More Like this

1. Survival of newly formed particles in haze conditions

   https://doi.org/10.1039/D2EA00007E  

   Marten, Ruby; Xiao, Mao; Rörup, Birte; Wang, Mingyi; Kong, Weimeng; He, Xu-Cheng; Stolzenburg, Dominik; Pfeifer, Joschka; Marie, Guillaume; Wang, Dongyu S.; et al (May 2022, Environmental Science: Atmospheres)

   Intense new particle formation events are regularly observed under highly polluted conditions, despite the high loss rates of nucleated clusters. Higher than expected cluster survival probability implies either ineffective scavenging by pre-existing particles or missing growth mechanisms. Here we present experiments performed in the CLOUD chamber at CERN showing particle formation from a mixture of anthropogenic vapours, under condensation sinks typical of haze conditions, up to 0.1 s −1 . We find that new particle formation rates substantially decrease at higher concentrations of pre-existing particles, demonstrating experimentally for the first time that molecular clusters are efficiently scavenged by larger sized particles. Additionally, we demonstrate that in the presence of supersaturated gas-phase nitric acid (HNO 3 ) and ammonia (NH 3 ), freshly nucleated particles can grow extremely rapidly, maintaining a high particle number concentration, even in the presence of a high condensation sink. Such high growth rates may explain the high survival probability of freshly formed particles under haze conditions. We identify under what typical urban conditions HNO 3 and NH 3 can be expected to contribute to particle survival during haze. 

   more » « less
2. The driving factors of new particle formation and growth in the polluted boundary layer

   https://doi.org/10.5194/acp-21-14275-2021  

   Xiao, Mao; Hoyle, Christopher R.; Dada, Lubna; Stolzenburg, Dominik; Kürten, Andreas; Wang, Mingyi; Lamkaddam, Houssni; Garmash, Olga; Mentler, Bernhard; Molteni, Ugo; et al (January 2021, Atmospheric Chemistry and Physics)

   Abstract. New particle formation (NPF) is a significant source of atmosphericparticles, affecting climate and air quality. Understanding the mechanismsinvolved in urban aerosols is important to develop effective mitigationstrategies. However, NPF rates reported in the polluted boundary layer spanmore than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have beenpostulated to participate in NPF, including sulfuric acid, ammonia, aminesand organics, but their relative roles remain unclear. We investigated NPFin the CLOUD chamber using mixtures of anthropogenic vapours that simulatepolluted boundary layer conditions. We demonstrate that NPF in pollutedenvironments is largely driven by the formation of sulfuric acid–baseclusters, stabilized by the presence of amines, high ammonia concentrationsand lower temperatures. Aromatic oxidation products, despite their extremelylow volatility, play a minor role in NPF in the chosen urban environment butcan be important for particle growth and hence for the survival of newlyformed particles. Our measurements quantitatively account for NPF in highlydiverse urban environments and explain its large observed variability. Suchquantitative information obtained under controlled laboratory conditionswill help the interpretation of future ambient observations of NPF rates inpolluted atmospheres. 

   more » « less
3. New particle formation from isoprene under upper-tropospheric conditions

   https://doi.org/10.1038/s41586-024-08196-0  

   Shen, Jiali; Russell, Douglas M; DeVivo, Jenna; Kunkler, Felix; Baalbaki, Rima; Mentler, Bernhard; Scholz, Wiebke; Yu, Wenjuan; Caudillo-Plath, Lucía; Sommer, Eva; et al (December 2024, Nature)

   Abstract Aircraft observations have revealed ubiquitous new particle formation in the tropical upper troposphere over the Amazon^1,2and the Atlantic and Pacific oceans^3,4. Although the vapours involved remain unknown, recent satellite observations have revealed surprisingly high night-time isoprene mixing ratios of up to 1 part per billion by volume (ppbv) in the tropical upper troposphere⁵. Here, in experiments performed with the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we report new particle formation initiated by the reaction of hydroxyl radicals with isoprene at upper-tropospheric temperatures of −30 °C and −50 °C. We find that isoprene-oxygenated organic molecules (IP-OOM) nucleate at concentrations found in the upper troposphere, without requiring any more vapours. Moreover, the nucleation rates are enhanced 100-fold by extremely low concentrations of sulfuric acid or iodine oxoacids above 10⁵ cm⁻³, reaching rates around 30 cm⁻³ s⁻¹at acid concentrations of 10⁶ cm⁻³. Our measurements show that nucleation involves sequential addition of IP-OOM, together with zero or one acid molecule in the embryonic molecular clusters. IP-OOM also drive rapid particle growth at 3–60 nm h⁻¹. We find that rapid nucleation and growth rates persist in the presence of NO_xat upper-tropospheric concentrations from lightning. Our laboratory measurements show that isoprene emitted by rainforests may drive rapid new particle formation in extensive regions of the tropical upper troposphere^1,2, resulting in tens of thousands of particles per cubic centimetre. 

   more » « less
4. Fast predictions of liquid-phase acid-catalyzed reaction rates using molecular dynamics simulations and convolutional neural networks

   https://doi.org/10.1039/d0sc03261a  

   Chew, Alex K.; Jiang, Shengli; Zhang, Weiqi; Zavala, Victor M.; Van Lehn, Reid C. (December 2020, Chemical Science)

   null (Ed.)

   The rates of liquid-phase, acid-catalyzed reactions relevant to the upgrading of biomass into high-value chemicals are highly sensitive to solvent composition and identifying suitable solvent mixtures is theoretically and experimentally challenging. We show that the complex atomistic configurations of reactant–solvent environments generated by classical molecular dynamics simulations can be exploited by 3D convolutional neural networks to enable accurate predictions of Brønsted acid-catalyzed reaction rates for model biomass compounds. We develop a 3D convolutional neural network, which we call SolventNet, and train it to predict acid-catalyzed reaction rates using experimental reaction data and corresponding molecular dynamics simulation data for seven biomass-derived oxygenates in water–cosolvent mixtures. We show that SolventNet can predict reaction rates for additional reactants and solvent systems an order of magnitude faster than prior simulation methods. This combination of machine learning with molecular dynamics enables the rapid, high-throughput screening of solvent systems and identification of improved biomass conversion conditions. 

   more » « less
5. Epistasis Creates Invariant Sites and Modulates the Rate of Molecular Evolution

   https://doi.org/10.1093/molbev/msac106  

   Patel, Ravi; Carnevale, Vincenzo; Kumar, Sudhir (May 2022, Molecular Biology and Evolution)

   Ozkan, Banu (Ed.)

   Abstract Invariant sites are a common feature of amino acid sequence evolution. The presence of invariant sites is frequently attributed to the need to preserve function through site-specific conservation of amino acid residues. Amino acid substitution models without a provision for invariant sites often fit the data significantly worse than those that allow for an excess of invariant sites beyond those predicted by models that only incorporate rate variation among sites (e.g., a Gamma distribution). An alternative is epistasis between sites to preserve residue interactions that can create invariant sites. Through computer-simulated sequence evolution, we evaluated the relative effects of site-specific preferences and site-site couplings in the generation of invariant sites and the modulation of the rate of molecular evolution. In an analysis of ten major families of protein domains with diverse sequence and functional properties, we find that the negative selection imposed by epistasis creates many more invariant sites than site-specific residue preferences alone. Further, epistasis plays an increasingly larger role in creating invariant sites over longer evolutionary periods. Epistasis also dictates rates of domain evolution over time by exerting significant additional purifying selection to preserve site couplings. These patterns illuminate the mechanistic role of epistasis in the processes underlying observed site invariance and evolutionary rates. 

   more » « less