Validating HONO as an Intermediate Tracer of the External Cycling of Reactive Nitrogen in the Background Atmosphere.

In the urban atmosphere, nitrogen oxide (NOx═NO + NO2)-related reactions dominate the formation of nitrous acid (HONO). Here, we validated an external cycling route of HONO and NOx, i.e., formation of HONO resulting from precursors other than NOx, in the background atmosphere. A chemical budget closure experiment of HONO and NOx was conducted at a background site on the Tibetan Plateau and provided direct evidence of the external cycling. An external daytime HONO source of 100 pptv h-1 was determined. Both soil emissions and photolysis of nitrate on ambient surfaces constituted likely candidate mechanisms characterizing this external source. The external source dominated the chemical production of NOx with HONO as an intermediate tracer. The OH production was doubled as a result of the external cycling. A high HONO/NOx ratio (0.31 ± 0.06) during the daytime was deduced as a sufficient condition for the external cycling. Literature review suggested the prevalence of high HONO/NOx ratios in various background environments, e.g., polar regions, pristine mountains, and forests. Our analysis validates the prevalence of external cycling in general background atmosphere and highlights the promotional role of external cycling regarding the atmospheric oxidative capacity.

Experimental and Modeling Studies on the Filtration of SiO2 Nanoparticles Aerosolized from Different Solvents.

The filtration performance of a fibrous filter in removing nano-SiO2 aerosols atomized using different solvents including methanol, ethanol, 1-propanol, water, and the ethanol/water mixture has been investigated. Through discrete element method (DEM) simulation and filtration experiments, the efficiency variation caused by the combinative interaction of the particle-filter adhesion and interparticle attraction has been analyzed and verified. The adhesion force between the solvent-coated nanoparticles and the filter is considered as the key factor to influence their initial filtration efficiency and can be balanced by their interparticle interaction. The stronger the adhesion, the higher the initial filtration efficiency. Primary aggregate is formed through the particle-fiber interaction, and further agglomerate is caused by particle migration on the fibers, i.e. secondary aggregate. Hydrogen bonding interaction is considered as the main factor causing interparticle secondary agglomeration, and plenty of OH groups existing in the nano-SiO2 aerosols yielded from alcohol promotes the particle secondary aggregation. As a result, the Brown diffusion capture of the filter is significantly abated, and the as-formed agglomerate is scraped off the filter surface by the alcohol molecules, causing the filtration efficiency decreases. This study highlights the surface affinity properties of nanoaerosols and their balance between particle-particle and particle-fiber interactions in the filtration process.

Gas-Phase Reactions of Methoxyphenols with NO3 Radicals: Kinetics, Products, and Mechanisms.

Methoxyphenols, a group of important tracers for wood smoke, are emitted to the atmosphere in large quantities, but their transformations are rarely studied. In this study, the kinetics and products of the gas-phase reactions of eugenol and 4-ethylguaiacol with NO3 radicals were investigated online using a vacuum ultraviolet photoionization gas time-of-flight mass spectrometer. The rate coefficients of the gaseous reactions of eugenol and 4-ethylguaiacol with NO3 radicals were (1.6 ± 0.4) × 10(-13) and (1.1 ± 0.2) × 10(-12) cm(3) molecule(-1) s(-1) (at 298 K), indicating that the atmospheric lifetimes of the NO3 radicals were 3.5 and 0.5 h, respectively. With the aid of gas-chromatography-mass-spectrometry analysis, several types of degradation products were identified with nitro derivatives as the major products. The configurations of the nitro-product isomers and their formation mechanisms were determined via theoretical calculations. On the basis of these products, degradation pathways of the methoxyphenols with NO3 radicals were proposed. This study determines the degradation rates and mechanisms of the methoxyphenols at night and implies the significant NO3 nighttime chemistry.

Effects of humidity and [NO3]/[N2O5] ratio on the heterogeneous reaction of fluoranthene and pyrene with N2O5/NO3/NO2.

Atmospheric 2-nitrofluoranthene (2-NFL) and 2-nitropyrene (2-NPY) were two important nitro-polycyclic aromatic hydrocarbons (NPAHs). Especially, 2-NFL was recognized to be the most abundant particle-associated NPAH (Ramdahl et al., 1986). In previous studies, these two products were observed in the gas-phase reaction between N2O5/NO3/NO2 and their parent polycyclic aromatic hydrocarbons (PAHs), while the heterogeneous reaction generated other nitro-PAH isomers (1, 3, 7, 8-NFL and 1-NPY) (Atkinson et al. 1990). To clarify the possible reasons for this difference, the heterogeneous reactions of suspended fluoranthene (FL) and pyrene (PY) particles under different relative humidity (RH; 0.5%-43%) and [NO3]/[N2O5] ratios were carried out. Under low humidity (0.5% RH) or a relatively high ratio of [NO3]/[N2O5], 2-NFL and 2-NPY were observed as the major nitro-FL isomers for the first time in the heterogeneous reaction. Decreasing the humidity or increasing the [NO3]/[N2O5] ratio in the reaction essentially increases the concentration radio of [NO3(g)]/[NO2(+)(aq)] on the particle surface (NO2(+) is derived from the ionization of N2O5). Thus, it can be concluded that under different atmospheric conditions, the change of [NO3(g)]/[NO2(+)(aq)] in the particle surface has an influence on the product distribution of FL and PY in the atmosphere. The experimental results provide evidence for the heterogeneous formations of particle-bound 2-NFL and 2-NPY. However, relative to the gas-phase formation, they will be negligible in the real atmosphere. 2-NFL and 2-NPY observed in the ambient particles should mainly derive from deposition of gas-phase reactions. Additionally, this study also clarifies the reason for different nitro-PAHs isomers observed between gas and particulate reactions.

Effects of Berberine on glucolipid metabolism among dehydroepiandrosterone-induced rats of polycystic ovary syndrome with insulin-resistance.

Polycystic ovary syndrome (PCOS) is a set of endocrine disorder syndrome characterized by ovulation disorder. Increased insulin resistance (IR) and compensatory hyperinsulinemia play a vital role in the pathogenesis of PCOS. Therefore, insulin sensitizing agents have been studied in the treatment of PCOS. Berberine (BBR) has been proved to alleviate IR in patients with PCOS, but the mechanism remained unclear. This study was aimed to verify the regulatory mechanism of BBR on PCOS-IR rats. Firstly, we established a female rat PCOS-IR model induced by dehydroepiandrosterone (DHEA) and found that estrus cycle was disrupted in the PCOS-IR group, serum fasting insulin (FINS) level and the homeostasis model assessment of insulin resistance (HOMA-IR) index were significantly higher than normal control group. BBR treatment could recover estrous cycle, reduce abnormal serum hormone levels like luteotropic hormone (LH) and testosterone (T). Most importantly, BBR could concentration-dependently reduce serum FINS level in PCOS-IR rat model. Meanwhile, BBR may improve the abnormal lipid metabolism levels in PCOS-IR group by decreasing low density lipoprotein (LDL), total cholesterol (TC) and triglyceride (TG). Histological results showed that BBR can also protect normal histological structures of ovaries in PCOS-IR rats. Our results indicated that BBR plays a protective role in PCOS-IR, increasing insulin sensitivity, improving hyperandrogens and recovering abnormal blood lipids. Therefore, Our research provides novel insights for therapeutic treatment of BBR in patients with glucolipid metabolic disturbances.

[Characteristics and Source Apportionment of VOCs Initial Mixing Ratio in Beijing During Summer].

To clarify the characteristics and source apportionment of the VOCs initial mixing ratio in Beijing in summer, continuous monitoring of VOCs was conducted in the Beijing urban area from May to August 2022, and the initial mixing ratio was calculated using the photochemical ratio method. The results showed that:① during the study period, initial φ(TVOCs) in the Beijing urban area were (30.0 ±11.5)×10-9, in which the proportion of VOCs and alkanes containing oxygen reached 34.2% and 33.2%, respectively. The species with high volume fractions were low carbon substances such as acetone, ethane, acetaldehyde, and propane. ② The initial TVOCs mixing ratio in Beijing showed a slightly unimodal trend, reaching the peak at 11:00 and slightly decreasing in the afternoon. ③ Isoprene, acetaldehyde, n-butanal, and ethylene were the major contributors to the generation of O3, whereas toluene, isoprene, m-paraxylene, and ethylbenzene were the major contributors to the generation of secondary organic aerosols. ④ Based on the initial mixing ratio of PMF analysis, it was found that aging background and secondary sources (30%) contributed the most to VOCs in Beijing, and motor vehicle sources (25%) were the main primary human sources. In addition, solvent and fuel volatile sources contributed 16%, combustion sources contributed 11%, industrial process sources contributed 9%, and natural sources contributed 9%. ⑤ The anthropogenic sources of Beijing were mainly from the eastern and southern regions, whereas the natural sources were from the western and northwestern regions. This research showed that vehicle emissions should be further reduced, and regional joint prevention and control to reduce VOCs in the whole region is an effective means to control VOCs in Beijing.

Exploring the Functioning of Online Self-Organizations during Public Health Emergencies: Patterns and Mechanism.

With the increasing use of social media, online self-organized relief has become a crucial aspect of crisis management during public health emergencies, leading to the emergence of online self-organizations. This study employed the BERT model to classify the replies of Weibo users and used K-means clustering to summarize the patterns of self-organized groups and communities. We then combined the findings from pattern discovery and documents from online relief networks to analyze the core components and mechanisms of online self-organizations. Our findings indicate the following: (1) The composition of online self-organized groups follows Pareto's law. (2) Online self-organized communities are mainly composed of sparse and small groups with loose connections, and bot accounts can automatically identify those in need and provide them with helpful information and resources. (3) The core components of the mechanism of online self-organized rescue groups include the initial gathering of groups, the formation of key groups, the generation of collective action, and the establishment of organizational norms. This study suggests that social media can establish an authentication mechanism for online self-organizations, and that authorities should encourage online interactive live streams about public health issues. However, it is important to note that self-organizations are not a panacea for all issues during public health emergencies.

Synthesizing evidence for the external cycling of NOx in high- to low-NOx atmospheres.

External cycling regenerating nitrogen oxides (NOx ≡ NO + NO2) from their oxidative reservoir, NOz, is proposed to reshape the temporal-spatial distribution of NOx and consequently hydroxyl radical (OH), the most important oxidant in the atmosphere. Here we verify the in situ external cycling of NOx in various environments with nitrous acid (HONO) as an intermediate based on synthesized field evidence collected onboard aircraft platform at daytime. External cycling helps to reconcile stubborn underestimation on observed ratios of HONO/NO2 and NO2/NOz by current chemical model schemes and rationalize atypical diurnal concentration profiles of HONO and NO2 lacking noontime valleys specially observed in low-NOx atmospheres. Perturbation on the budget of HONO and NOx by external cycling is also found to increase as NOx concentration decreases. Consequently, model underestimation of OH observations by up to 41% in low NOx atmospheres is attributed to the omission of external cycling in models.

Kinetic studies of heterogeneous reactions of polycyclic aromatic hydrocarbon aerosols with NO3 radicals.

Polycyclic aromatic hydrocarbons (PAHs) and their derivates are mutagenic and carcinogenic substances widely distributed in the atmospheric environment. In this study, effective rate constants for heterogeneous reactions of NO(3) radicals with five 4-ring PAHs [benzo[a]anthracene (BaA), chrysene (Ch), pyrene (Py), 1-nitropyrene (1-NP), and 1-hydroxypyrene (1-OHP)] adsorbed on suspended azelaic acid particles are investigated by a mixed-phase relative rate method with gas-phase isoprene as the reference substance. The concentrations of suspended PAH particles and gas-phase isoprene are monitored concurrently by a real-time vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an online atmospheric gas analysis mass spectrometer, respectively. The obtained effective rate constants for the reactions of BaA, Ch, Py, 1-NP, and 1-OHP particles with NO(3) radicals are 4.3 × 10(-12), 4.0 × 10(-12), 6.4 × 10(-12), 1.3 × 10(-12), and 1.0 × 10(-11) cm(3)·molecule(-1)·s(-1), respectively, and their corresponding atmospheric lifetimes range from several minutes to half an hour at the NO(3) radical concentration of 5 × 10(8) molecules·cm(-3). In addition, the NO(3) uptake coefficients on particulate PAHs are estimated according to the consumption of PAHs under the exposure of NO(3) radicals. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne PAHs particles.

Heterogeneous reactions of particulate methoxyphenols with NO3 radicals: kinetics, products, and mechanisms.

Methoxyphenols, tracers for wood smoke, are emitted into the atmosphere in large quantities, but their chemical degradation in the atmosphere has not been well characterized. In this study, heterogeneous kinetics of particulate syringaldehyde (SA), vanillic acid (VA), and coniferyl aldehyde (CA) with NO3 radicals is investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer and an atmospheric gas analysis mass spectrometer are used to monitor online the decays of particulate methoxyphenols and gas-phase isoprene synchronously. The reactive uptake coefficients of NO3 radicals on SA, VA, and CA particles are calculated to be 0.33, 0.31, and 0.28, respectively, according to the measured methoxyphenol loss ratios and the average NO3 concentrations. The effective rate constants for heterogeneous reactions of particulate SA, VA, and CA with NO3 radicals measured under experimental conditions are 5.7 × 10⁻¹², 5.2 × 10⁻¹², and 3.5 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, respectively. In addition, oxalic acid, 2,6-dimethoxybenzoquinone, 5-nitro-VA, 4,6-dinitrogaiacol, protocatechuic acid, vanillin, 5-nitrovanillin, VA, and 5-nitro-CA are identified as the reaction products by gas chromatography-mass spectrometry analysis. On the basis of the identified products, the reaction mechanisms of methoxyphenols with NO3 radicals are proposed. The main transformation pathway of methoxyphenols is the NO3 electrophilic addition, followed by H-abstraction and nitro-substituted processes. The experimental results might shed light on the chemical behaviors of methoxyphenols at night.

Heterogeneous reactions of pirimiphos-methyl and pirimicarb with NO3 radicals.

Pirimiphos-methyl (PMM) and pirimicarb (PM) are two typical N,N-dialkyl substituted pyrimidine pesticides. The heterogeneous reactions of suspended PMM and PM particles with NO(3) radicals are investigated using an online aerosol time-of-flight mass spectrometer and a real-time atmospheric gas analysis mass spectrometer. Three products for PMM and five products for PM are observed and assigned with the aid of GC/MS. Phosphoric acid 2-diethylamino-6-methyl-4-pyrimidinyl dimethyl ester and 2-(dimethylamino)-5,6-dimethyl-4-hydroxy-pyrimidine are the main reaction products observed for PMM and PM, respectively. The effective rate constants for the reactions of PMM and PM particles with NO(3) radicals are (9.9 ± 0.3) × 10(-12) and (7.5 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), respectively, obtained using a mixed-phase relative rate method. Geometries and energies of transition states (TS) and intermediates (IM) are obtained by DFT calculation to elucidate the detailed mechanism of the P═S group oxidation into the P═O group for PMM. The theoretical studies present the reasonable intermediates including the S-oxide and the diradical (IM1(a) and IM2(a)). The mechanism explanation may provide useful information for understanding the degradation mechanism of organothionophosphorus compounds in the environment.

Complex to simple: In vitro exposure of particulate matter simulated at the air-liquid interface discloses the health impacts of major air pollutants.

Particulate matter (PM) exposure poses many adverse effects on human health. However, it is challenging to clearly differentiate between the contributions of individual pollutants on toxicity from complex mixtures of ambient air pollutants. The aim of this study is to generate aerosols constituted by silica nanoparticles (NPs) and bisulfate to serve as simulators of particle-associated high-sulfur air pollution. Then, the health impacts of sulfur dioxide were evaluated at the cellular level using an air-liquid interface (ALI) exposure chamber. BEAS-2B cells were exposed to either nano-silica or bisulfite aerosol individually or bisulfate-coated silica (SiO2-NH2@HSO3) for 3 h using the ALI. The cellular toxicities were carefully compared based on the exposure dosages. The ALI exposure of SiO2 NPs alone did not produce any apparent cytotoxicity in cells, but the aerosol exposure of SiO2-NH2@HSO3 significantly decreased the cell viability and enhanced the production of cellular reactive oxygen species in a dose-dependent manner. Consequently, the excessive oxidative stress resulted in mitochondrial damage as well as cellular apoptosis. ALI exposure can possibly reflect the realistic physiological exposure condition of the human respiratory system. As a derivative of the sulfur dioxide component of air pollution, sulfate exacerbates the toxic effects of inhalable PMs. This result may be due to the large surface area of the nanoparticles, with the possibility of carrying more sulfite to the target cells during aerosol exposure. The sulfate levels offer a meaningful complement to the present PM2.5 index of air pollution for achieving better human health protection.

Theoretical study on the atmospheric transformation mechanism of pirimiphos-methyl initiated by O3.

Pirimiphos-methyl (PMM) is a widely used organophosphorus pesticide that can be released into the atmosphere in gas and condensed phases. It possesses a PS bond and an N,N-dialkyl group adjacent to pyrimidine, which are common functional groups for pesticides. Currently, the reaction mechanisms of O3 with these functional groups are poorly understood. In this study, the mechanisms and possible degradation products for O3-initiated atmospheric oxidation of PMM were investigated using the Density Functional Theory (DFT) method. The results show that H abstraction from the alpha carbon of the N,N-diethyl group and its subsequent reactions (hydroxylation, N-dealkylation, and carbonylation reactions), as well as the transformation of the PS bond to the PO oxone form, are the most favorable reaction pathways for PMM and O3. The Gibbs free energy (ΔG) indicates that the subsequent reactions tend to take place more spontaneously once the initial reaction occurs. In addition, theoretical calculations indicate that water can serve as an effective catalyst in the N-dealkylation reaction process. Water-assisted reactions lead to the activation energy decreasing by 20.2 kcal mol(-1) compared with direct reactions, and thus may represent a dominant reaction pathway for the N-dealkylation process in the atmosphere. These theoretical results provide new insights into O3-initiated degradation of PMM and its analogues.

Products and mechanisms of the heterogeneous reaction of three suspended herbicide particles with NO3 radicals.

Over 60% of herbicides are capable of disrupting the endocrine and/or reproductive systems of animals. These herbicides may be released into the atmosphere in both gas and particulate phases, but most of their degradation processes in the atmosphere are not well known. In this study, the heterogeneous reactions of suspended isopropalin, trifluralin, and alachlor particles with NO3 radicals were investigated using an online vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. The reaction products for the three herbicides were determined by the assistance of the gas chromatography-mass spectrometer analysis. Mono-dealkylated derivatives were detected as the main reaction products of isopropalin and trifluralin. In addition, an α-amino alcohol product was detected for isopropalin. The carbonylation derivative and the nitro-substituted derivative were the main reaction products observed for alachlor. The reaction mechanism of NO3 radical-induced N-dealkylation for isopropalin was clarified by density functional theory calculations. It began with the H-abstraction from the N-propyl group, followed by the formation of the α-peroxypropyl radical, α-propyloxy radical, and α-amino alcohol, as well as by the collapse of the α-amino alcohol. The oxidation mechanism for trifluralin is similar to that of isopropalin, whereas the mechanism for alachlor involves carbonylation and nitro-substitution. These results provided insights on the chemical transformation of these herbicides in the atmosphere. The data generated from this study can be used as fundamental information for future studies on their toxic effects to the environment.

Heterogeneous reactions of particulate benzo[b]fluoranthene and benzo[k]fluoranthene with NO(3) radicals.

Benzo[b]fluoranthene (B[b]F) and benzo[k]fluoranthene (B[k]F) are widespread priority pollutants of polycyclic aromatic hydrocarbons (PAHs), which can react with atmospheric oxidants during transport in the troposphere and lead to the formation of more toxic compounds. At present, the rates of heterogeneous reactions of B[b]F and B[k]F aerosols with NO3 radicals, an important atmospheric oxidant, are not fully understood. Thus, this study investigated the products and kinetics of heterogeneous reactions of suspended B[b]F and B[k]F particles with NO3 radicals in an aerosol reaction chamber at room temperature (293±2K) under atmospheric pressure. The reactions are monitored online using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer. The mono-nitro-, di-nitro-, tri-nitro-products, and those products containing both nitro and ketone groups are observed with VUV-ATOFMS. The effective rate constants for heterogeneous reactions of particulate B[b]F and B[k]F with NO3 radicals under the experimental conditions are respectively estimated to (1.2±0.1)×10(-12)cm(3)molecule(-1)s(-1) and (5.8±0.3)×10(-13)cm(3)molecule(-1)s(-1) using a mixed-phase relative rate method, and the corresponding effective uptake coefficients are respectively estimated to 0.22 and 0.65. The lifetimes of particulate B[b]F and B[k]F at a typical concentration of NO3 radicals (5×10(8)moleculecm(-3)) in the lower troposphere during the night are estimated to 3.0 and 3.9h, respectively. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne PAHs particles.

Kinetic and product study of the heterogeneous reactions of NO3 radicals with suspended resmethrin, phenothrin, and fenvalerate particles.

Resmethrin, phenothrin, and fenvalerate are the synthetic pyrethroids that have been used widely against groundling or flying insect pests both indoors and outdoors. In this study, the heterogeneous reactions of the three pyrethroid particles with NO(3) radicals are investigated with a mixed-phase relative rate method. The reactions are performed in a reaction chamber equipped with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer. The uptake coefficients of NO(3) radicals on resmethrin, phenothrin, and fenvalerate particles are ~0.20, 0.04, and 0.03 respectively, calculated with a spherical shell model. And the atmospheric lifetimes of the three pyrethroid particles toward NO(3) radicals are estimated to be ~2.6, 7.5, and 9.3 h, respectively. The molecular structures of reaction products and the reaction pathways are suggested based on the measurements of VUV-ATOFMS and off-line GC-MS.