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Title: Experimental particle formation rates spanning tropospheric sulfuric acid and ammonia abundances, ion production rates, and temperatures: Ternary NH 3 Particle Formation Rates
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  1. Abstract

    In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [CoII−Cl]+species results in the formation of [CoII4‐L)(OH2)]2+. Further reduction produces [CoI4‐L)(OH2)]+, which undergoes a rate‐limiting structural rearrangement to [CoI5‐L)]+before being protonated to form [CoIII−H]2+. The rate of [CoIII−H]2+formation is similar for all complexes in the series. UsingE1/2values of various Co species and pKavalues of [CoIII−H]2+estimated from PR experiments, we found that while the protonation of [CoIII−H]2+is unfavorable, [CoII−H]+reacts with protons to produce H2. The catalytic activity for H2evolution tracks the hydricity of the [CoII−H]+intermediate.

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  2. Abstract

    New particle formation (NPF) has been observed at various locations, but NPF does not occur in isoprene‐dominant forests. Recent laboratory studies were conducted to understand the role of isoprene in biogenic NPF, and these studies show that isoprene can suppress biogenic NPF, with contradicting theories. To reconcile these discrepancies, we conducted flow tube experiments of biogenic nucleation under a wide range of isoprene over monoterpene carbon ratios (R) and oxidant conditions (OH vs. ozone). Our results show isoprene either suppresses or enhances biogenic NPF, depending onRand oxidation regimes, demonstrating the synergetic effects of isoprene and HOx(OH and HO2) on biogenic NPF. Whereas the suppression of NPF by isoprene is due to the product suppression effects of monoterpene dimers (C20), RO2 + HO2termination reactions also play important roles in suppressing the dimer formation, another likely process to suppress NPF in the atmosphere.

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