Andrey Khlystov

Deriving a volatility basis set (VBS) from measurements of particle evaporation in a thermodenuder or single-particle levitation apparatus has traditionally relied on repeated numerical solution of the evaporation equations to find the VBS that best reproduces observed particle sizes. This approach is computationally demanding and offers little insight into the factors that control the retrieval. Building on the characteristic-time framework of Khlystov (2024), it is shown that the mass fraction remaining of each volatility bin can be expressed through a single integral evaluated directly from the measured particle-size evolution. This reduces VBS retrieval to a constrained linear inversion, eliminating iterative integration of differential equations and making the method about four orders of magnitude faster than the conventional approach. The temperature dependence of the saturation concentration and Kelvin effect is included in the inversion, and the enthalpy of vaporization may be prescribed per bin or retrieved as a single volatility-dependence parameter. Applied to thermodenuder thermograms measured at Duke Forest, NC, and Reno, NV, the method reproduces the VBS obtained with the conventional technique while requiring milliseconds rather than minutes. Using synthetic measurements, we quantify the method's accuracy and sensitivity to assumed surface tension and thermogram temperature resolution. The ambient thermograms constrain the enthalpy of vaporization dependence on bin volatility to be much weaker than the commonly assumed parameterization, with a steep dependence incompatible with the gradual evaporation observed. The method enables rapid processing of large volatility datasets and provides guidance for the design of evaporation measurements.

The increasing use of flavored electronic cigarettes (e-cigarettes) raises concerns about their potential impact on the emission of harmful chemicals, particularly carbonyl compounds. This study systematically examines the effects of eight representative flavoring chemicals from four major classes including esters (ethyl acetate, ethyl butyrate), alcohols (menthol, ethyl maltol), aromatic aldehydes (benzaldehyde, vanillin), and terpenes (limonene, linalool) under varying power outputs (50 and 90 W), base liquid composition [propylene glycol (PG)/vegetable glycerin (VG) ratios (80:20, 50:50, and 20:80)], and flavor concentrations (1 and 5 mg/mL). Across all conditions, flavored e-liquids tend to produce carbonyl emissions that are higher than those of unflavored controls. Terpene-based flavors showed the strongest effects, with formaldehyde emissions being up to 2-fold higher and acrolein emissions up to 8-fold higher, frequently exceeding short-term exposure limits. Aromatic aldehydes and alcohols also increased emissions, though to a lesser extent, while esters showed smaller or inconsistent effects. The influence of flavors was further modulated by their concentration, PG/VG ratio, and device power, with higher concentration, VG content, and power amplifying emissions. These results highlight the complex interactions among e-liquid composition, flavor class, and vaping conditions, demonstrating that certain flavorings substantially elevate toxicant emissions. These findings underscore the importance of considering flavor composition, device power, and base material in evaluating the potential health risks associated with e-cigarette use.

Introduction: This study evaluated the performance of three carbonyl collection media that are frequently used in electronic cigarette (e-cig) studies, namely: 2,4-Dinitrophenyl hydrazine (DNPH) silica impregnated cartridges (C), a DNPH-coated glass fiber filter (DF), and an impinger with a DNPH solution (I). Methods: These collection methods were tested with a ‘mod’ and a ‘pod’ e-cigs that represent devices producing different amounts of e-cig aerosols. The tests were performed using two different puff topography regimes to investigate the effect of puff flow rate on carbonyl collection efficiency. Carbonyls emitted from the e-cigs were collected using I-I (two impingers in series), C (a single DNPH cartridge), and DF-C (a DNPH filter followed by a DNPH cartridge). Samples were analyzed using high-performance liquid chromatography coupled with photodiode array detector. Results: Measured carbonyl levels varied between the three methods. For both devices, the highest values were measured with C and DF-C. Results from the ‘pod’ device measured with I-I were comparable with the other methods, but lower than the other two methods for the ‘mod’ device. For example, 1 LPM ‘mod’ acetaldehyde emissions measured with C (0.09 ± 0.02 µg/puff) and DF-C (0.14 ± 0.09 µg/puff) were significantly higher (p = 0.06 and 0.04, respectively) than I-I method (0.05 ± 0.02 µg/puff). Discussion: The likely cause for the underestimation by the I-I method is the inefficient collection of particle phase bound carbonyls by the impingers and, possibly, wall losses in the inlet of the impinger. Based on our results, C provides the best approach for carbonyl collection in e-cig aerosols, while I-I that is used in the standard testing method can underestimate carbonyl emissions when measuring high concentration aerosols such as those produced by ‘mod’ devices.

Rationale: Chemical aging of biological aerosols (bioaerosols) and their constituents in the atmosphere have not been well characterized so far. Thus, the goal of this research is to test the hypothesis that bioaerosol constituents undergo chemical transformations via simulated atmospheric oxidation by the hydroxyl radical (OH٠). Methodology: An oxidation flow reactor (OFR) was used in this work to expose pollen constituents and extracts of two pollen species (lodgepole pine and aspen) to OH٠ approximating 4.5 days of equivalent atmospheric age. Thermo-optical analysis and liquid and gas chromatography coupled to mass spectrometry were used to quantify changes in chemical composition upon oxidation. Results: The organic mass to organic carbon ratio (OM/OC) of pollen extracts increased. Saccharides did not decrease appreciably upon oxidation in the OFR. In contrast, oxidation of the free amino acid proline resulted in hydroxyproline formation. Changes in the abundance of individual amino acids upon oxidation of the aerosolized pollen extracts, notably an increase in hydroxyproline and otherwise general decreases in abundance of other free amino acids, were observed. Discussion: The results indicate that bioaerosol chemical composition can change significantly due to atmospheric photochemical transformations. Such transformations may lead to OM/OC ratios higher than those of other aerosol types, and those previously assumed for bioaerosols, potentially informing new estimates for elemental signatures of aged bioaerosols in future atmospheric budgeting studies. The observed formation of photochemical oxidation products (e.g. hydroxyproline) suggests potential chemical tracers for aged bioaerosols, and implies that health effects of bioaerosols could be modified while in the atmosphere, necessitating further investigation.

This study aims to understand the effects of wildfires in sagebrush ecosystem on soil properties by examining connections between Soil Water Repellency (SWR), reflectance, and chemistry. Ash and burned soil samples were collected after performing laboratory burns of three common sagebrush plants: sagebrush, rabbitbrush, and bitterbrush. The collected samples were analyzed for their physical properties, including SWR measured by Water Drop Penetration Time (WDPT) and Apparent Contact Angle (ACA), and solar spectral reflectance in the wavelength range of 350 to 2500 nm. Chemical functional groups of the samples were analyzed using Fourier-Transform Infrared (FTIR) spectroscopy. WDPT and ACA values were in the range of 1 to 600 s and ~10° to 88°, respectively, for all three tested fuels. The FTIR analysis showed a decrease (~2 to 4 times) in the ratio of COO⁻/C=C signals for the burned soil samples compared to the unburned soil samples. Overall, increase in temperature and ACA levels for the samples of burned and burned soil from a 2 cm depth led to increased formation of non-polar compounds with C=C functional groups, and decarboxylation.

The chemistry and atmospheric fate of biological aerosols (bioaerosols) have been largely unexplored, despite their significant contribution to atmospheric particulate matter and organic carbon. Although bioaerosols are typically larger than anthropogenic aerosols, up to 100 µm, they can be transported over long distances and thus affect cloud physics (CCN, IN) and play a role in atmospheric chemical reactions. Studies have found that bioaerosols are expected to increase in concentration due to rapid climate change. For example, pollen concentrations are anticipated to increase by 21% and the pollen season length to increase by 21 days. Further, increases in instances and intensities of harmful algal blooms are already being observed. Due to the growing importance of bioaerosols in the atmosphere and climate, the goal of this study was to determine the effects of simulated atmospheric aging on bioaerosol functional groups and polarity. Water extracts of bioaerosols, lodgepole pine pollen and spirulina algae, were aged in a Suntest CPS solar simulator for 24 hours, under simulated solar radiation and in the presence of H2O2 to promote oxidation with OH radicals. Proton Nuclear Magnetic Resonance Spectroscopy(1H-NMR) and Fourier-Transform Infrared Spectroscopy (FTIR) analyses were performed for fresh and aged bioaerosol extracts. FTIR results show an increase in polarity of both bioaerosols after aging with simulated solar radiation, up to 30.9% in pollen and 27.5% in algae, whereas 1H-NMR results are more complex, and a clear polarity increase was not observed. To our knowledge, this is the first study to analyze the effects of atmospheric aging on the chemistry of bioaerosols.

Wildfires are a major source of aerosols during summer in the western United States. Aerosols emitted from wildfires could significantly affect air quality, human health, and the global climate. This study conducted a comparison of aerosol characteristics during wildfire smoke-influenced and non-smoke-influenced days. Ambient particle size distribution (PSD) data were collected in Reno, Nevada, between July 2017 and October 2020. During this period, the site was impacted by smoke from over a hundred wildfires burning in a wide range of ecosystems in the western United States located at different distances from the measurement site. The smoke-influenced days were identified using satellite images, a hazard mapping system, and wind back-trajectory. Positive matrix factorization (PMF) was applied to identify the main sources and their characteristics. The wildfire aerosols were observed to have a number mode diameter of 212 nm, which is significantly larger than aerosols on non-smoke-influenced days (61 nm). In addition to the increase in particle size, wildfires made a large contribution to PM_2.5 and CO concentrations. During fire-prone months (July, August, and September) from 2016 to 2021, 56% to 65% of PM_2.5 and 18% to 26% of CO concentrations could be attributed to wildfire emissions in the study area. On an annual basis, wildfire emissions were responsible for 35% to 47% of PM_2.5 concentrations and 5% to 12% of CO concentrations.

Bioaerosols, or aerosol particles of biological origin, have been found to represent a significant mass fraction of atmospheric particulate matter (PM) and organic carbon (OC). These particles are larger in size (up to 100 µm) than most anthropogenic aerosols but are lighter and thus can be transported over long distances, affecting atmospheric processes and cloud physics (i.e., act as cloud condensation nuclei). Moreover, climate change is expected to increase pollen number concentrations (~21%) as well as pollen season length (+21 days) across North America. So far, only a few studies have been conducted on the chemical composition of bioaerosols and their behavior under atmospheric conditions. The goal of this research was to characterize the chemical composition of bioaerosols using multiple analytical techniques, such as Proton Nuclear Magnetic Resonance Spectroscopy (1H-NMR), Gas Chromatography-Mass Spectrometry (GC-MS), and Ultra-High Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS), thereby advancing atmospheric aerosol chemistry. Various common bioaerosols, including pollen, algae, fungi, and bacteria, are analyzed, and characterized under controlled laboratory conditions. All samples are analyzed for their chemical composition: saccharides with GC-MS, amino acids and fatty acids with UPLC-MS, and functional groups with 1H-NMR spectroscopy. The present research is one of the first studies of detailed chemical characterization of bioaerosols with the 1H-NMR technique, where the 1H-NMR results are also compared with GC- and UPLC-MS quantitative analyses of individual bioaerosol species.