Atmospheric Radicals Research Articles

Study on the reactions of n-pentanal and n-hexanal with Br atoms: Kinetics, gas-phase products, and SOA formation

Aldehydes are one of the most important oxygenated volatile organic compounds in the atmosphere, contributing to atmospheric radicals such as HO2 and RO2, which play a pivotal role in atmospheric chemistry and the oxidative capacity of the atmosphere. The kinetics, gas-phase products, and SOA formation of pentanal and n-hexanal initiated by Br atoms were studied in this work. The reaction rate constants of n-pentanal and n-hexanal reacting with Br atoms were determined to be (1.77 ± 0.25) × 10−11 cm3 molecule−1 s−1 and (2.07 ± 0.29) × 10−11 cm3 molecule−1 s−1 at 298 K and 760 Torr, respectively. Key gas-phase products, including smaller aldehydes, carboxylic acids, and alcohols, are known to contribute to atmospheric reactivity and have potential implications for air quality by promoting the formation of secondary pollutants and influencing the oxidative capacity of the atmosphere. The SOA yields were (5.24 ± 0.10)% and (6.00 ± 1.20)% for n-pentanal and n-hexanal, respectively, higher than the SOA yields of the aldehydes reaction initiated by OH radicals. The higher SOA yields observed from Br atoms oxidation compared to OH radical oxidation highlight the necessity to re-evaluate the role of halogen chemistry in atmospheric processes, particularly in regions where halogen compounds are prevalent. This research enhances our understanding of the atmospheric fate of aldehydes and highlights the importance of considering halogen-driven oxidation pathways in atmospheric models.

Atmospheric Degradation Mechanism of Isoamyl Acetate Initiated by OH Radicals and Cl Atoms Revealed by Quantum Chemical Calculations and Kinetic Modeling.

Isoamyl acetate is one of the volatile organic compound class molecules relevant to agricultural and industrial applications. With the growing interest in isoamyl acetate applications in industry, the atmospheric fate of isoamyl acetate must be considered. Reaction mechanisms, potential energy profiles, and rate constants of isoamyl acetate reaction with atmospheric relevant oxidant OH radicals and Cl atoms have been obtained from the quantum chemical calculations and kinetic modeling. The geometry optimizations were conducted using M06-2X/6-311++G(3df,3pd) followed by single point-energy calculations at the DLPNO-CCSD(T) method with an extrapolated complete basis set. The rate constants were calculated by solving the master equation. A hydrogen-abstraction reaction dominates the first step of isoamyl acetate degradation, while the addition-substitution reaction plays a small role in the degradation products. The kinetic study was conducted to evaluate the rate constants within a temperature range of 200-400 K. The total rate constants for the isoamyl acetate degradation reactions initiated by the OH radical and Cl atom were determined to be 6.96 × 10-12 and 1.27 × 10-10 cm3 molecule-1 s-1, respectively, under standard temperature and pressure conditions. The product degradation mechanism, ozone formation potential, and atmospheric impacts were discussed.

Measurements of Atmospheric HO2 Radicals Using Br-CIMS with Elimination of Potential Interferences from Ambient Peroxynitric Acid.

As a promising direct measurement method of atmospheric hydroperoxyl radicals (HO2), bromide chemical ionization mass spectrometry (Br-CIMS) has been first demonstrated by Sanchez et al. (Atmos. Meas. Tech. 2016, 9, 3851-3861). However, field application of this method is currently still sparse, and there is still a gap between measured HO2 concentrations and calculated ones derived from the atmospheric equilibrium between HO2 and peroxynitric acid (HO2NO2). In this work, we constructed an improved Br-CIMS with optimizations of custom-built front-end devices, chamber pressures, and instrumental voltages to achieve a 3σ detection limit of 0.5 ppt at an integration time of 60 s and a sensitivity of 1-3 cps ppt-1 under a total reagent ion signal of 0.2 MHz for HO2 detection. HO2NO2, a product from atmospheric reactions between HO2 and NO2, can also be detected by Br-CIMS, whose interference on the HO2 measurement was found but nearly eliminated by regulating key CIMS voltages to minimize the decomposition of (BrHO2NO2)- ions in the MS. In addition, a 2 week field campaign was carried out in urban Shanghai, demonstrating that the interference of HO2 from ambient HO2NO2 was less than 10% of the true HO2 signal under our optimized CIMS voltage setting. Our study suggests that Br-CIMS is a reliable technique for atmospheric HO2 measurements.

Atmospheric photo-oxidation of acetic anhydride: Kinetic study and reaction mechanism. Products distribution and fate of CH3C(O)OC(O)CH2O· radical

The rate coefficient for the gas-phase reaction of acetic anhydride (Ac2O) with chlorine atoms at 298 K and atmospheric pressure was experimentally determined (kAc2O+Cl= (1.3 ± 0.4) × 10-12 cm3molec−1s−1), while the rate coefficient for the reaction with the hydroxyl radical was estimated (kAc2O+OH=1.9 x 10-13 cm3molec−1s−1). For the Structure-Activity Relationship method, a value of 0.02 was determined for the −C(O)OC(O) group. The mechanism of photo-oxidation of acetic anhydride initiated by chlorine atoms was determined and CO, CO2, CH3C(O)OH (32 %), CH3C(O)OC(O)C(O)H, and 3-hydroxy-1,4-dioxane-2,6-dione (20 %) were identified as products by infrared spectroscopy. Here we determined for the first time the relative energies of the primary reaction pathways for the CH3C(O)OC(O)CH2O· radical using computational methods, which confirmed our experimental data. Finally, the environmental implications of acetic anhydride emissions were calculated, showing an atmospheric lifetime between 31 and 220 days for the reaction with atmospheric radicals, while its wet deposition lifetime is 1.5 years.

Sensitivity of atmospheric peroxyacetyl nitrate (PAN) formation and its impact on ozone pollution in a coastal city

Peroxyacetyl nitrate (PAN) ranks among the troposphere's most prevalent organic peroxy radicals, and the photochemical production and loss pathways of PAN are mainly related to the generation and consumption of PA radicals. PA radicals can affect the atmospheric O3 generation by competing or providing precursors and affecting the atmospheric radical cycling. Field measurements took place at two sites in Shenzhen: the suburban site of Yangmeikeng Station (YMK) from September to October 2018, and the urban site of University town of Shenzhen (DXC) from September to October 2019. The average PAN levels of YMK and DXC were 0.57 and 0.87 ppb, which were similar to PAN concentrations in other southeastern coastal regions and lower than those in inland and northern regions in China. The model simulations showed that except PAN thermal decomposition, acetaldehyde (40.7% and 24.9%), other OVOCs (40.0% and 59.2%) and radical cycling (19.3% and 16.0%) were the major production pathways peroxyacetyl (PA) radicals at YMK and DXC. During the sampling period, the production of PAN resulted in a decreasing of local O3 generation at YMK (5.32 ± 3.2 ppb) and DXC (3.53 ± 12.21 ppb). The findings could make us more comprehensively understand the mechanism of atmospheric formation of PAN in urban and suburban sites in Shenzhen and its influence on the process of atmospheric photochemical reaction in Shenzhen.

Roles of photochemical consumption of VOCs on regional background O3 concentration and atmospheric reactivity over the pearl river estuary, Southern China

Understanding of the photochemical ozone (O3) pollution over the Pearl River Estuary (PRE) of southern China remains limited. We performed an in-depth analysis of volatile organic compounds (VOCs) data collected on an island (i.e., the Da Wan Shan Island, DWS) located at the downwind of Pearl River Delta (PRD) from 26 November to 15 December 2021. Abundances of O3 and its precursors were measured when the air masses originated from the inland PRD. We observed that the VOCs levels at the DWS site were lower, while the mixing ratio of O3 was higher, compared to those reported at inland PRD, indicating the occurrence of photochemical consumption of VOCs during the air masses transport, which was further confirmed by the composition and diurnal variations of VOCs, as well as ratios of specific VOCs. The simulation results from a photochemical box model showed that the O3 level in the outflow air masses of inland PRD (O3(out-flow)) was the dominant factor leading to the intensification of O3 pollution and the enhancement of atmospheric radical concentrations (ARC) over PRE, which was mainly contributed by the O3 production via photochemical consumption of VOCs during air masses transport. Overall, our findings provided direct quantitative evidence for the roles of outflow O3 and its precursors from inland PRD on O3 abundance and ARC over the PRE area, highlighting that alleviation of O3 pollution over PRE should focus on the impact of photochemical loss of VOCs in the outflow air masses from inland PRD.

Measurement report: Atmospheric nitrate radical chemistry in the South China Sea influenced by the urban outflow of the Pearl River Delta

Abstract. The nitrate radical (NO3) is a critical nocturnal atmospheric oxidant in the troposphere, which widely affects the fate of air pollutants and regulates air quality. Many previous works have reported the chemistry of NO3 in inland regions of China, while fewer studies target marine regions. Here, we present a field measurement of the NO3 reservoir, dinitrogen pentoxide (N2O5), and related species at a typical marine site (Da Wan Shan Island) located in the South China Sea in the winter of 2021. Two patterns of air masses were captured during the campaign, including the dominant airmass from inland China (IAM) with a percentage of ∼ 84 %, and the airmass from eastern coastal areas (CAM) with ∼ 16 %. During the IAM period, the NO3 production rate reached 1.6 ± 0.9 ppbv h−1 due to the transportation of the polluted urban plume with high NOx and O3. The average nocturnal N2O5 and the calculated NO3 mixing ratios were 119.5 ± 128.6 and 9.9 ± 12.5 pptv, respectively, and the steady-state lifetime of NO3 was 0.5 ± 0.7 min on average, indicating intensive nighttime chemistry and rapid NO3 loss at this site. By examining the reaction of NO3 with volatile organic compounds (VOCs) and N2O5 heterogeneous hydrolysis, we revealed that these two reaction pathways were not responsible for the NO3 loss (< 20 %) since the NO3 reactivity (k(NO3)) towards VOCs was small (5.2×10-3 s−1) and the aerosol loading was low. Instead, NO was proposed to significantly contribute to nocturnal NO3 loss at this site, despite the nocturnal NO concentration always below the parts per billion by volume level and near the instrument detection limit. This might be from the local soil emission or something else. We infer that the nocturnal chemical NO3 reactions would be largely enhanced once without NO emission in the open ocean after the air mass passes through this site, thus highlighting the strong influences of the urban outflow to the downwind marine areas in terms of nighttime chemistry. During the CAM period, nocturnal ozone was higher, while NOx was much lower. The NO3 production was still very fast, with a rate of 1.2 ppbv h−1. With the absence of N2O5 measurement in this period, the NO3 reactivity towards VOCs and N2O5 uptake were calculated to assess NO3 loss processes. We showed that the average k(NO3) from VOCs (56.5 %, 2.6 ± 0.9 × 10−3 s−1) was higher than that from N2O5 uptake (43.5 %, 2.0 ± 1.5 × 10−3 s−1) during the CAM period, indicating a longer NO3 / N2O5 lifetime than that during IAM period. This study improves the understanding of the nocturnal NO3 budget and environmental impacts with the interaction of anthropogenic and natural activities in marine regions.

A study of theoretical mechanism on wastewater components of paper industry with process generated radicals in gaseous and aqueous phase

The paper and pulp industries release a diverse array of hazardous chemicals into the atmosphere, water bodies, and soil. Papermaking is characterized by intricate stages including debarking, pulping, bleaching and washing. Each of these stages possesses the capacity to generate a spectrum of toxic pollutants which may be present in both gaseous and liquid phases. This includes substances such as fatty acids, aromatic compounds, polycyclic aromatic hydrocarbons, acetaldehyde, chlorinated phenols, lignin, cellulose, hemicellulose and wood extractives. Consequently, these industrial discharges contribute to the contamination of wastewater with a complex mixture of harmful compounds. Some of these compounds persist even after the secondary treatment process. The effluent from these industries contains benzaldehyde which is one of the aromatic aldehydes with the highest reported retention time. The present study focuses on the reactions between benzaldehyde and atmospheric radicals (NO, NO2, HO2, O2, and OH radical) using computational methods. The study holds prime importance in understanding reactions involving these compounds and eventually assessing their impact on the environment. Density Functional Theory (DFT) is used to calculate Gibbs’s free energy which shows the spontaneity of reactions. The results show that the production of nitrobenzaldehyde is more feasible with ∼ -53.64 kcal/mol than the other products, and these nitro derivatives are proven to have a role in the formation and growth of the secondary organic aerosols. The aqueous solution environment promotes the production of these compounds, and they have a higher reaction energy of ∼ -3.34 kcal/mol than the gas phase. The products of these reactions adversely impact health and the atmosphere, making it a necessity to decrease the reactivity of these reactions or to take necessary actions to restrict the release of these toxic contaminants before they react with atmospheric radicals.

Furan-based fluorescent probe free radical capture membrane: Analysis of RO2 radical composition and transformation mechanism in urban atmosphere

Peroxyl radicals (RO2) are important components of atmospheric radical cycling and generation, but their formation, distribution and evolution mechanisms in the atmospheric environment have not been investigated. In this paper, we propose a novel atmospheric RO2 radical trapping membrane that can trap low carbon number (Rc ≤ 5) RO2 radicals and identify their R-group structures by fluorescence spectroscopy and chromatography. We also analyzed the composition and evolution mechanism of RO2 species under different meteorological conditions in the atmospheric environment of Lanzhou, China, to provide scientific support for the treatment and research of atmospheric chemical pollution.

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.

Feasibility study on the homogeneity and stability of megastigmatrienone isomers for the development of certified reference material

Megastigmatrienone is a natural flavoring food additive with a spicy and tobacco-like aroma. A feasibility study on the homogeneity and stability of megastigmatrienone preceded for the development of a certified reference material (CRM). Megastigmatrienone, a mixture of four diastereomers, was prepared using gram-scale synthesis. The purity values of candidate megastigmatrienone reference material (MRM) determined using two independent methods showed comparable results by GC–MS assay (90.89%) and mass balance method (92.42%). Candidate MRM aliquoted into vials was confirmed to be homogenous between the bottles. In the stability test, various packaging methods and environmental conditions capable of stabilizing megastigmatrienone were tested. Candidate MRM aliquoted into vials was unstable from –20 °C to 40 °C for 12 months. However, either antioxidant additive or argon-substituted heat-sealing package significantly improved its stability. These findings suggest that atmospheric reactive radicals may be critical factors resulting in the decomposition of megastigmatrienone. Argon-substituted packaging and storage temperatures below −20 °C are the practical alternatives to sustain its stability. This study systematically demonstrates strategies for stabilizing materials with poor stability. Our findings can be useful for developing megastigmatrienone CRM to guarantee the reliable quality of food additives or foods containing megastigmatrienone.

Resolving the Formation Mechanism of HONO via Ammonia-Promoted Photosensitized Conversion of Monomeric NO2 on Urban Glass Surfaces

Understanding the formation processes of nitrous acid (HONO) is crucial due to its role as a primary source of hydroxyl radicals (OH) in the urban atmosphere and its involvement in haze events. In this study, we propose a new pathway for HONO formation via the UVA-light-promoted photosensitized conversion of nitrogen dioxide (NO2) in the presence of ammonia (NH3) and polycyclic aromatic hydrocarbons (PAHs, common compounds in urban grime). This new mechanism differs from the traditional mechanism, as it does not require the formation of the NO2 dimer. Instead, the enhanced electronic interaction between the UVA-light excited triplet state of PAHs and NO2-H2O/NO2-NH3-H2O significantly reduces the energy barrier and facilitates the exothermic formation of HONO from monomeric NO2. Furthermore, the performed experiments confirmed our theoretical findings and revealed that the synergistic effect from light-excited PAHs and NH3 boosts the HONO formation with determined HONO fluxes of 3.6 × 1010 molecules cm-2 s-1 at 60% relative humidity (RH) higher than any previously reported HONO fluxes. Intriguingly, light-induced NO2 to HONO conversion yield on authentic urban grime in presence of NH3 is unprecedented 130% at 60% RH due to the role of NH3 acting as a hydrogen carrier, facilitating the transfer of hydrogen from H2O to NO2. These results show that NH3-assisted UVA-light-induced NO2 to HONO conversion on urban surfaces can be a dominant source of HONO in the metropolitan area.

Where, When, and Why Do Plant Volatiles Mediate Ecological Signaling? The Answer Is Blowing in the Wind.

Plant volatiles comprise thousands of molecules from multiple metabolic pathways, distinguished by sufficient vapor pressure to evaporate into the headspace under normal environmental conditions. Many are implicated as ecological signals, but what is the evidence-and how do they work? Volatiles diffuse, are carried by wind, and may be taken up by other organisms or degrade with exposure to atmospheric ozone, radicals, and UV light; visual signals such as color are not subject to these complications (but require a line of sight). Distantly related plants-and nonplants-produce many of the same volatiles, yet specific compounds and blends may be distinct. Here, I present a quantitative review of the literature on plant volatiles as ecological signals, illustrating a field that has focused on developing ideas as much as reporting primary data. I discuss advantages and constraints, review recent advances, and propose considerations for primary studies to elucidate particular functions of plant volatiles.

Retrieval of Martian Atmospheric CO Vertical Profiles From NOMAD Observations During the First Year of TGO Operations

AbstractWe present CO density profiles up to about 100 km in the Martian atmosphere obtained for the first time from retrievals of solar occultation measurements by the Nadir and Occultation for Mars Discovery (NOMAD) onboard ExoMars Trace Gas Orbiter (TGO). CO is an important trace gas on Mars, as it is controlled by CO2 photolysis, chemical reaction with the OH radicals, and the global dynamics. However, the measurements of CO vertical profiles have been elusive until the arrival of TGO. We show how the NOMAD CO variations describe very well the Mars general circulation. We observe a depletion of CO in the upper troposphere and mesosphere during the peak period, LS = 190°–200°, more pronounced over the northern latitudes, confirming a similar result recently reported by Atmospheric Chemistry Suite onboard TGO. However, in the lower troposphere around 20 km, and at least at high latitudes of the S. hemisphere, NOMAD CO mixing ratios increase over 1,500 ppmv during the GDS (Global Dust Storm) onset. This might be related to the downwelling branch of the Hadley circulation. A subsequent increase in tropospheric CO is observed during the decay phase of the GDS around LS = 210°–250° when the dust loading is still high. This could be associated with a reduction in the amount of OH radicals in the lower atmosphere due to lack of solar insolation. Once the GDS is over, CO steadily decreases globally during the southern summer season. A couple of distinct CO patterns associated with the Summer solstice and equinox circulation are reported and discussed.

Is There a Formaldehyde Deficit in Emissions Inventories for Southeast Michigan?

Formaldehyde is a key Volatile Organic Compound (VOC) and ozone precursor that plays a vital role in the urban atmospheric radical budget on par with water vapor, ozone, and nitrous acid. In addition to modulating radical and ozone production, ambient formaldehyde has both carcinogenic and non-carcinogenic inhalation health effects. This study concludes that ambient formaldehyde in the Southeast Michigan (SEMI) ozone nonattainment area may be underestimated up to a factor of two or more by regional air quality models. The addition of plausible amounts of primary formaldehyde to the U.S. National Emissions Inventory based on estimated formaldehyde-to-CO emission ratios partially alleviates this modeling deficit and indicates the presence of formaldehyde concentrations above 5 ppb at a previously unsuspected location northeast of Detroit. Standard 24-h formaldehyde samples obtained during the Michigan-Ontario Ozone Source Experiment (MOOSE) verified the presence of high ambient formaldehyde concentrations at this location. Moreover, the addition of plausible amounts of primary formaldehyde to VOC emissions inventories may add more than 1 ppb of ozone to ambient air in the SEMI nonattainment area, where ozone design values exceeded the U.S. National Ambient Air Quality Standard (NAAQS) by 1–2 ppb for the 2018–2020 design value period.

Dimeric Product of Peroxy Radical Self-Reaction Probed with VUV Photoionization Mass Spectrometry and Theoretical Calculations: The Case of C2H5OOC2H5

Organic peroxy radicals (RO2) as key intermediates in tropospheric chemistry exert a controlling influence on the cycling of atmospheric reactive radicals and the production of secondary pollutants, such as ozone and secondary organic aerosols (SOA). Herein, we present a comprehensive study of the self-reaction of ethyl peroxy radicals (C2H5O2) by using advanced vacuum ultraviolet (VUV) photoionization mass spectrometry in combination with theoretical calculations. A VUV discharge lamp in Hefei and synchrotron radiation at the Swiss Light Source (SLS) are employed as the photoionization light sources, combined with a microwave discharge fast flow reactor in Hefei and a laser photolysis reactor at the SLS. The dimeric product, C2H5OOC2H5, as well as other products, CH3CHO, C2H5OH and C2H5O, formed from the self-reaction of C2H5O2 are clearly observed in the photoionization mass spectra. Two kinds of kinetic experiments have been performed in Hefei by either changing the reaction time or the initial concentration of C2H5O2 radicals to confirm the origins of the products and to validate the reaction mechanisms. Based on the fitting of the kinetic data with the theoretically calculated results and the peak area ratios in the photoionization mass spectra, a branching ratio of 10 ± 5% for the pathway leading to the dimeric product C2H5OOC2H5 is measured. In addition, the adiabatic ionization energy (AIE) of C2H5OOC2H5 is determined at 8.75 ± 0.05 eV in the photoionization spectrum with the aid of Franck-Condon calculations and its structure is revealed here for the first time. The potential energy surface of the C2H5O2 self-reaction has also been theoretically calculated with a high-level of theory to understand the reaction processes in detail. This study provides a new insight into the direct measurement of the elusive dimeric product ROOR and demonstrates its non-negligible branching ratio in the self-reaction of small RO2 radicals.

Size-resolved environmentally persistent free radicals in cold region atmosphere: Implications for inhalation exposure risk.

Environmental persistent free radicals (EPFRs) have attracted more attentions recently due to their potential adverse effects to human. EPFRs in full-size range particles were comprehensively investigated in this study. The average EPFRs concentration during heating season was 3.01×1014 spins/m3, which was much higher than that in non-heating season (4.30×1013 spins/m3). The highest concentration of EPFRs presented in 0.56-1.0µm particles during heating season, while it shifted to 5.6-10µm particles during non-heating season. Besides, the contributions of EPFRs on PM>10 to the total concentration of EPFRs cannot be neglected, especially in the non-heating season. The International Commission on Radiological Protection model and the specific factors of the Chinese population were applied to evaluate the inhalation exposure risk of EPFRs. The results indicated that the exposure levels of EPFRs to the upper respiratory tract were much higher. The daily exposure dose of EPFRs suggested the inhalation exposure risk of 3-4 years old was higher than other age groups. In summary, these finding provided new insights for the full range particle size distribution and the inhalation exposure risk of EPFRs, which improved our understanding on the environmental fate and the health risk of EPFRs in atmosphere.

Increased night-time oxidation over China despite widespread decrease across the globe

Nitrogen oxides (NOx = NO + NO2) emitted from combustion and natural sources are reactive gases that regulate the composition of Earth’s atmosphere. Nocturnal oxidation driven by nitrate radicals is an important but poorly understood process in atmospheric chemistry, affecting the lifetimes of NOx and ozone and particulate pollution levels. Understanding the trends of nitrate radicals is important to formulating effective pollution mitigation strategies and understanding the influence of NOx on climate. Here we analyse publicly available monitoring data on NOx and ozone to assess production rates and trends of surface nitrate radicals from 2014 to 2021 across the globe. We show that nitrate radicals have undergone strong increases in China during 2014–2019 but exhibited modest decreases in the United States and the European Union. Accelerated night-time oxidation has shortened the lifetime of summer NOx in China by 30% during 2014–2019. This change will strongly affect ozone formation and has policy implications for the joint control of ozone and fine particulate pollution. Measurements show that night-time production of atmospheric nitrate radicals increased in China but decreased in the European Union and the United States from 2014 to 2019. This suggests the increasing contribution of night-time atmospheric oxidation in China to air pollution.

In situphotogenerated hydroxyl radicals in the reaction atmosphere for the accelerated crystallization of solution-processed functional metal oxide thin films

We propose a disruptive method to accelerate the crystallization at low temperatures of functional metal oxide films whereby hydroxyl radicals (•OH) are photogeneratedin situfrom the atmosphere where solution-deposited layers are UV-irradiated.

Combined Experimental and Computational Kinetics Studies for the Atmospherically Important BrHg Radical Reacting with NO and O2.

We report on the first experimental determination of the absolute rate constant of the reaction of BrHg + NO in N2 bath gas using a laser photolysis-laser-induced fluorescence (LP-LIF) system. The rate constant of the reaction of BrHg + NO is determined to be 7.0-0.9+1.3 × 10-12 cm3 molecule-1 s-1 over 50-700 Torr and 315-353 K. The absence of a pressure or temperature dependence suggests that this reaction leads mainly to mercury reduction (Hg + BrNO) rather than mercury oxidation (BrHgNO). Our theoretical calculations using NEVPT2 energies on density functional theory (DFT) geometries are consistent with a barrierless reaction to form Hg + BrNO. The equilibrium constants and the rate constants of the reaction BrHg + O2 ⇌ BrHgOO are computed theoretically because they are too low to be measured in the LP-LIF system. Molecular oxygen quenches the LIF signal of BrHg with a large rate constant of (1.7 ± 0.1) × 10-10 cm3 molecule-1 s-1. Thus, different techniques that capture the absolute [BrHg(X̃)] would be advantageous for kinetics studies of BrHg reactions in the presence of O2. The computed equilibrium constant suggests a non-negligible upper limit of the fraction of BrHg stored as BrHgOO (up to 0.5) at low-temperature conditions, e.g., in the upper troposphere and in polar winters at ground level. Preliminary results indicate that BrHgOO behaves like HOO or organic peroxy radicals in reactions with atmospheric radicals.