ACS ES&T Air最新文献

Organic UV filters like oxybenzone (BP3) in sunscreens are seawater pollutants suspected to transfer to the atmosphere via sea spray aerosol (SSA). This study examines the photoinitiated degradation of BP3 in artificial and real seawater compared to SSA mimics containing NaCl and 4-benzoylbenzoic acid (4-BBA). We investigated pure, binary, and ternary mixtures of BP3, NaCl, and 4-BBA using solar-simulated light to isolate the effects of salt and photosensitization on BP3 degradation. Results showed significantly faster degradation in the aerosol phase (J _eff,env ≈ 10^-3-10^-2 s^-1 or t _1/2 < 10 min) compared to bulk solutions (J _eff,env ≈ 10^-6 s^-1 or t _1/2 > 1 day). The photosensitizer enhanced BP3 photodegradation in both phases more than when mixed with salt or all three components in solutions. BP3 photodegradation was most enhanced by salt in the aerosol phase. High-resolution molecular analysis via Orbitrap LC-MS/MS revealed more acutely toxic compounds (benzophenone, benzoic acid, and benzaldehyde) in irradiated aerosols than in solution, supported by electronic structure and toxicity modeling. These findings highlight that seawater may serve as a reservoir for BP3 and other organic UV filters and that upon transfer into SSA, BP3 rapidly transforms, increasing aerosol toxicity.

Organic matter (OM) is a major contributor to the oxidative potential (OP) of indoor PM_2.5. Portable air purifiers equipped with high-efficiency particulate air (HEPA) filters are known to effectively remove indoor PM_2.5 mass concentrations. However, their impacts on the OP and sources of indoor PM_2.5 OM and whether these impacts could further affect the OP of indoor PM_2.5 metals remain poorly understood. In a crossover trial, each of the 43 asthmatic children underwent a 2-week true filtration (HEPA + activated carbon [AC]) and sham filtration (no HEPA + no AC), with randomized order. PM_2.5 samples, simultaneously collected in participants’ bedrooms and outside their homes, were measured for mass concentration, composition, mass-normalized OP (OP_m, OP per mass), and volume-normalized OP (OP_v, OP_m × mass concentration). Compared to the sham filtration, indoor PM_2.5 OM mass was 34% lower, OP_m was 70% lower, and OP_v was 80% lower during true filtration. The reduction in OM OP_v was largely attributed to removing more reactive outdoor OM and indoor secondary OM. The change in OM composition also contributed to the reduced PM_2.5 metals’ OP_m. Our results suggest that indoor air purifiers with HEPA and AC filters efficiently reduce PM_2.5 OP_v by removing OM.

Little is known regarding how portable air purifiers affect the organic matter (OM) in indoor PM_2.5. This study presents evidence showing that portable air purifiers equipped with HEPA and AC filters can effectively remove the OM’s oxidative potential by removing its mass concentration and more reactive OM species.

Organic UV filters like oxybenzone (BP3) in sunscreens are seawater pollutants suspected to transfer to the atmosphere via sea spray aerosol (SSA). This study examines the photoinitiated degradation of BP3 in artificial and real seawater compared to SSA mimics containing NaCl and 4-benzoylbenzoic acid (4-BBA). We investigated pure, binary, and ternary mixtures of BP3, NaCl, and 4-BBA using solar-simulated light to isolate the effects of salt and photosensitization on BP3 degradation. Results showed significantly faster degradation in the aerosol phase (J_eff,env ≈ 10^–3–10^–2 s^–1 or t_1/2 < 10 min) compared to bulk solutions (J_eff,env ≈ 10^–6 s^–1 or t_1/2 > 1 day). The photosensitizer enhanced BP3 photodegradation in both phases more than when mixed with salt or all three components in solutions. BP3 photodegradation was most enhanced by salt in the aerosol phase. High-resolution molecular analysis via Orbitrap LC-MS/MS revealed more acutely toxic compounds (benzophenone, benzoic acid, and benzaldehyde) in irradiated aerosols than in solution, supported by electronic structure and toxicity modeling. These findings highlight that seawater may serve as a reservoir for BP3 and other organic UV filters and that upon transfer into SSA, BP3 rapidly transforms, increasing aerosol toxicity.

When exposed to solar-simulated light, oxybenzone (a sunscreen active ingredient) is long-lasting in seawater but rapidly degrades in sea spray aerosol mimics, forming toxic photoproducts.

Air quality managers in areas exceeding air pollution standards are motivated to understand where there are further opportunities to reduce NO _x emissions to improve ozone and PM_2.5 air quality. In this project, we use a combination of aircraft remote sensing (i.e., GCAS), source apportionment models (i.e., CAMx), and regression models to investigate NO _x emissions from individual source-sectors in Houston, TX. In prior work, GCAS column NO₂ was shown to be close to the "truth" for validating column NO₂ in model simulations. Column NO₂ from CAMx was substantially low biased compared to Pandora (-20%) and GCAS measurements (-31%), suggesting an underestimate of local NO _x emissions. We applied a flux divergence method to the GCAS and CAMx data to distinguish the linear shape of major highways and identify NO₂ underestimates at highway locations. Using a multiple linear regression (MLR) model, we isolated on-road, railyard, and "other" NO _x emissions as the likeliest cause of this low bias, and simultaneously identified a potential overestimate of shipping NO _x emissions. Based on the MLR, we modified on-road and shipping NO _x emissions in a new CAMx simulation and increased the background NO₂, and better agreement was found with GCAS measurements: bias improved from -31% to -10% and r² improved from 0.78 to 0.80. This study outlines how remote sensing data, including fine spatial information from newer geostationary instruments, can be used in concert with chemical transport models to provide actionable information for air quality managers to identify further opportunities to reduce NO _x emissions.

Air quality managers in areas exceeding air pollution standards are motivated to understand where there are further opportunities to reduce NO_x emissions to improve ozone and PM_2.5 air quality. In this project, we use a combination of aircraft remote sensing (i.e., GCAS), source apportionment models (i.e., CAMx), and regression models to investigate NO_x emissions from individual source-sectors in Houston, TX. In prior work, GCAS column NO₂ was shown to be close to the “truth” for validating column NO₂ in model simulations. Column NO₂ from CAMx was substantially low biased compared to Pandora (−20%) and GCAS measurements (−31%), suggesting an underestimate of local NO_x emissions. We applied a flux divergence method to the GCAS and CAMx data to distinguish the linear shape of major highways and identify NO₂ underestimates at highway locations. Using a multiple linear regression (MLR) model, we isolated on-road, railyard, and “other” NO_x emissions as the likeliest cause of this low bias, and simultaneously identified a potential overestimate of shipping NO_x emissions. Based on the MLR, we modified on-road and shipping NO_x emissions in a new CAMx simulation and increased the background NO₂, and better agreement was found with GCAS measurements: bias improved from −31% to −10% and r² improved from 0.78 to 0.80. This study outlines how remote sensing data, including fine spatial information from newer geostationary instruments, can be used in concert with chemical transport models to provide actionable information for air quality managers to identify further opportunities to reduce NO_x emissions.

Sector NO_x emissions in Houston, Texas are constrained by combining GCAS remote sensing NO₂ measurements and source apportioned chemical transport modeling using regression analysis; on-road NO_x underestimated, shipping NO_x overestimated.

Per- and polyfluoroalkyl substances (PFAS) are persistent, widely spread, and harmful pollutants. They can travel through the air, be transformed by radicals, and deposit into water or onto surfaces. They enter the atmosphere via direct emission, degradation of precursors, or aerosol formation. A recent investigation found novel compounds in rainwater, meaning PFAS may undergo transformations in the atmosphere. These transformations might exhibit distinct behavior compared to more well-researched reactions, creating difficulties in the identification of any new compounds being produced. Using density functional theory (DFT), we simulated reactions of PFAS with a major atmospheric radical, the hydroxyl radical, revealing activation energies and other thermodynamic insights. The activation energies aid in predicting likely reactions and understanding speciation. Identifying new species can guide future analyses and remediation efforts. We focused on the nine most widely studied families of PFAS, finding that radical abstraction along the alkyl chain is favored over functional groups regardless of chain length. These results establish a new foundation for understanding PFAS transformations in the atmosphere, especially when decarboxylation is not followed.

Brown carbons (BrCs) play a pivotal role in the light absorption by aerosol particulates by exerting a positive radiative forcing effect that contributes to global warming. Beyond impacts on radiative balance, some BrCs, as photosensitizers, can generate reactive triplet-state molecules toward various atmospheric molecules upon photoexcitation. The significance of photosensitization has been increasingly recognized, particularly in the context of escalated global wildfire incidents that emit substantial BrCs. We focus on the complex atmospheric photosensitization by discussing the current challenges, including (1) the diverse reactivities of the photosensitizer mixture in atmospheric particles, (2) the methodologies for investigating photosensitization processes, (3) the driving factors of photosensitization, and (4) the typical pathways and mechanisms of atmospheric photosensitized reactions. Lastly, we advise future research to focus on the refined parametrization of triplet and singlet oxygen concentrations, alongside their complex reactivities.

Atmospheric photosensitization, especially in light-absorbing particles, can drive secondary pollutant formation under light. This work comprehensively discusses the existing findings, remaining challenges, and future directions in this emerging research field.

Ground-level ozone, a highly reactive air pollutant, is known to cause significant damage to biological surfaces. Understanding the interaction between ozone and pollen is crucial, as it may influence pollen allergenicity and reproductive viability. Measurements were conducted to determine the kinetics and extent of ozone uptake for 12 different types of tree pollen (Birch, Sycamore Maple, Box Elder Maple, Alder Gray, Cypress, Ash, Mulberry, Juniper, White Pine, Lombardy Poplar, Red Oak, and Black Oak). The results revealed an initial rapid uptake of ozone, followed by a gradual decline due to the saturation of surface reaction sites and the depletion of reactive substances. The geometric initial uptake coefficients (γ₀-geo) ranged from 0.4 to 6.4 ×  10^–5, and surface saturation was reached under our experimental conditions on a time scale of 1500–10,000 s. Using the integrated uptake of ozone over the observation period, we calculated surface site concentrations of 10¹⁴–10¹⁶ sites cm^–2. Most experiments were performed under dry conditions, but tests with Birch at intermediate relative humidities, up to 60%, showed that the presence of water may decrease the uptake coefficient by a factor of 2. When Ash, Birch and Black Oak pollen grains were manually crushed to mimic subpollen particles, they were found to take up orders of magnitude more ozone for the same mass of pollen. For pollen grains washed in acetone to extract soluble molecules from the pollen coat, the cumulative ozone uptake for some pollen types was significantly reduced. This reduction was interpreted to arise as a loss of reactive surface sites and lipids with C═C bonds, which are crucial for ozone interactions. The presence of highly antioxidant molecules, like carotenoids in Ash, was confirmed spectroscopically, and linked to the extremely high cumulative uptake of ozone, suggesting a protective role for the pollen coat. A box model representing diurnally varying emissions, ozone oxidation and deposition was used to estimate the typical extent of oxidation of airborne pollen. The model indicated that surface oxidation peaked in the afternoon and evening concurrent with high ozone levels, and the percent oxidation ranged from 24% to 97% depending on the pollen species. Sensitivity analysis suggested that conclusively determining whether pollen grains are fully oxidized or unoxidized in the atmosphere is challenging. Instead, the extent of oxidation falls within a range that warrants further investigation into its impact on pollen and human exposure.

The secondary organic aerosol (SOA) production from the reactions of anthropogenic large volatile (VOCs) and intermediate volatility organic compounds (IVOCs) with hydroxyl radicals under high NO_x conditions was investigated. The organic compounds studied include cyclic alkanes of increasing size (amylcyclohexane, hexylcyclohexane, nonylcyclohexane, and decylcyclohexane) and aromatic compounds (1,3,5-trimethylbenzene, 1,3,5-triethylbenzene and 1,3,5-tritert-butylbenzene). A considerable amount of SOA was formed from all examined compounds. For the studied cyclohexanes (C₁₁–C₁₆) there appears that the SOA yield depends nonlinearly on the length of their substitute chain. The large cyclohexanes had higher yields than the aromatic compounds, but the aromatic precursors produced a more oxidized SOA. This was due to the production of lower volatility and O:C first generation products by the cyclohexanes. Most oxidation products (with C* < 10⁴ μg m^–3) in the case of cyclohexanes are SVOCs (∼50%), while of aromatics are IVOCs (∼60%). Structure, molecular size, and length of the substitute chain of the parent hydrocarbon were found to play key roles in SOA formation, oxidation state, and volatility. The SOA volatility distribution, effective vaporization enthalpy, and effective accommodation coefficient were also quantified by combining SOA yields, thermodenuder (TD) and isothermal dilution measurements. Parameterizations for the Volatility Basis Set (VBS) are proposed for future use in chemical transport models.

SOA production from large anthropogenic aromatic and cyclic alkanes oxidized with hydroxyl radicals under high NO_x conditions is explored and parameterized for the Volatility Basis Set.

The secondary organic aerosol (SOA) production from the reactions of anthropogenic large volatile (VOCs) and intermediate volatility organic compounds (IVOCs) with hydroxyl radicals under high NO _x conditions was investigated. The organic compounds studied include cyclic alkanes of increasing size (amylcyclohexane, hexylcyclohexane, nonylcyclohexane, and decylcyclohexane) and aromatic compounds (1,3,5-trimethylbenzene, 1,3,5-triethylbenzene and 1,3,5-tritert-butylbenzene). A considerable amount of SOA was formed from all examined compounds. For the studied cyclohexanes (C₁₁-C₁₆) there appears that the SOA yield depends nonlinearly on the length of their substitute chain. The large cyclohexanes had higher yields than the aromatic compounds, but the aromatic precursors produced a more oxidized SOA. This was due to the production of lower volatility and O:C first generation products by the cyclohexanes. Most oxidation products (with C* < 10⁴ μg m^-3) in the case of cyclohexanes are SVOCs (∼50%), while of aromatics are IVOCs (∼60%). Structure, molecular size, and length of the substitute chain of the parent hydrocarbon were found to play key roles in SOA formation, oxidation state, and volatility. The SOA volatility distribution, effective vaporization enthalpy, and effective accommodation coefficient were also quantified by combining SOA yields, thermodenuder (TD) and isothermal dilution measurements. Parameterizations for the Volatility Basis Set (VBS) are proposed for future use in chemical transport models.