration are evaluated. The system Pt/Ni-PHI/PIM-1 is employed in a single-compartment photo-fuel cell.Graphical

Comparison of the ozone formation mechanisms and VOCs apportionment in different ozone pollution episodes in urban Beijing in 2019 and 2020: Insights for ozone pollution control strategies

Ground-level ozone (O3) pollution has been a tough issue in urban areas of China in the past decade. Clarifying the formation mechanisms of O3 and the sources of its precursors is necessary for the effective prevention of O3 pollution. In this study, a comparative analysis of O3 formation mechanisms and VOCs apportionment for five O3 pollution episodes was carried out at two urban sites (CRAES and CGZ) in Beijing in 2019 and 2020 by applying an observation-based modeling approach in order to obtain insights into O3 pollution control strategies. Results indicated that O3 pollution levels were generally more severe in 2019 than in 2020 during the observation periods. O3 formation at the two sites was both VOCs-limited on O3 polluted days and non-O3 polluted days. Stronger atmospheric oxidation capacity and ROx radicals cycling processes were found on O3 polluted days which could accelerate the local production of O3, and local photochemical production dominated the observed O3 concentrations at the two sites even on non-O3 polluted days. Emission reduction of VOCs should be a priority for mitigating O3 pollution, and alkenes and biogenic VOCs was the priority species at the CRAES and CGZ sites, respectively. Additionally, the reduction of oxygenated VOCs should also be important for the ozone control. Gasoline exhaust at the CRAES site, and solvent utilization and fuel evaporation at the CGZ site were main anthropogenic sources of VOCs. Therefore, local control measures should be further strengthened and differentiated control strategies of VOCs in the aspects of area, time, sources and species should be adopted in urban Beijing in the future. Overall, the findings of this study could provide a scientific understanding of the causes of O3 pollution and significant guidelines for formulating O3 control strategies from the perspective of different ozone pollution episodes in urban Beijing.

The Importance of the Upper Atmosphere to CO/O2 Runaway on Habitable Planets Orbiting Low-mass Stars

Efforts to spectrally characterize the atmospheric compositions of temperate terrestrial exoplanets orbiting M dwarf stars with JWST are now underway. Key molecular targets of such searches include O2 and CO, which are potential indicators of life. Recently, it was proposed that CO2 photolysis generates abundant (≳0.1 bar) abiotic O2 and CO in the atmospheres of habitable M dwarf planets with CO2-rich atmospheres, constituting a strong false positive for O2 as a biosignature and further complicating efforts to use CO as a diagnostic of surface biology. Importantly, this implied that TRAPPIST-1e and TRAPPIST-1f, now under observation with JWST, would abiotically accumulate abundant O2 and CO, if habitable. Here, we use a multi-model approach to reexamine photochemical O2 and CO accumulation on planets orbiting M dwarf stars. We show that photochemical O2 remains a trace gas on habitable CO2-rich M dwarf planets, with earlier predictions of abundant O2 and CO due to an atmospheric model top that was too low to accurately resolve the unusually high CO2 photolysis peak on such worlds. Our work strengthens the case for O2 as a biosignature gas, and affirms the importance of CO as a diagnostic of photochemical O2 production. However, observationally relevant false-positive potential remains, especially for O2's photochemical product O3, and further work is required to confidently understand O2 and O3 as biosignature gases on M dwarf planets.

PM chemical characterization at a semi-arid urban environment in Central Mexico

The central part of Mexico, a semi-arid region, hosts many anthropogenic activities that might affect the air quality of the several large cities within; however, the processes that occur in its atmosphere are poorly understood. Here, we investigated the concentration and chemical composition of the particulate matter in the Metropolitan Area of Queretaro for one year, together with meteorological variables and other pollutants data. Seasonal concentrations were determined mainly by meteorology. The secondary components comprised the largest fraction of PM2.5, followed by resuspension and the typical primary combustion sources in an urban area. Regional processing played a very important role in the formation of secondary aerosols. Local oxidation producing nitrate and less oxidized organic aerosols occurred more rapidly at night, although photochemical production in the morning was also observed. These results represent the first report of long-term real-time chemical characterization with high time resolution in the region. In addition, they might be important for better understanding the production of secondary aerosols in other semi-arid urban areas.