More Like this

1. Molecular understanding of new-particle formation from <i>α</i>-pinene between −50 and +25 °C

   https://doi.org/10.5194/acp-20-9183-2020  

   Simon, Mario ; Dada, Lubna ; Heinritzi, Martin ; Scholz, Wiebke ; Stolzenburg, Dominik ; Fischer, Lukas ; Wagner, Andrea C. ; Kürten, Andreas ; Rörup, Birte ; He, Xu-Cheng ; et al ( January 2020 , Atmospheric Chemistry and Physics)

   Abstract. Highly oxygenated organic molecules (HOMs) contributesubstantially to the formation and growth of atmospheric aerosol particles,which affect air quality, human health and Earth's climate. HOMs are formedby rapid, gas-phase autoxidation of volatile organic compounds (VOCs) suchas α-pinene, the most abundant monoterpene in the atmosphere. Due totheir abundance and low volatility, HOMs can play an important role innew-particle formation (NPF) and the early growth of atmospheric aerosols,even without any further assistance of other low-volatility compounds suchas sulfuric acid. Both the autoxidation reaction forming HOMs and theirNPF rates are expected to be strongly dependent ontemperature. However, experimental data on both effects are limited.Dedicated experiments were performed at the CLOUD (Cosmics Leaving OUtdoorDroplets) chamber at CERN to address this question. In this study, we showthat a decrease in temperature (from +25 to −50 ∘C) results ina reduced HOM yield and reduced oxidation state of the products, whereas theNPF rates (J1.7 nm) increase substantially.Measurements with two different chemical ionization mass spectrometers(using nitrate and protonated water as reagent ion, respectively) providethe molecular composition of the gaseous oxidation products, and atwo-dimensional volatility basis set (2D VBS) model provides their volatilitydistribution. The HOM yield decreases with temperature from 6.2 % at 25 ∘C to 0.7 % at −50 ∘C. However, there is a strongreductionmore »of the saturation vapor pressure of each oxidation state as thetemperature is reduced. Overall, the reduction in volatility withtemperature leads to an increase in the nucleation rates by up to 3orders of magnitude at −50 ∘C compared with 25 ∘C. Inaddition, the enhancement of the nucleation rates by ions decreases withdecreasing temperature, since the neutral molecular clusters have increasedstability against evaporation. The resulting data quantify how the interplaybetween the temperature-dependent oxidation pathways and the associatedvapor pressures affect biogenic NPF at the molecularlevel. Our measurements, therefore, improve our understanding of purebiogenic NPF for a wide range of tropospherictemperatures and precursor concentrations.« less
2. Solid organic-coated ammonium sulfate particles at high relative humidity in the summertime Arctic atmosphere

   https://doi.org/10.1073/pnas.2104496119  

   Kirpes, Rachel M. ; Lei, Ziying ; Fraund, Matthew ; Gunsch, Matthew J. ; May, Nathaniel W. ; Barrett, Tate E. ; Moffett, Claire E. ; Schauer, Andrew J. ; Alexander, Becky ; Upchurch, Lucia M. ; et al ( April 2022 , Proceedings of the National Academy of Sciences)

   The ability of atmospheric aerosols to impact climate through water uptake and cloud formation is fundamentally determined by the size, composition, and phase (liquid, semisolid, or solid) of individual particles. Particle phase is dependent on atmospheric conditions (relative humidity and temperature) and chemical composition and, importantly, solid particles can inhibit the uptake of water and other trace gases, even under humid conditions. Particles composed primarily of ammonium sulfate are presumed to be liquid at the relative humidities (67 to 98%) and temperatures (−2 to 4 °C) of the summertime Arctic. Under these atmospheric conditions, we report the observation of solid organic-coated ammonium sulfate particles representing 30% of particles, by number, in a key size range (<0.2 µm) for cloud activation within marine air masses from the Arctic Ocean at Utqiaġvik, AK. The composition and size of the observed particles are consistent with recent Arctic modeling and observational results showing new particle formation and growth from dimethylsulfide oxidation to form sulfuric acid, reaction with ammonia, and condensation of marine biogenic sulfate and highly oxygenated organic molecules. Aqueous sulfate particles typically undergo efflorescence and solidify at relative humidities of less than 34%. Therefore, the observed solid phase is hypothesized to occur from contactmore »efflorescence during collision of a newly formed Aitken mode sulfate particle with an organic-coated ammonium sulfate particle. With declining sea ice in the warming Arctic, this particle source is expected to increase with increasing open water and marine biogenic emissions.« less
3. Chemical composition of nanoparticles from <i>α</i>-pinene nucleation and the influence of isoprene and relative humidity at low temperature

   https://doi.org/10.5194/acp-21-17099-2021  

   Caudillo, Lucía ; Rörup, Birte ; Heinritzi, Martin ; Marie, Guillaume ; Simon, Mario ; Wagner, Andrea C. ; Müller, Tatjana ; Granzin, Manuel ; Amorim, Antonio ; Ataei, Farnoush ; et al ( January 2021 , Atmospheric Chemistry and Physics)

   Abstract. Biogenic organic precursors play an important role inatmospheric new particle formation (NPF). One of the major precursor speciesis α-pinene, which upon oxidation can form a suite of productscovering a wide range of volatilities. Highly oxygenated organic molecules(HOMs) comprise a fraction of the oxidation products formed. While it isknown that HOMs contribute to secondary organic aerosol (SOA) formation,including NPF, they have not been well studied in newly formed particles dueto their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures(−50 and −30 ∘C) and relativehumidities (20 % and 60 %) relevant in the upper free troposphere. Themeasurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD)chamber. The particle chemical composition was analyzed by a thermaldesorption differential mobility analyzer (TD-DMA) coupled to a nitratechemical ionization–atmospheric pressure interface–time-of-flight(CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Ourmeasurements revealed the presence of C8−10 monomers and C18−20dimers as the major compounds in the particles (diameter up to∼ 100 nm). Particularly, for the system with isoprene added,C5 (C5H10O5−7) and C15 compounds(C15H24O5−10) were detected. This observation is consistentwith the previously observed formation ofmore »such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate,our measurements indicate that they can still contribute to the particlegrowth at free tropospheric conditions. For the experiments reported here,most likely isoprene oxidation products enhance the growth of particleslarger than 15 nm. Additionally, we report on the nucleation rates measuredat 1.7 nm (J1.7 nm) and compared with previous studies, we found lowerJ1.7 nm values, very likely due to the higher α-pinene andozone mixing ratios used in the present study.« less
4. Raman Microspectroscopy of Individual IEPOX-derived Secondary Organic Aerosol Particles After OH Oxidation

   Chen, Weiyu ; Fankhauser, Alison ; Yan, Jin ; Cooke, Madeline ; Waters, Cara ; Parham, Rebecca ; Armstrong, N. Cazimir ; Xiao, Yao ; Kolozsvari, Katherine ; Zhang, Zhenfa ; et al ( December 2022 , 2022 AGU Fall Meeting)

   Isoprene is one of the most common biogenic volatile organic compounds (BVOC) in the atmosphere, produced by many plants. Isoprene undergoes oxidation to form gaseous isoprene epoxydiols (IEPOX) under low-NOx conditions, which can lead to the formation of secondary organic aerosol (SOA) particles. SOA-containing particles affect climate by scattering and absorbing solar radiation or acting as cloud condensation nuclei (CCN). High concentrations of SOA are also associated with adverse health impacts in people. While in the atmosphere, IEPOX SOA particles continue to undergo reactions with atmospheric oxidants, including hydroxyl radical (OH). To isolate and probe this process, we studied atmospheric chemical processes in an aerosol chamber to better understand the evolution of heterogeneous OH oxidation of IEPOX-derived SOA particles. Since very little is understood about the structural and spectroscopic properties because of the complexity of their many sources and atmospheric processing, individual particle measurements are necessary to provide better understanding of the composition of IEPOX SOA. We injected particles composed of mixtures of ammonium sulfate and sulfuric acid across a range of acidities(PH = 0.5 – 2.5) and gas-phase IEPOX into the chamber to generate SOA. The SOA particles were then sent to an oxidation flow reactor, and exposed tomore »different OH concentrations representative of aging of a number of days. We kept relative humidity (RH) constant at ~65%, the temperature was ~23 °C, and levels of oxidation were controlled by adjusting lamp intensity. After oxidized SOA was impacted on quartz substrates, we used single-particle Raman microspectroscopy to identify their functional group compositions. From the Raman vibrational spectra of submicron particles (~500-1000 nm aerodynamic diameter), we observed a distinct difference in core-shell morphology and composition: an organic outer layer and an aqueous-inorganic core. The core also has significantly more CH-stretch than the shell. Small changes were also observed with increasing oxidation, which are important to consider when predicting SOA particle evolution in the atmosphere.« less
5. Molecular understanding of the suppression of new-particle formation by isoprene

   https://doi.org/10.5194/acp-20-11809-2020  

   Heinritzi, Martin ; Dada, Lubna ; Simon, Mario ; Stolzenburg, Dominik ; Wagner, Andrea C. ; Fischer, Lukas ; Ahonen, Lauri R. ; Amanatidis, Stavros ; Baalbaki, Rima ; Baccarini, Andrea ; et al ( January 2020 , Atmospheric Chemistry and Physics)

   Abstract. Nucleation of atmospheric vapours produces more than half of global cloudcondensation nuclei and so has an important influence on climate. Recentstudies show that monoterpene (C10H16) oxidation yieldshighly 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 organicvapours. Previous studies have shown that isoprene suppresses new-particleformation from monoterpenes, but the cause of this suppression is underdebate. Here, in experiments performed under atmospheric conditions in theCERN CLOUD chamber, we show that isoprene reduces the yield ofhighly oxygenated dimers with 19 or 20 carbon atoms – which drive particlenucleation and early growth – while increasing the production of dimers with14 or 15 carbon atoms. The dimers (termed C20 and C15,respectively) are produced by termination reactions between pairs of peroxyradicals (RO2⚫) arising from monoterpenes or isoprene.Compared with pure monoterpene conditions, isoprene reduces nucleation ratesat 1.7 nm (depending on the isoprene ∕ monoterpene ratio) and approximatelyhalves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm,C15 dimers contribute to secondary organic aerosol, and the growth ratesare unaffected by isoprene. We further show that increased hydroxyl radical(OH⚫) reduces particle formation in our chemical system ratherthan enhances it as previously proposed,more »since it increases isoprene-derivedRO2⚫ radicals that reduce C20 formation.RO2⚫ termination emerges as the critical step that determinesthe highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Speciesthat reduce the C20 yield, such as NO, HO2 and as we showisoprene, can thus effectively reduce biogenic nucleation and early growth.Therefore the formation rate of organic aerosol in a particular region ofthe atmosphere under study will vary according to the precise ambientconditions.« less