Hydrogen Peroxide Enhances the Oxidation of Oxygenated Volatile Organic Compounds on Mineral Dust Particles: A Case Study of Methacrolein

Heterogeneous oxidation of oxygenated volatile organic compounds (OVOCs) serves as an important sink of OVOCs as well as a source of secondary organic material. However, the roles of gas phase oxidants in these reactions are poorly understood. In this work, we present the first laboratory study of the heterogeneous reactions of methacrolein (MACR) on various mineral dust particles in the presence of gaseous H₂O₂. It is found that the presence of gaseous H₂O₂ significantly promotes both the uptake and oxidation of MACR on kaolinite, α-Al₂O₃, α-Fe₂O₃, and TiO₂, but not on CaCO₃. The oxidation of MACR produces organic acids as its major low-molecular-weight product, whose yields are enhanced by a factor of 2–6 in the presence of H₂O₂. In addition, organic peroxides such as methyl hydroperoxide, peroxyformic acid, and peroxyacetic acid are only formed in the presence of H₂O₂, and the formation of methyl hydroperoxide indicates that MACR oxidation on the surface involves reaction with OH radicals. A probe reaction using salicylic acid verifies the production of OH radicals from H₂O₂ decomposition on kaolinite, α-Al₂O₃, α-Fe₂O₃, and TiO₂, which rationalizes the enhanced MACR oxidation observed on these particles. The uptake coefficients of MACR on kaolinite, α-Fe₂O₃, and TiO₂ in the presence of H₂O₂ are on the order of 10^–5–10^–4. Our results provide new insights into the formation and chemical evolution of organic species in the atmosphere

Kinetics of Heterogeneous Reaction of Sulfur Dioxide on Authentic Mineral Dust: Effects of Relative Humidity and Hydrogen Peroxide

Heterogeneous reaction of SO₂ on mineral dust seems to be an important sink for SO₂. However, kinetic data about this reaction on authentic mineral dust are scarce and are mainly limited to low relative humidity (RH) conditions. In addition, little is known about the role of hydrogen peroxide (H₂O₂) in this reaction. Here, we investigated the uptake kinetics of SO₂ on three authentic mineral dusts (i.e., Asian mineral dust (AMD), Tengger desert dust (TDD), and Arizona test dust (ATD)) in the absence and presence of H₂O₂ at different RHs using a filter-based flow reactor, and applied a parameter (effectiveness factor) to the estimation of the effective surface area of particles for the calculation of the corrected uptake coefficient (γ_<i>c</i>). We found that with increasing RH, the γ_<i>c</i> decreases on AMD particles, but increases on ATD and TDD particles. This discrepancy is probably due to the different mineralogy compositions and aging extents of these dust samples. Furthermore, the presence of H₂O₂ can promote the uptake of SO₂ on mineral dust at different RHs. The probable explanations are that H₂O₂ rapidly reacts with SO₂ on mineral dust in the presence of adsorbed water, and OH radicals, which can be produced from the heterogeneous decomposition of H₂O₂ on the mineral dust, immediately react with adsorbed SO₂ as well. Our results suggest that the removal of SO₂ via the heterogeneous reaction on mineral dust is an important sink for SO₂ and has the potential to alter the physicochemical properties (e.g., ice nucleation ability) of mineral dust particles in the atmosphere

Formation of Organosulfur Compounds through Transition Metal Ion-Catalyzed Aqueous Phase Reactions

Organosulfur compounds, particularly organosulfates, are considered as important tracers of secondary organic aerosol formation. However, the mechanistic pathways for the formation of these compounds in the atmosphere are still not well understood. In this study, we show for the first time that C₂–C₄ organosulfur compounds, as well as their oligomers, can form in the aqueous phase from reactions of unsaturated carbonyl compounds, i.e., methacrolein (MACR) and methyl vinyl ketone (MVK), with the bisulfite anion (HSO₃^–) in the presence of Fe³⁺. The mechanism for product formation in the presence of Fe³⁺ involves sulfite and sulfate ion radicals. As shown here, the formation of specific organosulfur compounds depends on the concentrations of MVK and MACR and the solution pH. Our findings provide new insights into pathways for forming organosulfur compounds in the atmosphere and the role that transition metal ions, such as Fe³⁺, play in catalyzing these reactions

Double-Edged Role of VOCs Reduction in Nitrate Formation: Insights from Observations during the China International Import Expo 2018

Aerosol nitrate (NO3–) constitutes a significant component of fine particles in China. Prioritizing the control of volatile organic compounds (VOCs) is a crucial step toward achieving clean air, yet its impact on NO3– pollution remains inadequately understood. Here, we examined the role of VOCs in NO3– formation by combining comprehensive field measurements conducted during the China International Import Expo (CIIE) in Shanghai (from 10 October to 22 November 2018) and multiphase chemical modeling. Despite a decline in primary pollutants during the CIIE, NO3– levels increased compared to pre-CIIE and post-CIIENO3– concentrations decreased in the daytime (by −10 and −26%) while increasing in the nighttime (by 8 and 30%). Analysis of the observations and backward trajectory indicates that the diurnal variation in NO3– was mainly attributed to local chemistry rather than meteorological conditions. Decreasing VOCs lowered the daytime NO3– production by reducing the hydroxyl radical level, whereas the greater VOCs reduction at night than that in the daytime increased the nitrate radical level, thereby promoting the nocturnal NO3– production. These results reveal the double-edged role of VOCs in NO3– formation, underscoring the need for transferring large VOC-emitting enterprises from the daytime to the nighttime, which should be considered in formulating corresponding policies