CircVMP1 promotes glycolysis and disease progression by upregulating HKDC1 in colorectal cancer.

BACKGROUND: Circular RNAs (circRNAs) have been reported to play important roles in cancers. Here, we characterized circVMP1 (hsa_circ_0006508), an important circRNA which promoted glycolysis and disease progression in colorectal cancer (CRC). In this study, we aimed to explore the mechanism by which circVMP1 regulated tumor glycolysis and its related pathways in promoting CRC cell proliferation and metastasis. METHODS: The expression level of circVMP1 in CRC tissues and adjacent normal tissues was detected using quantitative PCR. In vitro and in vivo functional experiments were used to evaluate the effects of circVMP1 in the regulation of CRC cell proliferation and migration. Mitochondrial stress tests and glycolysis stress tests were conducted to detect the effect of circVMP1 on oxidative phosphorylation and glycolysis. Dual-luciferase reporter and RNA immunoprecipitation assays were used to evaluate the interaction between circVMP1, miR-3167, and HKDC1. RESULTS: We demonstrated that the level of circVMP1 was significantly upregulated in CRC tissues compared with normal tissues. In HCT116 and SW480 cells, overexpression of circVMP1 promoted proliferation, metastasis, and glycolysis. In vivo analysis indicated that circVMP1 accelerated the proliferation of xenograft tumors. As for the mechanism, overexpression of circVMP1 increased the levels of hexokinase domain component 1 (HKDC1) through competitive binding with miR-3167. CONCLUSION: Our study reported that circVMP1 was one of the tumor driver genes that promoted CRC malignant progression and glycolysis by upregulating HKDC1. CircVMP1/miR-3167/HKDC1 was a signaling axis that might be a target for CRC therapy.

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.

Amplitude-Modulated Cavity-Enhanced Absorption Spectroscopy with Phase-Sensitive Detection: A New Approach Applied to the Fast and Sensitive Detection of NO2.

Accurate and sensitive measurements of NO2 play an extremely important role in atmospheric studies. Increasingly, studies require NO2 measurements with parts per trillion by volume (pptv-level) detection limits. Other desirable instrument attributes include ease of use, long-term stability, and low maintenance. In this work, we report the development of an amplitude-modulated multimode-diode-laser-based cavity-enhanced absorption spectroscopy (AM-CEAS) system operating at 406 nm that uses phase-sensitive detection for extremely sensitive NO2 detection. The laser was TTL-modulated at 35 kHz. The mirror reflectivity was determined to be 99.985% based on the ring-down time measurement. The cavity base length was 47.5 cm, giving an effective absorption pathlength of ∼3.26 km. AM-CEAS achieved a 1σ detection precision of 35 pptv in a 1 s data acquisition time (4.98 × 10-10 cm-1), over 4 times lower than that attained using a ring-down approach and the same optical system. The AM-CEAS precision improved to 8 pptv over a data acquisition time of 30 s (1.14 × 10-10 cm-1). The AM-CEAS method with the multimode diode laser integrates the advantages of high light injection efficiency like on-axis alignment cavity ring-down spectroscopy, low cavity-mode noise like off-axis alignment CEAS, and narrow-bandwidth high-sensitivity weak signal detection of modulation spectroscopy, providing a powerful, straightforward, and general method for ultrasensitive absorption and extinction measurements.

Rapid cycling of reactive nitrogen in the marine boundary layer.

Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

Long-term outcomes after extra-levator versus conventional abdominoperineal excision for low rectal cancer.

PURPOSE: Extralevator (ELAPE) and abdominoperineal excision (APE) are two major surgical approaches for low rectal cancer patients. Although excellent short-term efficacy is achieved in patients undergoing ELAPE, the long-term benefits have not been established. In this study we evaluated the safety, pathological and survival outcomes in rectal cancer patients who underwent ELAPE and APE. METHODS: One hundred fourteen patients were enrolled, including 68 in the ELAPE group and 46 in the APE group at the Beijing Chaoyang Hospital, Capital Medical University from January 2011 to November 2020. The baseline characteristics, overall survival (OS), progression-free survival (PFS), and local recurrence-free survival (LRFS) were calculated and compared between the two groups. RESULTS: Demographics and tumor stage were comparable between the two groups. The 5-year PFS (67.2% versus 38.6%, log-rank P = 0.008) were significantly improved in the ELAPE group compared to the APE group, and the survival advantage was especially reflected in patients with pT3 tumors, positive lymph nodes or even those who have not received neoadjuvant chemoradiotherapy. Multivariate analysis showed that APE was an independent risk factor for OS (hazard ratio 3.000, 95% confidence interval 1.171 to 4.970, P = 0.004) and PFS (hazard ratio 2.730, 95% confidence interval 1.506 to 4.984, P = 0.001). CONCLUSION:  Compared with APE, ELAPE improved long-term outcomes for low rectal cancer patients, especially among patients with pT3 tumors, positive lymph nodes or those without neoadjuvant chemoradiotherapy.

Insights into air pollution chemistry and sulphate formation from nitrous acid (HONO) measurements during haze events in Beijing.

Wintertime urban air pollution in many global megacities is characterised by episodic rapid increase in particulate matter concentrations associated with elevated relative humidity - so-called haze episodes, which have become characteristic of cities such as Beijing. Atmospheric chemistry within haze combines gas- and condensed-phase chemical processes, leading to the growth in secondary species such as sulphate aerosols. Here, we integrate observations of reactive gas phase species (HONO, OH, NOx) and time-resolved aerosol composition, to explore observational constraints on the mechanisms responsible for sulphate growth during the onset of haze events. We show that HONO abundance is dominated by established fast gas-phase photochemistry, but the consideration of the additional formation potentially associated with condensed-phase oxidation of S species by aqueous NO2 leading to NO2- production and hence HONO release, improves agreement between observed and calculated gas-phase HONO levels. This conclusion is highly dependent upon aerosol pH, ionic strength and particularly the parameterisation employed for S(iv) oxidation kinetics, for which an upper limit is derived.

Comprehensive Study about the Photolysis of Nitrates on Mineral Oxides.

Nitrates formed on mineral dust through heterogeneous reactions in high NOx areas can undergo photolysis to regenerate NOx and potentially interfere in the photochemistry in the downwind low NOx areas. However, little is known about such renoxification processes. In this study, photolysis of various nitrates on different mineral oxides was comprehensively investigated in a flow reactor and in situ diffuse reflectance Fourier-transform infrared spectroscopy (in situ DRIFTS). TiO2 was found much more reactive than Al2O3 and SiO2 with both NO2 and HONO as the two major photolysis products. The yields of NO2 and HONO depend on the cation basicity of the nitrate salts or the acidity of particles. As such, NH4NO3 is much more productive than other nitrates like Fe(NO3)3, Ca(NO3)2, and KNO3. SO2 and water vapor promote the photodegradation by increasing the surface acidity due to the photoinduced formation of H2SO4/sulfate and H+, respectively. O2 enables the photo-oxidation of NOx to regenerate nitrate and thus inhibits the NOx yield. Overall, our results demonstrated that the photolysis of nitrate can be accelerated under complex air pollution conditions, which are helpful for understanding the transformation of nitrate and the nitrogen cycle in the atmosphere.

The Key Role of Sulfate in the Photochemical Renoxification on Real PM2.5.

The active nitrogen species (HONO, NO, and NO2) have important impacts on the atmospheric oxidative capacity and the transformation of many atmospheric species. In this study, a fast photochemical renoxification rate of adsorbed HNO3/NO3- to active nitrogen species (HONO, NO, and NO2) was detected on real urban PM2.5, and sulfate was found to play a key role in this process. Different from the reported direct photolysis pathway, the photochemical reaction of HNO3/NO3- on PM2.5 is dominated by a photosensitizing mechanism. Acidic protons are proved to be essential for this pathway. The role of sulfate, because of the nonvolatility of its conjugated acid, is to conserve the necessary acidic protons when interacting with HNO3 and thus maintain its photoreactivity. This work implies that sulfate will have important implications in atmospheric nitrogen cycling by accelerating the release of nitrogen oxides from photochemical renoxification of HNO3/NO3- adsorbed on ambient particulates and thus can cause major environmental problems.

Repressor activator protein 1-promoted colorectal cell migration is associated with the regulation of Vimentin.

Repressor activator protein 1 plays important roles in telomere protection, while repressor activator protein 1 binds to extra-telomeric DNA and exerts the function as a transcriptional regulator. Previous study showed that repressor activator protein 1 regulates the transcriptional activity of nuclear factor-κB, and it was highly expressed in breast cancer tissues; however, the clinical significance of repressor activator protein 1 expression in cancer remains to be elucidated. In this study, we discovered that repressor activator protein 1 was highly expressed in colorectal cancer tissues. High expression of repressor activator protein 1 was significantly correlated with poor prognosis and distant metastasis. Knockdown of repressor activator protein 1 in colorectal cancer cells did not affect cell proliferation or colony formation, but dramatically decreased cell migration and F-actin-enriched membrane protrusions. Microarray screening revealed that Vimentin was downregulated after repressor activator protein 1 knockdown, which was validated by analysis of a colorectal cancer dataset. Furthermore, knockdown of Vimentin attenuated repressor activator protein 1-enhanced cell migration. Thus, our study suggests that repressor activator protein 1 is a prognostic marker and a potential target for colorectal cancer therapy.

Photolysis of Particulate Nitrate as a Source of HONO and NOx.

Photolysis of nitric acid on the surface has been found recently to be greatly enhanced from that in the gas phase. Yet, photolysis of particulate nitrate (pNO3) associated with atmospheric aerosols is still relatively unknown. Here, aerosol filter samples were collected both near the ground surface and throughout the troposphere on board the NSF/NACR C-130 aircraft. The photolysis rate constants of pNO3 were determined from these samples by directly monitoring the production rates of nitrous acid (HONO) and nitrogen dioxide (NO2) under UV light (>290 nm) irradiation. Scaled to the tropical noontime condition on the ground level (solar zenith angle = 0°), the normalized photolysis rate constants (jpNO3N) are in the range from 6.2 × 10-6 s-1 to 5.0 × 10-4 s-1 with a median of 8.3 × 10-5 s-1 and a mean (±1 SD) of (1.3 ± 1.2) × 10-4 s-1. Chemical compositions, specifically nitrate loading and organic matter, affect the rate of photolysis. Extrapolated to ambient pNO3 loading conditions, e.g. ≤ 10 nmol m-3, the mean jpNO3N value is over 1.8 × 10-4 s-1 in the suburban, rural, and remote environments. Photolysis of particulate nitrate is thus a source of HONO and NO2 in the troposphere.

Evaluation of Novel Routes for NOx Formation in Remote Regions.

Photochemical cycling of nitrogen oxides (NOx) produces tropospheric ozone (O3), and NOx is traditionally considered to be directly emitted. The inability of current global models to accurately calculate NOx levels, and concurrently, difficulties in performing direct NOx measurements in low-NOx regimes (several pptv or several tens of pptv) globally introduce a large uncertainty in the modeling of O3 formation. Here, we use the near-explicit Master Chemical Mechanism (MCM v3.2) within a 0D box-model framework, to describe the chemistry of NOx and O3 in the remote marine boundary layer at Cape Verde. We explore the impact of a recently discovered NOx recycling route, namely photolysis of particulate nitrate, on the modeling of NOx abundance and O3 formation. The model is constrained to observations of long-lived species, meteorological parameters, and photolysis frequencies. Only a model with this novel NOx recycling route reproduces levels of gaseous nitrous acid, NO, and NO2 within the model and measurement uncertainty. O3 formation from NO oxidation is several times more efficient than previously considered. This study highlights the need for the inclusion of particulate nitrate photolysis in future models for O3 and for the photolysis rate of particulate nitrate to be quantified under variable atmospheric conditions.

Suppression of CD26 inhibits growth and metastasis of pancreatic cancer.

CD26/DPPIV is a glycosylated transmembrane type II protein and has a multitude of biological functions, while its impact on the malignant phenotypes of cancer cells has not been fully understood. This study aimed to investigate the effect of CD26 on growth and metastasis of pancreatic cancer cells in vitro and in vivo. We found in this study that CD26 expression was higher in cell lines that derived from the metastatic sites than those from the primary tumor sites. In specimens of pancreatic cancer patients, CD26 expression was higher in cancerous tissues than in paired normal tissues. In in vitro experiments, knockdown of CD26 expression inhibited cell growth, migration, invasion, colony formation, and increased cell apoptosis of pancreatic cancer cells. Knockdown of CD26 also decreased tumor growth and liver metastasis in vivo by using xenograft animal models. Suppression of CD26 could inhibit expression of epithelial-mesenchymal transition (EMT) regulatory genes. Our results indicated that CD26 may represent a new therapeutic target for pancreatic cancer.

The effect of Vasohibin-1 expression and tumor-associated macrophages on the angiogenesis in vitro and in vivo.

Vasohibin-1 is an intrinsic inhibitor of angiogenesis induced by VEGF-A. However, there little is known about the relationship between Vasohibin-1 expression, angiogenesis, and tumor-associated macrophages (TAMs). Vasohibin-1 expression, VEGF-A expression, microvessel density (MVD) marked with CD34, and density of cells marked with CD68 were measured in 111 paraffin-embedded tissues of gastric cancer by immunohistochemistry. The length of tube forming structures of endothelial cells and mobility rate of gastric cancer cells in Matrigel were tested by three-dimensional live cell imaging system. The effect of TAMs on the tumor growth, MVD, and Vasohibin-1 expression was measured by nude mice tumor genesis assay in vivo. We found that high Vasohibin-1 protein expression correlated significantly with worse TNM stage (P = 0.002), metastatic lymph node (P = 0.014), distant metastasis (P = 0.022), overall survival (P < 0.001), and progression-free survival (P < 0.001) compared to those with low Vasohibin-1 expression. Vasohibin-1 protein expression had statistical correlation with the MVD (r = 0.860, P < 0.001), density of CD68(+) cells (r = 0.882, P < 0.001), and VEGF-A expression (r = 0.719, P < 0.001) in the gastric cancer tissues. Decreasing Vasohibin-1 expression with siRNA increased the length of tube forming structures of endothelial cells in co-culture with endothelial cells (EA-hy923), macrophages, and gastric cancers (Hs746T). Tumor volume (P = 0.001), Vasohibin-1 (P < 0.001), and VEGF-A (P < 0.001) expression in mice inoculated with AGS and THP (10:1) was significantly higher than that with AGS alone (P = 0.001). Vasohibin-1 protein expression had statistical correlation with VEGF expression (r = 0.786, P < 0.001) and MVD (r = 0.496, P = 0.014) in gastric xenografted tumor. Therefore, Vasohibin-1 might be a potential marker of worse prognosis and therapeutic target in gastric cancer. Vasohibin-1 might play an important role in the process of angiogenesis regulated by TAMs.

Photolysis of Nitric Acid and Nitrate on Natural and Artificial Surfaces.

Photolysis of nitric acid and nitrate (HNO3/nitrate) was investigated on the surfaces of natural and artificial materials, including plant leaves, metal sheets, and construction materials. The surfaces were conditioned in the outdoor air prior to experiments to receive natural depositions of ambient HNO3/nitrate and other atmospheric constituents. The photolysis rate constant (JHNO3(s)) of the surface HNO3/nitrate was measured based on the production rates of nitrous acid (HONO) and nitrogen oxides (NOx). The JHNO3(s) values, from 6.0 × 10(-6) s(-1) to 3.7 × 10(-4) s(-1), are 1 to 3 orders of magnitude higher than that of gaseous HNO3. The HONO was the major product from photolysis of HNO3/nitrate on most plant leaves, whereas NOx was the major product on most artificial surfaces. The JHNO3(s) values decreased with HNO3/nitrate surface density and could be described by a simple analytical equation. Within a typical range of HNO3/nitrate surface density in the low-NOx forested areas, photolysis of HNO3/nitrate on the forest canopy can be a significant source for HONO and NOx for the overlying atmosphere.

Expression of CD147 and matrix metalloproteinase-11 in colorectal cancer and their relationship to clinicopathological features.

BACKGROUND: This study aimed to investigate the expression of CD147 and MMP-11 in human colorectal cancer (CRC) and to evaluate their clinical significance. METHODS: Real-time polymerase chain reaction was used to evaluate CD147 and MMP-11 mRNA level in 56 pairs of fresh CRC samples matched with adjacent normal mucosa. The protein expression of CD147 and MMP-11 in CRC specimens and corresponding normal colorectal mucosa were evaluated by immunohistochemistry on CRC tissue microarrays. Expression and co-localization of these two proteins in human colorectal cancer tissue were also evaluated by laser scanning confocal microscopy. Furthermore, their correlations with clinicopathological factors and overall survival after surgery were evaluated. RESULTS: Both CD147 and MMP-11 were demonstrated to be over-expressed at mRNA level (P < 0.001, both) and protein level (P < 0.001, both) in CRC tissue than paired normal mucosa. Spearman rank test showed a positive correlation between these two proteins (P = 0.025). Immunofluorescence double staining confirmed the co-localization of CD147 and MMP-11 in paraffin-embedded tissues of CRC patients. Expression of CD147 and MMP-11 were both correlated with CRC lymph node metastasis (P = 0.021 and P = 0.031, respectively), distant metastasis (P < 0.001 and P = 0.013, respectively) and TNM stage (P = 0.006 and P = 0.049, respectively). Univariate survival analysis showed that both CD147 and MMP11 expression was significantly associated with shorter survival time (P = 0.001 and P = 0.009, respectively). Additionally, in multivariate analysis, both CD147 and MMP-11 were proved to be independent prognostic factors (P = 0.009, 0.028, respectively). CONCLUSIONS: These results indicated that both CD147 and MMP-11 may be involved in the progression of colorectal cancer, and they are potential prognostic factors and might become new therapeutic targets for CRC patients.

Optimizing a twin-chamber system for direct ozone production rate measurement.

High Ozone Production Rate (OPR) leads to O3 pollution episodes and adverse human health outcomes. OPR observation (Obs-OPR) and OPR modelling (Mod-OPR) have been obtained from observed and modelled peroxy radicals and nitrogen oxides. However, discrepancies between them remind of an imperfect understanding of O3 photochemistry. Direct measurement of OPR (Mea-OPR) by a twin-chamber system emerges. Herein, we optimized Mea-OPR design, i.e., minimizing the chamber surface area to volume ratio (S/V) to 9.8 m-1 from 18 m-1 and the dark uptake coefficient of O3 to 9.9 × 10-9 from 7.1 × 10-8 in the literature. In addition, control experiments further revealed and quantified a photo-enhanced O3 uptake, and therefore recommended an essential correction of Mea-OPR. We finally characterized a measurement uncertainty of ±38% and a detection limit of 3.2 ppbv h-1 (3SD), which suggested that Mea-OPR would be sensitive enough to measure OPR in urban or suburban environments. Further application of this system in urban Beijing during the Beijing 2022 Olympic Winter Games recorded a noontime OPR of 7.3 (±3.3, 1SD) ppbv h-1. These observational results added up to our confidence in future field application of Mea-OPR, to facilitate pollution control policy evaluation and to shed light on O3 photochemistry puzzle.

Heterogeneous reactions significantly contribute to the atmospheric formation of nitrated aromatic compounds during the haze episode in urban Beijing.

Nitrated aromatic compounds (NACs) are key components of air pollution; however, due to the presence of complex mixtures of primary and secondary species, especially in urban environments, their atmospheric formation is poorly understood. Here we conducted a field campaign during a winter haze episode in urban Beijing, China to monitor gaseous and particulate NACs at 2-h time resolution. Through a standard-independent non-targeted approach, a total of 238 NACs were screened, of which 127 species were assigned chemical formula and 25 structures were confirmed. Four main classes were identified: nitrated aromatic hydrocarbons, nitrophenols, oxygenated nitrated aromatic compounds, and nitrated heterocyclic aromatic compounds. Hierarchical clustering analysis revealed disparate temporal variances of diurnal or nocturnal elevation, among which different nitration formations were captured, i.e., daytime photochemical oxidation and nighttime heterogeneous reactions. Isomeric information, particularly the substitution position of the nitro group on biphenyl, further demonstrated a potential heterogeneous mechanism of electrophilic nitration by NO2+. Assisted by source apportionment, we found that nighttime heterogeneous reactions significantly contributed to NAC formation, e.g., 31.3 % and 60.8 %, respectively, to 2-nitrofluoranthene and 2-nitropyrene, which were previously considered as classical daytime gas-phase products. This study provides comprehensive information on urban NAC species and highlights the importance of unheeded heterogeneous reactions in the atmosphere.

circ-ZEB1 regulates epithelial-mesenchymal transition and chemotherapy resistance of colorectal cancer through acting on miR-200c-5p.

Circular RNAs (circRNAs) have been demonstrated to be important regulators in human malignant tumors, including colorectal cancer (CRC). While the role circ-ZEB1 played in CRC remains unclear. In this study, we aim to explore the biological function and the underlying mechanism of circ-ZEB1 in CRC. RNAscope was used to analyze the expression and localization of circ-ZEB1 in CRC tissues. Loss of function experiments were conducted, including CCK-8, transwell assays, flow cytometry analysis, and murine xenograft models, so as to detect the effect of circ-ZEB1 on CRC cells. IC50 assay was used to evaluate the influence of circ-ZEB1 on the chemoresistance of CRC cells. Epithelial-mesenchymal transition (EMT) related markers were detected. The relationship between circ-ZEB1 and miR-200c-5p was investigated by FISH, dual-luciferase reporter assay, and RIP assay. We found in our study that circ-ZEB1 was significantly upregulated in CRC tissues. Downregulation of circ-ZEB1 inhibited cell proliferation, colony formation, as well as cell migration and invasion abilities of CRC cell lines. In vivo experiments indicated that knockdown of circ-ZEB1 suppressed tumorigenesis and distant metastasis of CRC cells in nude mice. What's more, EMT and chemoresistance of CRC cells were also attenuated following circ-ZEB1 knockdown. Mechanistically, we proved that circ-ZEB1 could directly bind with miR-200c and functioned as miR-200c sponge to exert its biological functions in CRC cells. In conclusion, circ-ZEB1 could promote CRC cells progression, EMT, and chemoresistance via acting on miR-200c, elucidating a potential therapeutic target to inhibit CRC progression.

Quantifying evolution of soot mixing state from transboundary transport of biomass burning emissions.

Incomplete combustion of fossil fuels and biomass burning emit large amounts of soot particles into the troposphere. The condensation process is considered to influence the size (Dp) and mixing state of soot particles, which affects their solar absorption efficiency and lifetimes. However, quantifying aging evolution of soot remains hampered in the real world because of complicated sources and observation technologies. In the Himalayas, we isolated soot sourced from transboundary transport of biomass burning and revealed soot aging mechanisms through microscopic observations. Most of coated soot particles stabilized one soot core under Dp < 400 nm, but 34.8% of them contained multi-soot cores (nsoot ≥ 2) and nsoot increased 3-9 times with increasing Dp. We established the soot mixing models to quantify transformation from condensation- to coagulation-dominant regime at Dp ≈ 400 nm. Studies provide essential references for adopting mixing rules and quantifying the optical absorption of soot in atmospheric models.

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.