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The Tibetan Plateau, known as the "Third Pole", is susceptible to ground-level ozone (O 3 ) and fine particulate matter (PM 2.5 ) pollution due to its unique high-altitude environment. This study constructed random forest regression models using multi-source data from ground measurements and meteorological satellites to predict variations in ground-level O 3 and PM 2.5 concentrations and their influencing factors across seven major cities in the Tibetan Plateau over two-year periods. The models successfully reproduced O 3 and PM 2.5 levels with satisfactory R-squared values of 0.71 and 0.73, respectively. Results reveal combustion-related carbon monoxide (CO) and nitrogen dioxide (NO 2 ) as the most substantial influences on O 3 and PM 2.5 concentrations. Solar radiation, geographical factors, and meteorological variables also played crucial roles in driving pollutant variations. Conversely, transport-related and human activity factors exhibited relatively lower significance. High O 3 and PM 2.5 pollution occurred during pre-monsoon and post-monsoon/winter seasons, driven by solar radiation and emissions, respectively. While CO consistently contributed across cities and seasons, key influencing factors varied locally. This study unveils the key driving forces governing air pollutant variations across the Tibetan Plateau, shedding light on complex atmospheric processes in this unique high-altitude region., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Glyoxal (Gly) and methylglyoxal (Mgly) are key precursors globally for secondary organic aerosol (SOA) formation. These two species were often thought to be formed in the atmosphere via photochemical oxidation of organics from biogenic and anthropogenic origins, although few studies have shown their direct emissions. In this study, we report direct emissions of particulate Gly and Mgly from different residential fuels typically used in north China. The emission ratios (ERs) and emission factors (EFs) of particulate Gly and Mgly for biomass burning were approximate 5-fold and 7-fold higher than those for coal combustion, respectively. The large variances in emissions of Gly and Mgly could be attributed to the different combustion processes, which influenced by the fuel types and combustion conditions. The averaged ERs and EFs of particulate Gly and Mgly were about one order of magnitude lower than their gaseous counterparts due to the low Henry's law constant, which was also consistent with the low particle-to-gas ratio of Gly (0.04) and Mgly (0.02). Our results suggest that the direct emissions of Gly and Mgly from emission sources should be considered when estimating the formation of SOA from Gly and Mgly., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Carbon isotope signatures are used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions) using a dual 14 C- 13 C isotope approach. The dual-isotope source apportionment crucially relies on accurate knowledge of 13 C source signatures, which are seldom measured for EC. In this work, we present 13 C signatures of organic carbon (OC) and EC for relevant sources in China. EC was isolated for 13 C analysis based on the OC/EC split point of a thermal-optical method (EUSAAR_2 protocol). A series of sensitivity studies were conducted to investigate the EC separation and the relationship of the thermal-optical method to other EC isolation methods. Our results show that, first, the 13 C signatures of raw materials and EC related to traffic emissions can be separated into three groups according to geographical location. Second, the 13 C signature of OC emitted by the flaming combustion of C4 plants is strongly depleted in 13 C compared to the source materials, and therefore EC is a better tracer for this source than total carbon (TC). A comprehensive literature review of 13 C source signatures (of raw materials, of TC, and of EC isolated using a variety of thermal methods) was conducted. Accordingly, we recommend composite 13 C source signatures of EC with uncertainties and detailed application conditions. Using these source signatures of EC in an example dual-isotope source apportionment study shows an improvement in precision. In addition, 13 C signatures of OC were measured at three different desorption temperatures roughly corresponding to semi-volatile, low-volatile, and non-volatile OC fractions. Each source category shows a characteristic trend of 13 C signatures with desorption temperature, which is likely related to different OC formation processes during combustion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

We describe and thoroughly evaluate a method for 13 C analysis in different fractions of carbonaceous aerosols, especially elemental carbon (EC). This method combines a Sunset thermal-optical analyzer and an isotope ratio mass spectrometer (IRMS) via a custom-built automated separation, purification, and injection system. Organic carbon (OC), EC, and other specific fractions from aerosol filter samples can be separated and analyzed automatically for 13 C based on thermal-optical protocols (EUSAAR_2 in this study) at sub-μgC levels. The main challenges in isolating EC for 13 C analysis are the possible artifacts during OC/EC separation, including the premature loss of EC and the formation of pyrolyzed OC (pOC) that is difficult to separate from EC. Since those artifacts can be accompanied with isotope fractionation, their influence on the stable isotopic composition of EC was comprehensively investigated with various test compounds. The results show that the thermal-optical method is relatively successful in OC/EC separation for 13 C analysis. The method was further tested on real aerosols samples. For biomass-burning source samples, (partial) inclusion of pOC into EC has negligible influence on the 13 C signature of EC. However, for ambient samples, the influence of pOC on the 13 C signature of EC can be significant, if it is not well separated from EC, which is true for many current methods for measuring 13 C on EC. A case study in Xi'an, China, where pOC is enriched in 13 C compared to EC, shows that this can lead to an overestimate of coal and an underestimate of traffic emissions in isotope-based source apportionment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A low-cost, portable bioluminescence detector based on a silicon photomultiplier (SiPM) was developed for on-site colony detection, the main components of which are a low-noise photoelectric signal detection and processing circuit, power management module, and high-performance embedded microcontroller subsystem with peripheral circuits. Balanced chopper modulation and lock-in amplification techniques were adopted to improve the signal-to-noise ratio, and a zero-adjustment technique was used to eliminate the dark current of the SiPM to expand the dynamic range. Using this bioluminescence detector, adenosine triphosphate could be determined in the range of 3.6 × 10 -6 to 3.6 × 10 -11  mol/L, and bacterial colonies could be determined in the range of 1.0 × 10 3 to 1.0 × 10 9  CFU/mL, with a limit of quantitation of 1.0 × 10 3  CFU/mL. Satisfactory recoveries and precision were obtained. Actual samples were accurately tested and the data were verified by comparison with those from the national standard method. The manufacturing cost of the bioluminescence detector was only $30, which is only approximately 1% of the price of current commercial instruments. This study provides a tool for rapid on-site detection of bacterial colonies, as well as a new concept for the development of low-cost portable detection equipment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Humic-like substances (HULIS) are ubiquitous in the atmospheric environment, which affects both human health and climate. We present here the mass concentration and optical characteristics of HULIS isolated from aerosol samples collected in Xi'an, China. Both mass concentration and absorption coefficient (Abs 365 ) of HULIS show clear seasonal differences, with the highest average in winter (3.91 μgC m -3 and 4.78 M m -1 , respectively) and the lowest in summer (0.65 μgC m -3 and 0.55 M m -1 , respectively). The sources of HULIS_C and light absorption of HULIS were analyzed by positive matrix factorization (PMF) and four major sources were resolved, including secondary formation, biomass burning, coal burning, and vehicle emission. Our results show that secondary formation (i.e., gas-to-particle conversion from e.g., photochemical oxidation) was the major contributor to both HULIS_C (50%) and light absorption (55%) of HULIS in summer, biomass burning and coal burning were major sources of HULIS_C (~70%) and light absorption (~80%) of HULIS in winter. It is worth noting that biomass burning and coal burning had higher contribution to HULIS light absorption (47% in spring, 37% in summer, 73% in fall, and 77% in winter) than their corresponding contribution to HULIS_C concentration (41% in spring, 37% in summer, 54% in fall, and 69% in winter). However, vehicle emission had lower contribution to HULIS light absorption (26% in spring, 8% in summer, 18% in fall, and 11% in winter) than to HULIS_C concentration (24% in spring, 13% in summer, 28% in fall, and 18% in winter). These results suggest that HULIS from biomass burning and coal burning have higher light absorption ability than from vehicle emission., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Secondary organic aerosol (SOA) is an important contributor to organic aerosol (OA), however, the model simulations of SOA concentrations and oxidation states remain significant uncertainties because of inadequate cognition of its formation and aging chemistry. In this study, SOA formation and evolution processes during summer in Xi'an were investigated, based on high-resolution online measurements of non-refractory PM 2.5 (NR-PM 2.5 ) species and OA source apportionment using positive matrix factorization. The results showed that the total SOA, including less oxidized-oxygenated OA (LO-OOA), more oxidized-oxygenated OA (MO-OOA), and aqueous-phase-processed oxygenated OA (aq-OOA), on average constituted 69% of OA, and 43% of NR-PM 2.5 , suggesting the high atmospheric oxidation capacity and the dominance of SOA during summer in Xi'an. Photochemical oxidation processes dominated the summertime SOA formation both during non-fog-rain days and fog-rain days, which were responsible for the formation of both LO-OOA and MO-OOA. Consistently, LO-OOA and MO-OOA in total contributed 59% to OA during non-fog-rain days and 56% to OA during fog-rain days, respectively. On the contrary, aq-OOA was mainly observed during fog-rain days, which increased dramatically from 2% of OA during non-fog-rain days to 19% of OA during fog-rain days with the mass concentration increasing accordingly from 0.3 μg m -3 to 2.5 μg m -3 . Episodic analyses further highlighted the persistently high RH period with high aerosol liquid water content (ALWC) was the driving factor of aq-OOA formation, and high O x condition could further enhance its formation. Meanwhile, air masses from east and southeast were much favorable for the formation of long-time fog-rain days, which facilitated aq-OOA production during summer in Xi'an., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Organic aerosol (OA) is a major component of fine particulate matter (PM); however, only 10%-30% of OA have been identified as individual compounds, and some are used as markers to trace the sources and formation mechanisms of OA. The temporal and spatial coverage of these OA markers nonetheless remain inadequately characterized. This study presents a year-long measurement of 92 organic markers in PM 2.5 samples collected at an urban site in Beijing from 2014 to 2015. Saccharides were the most abundant (340.1 ng m -3 ) species detected, followed by phthalic acids (283.4 ng m -3 ). In summer, high proportions (8%-24%) of phthalic acids, n-alkanes, fatty acids, and n-alcohols indicate dominant contributions of biogenic emission and atmospheric oxidation to OA in Beijing. In winter, when anthropogenic sources prevail, saccharides, polycyclic aromatic hydrocarbons, and hopanes are more prominent (4%-25%). The spatial distributions of these OA markers in China show higher concentrations in northern cities (mainly from coal combustion and biomass burning) than in southern cities (mainly from vehicular emission). The inter-annual variations of OA markers, except for hopanes, from 2001 to 2015 suggest significant alleviation of the primary OA pollution in Beijing, with an average reduction of 35%-89% compared with those before 2008. The diagnostic ratio analyses between OA markers indicate that contributions from coal combustion and biomass burning decreased, whereas those from vehicular emission increased. Increasingly large vehicle fleets have increased hopane concentrations since 2008, but the levels were 35% lower in 2015 than those in 2010-2011 because of the tightening of emission controls for vehicles. This study provides a long-term and geographical comparison (from Beijing to other locations in China and beyond) of OA markers, demonstrating the temporal and spatial variations in primary OA, and calls for more studies on secondary OA., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The Guanzhong basin is a part of the three top priority regions in China's blue sky action as of 2019. Understanding the chemical composition, sources, and atmospheric process of aerosol in this region is therefore imperative for improving air quality. In this study, we present, for the first time, the seasonal variations of organic aerosol (OA) in Xi'an, the largest city in the Guanzhong basin. Biomass burning OA (BBOA) and oxidized OA (OOA) contributed >50% of OA in both autumn and winter. The average concentrations of BBOA in autumn (14.8 ± 5.1 μg m -3 ) and winter (11.6 ± 6.8 μg m -3 ) were similar. The fractional contribution of BBOA to total OA, however, decreased from 31.9% in autumn to 15.3% in winter, because of enhanced contributions from other sources in winter. The OOA fraction in OA increased largely from 20.9% in autumn to 34.9% in winter, likely due to enhanced emissions of precursors and stagnant meteorological conditions which facilitate the accumulation and secondary formation. A large increase in OOA concentration was observed during polluted days, by a factor of ~4 in autumn and ~6 in winter compared to clean days. In both seasons, OOA formation was most likely dominated by photochemical oxidation when aerosol liquid water content was <30 μg m -3 or by aqueous-phase processes when O x was <35 ppb. A higher concentration of BBOA was observed for air masses circulated within the Guanzhong basin (16.5-18.1 μg m -3 ), compared to air masses from Northwest and West (10.9-14.5 μg m -3 ). Furthermore, compared with OA fraction in non-refractory PM 1 in other regions of China, BBOA (17-19%) and coal combustion OA (10-20%) were major emission sources in the Guanzhong Basin and the BTH region, respectively, whereas OOA (10-34%) was an important source in all studied regions., Competing Interests: Declaration of competing interest We declare that the manuscript entitled “Seasonal variations in the sources of organic aerosol in Xi'an, Northwest China: the importance of biomass burning and secondary formation” is original, has not been full or partly published before, and is not currently being considered for publication elsewhere. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved. We understand that the Corresponding Author is the sole contact for the editorial process. The corresponding author “Ru-Jin Huang” is responsible for communicating with the other authors about process, submissions of revisions, and final approval of proofs., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Sulfate and nitrate from secondary reactions remain as the most abundant inorganic species in atmospheric particle matter (PM). Their formation is initiated by oxidation (either in gas phase or particle phase), followed by neutralization reaction primarily by NH 3 , or by other alkaline species such as alkaline metal ions if available. The different roles of NH 3 and metal ions in neutralizing H 2 SO 4 or HNO 3 , however, are seldom investigated. Here we conducted semi-continuous measurements of SO 4 2- , NO 3 - , NH 4 + , and their gaseous precursors, as well as alkaline metal ions (Na + , K + , Ca 2+ , and Mg 2+ ) in wintertime Beijing. Analysis of aerosol acidity (estimated from a thermodynamic model) indicated that preferable sulfate formation was related to low pH conditions, while high pH conditions promote nitrate formation. Data in different mass fraction ranges of alkaline metal ions showed that in some ranges the role of NH 3 was replaced by alkaline metal ions in the neutralization reaction of H 2 SO 4 and HNO 3 to form particulate SO 4 2- and NO 3 - . The relationships between mass fractions of SO 4 2- and NO 3 - in those ranges of different alkaline metal ion content also suggested that alkaline metal ions participate in the competing neutralization reaction of sulfate and nitrate. The implication of the current study is that in some regions the chemistry to incorporate sulfur and nitrogen into particle phase might be largely affected by desert/fugitive dust and sea salt, besides NH 3 . This implication is particularly relevant in coastal China and those areas with strong influence of dust storm in the North China Plain (NCP), both of which host a number of megacities with deteriorating air quality., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

29 parent- and alkyl-polycyclic aromatic hydrocarbons (PAHs), 15 oxygenated-PAHs (OPAHs), 11 nitrated-PAHs (NPAHs) and 4 azaarenes (AZAs) in both the gaseous and particulate phases, as well as the particulate-bound carbon fractions (organic carbon, elemental carbon, char, and soot) in ambient air sampled in March and September 2012 from an urban site in Xi'an, central China were extracted and analyzed. The average concentrations (gaseous+particulate) of ∑29PAHs, ∑15OPAHs, ∑11NPAHs and ∑4AZAs were 1267.0 ± 307.5, 113.8 ± 46.1, 11.8 ± 4.8 and 26.5 ± 11.8 ng m(-3) in March and 784.7 ± 165.1, 67.2 ± 9.8, 9.0 ± 1.5 and 21.6 ± 5.1 ng m(-3) in September, respectively. Concentrations of ∑29PAHs, ∑15OPAHs and ∑11NPAHs in particulates were significantly correlated with those of the carbon fractions (OC, EC, char and soot). Both absorption into organic matter in particles and adsorption onto the surface of particles were important for PAHs and OPAHs in both sampling periods, with more absorption occurring in September, while absorption was always the most important process for NPAHs. The total carcinogenic risk of PAHs plus the NPAHs was higher in March. Gaseous compounds, which were not considered in most previous studies, contributed 29 to 44% of the total health risk in March and September, respectively., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In this paper, differential-pulse voltammetry (DPV) was applied to study the effects of aluminum (Al(III)) on the lactate dehydrogenase (LDH) activity, K(m)(NADH) and nu(max) in the enzyme promoting catalytic reaction of "Pyruvate+NADH+H(+)right arrow over left arrowLDHLactate+NAD(+)" by monitoring DPV reduction current of NAD(+). The changes of Al's influence on the LDH activities caused by the concentration of LDH, pH, temperature as well as Al speciation including Al hydroxide (Al-OH), Al fluoride (Al-F) and organically complexing Al (Al-Org) compounds have been investigated. The results showed that the effects of Al on the LDH activity exhibited two kinds of behaviors under different conditions, i.e. inhibitory effects or slightly increased LDH activity at low concentrations and inhibited at high concentrations. To analyze the values of K(m)(NADH) and nu(max) of LDH reaction system in the absence and presence of 0.04mmol/L Al(III), it was found that the types of the inhibition of Al(III) varied with experimental conditions. The comparisons of effects of Al(III) with Pb(II), Cd(II) and Cr(III) on the LDH activities were also inspected.