Mixing state and influence factors controlling diurnal variation of particulate nitrophenol compounds at a suburban area in northern China.

Nitrophenols have received extensive attention due to their strong light-absorbing ability in the near-ultraviolet-visible region, which could be influenced by the atmospheric processes of nitrophenols. However, our knowledge and understanding of the formation and evolution of nitrophenols are still in the nascent stages. In the present study, the mixing states of four mononitrophenol particles (i.e., nitrophenol, methynitrophenol, nitrocatechol, and methoxynitrophenol), and one nitropolycyclic aromatic hydrocarbon particles (i.e., nitronaphthol (NN)) were investigated using a single-particle aerosol mass spectrometer (SPAMS) in November 2019 in Qingdao, China. The results showed, for the first time, that mononitrophenols and NN exhibit different mixing states and diurnal variations. Four mononitrophenols were internally mixed well with each other, and with organic acids, nitrates, potassium, and naphthalene. The diurnal variation in the number fraction of mononitrophenols presented two peaks at 07:00 to 09:00 and 18:00 to 20:00, and a valley at noon. Atmospheric environmental conditions, including NO2, O3, relative humidity, and temperature, can significantly influence the diurnal variation of mononitrophenols. Multiple linear regression and random forest regression models revealed that the main factors controlling the diurnal variation of mononitrophenols were photochemical reactions during the day and aqueous-phase reactions during the night. Unlike mononitrophenols, about 62-83% of NN were internally mixed with [NH4]+ and [H(NO3)2]-, but not with organic acids and potassium. The diurnal variation of NN was also different from that of mononitrophenols, generally increased from 17:00 to 10:00 and then rapidly decreaed from 11:00 to 16:00. These results imply that NN may have sources and atmospheric processes that are different from mononitrophenols. We speculate that this is mostly controlled by photochemical reactions and mixing with [NH4]+, which may influence the diurnal variation of NN in the ambient particles; however, this requires further confirmation. These findings extend our current understanding of the atmospheric formation and evolution of nitrophenols.

Molecular characteristics, sources and transformation of water-insoluble organic matter in cloud water.

Studies have shown that water-insoluble organic matter (WIOM) accounts for a large part of the organic components in cloud water and significantly contributes to brown carbon. However, the molecular characteristics of WIOM in cloud droplets remain unclear, hampering the understanding of their climate effects. In this study, cloud water was collected at a remote mountain site in South China during the winter of 2020, and WIOM was separated by membrane filtration, extracted by methanol, and characterized using Fourier transform ion cyclotron resonance mass spectrometry coupled with an electrospray ionization source. A total of 697-1637 molecules were identified in WIOM. WIOM is characterized by lower oxidation states of carbon atoms (-1.10 âˆ¼ -0.84 in WIOM vs. -0.58 âˆ¼ -0.51 in water-soluble organic matter (WSOM) on average), higher carbon number (14.12-20.59 vs. 9.87-10.56) and lower unsaturation (double-bond equivalent 4.55-4.95 vs. 4.84-5.23) relative to WSOM. More abundant lipid-like compounds (12.2-41.9% in WIOM vs. <2% in WSOM) but less highly oxygenated compounds (<7% vs. 28.6-35.3%) exist in WIOM. More than 30% of WIOM molecules in cloud water are common with interstitial particles, implying that WIOM in cloud water may originate from aerosol activation and/or collision. Some unique molecules in WIOM in cloud water are identified as aqueous-phase oligomerization products, indicating the aqueous-phase formation of WIOM. Further analysis of the intermolecular relationship shows that WIOM has the potential to transform into WSOM by partitioning into the dissolved phase, oxidation and functionalization by heteroatom-containing groups, representing a previously unidentified pathway for WSOM formation in cloud water. The results provide new insights into the in-cloud chemistry, which would assist in the understanding of the aqueous formation and evolution of WIOM.

Influence of meteorological parameters and oxidizing capacity on characteristics of airborne particulate amines in an urban area of the Pearl River Delta, China.

Nine amine species in atmospheric particles during haze and low-pollution days with low and high relative humidity (RH) were analyzed in urban Guangzhou, China. The mean concentrations of total measured amines (Æ©amines) in fine particles were 208 ± 127, 63.7 ± 21.3, and 120 ± 20.1 ng m-3 during haze, low pollution-low RH (LP-LRH), and low pollution-high RH (LP-HRH) episodes, respectively. The dominant amine species were methylamine (MA), dimethylamine (DMA), diethylamine (DEA) and dibutylamine (DBA), which in total accounted for 82-91% of the Æ©amines during different pollution episodes. The contributions of Æ©amines-C to water-soluble organic carbon (WSOC) and Æ©amines-N to water-soluble organic nitrogen (WSON) were 1.52% and 2.49% during haze, 1.24% and 1.96% during LP-LRH, and 2.00 and 2.98% during LP-HRH days, respectively. The mass proportion of Æ©amines in fine particles was higher during LP-HRH periods (0.19%) than during haze and LP-LRH periods (0.16%). The mass proportion of DBA in Æ©amines increased from 7% during haze and LP-LRH episodes to 25% during LP-HRH episodes. Compared with other amines, DBA showed a stronger linear relationship with RH (r = 0.867, p < 0.01), which demonstrates its high sensitivity to high RH conditions. Meteorological parameters (including RH, the mixed layer depth, wind speed and temperature), the oxidizing capacity (ozone concentration), and gaseous pollutants (NOx and SO2) correlated with amines under different pollution conditions. Under high RH, acid-base reactions were the dominant pathway for the gas-to-particle distribution of amines in urban areas, while direct dissolution dominated in the background site. To our knowledge, this study is the first attempt to conduct in situ measurements of particulate amines during different pollution conditions in China, and further research is needed to in-depth understanding of the influence of amines on haze formation.

Upregulation of thioredoxin contributes to inhibiting diabetic hearing impairment.

AIMS: Hair cell reduction was related to diabetes-induced hearing loss. Oxidative stress, endoplasmic reticulum stress, and autophagy participate in this process. Thioredoxin (Trx) is a protein with many biological functions which can regulate them. In this study, aiming to clarify protective effect of Trx on diabetic hearing loss and to identify an early potential therapeutic target for diabetic hearing impairment in the future. METHODS: Trx transgenic (Tg) mice were used to establish a diabetic model by intraperitoneally injecting streptozotocin (STZ) and with/without SF or PX12 treatment. Succinate dehydrogenase (SDH) staining was used to evaluate the loss of hair cells. The relative expression of related proteins and genes was detected using western blotting and qRT-PCR. RESULTS: In vivo, loss of outer hair cells was observed. However, it can be delayed Trx overexpression. Moreover, the expression of PGC-1α, bcl-2 and LC3 was increased in Tg(+)-DM mice compared with Tg(-)-DM mice. The expression of ASK1, Txnip, GRP78, CHOP and p62 was decreased in Tg(+)-DM mice compared with Tg(-)-DM mice. CONCLUSIONS: Upregulation of Trx protects diabetes-induced cochlear hair cells reduction. The underlying mechanisms were related to the regulation of ER stress through ASK1 and the mitochondrial pathway or autophagy via Txnip.

Different characteristics of individual particles from light-duty diesel vehicle at the launching and idling state by AAC-SPAMS.

The rapid development of cities and economic prosperity greatly motivates the growth of vehicular exhaust particles, especially the diesel-exhausted particles from the large fleet of passenger and freight, which present profound implications on climate, air quality, and biological health (e.g., pulmonary, autoimmune and cardiovascular diseases). As important physiochemical properties of atmospheric aerosols, however, the mixing state and effective density of individual particles emitted from diesel-powered vehicles under different driving conditions and their environmental implications remain uncertain. Here, a single-particle aerosol mass spectrometer (SPAMS) was used to investigate the chemical composition and vacuum aerodynamic diameter (Dva), along with the aerodynamic diameter (Da) from an aerodynamic aerosol classifier (AAC), to determine the effective density of primary particles emitted from a light- duty diesel vehicle (LDDV) under the launching and idling engine states. Interestingly, the particle types and effective density appear to vary significantly with the engine status. A single particle type of Ca-rich particles, named Na-Ca-PAH, was predominant in the idling state, whose chemical components may be affected by the lubricants and incomplete combustion, contributing to a higher effective density (0.66 ± 0.21 g cm-3). In contrast, launching particles exhibited a lower effective density (0.34 ± 0.17 g cm-3) because of the substantial elemental carbon (EC). In addition, the effective density depends not only on the particle size but also on the chemical components with various abundances. EC and Ca play opposite roles in the effective density of LDDV emissions. Notably, a higher proportion of polycyclic aromatic hydrocarbons (PAHs) was observed in the idling particles, contributing to 78 ± 1.2%. Given the high contribution to these PAH-containing particles in the idling state, indispensable precautions should be taken at bus stops or waiting for pedestrians. This study provides more comprehensive insights into the initial characteristics of LDDV particles due to the launching and idling states, which is beneficial for improving the model results of source apportionment and understanding its environmental behavior regarding human health.

Individual particle investigation on the chloride depletion of inland transported sea spray aerosols during East Asian summer monsoon.

Inland transported sea spray aerosol (SSA) particles along with multiphase reactions are essential to drive the regional circulation of nitrogen, sulfur and halogen species in the atmosphere. Specially, the physicochemical properties of SSA will be significantly affected by the displacement reaction of chloride. However, the role of organic species and the mixing state on the chloride depletion of SSA during long-range inland transport remains unclear. Hence, a single particle aerosol mass spectrometer (SPAMS) was employed to investigate the particle size and chemical composition of individual SSA particles over inland southern China during the East Asian summer monsoon. Based on the variation of chemical composition, SSA particles were clustered into SSA-Aged, SSA-Bio and SSA-Ca. SSA-Aged was regarded as the aged Na-rich SSA particles. In comparison to the SSA-Aged, SSA-Bio involved some extra organic species associated with biological origin (i.e., organic nitrogen and phosphate). Each type occupies for approximately 50% of total detected SSA particles. Besides, SSA-Ca may relate to organic shell of Na-rich SSA particles, which is negligible (~3%). Tight correlation between Na and diverse organic acids was exhibited for the SSA-Aged (r2 = 0.52, p < 0.01) and SSA-Bio (r2 = 0.61, p < 0.01), reflecting the impact of organic acids to the chloride displacement during inland transport SSA particles. The chloride depletion occupied by organic acids is estimated to be up to 34%. It is noted that distinctly different degree of chloride depletion was observed between SSA-Aged and SSA-Bio. It is more likely to be attributed to the associated organic coatings for the SSA-Bio particles, which inhibits the displacement reactions between acids and chloride. As revealed from the mixing state of SSA-Bio, defined hourly mean peak area ratio of Cl / Na increases with the increasing phosphate and organic nitrogen. This finding provides additional basis for the improvement of modeling simulations in chlorine circulation and a comprehensive understanding of the effects of organics on chloride depletion of SSA particles.

Filter-based absorption enhancement measurement for internally mixed black carbon particles over southern China.

The effect of the mixing state of black carbon (BC) on light absorption is of enduring interest due to its close connection to regional/global climate. Herein, we present concurrent measurements of both BC absorption enhancement (Eabs) and the chemical mixing state in southern China. Eabs was obtained by simultaneous measuring the light absorption coefficient using an aethalometer before and after being heated. The observed Eabs was categorized into non- (Eabs ≤ 1.0), slight (1.0 < Eabs ≤ 1.2), and higher (Eabs > 1.2) enhancement groups, and it was compared to the mixing state of elemental carbon (EC) particles detected by a single particle aerosol mass spectrometer (SPAMS). The individual EC-containing particles were classified into four types, including EC with sodium and potassium ion peaks (NaK-EC), long EC cluster ions (Cn+/-, n ≥ 6) with sulfate (EC-Sul1), short EC cluster ions (Cn+/-, n < 6) with sulfate (EC-Sul2), and EC with OC and sulfate (ECOC-Sul). NaK-EC and EC-Sul2 are the dominant EC types. Slight enhancement group is mainly explained by the photochemical production of ammonium sulfate and organics on EC-Sul2 during afternoon hours. In contrast, the higher Eabs is primarily attributed to the enhanced mixing of ammonium chloride with NaK-EC during morning hours, without photochemistry. The characterization of source emissions indicates that NaK-EC is likely from coal combustion and is associated with a relatively higher amount of ammonium chloride. To our knowledge, this is the first report to state that EC particles associated with ammonium chloride have a relatively higher Eabs.

Thioredoxin plays a key role in retinal neuropathy prior to endothelial damage in diabetic mice.

Diabetes is a chronic metabolic syndrome that results in changes in carbohydrate, lipid and protein metabolism. With diabetes for a long time, it increases the risk of diabetic retinopathy (DR) and long-term morbidity and mortality. Moreover, emerging evidence suggests that neuron damage occurs earlier than microvascular complications in DR patients, but the underlying mechanism is unclear. We investigated diabetes-induced retinal neuropathy and elucidated key molecular events to identify new therapeutic targets for the clinical treatment and prevention of DR. For in vivo studies, a high-fat diet and streptozotocin (STZ) injection were used to generate the diabetes model. Hematoxylin-eosin staining was used for morphological observations and measurements of the outer nuclear layer thickness. Electroretinography (ERG) was used to assess retinal function. For in vitro studies, Neuro2a cells were incubated in normal (5.5 mM) and high-glucose (30 mM) conditions. Flow cytometry assays were performed to analyze apoptosis. Additionally, real-time PCR and Western blotting analyses were carried out to determine gene and protein expression in vitro and in vivo. Taken together, the results indicated that retinal neuropathy occurred prior to endothelial damage induced by diabetes, and thioredoxin (Trx) plays a key role in this process. This underlying mechanism may be related to activation of the Trx/ASK1/p-p38/Trx-interacting protein pathway.