ACS ES&T Air最新文献

This study leverages explainable machine learning, specifically XGBoost models with Shapley Additive Explanations (SHAP), to explore the chemical properties of atmospheric aerosols in Seoul, Korea, during the summer of 2019. Focusing on non-refractory particulate matter (NR-PM₁) properties measured by high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), the research extends to organic aerosol (OA) sources identified via positive matrix factorization of high-resolution MS data. The models achieved good predictive accuracy (R² > 0.90) for all species concentrations, except for hydrocarbon-like OA (HOA) due to frequent concentration fluctuations. The model outcomes aligned well with those previously achieved using conventional methods (chemical transport model and correlational analysis), confirming that relative humidity is associated with nocturnal nitrate concentration and photochemistry associated with sulfate concentration in the summertime in Seoul. Importantly, the models revealed mostly nonlinear relationships between atmospheric factors, such as temperature and particulate matter (PM) components, thereby deepening the understanding of formation processes. Notably, different potential formation mechanisms were discerned for more oxidized oxygenated OA (MO-OOA) and oxidized primary OA (OPOA). For MO-OOA, SHAP analysis showed a plateau in SHAP values at an O_x concentration of 0.085 ppm, which suggested potential fragmentation from further oxidation and agreed with previous chamber experiments. Conversely, the lack of a plateau in the O_x values for OPOA implied potential ongoing oxidation, suggesting a higher and longer atmospheric oxidation potential. This approach offers rapid and potential insights into complex atmospheric aerosol formation processes. It is essential to acknowledge that SHAP values do not establish causality, and knowledge of the underlying physical and chemical processes was required to conclude valid and comprehensive interpretations of the ML results.

This study represents a pioneering effort in applying explainable machine learning techniques to HR-ToF-AMS data, achieving rapid results yet providing potential insights of OA formation mechanisms, such as the oxidation turning point for MO-OOA and OPOA.

This work, as part of the Georgia Wildland fire Simulation Experiment (G-WISE) campaign, explores the aqueous photolysis of water-soluble brown carbon (W-BrC) in biomass burning aerosols from the combustion of fuel beds collected from three distinct ecoregions in Georgia: Piedmont, Coastal Plain, and Blue Ridge. Burns were conducted under conditions representative of wildfires, which are common unplanned occurrences in Southeastern forests (low fuel moisture content), and prescribed fires, which are commonly used in forest management (higher fuel moisture content). Upon exposure to radiation from UV lamps equivalent to approximately 5 h in the atmosphere, the absorption spectra of all six samples exhibited up to 40% photobleaching in the UV range (280–400 nm) and as much as 30% photo-enhancement in the visible range (400–500 nm). Together, these two effects reduced the absorption Ångström exponent (AAE), a measure of the wavelength dependence of the spectrum, from 6.0–7.9 before photolysis to 5.0–5.7 after. Electrospray ionization ultrahigh-resolution mass spectrometry analysis shows the potential formation of oligomeric chromophores due to aqueous photolysis. This work provides insight into the impacts that aqueous photolysis has on W-BrC in biomass burning aerosols and its dependence on fuel bed composition and moisture content.

This work studies the effect of UV photolysis on the absorption spectra and chemical composition of the water-soluble fraction of biomass burning aerosol generated from simulated wildfire and prescribed burning of fuel beds from three different ecoregions.

Recent studies reveal that urea (CO(NH₂)₂) is often a significant component of tropospheric reactive nitrogen in both the gas- and the condensed-phases; however, little is known about urea sources and sinks. Although it is generally assumed that deposition is the major sink, aqueous reactions in aerosols and clouds may be possible but have yet to be considered. Here, we report a study of the aqueous reactions of urea with methylglyoxal as a function of pH using optical property measurements as a proxy for reaction. UV-vis absorption spectroscopy is used to monitor bulk-phase browning while cavity ringdown and photoacoustic spectroscopies are used to measure the aerosol optical properties. We observe the reaction of urea with methylglyoxal produces brown carbon at low and high pH, with little absorption at mid-pH ranges. The urea brown carbon products absorb well into the visible range, providing a greater overlap with the solar emission spectrum than previously studied brown carbon systems including that of methylglyoxal and ammonium. These experiments suggest that urea could be chemically transformed in aqueous aerosol with the products contributing to aerosol absorption.

We perform temperature-programmed desorption (TPD) directly on cryo-milled polymeric samples with selected ion flow tube mass spectrometry, SIFT-MS, to measure outgassing kinetics and the onset of thermal decomposition. Specifically, we monitored siloxane outgassing from the silicone elastomer encapsulant Sylgard 184. The TPD spectra reveal a rich and complex VOC emission landscape up to the point of thermal decomposition. We performed experiments at multiple ramp rates and successfully applied Kissinger analysis to all observed emission peaks, which indicated activation energies in the range of 30–55 kJ/mol and exponential prefactors of 10²–10⁵ s^–1. Finally, we relate reagent ion depletion in the SIFT-MS and total mass loss from thermogravimetric analysis (TGA) and find that the two techniques agree well on the onset of thermal decomposition, which was found to be approximately 250 °C. This novel application of TPD-SIFT-MS to obtain emission kinetics could prove useful in indoor air quality studies, where understanding the rate of VOC emission is crucial for model development.

In March 2023, Pakistan’s Cabinet approved a Clean Air Policy which established ambient air quality targets and identified priority actions in the major air pollutant-emitting sectors. This work describes a quantitative air pollutant and greenhouse gas mitigation modeling assessment at national and subnational scale that provided evidence to inform Pakistan’s Clean Air Policy. Air pollutant emissions are quantified historically (2010–2021) and projected to 2050 for baseline (without implementation of mitigation measures) and for scenarios which model the implementation of 18 specific mitigation measures. The assessment identified five major air pollutant-emitting sources nationally: Households (35% national total primary PM_2.5 emissions), Transport (5%), Industry (16%), Agriculture (17%), and Waste (24%). Pakistan’s Clean Air Policy identifies a priority mitigation measure for each of these sectors, which collectively could reduce national PM_2.5 emissions by 36.4% in 2030 compared to the baseline. Full implementation of all 18 mitigation measures would reduce primary PM_2.5 emissions by 80% in 2050 compared with the baseline. Developing a Clean Air Policy was committed to in Pakistan’s Nationally Determined Contribution (NDC) to help achieve Pakistan’s climate change commitment while improving public health. This study shows that the Clean Air Policy could also have benefits for Pakistan meeting its climate change goals, with an estimated 5% reduction in carbon dioxide emissions and 42% reduction in methane emissions achievable by 2050 from full implementation of the actions evaluated in this assessment. As Pakistan’s Clean Air Policy is implemented, progressively updating this air pollutant and climate change mitigation assessments can help track progress on its achievement.

In 2023, Pakistan published a Clean Air Policy to improve air quality. This study shows how its implementation could reduce emissions of air pollutants by up to 80% by 2050.

This study investigates the relationship between aircraft activities and ultrafine particle (UFP) concentrations near a regional airport in Toronto, Canada, positioned within a mile southwest of a densely populated downtown neighborhood. The analysis particularly considers the effect of the southerly winds on the UFP emissions from the airport. To achieve this, we conducted a measurement campaign at five locations between June 2022 and August 2022. Concurrently, detailed aircraft activity data were collected. Turboprop and propeller aircraft were the predominant categories. Results indicate a 20% increase in mean UFP levels north of the airport when winds originated from the south or southwest, coinciding with aircraft predominantly taking off eastward and landing westward on the runway. Smaller, older aircraft, often used for flight training and corporate travel, significantly contributed to UFP spikes, surpassing 50000 particles/cm³. In contrast, the prevalent large commercial aircraft had a lesser impact on UFP spikes. Airport activities are the primary source of UFP in the neighborhood. Under southerly winds, at the Ferry Terminal near the airport, diesel ferry operations, background UFP levels, and airport activities contributed 8%, 32%, and 60% of UFP concentrations, respectively.

After being transported from outdoor to indoor environments, a large portion of ozone (O₃) reacts with indoor chemicals to generate O₃ reaction products. A fraction of these products can partition to fine particulate matter (PM_2.5). Hence, we hypothesize that PM_2.5 serves as a carrier to deliver O₃ reaction products to the deep lung, leading to synergistic adverse pulmonary effects. In a panel study involving 43 children with asthma, each was assessed 4 times (2-week interval) for biomarkers of respiratory pathophysiology and personal exposures to PM_2.5 and O₃. We also assessed O₃ loss exposures, calculated by taking the difference between the outdoor and indoor O₃ concentrations, which was proportional to the net exposure to O₃ reaction products. We found the adverse effects of O₃ loss exposure on biomarkers of pulmonary inflammation, airway (especially lower airway) mechanics, and spirometry lung function were greater at higher PM_2.5 exposure levels. We also found that the adverse effects of PM_2.5 exposure were greater at higher O₃ loss exposure levels. This suggests an additional mechanism for the synergistic pulmonary effects: PM_2.5 predisposes the lung to be more susceptible to O₃ reaction products and vice versa. However, our data is limited in differentiating the two potential mechanisms.

Little is known regarding the health impacts of O₃ reaction products. This study presents mechanistic explanations for the synergistic effects of O₃ reaction products and PM_2.5 on respiratory pathophysiology.

The present study investigates the reaction characteristics and mechanisms involved in the aqueous-phase photooxidation of vanillin (VL) in the presence of nitrite (NO₂^–). The research entails a comprehensive analysis of the decay kinetics of VL, the composition of reaction products, and changes in absorbance under different pH conditions and VL/NO₂^– molar ratios. The results indicate a notably rapid decay rate of VL under acidic conditions, with the VL/NO₂^– molar ratio emerging as a crucial factor in the photooxidation process. Notably, the photoreaction between VL and NO₂^– leads to the formation of aqueous-phase secondary organic aerosols (aqSOA) comprising hydroxylation products, nitration products, and oligomers that exhibit strong absorption in the near-ultraviolet and visible light regions. The research findings, through theoretical calculations, shed light on the reaction pathways involved in the photooxidation process. This investigation contributes valuable insights into the atmospheric aqueous-phase photooxidation of phenolic compounds initiated by NO₂^–. The obtained results are particularly significant for understanding the formation and evolution of aqSOA and brown carbon (BrC).

This work presents a detailed theoretical study of the CHF₂OCH₂CF₂CHF₂ + OH reaction and its atmospheric implications. Twelve conformers of CHF₂OCH₂CF₂CHF₂ have been identified, and the three lowest energy conformers below 4.184 kJ mol^–1 were considered in this work. The rate coefficient is calculated using the DFT-based M06-2X/6-311++g(d,p) method combined with canonical transition state theory (CTST) and variable reaction coordinates–variational transition state theory (VRC-VTST). At 298 K, our calculated rate coefficient of 2.96 × 10^–14 cm³ molecule^–1 s^–1 is very close to the experimental result. This work investigates the ozone formation potential (OFP) and atmospheric degradation pathways of CHF₂OCH₂CF₂CHF₂.