Synergistic HNO3-H2SO4-NH3 upper tropospheric particle formation.

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)1-4. However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles-comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3-H2SO4-NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.

Comparison between Spatially Resolved Airborne Flux Measurements and Emission Inventories of Volatile Organic Compounds in Los Angeles.

Los Angeles is a major hotspot for ozone and particulate matter air pollution in the United States. Ozone and PM2.5 in this region have not improved substantially for the past decade, despite a reduction in vehicular emissions of their precursors, NOx and volatile organic compounds (VOCs). This reduction in "traditional" sources has made the current emission mixture of air pollutant precursors more uncertain. To map and quantify emissions of a wide range of VOCs in this urban area, we performed airborne eddy covariance measurements with wavelet analysis. VOC fluxes measured include tracers for source categories, such as traffic, vegetation, and volatile chemical products (VCPs). Mass fluxes were dominated by oxygenated VOCs, with ethanol contributing ∼29% of the total. In terms of OH reactivity and aerosol formation potential, terpenoids contributed more than half. Observed fluxes were compared with two commonly used emission inventories: the California Air Resources Board inventory and the combination of the Biogenic Emission Inventory System with the Fuel-based Inventory of Vehicle Emissions combined with Volatile Chemical Products (FIVE-VCP). The comparison shows mismatches regarding the amount, spatial distribution, and weekend effects of observed VOC emissions with the inventories. The agreement was best for typical transportation related VOCs, while discrepancies were larger for biogenic and VCP-related VOCs.

Methane Emissions from Dairy Operations in California's San Joaquin Valley Evaluated Using Airborne Flux Measurements.

State inventories indicate that dairy operations account for nearly half of California's methane budget. Recent analyses suggest, however, that these emissions may be underestimated, complicating efforts to develop emission reduction strategies. Here, we report estimates of dairy methane emissions in the southern San Joaquin Valley (SJV) of California in June 2021 using airborne flux measurements. We find average dairy methane fluxes of 512 ± 178 mg m-2 h-1 from a region of 300+ dairies near Visalia, CA using a combination of eddy covariance and mass balance-based techniques, corresponding to 118 ± 41 kg dairy-1 h-1. These values estimated during our June campaign are 39 ± 48% larger than annual average estimates from the recently developed VISTA-CA inventory. We observed notable increases in emissions with temperature. Our estimates align well with inventory predictions when parametrizations for the temperature dependence of emissions are applied. Our measurements further demonstrate that the VISTA-CA emission inventory is considerably more accurate than the EPA GHG-I inventory in this region. Source apportionment analyses confirm that dairy operations produce the majority of methane emissions in the southern SJV (∼65%). Fugitive oil and gas (O&G) sources account for the remaining ∼35%. Our results support the accuracy of the process-based models used to develop dairy emission inventories and highlight the need for additional investigation of the meteorological dependence of these emissions.

Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere.

The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidation of isoprene affects both the concentration and distribution of nitrogen oxide free radicals (NOx). Experiments performed in an atmospheric simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent with these chamber studies, NMR kinetic experiments constrain the 1,2-IHN hydrolysis lifetime to less than 10 s in deuterium oxide (D2O) at 298 K, whereas the 4,3-IHN isomer has been observed to hydrolyze much less efficiently. These laboratory findings are used to interpret observations of the IHN isomer distribution in ambient air. The IHN isomer ratio (1,2-IHN to 4,3-IHN) in a high NOx environment decreases rapidly in the afternoon, which is not explained using known gas-phase chemistry. When simulated with an observationally constrained model, we find that an additional loss process for the 1,2-IHN isomer with a time constant of about 6 h best explains our atmospheric measurements. Using estimates for 1,2-IHN Henry's law constant and atmospheric liquid water volume, we show that condensed-phase hydrolysis of 1,2-IHN can account for this loss process. Simulations from a global chemistry transport model show that the hydrolysis of 1,2-IHN accounts for a substantial fraction of NOx lost (and HNO3 produced), resulting in large impacts on oxidant formation, especially over forested regions.

Anion receptors based on halogen bonding with halo-1,2,3-triazoliums.

A systematic series of anion receptors based on bidentate halogen bonding by halo-triazoles and -triazoliums is presented. The influence of the halogen bond donor atom, the electron-withdrawing group, and the linker group that bridges the two donor moieties is investigated. Additionally, a comparison with hydrogen bond-based analogues is provided. A new, efficient synthetic approach to introduce different halogens into the heterocycles is established using silver(I)-triazolylidenes, which are converted to the corresponding halo-1,2,3-triazoliums with different halogens. Comprehensive nuclear magnetic resonance binding studies supported by isothermal titration calorimetry studies were performed with different halides and oxo-anions to evaluate the influence of key parameters of the halogen bond donor, namely, polarization of the halogen and the bond angle to the anion. The results show a larger anion affinity in the case of more charge-dense halides as well as a general preference of the receptors to bind oxo-anions, in particular sulfate, over halides.

Beyond click chemistry - supramolecular interactions of 1,2,3-triazoles.

The research on 1,2,3-triazoles has been lively and ever-growing since its stimulation by the advent of click chemistry. The attractiveness of 1H-1,2,3-triazoles and their derivatives originates from their unique combination of facile accessibility via click chemistry and truly diverse supramolecular interactions, which enabled myriads of applications in supramolecular and coordination chemistry. The nitrogen-rich triazole features a highly polarized carbon atom allowing the complexation of anions by hydrogen and halogen bonding or, in the case of the triazolium salts, via charge-assisted hydrogen and halogen bonds. On the other hand, the triazole offers several N-coordination modes including coordination via anionic and cationic nitrogen donors of triazolate and triazolium ions, respectively. After CH-deprotonation of the triazole and the triazolium, powerful carbanionic and mesoionic carbene donors, respectively, are available. The latter coordination mode even features non-innocent ligand behavior. Moreover, these supramolecular interactions can be combined, e.g., in ion-pair recognition, preorganization by intramolecular hydrogen bond donation and acceptance, and in bimetallic complexes. Ultimately, by clicking two building blocks into place, the triazole emerges as a most versatile functional unit allowing very successful applications, e.g., in anion recognition, catalysis, and photochemistry, thus going far beyond the original purpose of click chemistry. It is the intention of this review to provide a detailed analysis of the various supramolecular interactions of triazoles in comparison to established functional units, which may serve as guidelines for further applications.

Designing cyclometalated ruthenium(II) complexes for anodic electropolymerization.

The anodic electropolymerization of thiophene-functionalized cyclometalated ruthenium(II) complexes is shown for the first time. Oxidative decomposition reactions can be overcome by modification of the involved redox potentials through the introduction of electron-withdrawing substituents, namely nitro groups, at the cyclometalating phenyl ring. The generated functionalized ruthenium(II) complexes allow the electrochemical preparation of thin polymer films, which show a broad UV/Vis absorption as well as reversible redox switchability. The presented complexes are promising candidates for future photovoltaic applications based on photo-redox-active films.

A heteroleptic bis(tridentate) ruthenium(II) platform featuring an anionic 1,2,3-triazolate-based ligand for application in the dye-sensitized solar cell.

A series of bis(tridentate) ruthenium(II) complexes featuring new anionic 1,2,3-triazolate-based tridentate ligands and 2,2':6',2''-terpyridine is presented. For a complex equipped with carboxy anchoring groups, the performance in a dye-sensitized solar cell is evaluated. The title complexes are readily synthesized and can be decorated with alkyl chains utilizing azide-alkyne cycloaddition methods, in order to improve the device stability and allow the use of alternative electrolytes. On account of the strong electron donation from the 1,2,3-triazolates, the complexes exhibit a broad metal-to-ligand charge-transfer absorption (up to 700 nm), leading to an electron transfer toward the anchoring ligand. The lifetimes of the charge-separated excited states are in the range of 50 to 80 ns. In addition, the ground- and excited-state redox potentials are appropriate for the application in dye-sensitized solar cells, as demonstrated by power conversion efficiencies of up to 4.9% (vs 6.1% for N749).

Physicochemical analysis of ruthenium(II) sensitizers of 1,2,3-triazole-derived mesoionic carbene and cyclometalating ligands.

A series of heteroleptic bis(tridentate) ruthenium(II) complexes bearing ligands featuring 1,2,3-triazolide and 1,2,3-triazolylidene units are presented. The synthesis of the C^N^N-coordinated ruthenium(II) triazolide complex is achieved by direct C-H activation, which is enabled by the use of a 1,5-disubstituted triazole. By postcomplexation alkylation, the ruthenium(II) 1,2,3-triazolide complex can be converted to the corresponding 1,2,3-triazolylidene complex. Additionally, a ruthenium(II) complex featuring a C^N^C-coordinating bis(1,2,3-triazolylidene)pyridine ligand is prepared via transmetalation from a silver(I) triazolylidene precursor. The electronic consequences of the carbanion and mesoionic carbene donors are studied both experimentally and computationally. The presented complexes exhibit a broad absorption in the visible region as well as long lifetimes of the charge-separated excited state suggesting their application in photoredox catalysis and photovoltaics. Testing of the dyes in a conventional dye-sensitized solar cell (DSSC) generates, however, only modest power conversion efficiencies (PCEs).

Estimating the shape and size of supramolecular assemblies by variable temperature diffusion ordered spectroscopy.

Reported is characterization of the self-assembly of π-conjugated oligomers, molecules studied recently in photovoltaic devices, using variable temperature diffusion ordered spectroscopy (VT-DOSY). Iterative fitting of diffusion coefficient versus temperature data to a modified Stokes-Einstein equation, molecular modelling, and comparison to non-assembling model compounds, has allowed estimation of assembly size, shape, and molecularity.

Temperature-dependent emissions dominate aerosol and ozone formation in Los Angeles.

Despite declines in transportation emissions, urban North America and Europe still face unhealthy air pollution levels. This has challenged conventional understanding of the sources of their volatile organic compound (VOC) precursors. Using airborne flux measurements to map emissions of a wide range of VOCs, we demonstrate that biogenic terpenoid emissions contribute ~60% of emitted VOC OH reactivity, ozone, and secondary organic aerosol formation potential in summertime Los Angeles and that this contribution strongly increases with temperature. This implies that control of nitrogen oxides is key to reducing ozone formation in Los Angeles. We also show some anthropogenic VOC emissions increase with temperature, which is an effect not represented in current inventories. Air pollution mitigation efforts must consider that climate warming will strongly change emission amounts and composition.

A better representation of VOC chemistry in WRF-Chem and its impact on ozone over Los Angeles.

The declining trend in vehicle emissions has underscored the growing significance of Volatile Organic Compound (VOC) emissions from Volatile Chemical Products (VCP). However, accurately representing VOC chemistry in simplified chemical mechanisms remains challenging due to its chemical complexity including speciation and reactivity. Previous studies have predominantly focused on VOCs from fossil fuel sources, leading to an underrepresentation of VOC chemistry from VCP sources. We developed an integrated chemical mechanism, RACM2B-VCP, that is compatible with WRF-Chem and is aimed to enhance the representation of VOC chemistry, particularly from VCP sources, within the present urban environment. Evaluation against the Air Quality System (AQS) network data demonstrates that our model configured with RACM2B-VCP reproduces both the magnitude and spatial variability of O3 as well as PM2.5 in Los Angeles. Furthermore, evaluation against comprehensive measurements of O3 and PM2.5 precursors from the Reevaluating the Chemistry of Air Pollutants in California (RECAP-CA) airborne campaign and the Southwest Urban NO x and VOC Experiment (SUNVEx) ground site and mobile laboratory campaign, confirm the model's accuracy in representing NOx and many VOCs and highlight remaining biases. Although there exists an underprediction in the total VOC reactivity of observed VOC species, our model with RACM2B-VCP exhibits good agreement for VOC markers emitted from different sectors, including biogenic, fossil fuel, and VCP sources. Through sensitivity analyses, we probe the contributions of VCP and fossil fuel emissions to total VOC reactivity and O3. Our results reveal that 52% of the VOC reactivity and 35% of the local enhancement of MDA8 O3 arise from anthropogenic VOC emissions in Los Angeles. Significantly, over 50% of this anthropogenic fraction of either VOC reactivity or O3 is attributed to VCP emissions. The RACM2B-VCP mechanism created, described, and evaluated in this work is ideally suited for accurately representing ozone for the right reasons in the present urban environment where mobile, biogenic, and VCP VOCs are all important contributors to ozone formation.

Cyclometalated ruthenium(II) complexes featuring tridentate click-derived ligands for dye-sensitized solar cell applications.

A series of heteroleptic bis(tridentate) Ru(II) complexes featuring N^C^N-cyclometalating ligands is presented. The 1,2,3-triazole-containing tridentate ligands are readily functionalized with hydrophobic side chains by means of click chemistry and the corresponding cyclometalated Ru(II) complexes are easily synthesized. The performance of these thiocyanate-free complexes in a dye-sensitized solar cell was tested and a power conversion efficiency (PCE) of up to 4.0 % (Jsc =8.1 mA cm(-2) , Voc =0.66 V, FF=0.70) was achieved, while the black dye ((NBu4 )3 [Ru(Htctpy)(NCS)3 ]; Htctpy=2,2':6',2''-terpyridine-4'-carboxylic acid-4,4''-dicarboxylate) showed 5.2 % (Jsc =10.7 mA cm(-2) , Voc =0.69 V, FF=0.69) under comparable conditions. When co-adsorbed with chenodeoxycholic acid, the PCE of the best cyclometalated dye could be improved to 4.5 % (Jsc =9.4 mA cm(-2) , Voc =0.65 V, FF=0.70). The PCEs correlate well with the light-harvesting capabilities of the dyes, while a comparable incident photon-to-current efficiency was achieved with the cyclometalated dye and the black dye. Regeneration appeared to be efficient in the parent dye, despite the high energy of the highest occupied molecular orbital. The device performance was investigated in more detail by electrochemical impedance spectroscopy. Ultimately, a promising Ru(II) sensitizer platform is presented that features a highly functionalizable "click"-derived cyclometalating ligand.

Bis(tridentate) ruthenium-terpyridine complexes featuring microsecond excited-state lifetimes.

A series of heteroleptic bis(tridentate) ruthenium(II) complexes, each bearing a substituted 2,2':6',2″-terpyridine (terpy) ligand, is characterized by room temperature microsecond excited-state lifetimes. This observation is a consequence of the strongly σ-donating and weakly π-accepting tridentate carbene ligand, 2',6'-bis(1-mesityl-3-methyl-1,2,3-triazol-4-yl-5-idene)pyridine (C^N^C), adjacent to the terpy maintaining a large separation between the ligand field and metal-to-ligand charge transfer (MLCT) states while also preserving a large (3)MLCT energy. The observed lifetimes are the highest documented lifetimes for unimolecular ruthenium(II) complexes and are four orders in magnitude higher than that associated with [Ru(terpy)(2)](2+).

Ruthenium(II) photosensitizers of tridentate click-derived cyclometalating ligands: a joint experimental and computational study.

A systematic series of heteroleptic bis(tridentate)ruthenium(II) complexes of click-derived 1,3-bis(1,2,3-triazol-4-yl)benzene N^C^N-coordinating ligands was synthesized, analyzed by single crystal X-ray diffraction, investigated photophysically and electrochemically, and studied by computational methods. The presented comprehensive characterization allows a more detailed understanding of the radiationless deactivation mechanisms. Furthermore, we provide a fully optimized synthesis and systematic variations towards redox-matched, broadly and intensely absorbing, cyclometalated ruthenium(II) complexes. Most of them show a weak room-temperature emission and a prolonged excited-state lifetime. They display a broad absorption up to 700 nm and high molar extinction coefficients up to 20 000 M(-1)cm(-1) of the metal-to-ligand charge transfer bands, resulting in a black color. Thus, the complexes reveal great potential for dye-sensitized solar-cell applications.

Ruthenium(II) metallo-supramolecular polymers of click-derived tridentate ditopic ligands.

New ditopic 2,6-bis(1,2,3-triazol-4-yl)pyridine ligands featuring a π-conjugated spacer and clicked-on solubilizing groups were employed in the synthesis of Ru(II) metallo-supramolecular polymers that exhibit an intense metal-to-ligand charge transfer absorption in the visible light region. The coordination polymers obtained were studied in solution by means of size exclusion chromatography and analytical ultracentrifugation, revealing a comparably high molar mass and moderate rigidity. Investigations in the solid state by atomic force and transmission electron microscopy confirmed the formation of rod-like polymers. Furthermore, film preparation by drop-casting showed good film-forming properties. Thus, the solution-processable, photoredoxactive polymers might be applicable in solar cells.

Traffic, transport, and vegetation drive VOC concentrations in a major urban area in Texas.

The population of Texas has increased rapidly in the past decade. The San Antonio Field Study (SAFS) was designed to investigate ozone (O3) production and precursors in this rapidly changing, sprawling metropolitan area. There are still many questions regarding the sources and chemistry of volatile organic compounds (VOCs) in urban areas like San Antonio which are affected by a complex mixture of industry, traffic, biogenic sources and transported pollutants. The goal of the SAFS campaign in May 2017 was to measure inorganic trace gases, VOCs, methane (CH4), and ethane (C2H6). The SAFS field design included two sites to better assess air quality across the metro area: an urban site (Traveler's World; TW) and a downwind/suburban site (University of Texas at San Antonio; UTSA). The results indicated that acetone (2.52 ± 1.17 and 2.39 ± 1.27 ppbv), acetaldehyde (1.45 ± 1.02 and 0.93 ± 0.45 ppbv) and isoprene (0.64 ± 0.49 and 1.21 ± 0.85 ppbv; TW and UTSA, respectively) were the VOCs with the highest concentrations. Additionally, positive matrix factorization showed three dominant factors of VOC emissions: biogenic, aged urban mixed source, and acetone. Methyl vinyl ketone and methacrolein (MVK + MACR) exhibited contributions from both secondary photooxidation of isoprene and direct emissions from traffic. The C2H6:CH4 demonstrated potential influence of oil and gas activities in San Antonio. Moreover, the high O3 days during the campaign were in the NOx-limited O3 formation regime and were preceded by evening peaks in select VOCs, NOx and CO. Overall, quantification of the concentration and trends of VOCs and trace gases in a major city in Texas offers vital information for general air quality management and supports strategies for reducing O3 pollution. The SAFS campaign VOC results will also add to the growing body of literature on urban sources and concentrations of VOCs in major urban areas.

Chemical nature of PM2.5 and PM10 in Xi'an, China: Insights into primary emissions and secondary particle formation.

In Xi'an, a city that frequently experiences serious PM pollution in northern China, 1476 PM10 and 1464 PM2.5 valid daily filter samples were collected at six sites from December 2014 to November 2015 and analyzed for 29 species. The annual mean PM10 and PM2.5 concentrations were 149.4 ±â€¯93.1, 108.0 ±â€¯70.9 µg/m3, respectively. Organic carbon (OC) is the predominant PM2.5 component while crustal material predominated in PM10. Sulfate concentrations, which was the largest component in Xi'an PM in previous studies, were lower than nitrate. Winter sulfate, OC, and elemental carbon (EC) have decreased since 2003, while nitrate remained constant in recent years and the ratio of NO3-/SO42- increased from 0.4 in 2006 to 1.3 in 2014. This result suggests that the motor vehicle contribution to PM has increased relative to coal-fired power plant emissions over the past decade. The mass fractions of crustal material, sulfate, and EC in PM2.5 decreased as the PM2.5 concentrations increased from "clean" days (<50 µg/m3) to the highest values, while nitrate significantly increased. Despite forming through secondary reactions, the high concentrations of SOC and SO42- in winter are attributed to primary emissions and particularly to residential heating and cooking with coal. Primary SOC and SO42- accounted for 33% and 42% of their total PM2.5 concentrations in winter, respectively. Therefore, control measures applied to these primary sources can substantially improve air quality.

Soluble PtII-Containing Polymers Based on a 2,6-Bis(1H-1,2,3-triazol-4-yl)-4-ethynylpyridine Ligand.

A soluble PtII-acetylide polymer 6 was prepared in a supramolecular polymerization of a PtII-chloro precursor complex 5, which represents a self-complementary AB-type monomer. This new type of polymer combines the structural features of the common polyplatinynes and cationic PtII-acetylide complexes. Though the photophysical and electrochemical properties of the material still need to be advanced, a versatile and straightforward method for the preparation of soluble, cationic PtII-acetylide polymers with phosphorescent behavior is offered.

Halogen-bond-based cooperative ion-pair recognition by a crown-ether-embedded 5-iodo-1,2,3-triazole.

A crown-ether containing the iodo-triazole moiety for simultaneous cation-anion binding through Lewis-basic nitrogen atoms and C-II halogen-bond-donating iodine atoms was prepared. The complexation of the heteroditopic receptor was illustrated by X-ray and DFT analysis. The cooperative effect boosting the anion affinity was quantified by 1H/13C NMR titration experiments.