ACS Earth and Space Chemistry最新文献

Understanding the mechanism for catalytic destruction of stratospheric ozone by chlorine radicals led to international restrictions on the emission of harmful chemicals. Measurements of chlorate (ClO₃^–) and perchlorate (ClO₄^–) anions in the atmosphere suggest that chloride and chlorine oxide anions could also play a role in ozone destruction, but the pathways for these gas-phase reactions are poorly understood. Here, reactions of hypochlorite (ClO^–) and chlorite (ClO₂^–) with ozone were directly observed using linear ion-trap mass spectrometry and rate constants determined to be 6.6 (±0.7) × 10^–11 cm³ molecule^–1 s^–1 (6.7% collision efficient) and 3.5 (±0.4) × 10^–10 cm³ molecule^–1 s^–1 (38% efficient), respectively. Compared to the analogous bromine and iodine oxides, which undergo efficient stepwise oxidation terminating in XO₃^– (X = Br or I), the reaction products of ClO₂^– with ozone include both (i) oxidation to ClO₃^– and neutral O₂ (30%) and (ii) charge transfer to yield the ozonide anion O₃^• – and neutral ClO₂^• (70%). Branching ratio measurements for ClO^– show a more complex reaction manifold with production of Cl^– (50%), ClO₂^– (9%), and O₃^• – (41%), with the change in redox reactivity rationalized by coupled-cluster CCSD(T) calculations. These experiments highlight that, in addition to consuming ozone, these anions are precursors to the formation of the neutral radicals ClO₂^• and ClO^•, which themselves are critical intermediates in atomic chlorine pathways that are implicated in ozone depletion in the stratosphere.

Understanding the phase state of aerosol particles is important for both atmospheric chemistry and physics. Phase transitions of aerosol particles are induced by changes in the temperature (T) and relative humidity (RH). In the case of atmospherically important inorganic chemical species such as (NH₄)₂SO₄ and NaCl, phase transitions occur as deliquescence and efflorescence. The temperature dependence of deliquescence is well described by the Clausius–Clapeyron equation. However, the temperature dependence of the efflorescence RH (ERH) of inorganic salts has not been theoretically well described. We employed the classical nucleation theory (CNT) for modeling the ERH of (NH₄)₂SO₄ and NaCl particles. The model outputs were compared to literature data. The literature data included a recent ERH measurement for size-selected particles using the low-temperature hygroscopicity tandem differential analyzer (low-T HTDMA). In the case of (NH₄)₂SO₄, the temperature dependence of water solubility and interfacial energy between the nuclei and aqueous phase (γ_{aq_nu}) needed to be considered to reproduce the experimental ERH values. That is, γ_{aq_nu} needed to be represented by the following equation: γ_{aq_nu} (T) = γ_{aq_nu} (298.15 K)(T/298.15 K)ⁿ (where n is an empirically determined parameter). The value of n for (NH₄)₂SO₄ was identified as 0.6. In the case of NaCl, the CNT estimation and low-T HTDMA result agreed well when n = 0.7, while the temperature dependence of ERH in the literature was highly variable. Further studies employing laboratory experiments and numerical simulations are required to facilitate a molecular-level understanding of the temperature dependence of ERH.

The 3-methyl-3-penten-2-one (3M3P2) reaction with OH radicals was studied in theoretical calculations based on QCISD(T)//BH&HLYP quantum chemistry results. The rate coefficients for the OH radical reaction with 3M3P2 were obtained with the conventional transition state theory including Eckart tunneling corrections. The room-temperature rate coefficient k was found to be 6.01 × 10^–11 cm³ molecule^–1 s^–1, which is aligned to the experimental result. The rate coefficient over the temperature range 260–400 K can be approximated by a modified Arrhenius expression k (T) = 4.00 × 10^–18 × T^1.8 × exp(1870.7/T) cm³ molecule^–1 s^–1. The calculated rate coefficient shows a negative temperature dependence at the temperatures ranging from 260 to 400 K. The kinetics was governed by the formation of two addition intermediates. Under atmospheric conditions, these two intermediates can react with O₂/NO_x to produce acetaldehyde, biacetyl (2,3-butanedione), acetoin (3-hydroxy-2-butanone), CO₂, and peroxyacetyl nitrate (PAN) as the predominant products, which is in line with the experimental observations. A reasonable reaction mechanism for the OH radical reaction with 3M3P2 in the atmosphere is proposed, and the atmospheric implications are also discussed.

Despite the importance of aqueous secondary organic aerosol (aqSOA), several uncertainties remain regarding its formation. These include the seasonal contributions of aqSOA to the total SOA mass and the relative proportions formed via reversible versus irreversible pathways. In this study, we use measurements of seasonal water-soluble organic compounds in the particle and gaseous phases (i.e., WSOC_p and WSOC_g, respectively) at a site in the eastern U.S. to quantify aqSOA concentrations as well as its reversible and irreversible fractions within each season. We show evidence that aqSOA concentrations present a significant contribution to total SOA mass during the nighttime in the eastern U.S. with ∼30 and ∼50% in the cold and warm seasons, respectively. Further, aqSOA mass is mostly formed through irreversible pathways, except during the warm seasons, where reversible partitioning of WSOC_g accounts for ∼10% of the total SOA mass (∼20% of aqSOA mass). Comparisons between the seasonally measured aqSOA concentrations and their counterpart community multiscale air quality (CMAQ) modeled mass provide evidence that accounting for additional reversible and irreversible aqSOA pathways could improve model predictions of SOA concentrations and close the current gap between those predictions and field observations. This work holds valuable implications for the atmospheric chemistry of multiphase aerosol formation and its accurate representation in chemical transport models.

The rotationally resolved spectrum of the degenerate ν₄ antisymmetric C–H stretching band of the cyclopropenyl cation, c-C₃H₃⁺, the smallest aromatic hydrocarbon cation, has been recorded employing leak-out-spectroscopy (LOS) in a cryogenic 22-pole ion trap instrument operated at T = 42 K. About 370 lines were measured in the region 3110–3150 cm^–1 and assigned to rovibrational transitions of the fundamental antisymmetric C–H stretching band. Spectroscopic parameters have been refined compared to the previous experimental work from the group of Harold Linnartz [Zhao et al., Astrophys. J. Lett. 2014, 791, L28] and previous high-level theoretical predictions [Huang et al., J. Phys. Chem. A 2011, 115, 5005–5016]. Details of the spectral signatures allow for a thorough comparison of action spectroscopy in low-temperature ion traps to cavity ring down spectroscopy in a free-jet cooled discharge.

This study focuses on the characterization of fine particulate matter (PM_2.5) and the assessment of health risks associated with it. PM_2.5 samples were collected in Serpong using the SuperSASS (speciation air sampling system) every 3 days from August to October 2022. The mass concentration of PM_2.5 was determined gravimetrically, while black carbon (BC) was measured using a reflectance method. Energy-dispersive X-ray fluorescence (EDXRF) was employed to quantify the elemental composition. Additionally, measurement of the reconstructed mass (RCM) for PM_2.5 was conducted to enhance the understanding of PM_2.5 composition and its sources. The PM_2.5 measurements indicated concentrations ranging from 13.07 to 71.26 μg/m³, with an average concentration of 41.80 ± 0.99 μg/m³. Sulfur (S) and lead (Pb) were identified as the predominant metals, with average concentrations of 2.71 ± 1.24 and 1.42 ± 1.28 μg/m³, respectively. The average RCM for PM_2.5 was 49.2 ± 12.2%, comprising 15.2% black carbon, 25.7% sulfate, 1.73% soil, 0.84% sea salt, 1.05% smoke and 4.62% trace elements. The health implications of PM_2.5 were assessed using the hazard quotient (HQ) and excess lifetime cancer risk (ELCR) for Pb, Cr and nickel Ni. The HQ and ELCR values for the studied metals were within the safe range. The order of HQ values was Pb > Cr > Ni, while the trend of ELCR values was Cr > Pb > Ni across all age groups. These findings provide reliable information regarding PM_2.5 concentration and composition, potential sources of PM_2.5 and health effect, thereby contributing to the development of an early warning system for air pollution in Serpong, Indonesia.

The kinetics of imidazole formation in optically levitated glyoxal/ammonium sulfate aqueous microdroplets has been investigated using single-particle Raman spectroscopy. The microdroplet diameters (∼25 μm) were measured using brightfield microscopy. Individual microdroplets were produced from bulk solutions with pH in the range 4.0–9.3 and confined for up to 6 h in the optical levitation apparatus, which was maintained at a constant relative humidity (RH) of ∼70%. Imidazole bands at 920, 1230, and 1470 cm^–1 were observed to grow in as the confined microdroplets aged; the effective formation rate constants increased with initial bulk solution pH, reflecting the increased concentration of nucleophilic NH₃ as the acid–base equilibrium is shifted. However, the imidazole formation rates do not increase to the extent that would be expected based on previous bulk kinetics measurements. Preliminary experiments observing microdroplets dispensed sequentially from the same bulk solution suggest that imidazole formation is accelerated in the microdroplets by a factor of ∼7. The apparent rate acceleration can be explained by preconcentration of the reactants as the initially dispensed microdroplets lose water and equilibrate with the apparatus RH.

Alkyl amines are N-containing bases that impact the formation and composition of atmospheric particles despite their trace abundance in the atmosphere. Amine concentrations strongly depend on local sources due to their relatively short atmospheric lifetimes, and given their temperature and pH-dependent aqueous solubility, simultaneous measurements in both gas and particle phases are essential for understanding their atmospheric fate. From November 2022 to May 2024, size-resolved particulate amines were measured across the Greater Toronto Area using a 10-stage micro-orifice uniform deposition impactor (MOUDI) in 51 independent multiday observation periods. For 18 of those periods, a denuder was used to simultaneously collect gaseous ammonia and amines. Dimethylamine (DMA) and diethylamine (DEA) were the only amines consistently measured above the limit of detection by ion chromatography. Concentrations of particulate DMAH⁺ and DEAH⁺ exhibited stronger spatial and temporal variations than ammonium (NH₄⁺). Between 79 and 97% of total diethylamine was in the particle phase, significantly higher than the particulate fraction of dimethylamine (39–95%) and ammonia (NH₃) (2–25%). The phase partitioning of ammonia and amines in the atmosphere predicted by the E-AIM model was reasonably consistent with the observed results. Particulate amine/ammonia ratios were higher in the smallest particles, and on some sampling dates, the DEAH⁺/ DMAH⁺ ratios clearly decreased with size over the 0.18–1 μm range. Estimating the loss rates to gas and aqueous phase oxidation of the amines indicates the importance of investigating their phase partitioning for a better understanding of their atmospheric fates.

The mass spectra of negative ions from the aqueous solutions of monochloroacetic (MCA), dichloroacetic (DCA), and trichloroacetic (TCA) acids, obtained earlier using a mass spectrographic method involving electrospraying of electrolyte solutions in a vacuum, were reanalyzed, enabling the acquisition of new information about the hydration of the anions of acid residues (RCOO^–). The structures of the hydration shells at both the Cl and COO^– sites of the residue were determined due to the presence of the lines of both hydrated ions of acid residues (RCOO)⁻ and chlorine ions Cl^– in the mass spectra. Eight water molecules in the hydration shell at the Cl site were observed in the spectrum of MCA in a 0.001 M solution. It was found that the hydration of the COO^– site depends on the number of chlorine atoms in the acid: the most probable number of water molecules in the first hydration layer around COO^– is 1 for MCA, 1–2 for DCA, and 1–3 for TCA. The importance of the hydration state of the chloroacetic acids for their transformation in the liquid phase is discussed.

Broadband measurements of glycidaldehyde in the frequency ranges 75–170 and 500–750 GHz were recorded to extend previous analyses of its pure rotational spectrum in the microwave region. The rotational parameters of the ground vibrational states for the main isotopologue and the three singly ¹³C-substituted isotopologues were considerably improved, and additional higher-order parameters were determined. To identify new vibrationally excited states in the dense and convoluted spectrum, an updated version of the double-modulation double-resonance spectroscopy technique was used. Connecting transitions with a shared energy level into series and expanding these via Loomis–Wood plots proved to be a powerful method, which allowed the identification of 11 new vibrationally excited states in addition to the already known aldehyde torsions, v₂₁ = 1 to v₂₁ = 6. Interactions between several vibrational states were observed, and three interacting systems were treated successfully. Rotational transitions of glycidaldehyde were searched for in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). Glycidaldehyde, an oxirane derivative, was not detected toward Sgr B2(N2b). The upper limit on its column density implies that it is at least six times less abundant than oxirane in this source.