From the measurement of halogenated species to iodine particle formation

Halogenated species have a significant impact on atmospheric composition, including catalytic ozone destruction and influence on HOx and NOx cycles. Halogens are also involved in marine and coastal new particle formation, a process that can ultimately affect Earth's radiation balance. However, the exact processes governing halogen chemistry and halogen new particle formation have been puzzling the community for years. One of the major difficulties in understanding these processes has been the lack of techniques able to measure inorganic halogenated radicals and stable species simultaneously both in laboratory studies and in ambient conditions. This is because previous spectroscopic and mass spectrometric methods utilized could only measure one, or a few halogenated species at once, while most of the halogenated species existing in the atmosphere were likely un-measurable. Here we present new chemical ionization (CI) mass spectrometric methods to measure over 20 halogenated species simultaneously at ambient pressure. These species include halogen oxides, halogen acids, nitrogen containing halogen species, halogen radicals and molecular halogens, covering the major categories present in the ambient atmosphere. The methods will further be deployed into field measurements in various locations around the world to better understand the impact of halogenated species to the atmosphere. A recent study revealed homogeneous nucleation processes by (HIO3) (brackets here indicate all the isomers). However, the exact formation mechanism of (HIO3) has not been investigated in laboratory experiments. We deployed the above mentioned new measurements methods to study the formation mechanism of (HIO3) in dedicated flow tube experiments. The results show that OIO and OH radical could form (HIO3) as indicated by previous quantum mechanism calculations. In addition, two novel (HIO3) formation pathways from photo-oxidation of CH2I2 and molecular iodine were suggested. One pathway shows that the homogeneous bimolecular reaction of CH2IOO could form (HIO3), while the other suggests either iodine radical or iodine monoxide could react with ozone and water vapor to form (HIO3). These findings could potentially explain the large amount of (HIO3) observed. Beside from coastal areas, the first ambient data showing the existence of (HIO3) in various locations in the world, including a boreal forest site, a wet land site, Greenland and Antarctica are also presented here. These findings indicate that the (HIO3) might be involved in nucleation processes in locations other than coastal areas. More than (HIO3), sulfuric acid is known for its active role in atmospheric nucleation over different environments. However, the knowledge of its gas phase oxidation processes is not complete. Our laboratory results imply that iodinated species might be able to oxidize SO2 to sulfuric acid through some yet unknown mechanisms. Further studies are needed to understand the exact mechanisms in the oxidation processes and how important this mechanism could be in the ambient atmosphere

Computational and Experimental Investigation of the Detection of HO2 Radical and the Products of Its Reaction with Cyclohexene Ozonolysis Derived RO2 Radicals by an Iodide-Based Chemical Ionization Mass Spectrometer

The HO2 radical is an important atmospheric molecule that can potentially influence the termination of autoxidation processes of volatile organic compounds (VOCs) that lead to the formation of highly oxygenated multifunctional compounds (HOMs). In this work, we demonstrate the direct detection of the HO2 radical using an iodide-based chemical ionization mass spectrometer (iodide-CIMS). Expanding on the previously established correlation between molecule-iodide binding enthalpy and iodide-CIMS instrument sensitivity, the experimental detection of the HO2 radical was preceded by the quantum chemical calculation of the HO2*I- cluster (PBE/aug-cc-pVTZ-PP level), which showed a reasonably strong binding enthalpy of 21.60 kcal/mol. Cyclohexene ozonolysis intermediates and closed-shell products were next detected by the iodide-CIMS. The ozone-initiated cyclohexene oxidation mechanism was perturbed by the introduction of the HO2 radical, leading to the formation of closed-shell hydroperoxides. The experimental investigation once again followed the initial computational molecule-iodide binding enthalpy calculations. The quantum chemical calculations were performed at the PBE/aug-cc-pVTZ-PP level for radicals and DLPNO-CCSD(T)/def2-QZVPP//PBE/aug-cc-pVTZ-PP level for the closed-shell products. A comparison between the iodide-CIMS and nitrate-CIMS spectra with identical measurement steps revealed that the iodide-CIMS was able to detect the low-oxidized (O/C ratio 0.5 and 0.66) cyclohexene ozonolysis monomer products more efficiently than nitrate-CIMS. Higher-oxidized monomers (O/C ratio 1 to 1.5) were detected equally well by both methods. An investigation of dimers showed that both iodide- and nitrate-CIMS were able to detect the dimer compositions possibly formed from reactions between the peroxy radical monomers considered in this study. Additionally, iodide-CIMS detected organic ions that were formed by a previously suggested mechanism of dehydroxylation of peroxy acids (and deoxygenation of acyl peroxy radicals) by H2O*I- clusters. These mechanisms were computationally verified.Peer reviewe

Formation of highly oxygenated organic molecules from chlorine-atom-initiated oxidation of alpha-pinene

Highly oxygenated organic molecules (HOMs) from atmospheric oxidation of alpha-pinene can irreversibly condense to particles and contribute to secondary organic aerosol (SOA) formation. Recently, the formation of nitryl chloride (C1NO(2)) from heterogeneous reactions, followed by its subsequent photolysis, is suggested to be an important source of chlorine atoms in many parts of the atmosphere. However, the oxidation of monoterpenes such as alpha-pinene by chlorine atoms has received very little attention, and the ability of this reaction to form HOMs is completely unstudied. Here, chamber experiments were conducted with alpha-pinene and chlorine under low- and high-nitrogen-oxide (NOx, NOx = NO+NO2) conditions. A nitrate-based CI-APi-ToF (chemical ionization-atmospheric pressure interface-time of flight) mass spectrometer was used to measure HOM products. Clear distributions of monomers with 9-10 carbon atoms and dimers with 18-20 carbon atoms were observed under low-NOx conditions. With increased concentration of NOx within the chamber, the formation of dimers was suppressed due to the reactions of peroxy radicals with NO. We estimated the HOM yields from chlorine-initiated oxidation of alpha-pinene under low-NOx conditions to be around 1.8 %, though with a substantial uncertainty range (0.8 %-4 %) due to lack of suitable calibration methods. Corresponding yields at high NOx could not be determined because of concurrent ozonolysis reactions. Our study demonstrates that also the oxidation of alpha-pinene by chlorine atoms and yield low-volatility organic compounds.Peer reviewe

Particle growth with photochemical age from new particle formation to haze in the winter of Beijing, China

Secondary aerosol formation in the aging process of primary emission is the main reason for haze pollution in eastern China. Pollution evolution with photochemical age was studied for the first time at a comprehensive field observation station during winter in Beijing. The photochemical age was used as an estimate of the time scale attributed to the aging process and was estimated from the ratio of toluene to benzene in this study. A low photochemical age indicates a fresh emission. The photochemical age of air masses during new particle formation (NPF) days was lower than that on haze days. In general, the strongest NPF events, along with a peak of the formation rate of 1.5 nm(J(1.5)) and 3 nmparticles (J(3)), were observed when the photochemical age was between 12 and 24 h while rarely took place with photochemical ages less than 12 h. When photochemical age was larger than 48 h, haze occurred and NPF was suppressed. The sources and sinks of nanoparticles had distinct relation with the photochemical age. Our results show that the condensation sink (CS) showed a valley with photochemical ages ranging from 12 to 24 h, while H2SO4 concentration showed no obvious trend with the photochemical age. The high concentrations of precursor vapours within an air mass lead to persistent nucleation with photochemical age ranging from 12 to 48 h in winter. Coincidently, the fast increase of PM2.5 mass was also observed during this range of photochemical age. Noteworthy, CS increased with the photochemical age on NPF days only, which is the likely reason for the observation that the PM2.5 mass increased faster with photochemical age on NPF days compared with other days. The evolution of particles with the photochemical age provides new insights into understanding how particles originating from NPF transform to haze pollution. (C) 2020 Elsevier B.V. All rights reserved.Peer reviewe

Serum Activity of Platelet-Activating Factor Acetylhydrolase Is a Potential Clinical Marker for Leptospirosis Pulmonary Hemorrhage

Pulmonary hemorrhage has been recognized as a major, often lethal, manifestation of severe leptospirosis albeit the pathogenesis remains unclear. The Leptospira interrogans virulent serogroup Icterohaemorrhagiae serovar Lai encodes a protein (LA2144), which exhibited the platelet-activating factor acetylhydrolase (PAF-AH) activity in vitro similar to that of human serum with respect to its substrate affinity and specificity and thus designated L-PAF-AH. On the other hand, the primary amino acid sequence of L-PAF-AH is homologous to the α1-subunit of the bovine brain PAF-AH isoform I. The L-PAF-AH was proven to be an intracellular protein, which was encoded unanimously and expressed similarly in either pathogenic or saprophytic leptospires. Mongolian gerbil is an appropriate experimental model to study the PAF-AH level in serum with its basal activity level comparable to that of human while elevated directly associated with the course of pulmonary hemorrhage during severe leptospirosis. Mortality occurred around the peak of pulmonary hemorrhage, along with the transition of the PAF-AH activity level in serum, from the increasing phase to the final decreasing phase. Limited clinical data indicated that the serum activity of PAF-AH was likely to be elevated in the patients infected by L. interrogans serogroup Icterohaemorrhagiae, but not in those infected by other less severe serogroups. Although L-PAF-AH might be released into the micro-environment via cell lysis, its PAF-AH activity apparently contributed little to this elevation. Therefore, the change of PAF-AH in serum not only may be influential for pulmonary hemorrhage, but also seems suitable for disease monitoring to ensure prompt clinical treatment, which is critical for reducing the mortality of severe leptospirosis

Enhanced growth rate of atmospheric particles from sulfuric acid

In the present-day atmosphere, sulfuric acid is the most important vapour for aerosol particle formation and initial growth. However, the growth rates of nanoparticles (<10 nm) from sulfuric acid remain poorly measured. Therefore, the effect of stabilizing bases, the contribution of ions and the impact of attractive forces on molecular collisions are under debate. Here, we present precise growth rate measurements of uncharged sulfuric acid particles from 1.8 to 10 nm, performed under atmospheric conditions in the CERN (European Organization for Nuclear Research) CLOUD chamber. Our results show that the evaporation of sulfuric acid particles above 2 nm is negligible, and growth proceeds kinetically even at low ammonia concentrations. The experimental growth rates exceed the hard-sphere kinetic limit for the condensation of sulfuric acid. We demonstrate that this results from van derWaals forces between the vapour molecules and particles and disentangle it from charge-dipole interactions. The magnitude of the enhancement depends on the assumed particle hydration and collision kinetics but is increasingly important at smaller sizes, resulting in a steep rise in the observed growth rates with decreasing size. Including the experimental results in a global model, we find that the enhanced growth rate of sulfuric acid particles increases the predicted particle number concentrations in the upper free troposphere by more than 50 %.Peer reviewe

Molecular understanding of the suppression of new-particle formation by isoprene

Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms - which drive particle nucleation and early growth - while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C-20 and C-15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2 center dot) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene = monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C-15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH center dot) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2 center dot radicals that reduce C-20 formation. RO2 center dot termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C-20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.Peer reviewe

Phytochemical Properties and In Vitro Biological Activities of Phenolic Compounds from Flower of Clitoria ternatea L.

Phenolic compounds from the flower of Clitoria ternatea L. (PCFCTL) were extracted using a high-speed shearing extraction technique and purified by AB-8 macroporous resins, and the phytochemical composition of the purified phenolic compounds from the flower of Clitoria ternatea L. (PPCFCTL) was then analyzed. Subsequently, its bioactivities including antioxidant properties, enzyme inhibitory activities, and antiproliferative activities against several tumor cell lines were evaluated. Results indicated that the contents of total phenolics, flavonoids, flavonols, flavanols, and phenolic acids in PPCFCTL were increased by 3.29, 4.11, 2.74, 2.43, and 2.96-fold, respectively, compared with those before being purified by AB-8 macroporous resins. The results showed PPCFCTL have significant antioxidant ability (measured by reducing power, RP, and ferric reducing antioxidant power method, FRAP) and good DPPH, ABTS+, and superoxide anion radical scavenging activities. They can also significantly inhibit lipase, &alpha;-amylase, and &alpha;-glucosidase. In addition, morphological changes of HeLa, HepG2, and NCI-H460 tumor cells demonstrated the superior antitumor performance of PPCFCTL. However, the acetylcholinesterase inhibitory activity was relatively weak. These findings suggest that PPCFCTL have important potential as natural antioxidant, antilipidemic, anti-glycemic and antineoplastic agents in health-promoting foods