When Does Multiphase Chemistry Influence Indoor Chemical Fate?

Human chemical exposure often occurs indoors, where large variability in contaminant concentrations and indoor chemical dynamics make assessments of these exposures challenging. A major source of uncertainty lies in the rates of chemical transformations which, due to high surface-to-volume ratios and rapid air change rates relative to rates of gas-phase reactions indoors, are largely gas-surface multiphase processes. It remains unclear how important such chemistry is in controlling indoor chemical lifetimes and, therefore, human exposure to both parent compounds and transformation products. We present a multimedia steady-state fugacity-based model to assess the importance of multiphase chemistry relative to cleaning and mass transfer losses, examine how the physicochemical properties of compounds and features of the indoor environment affect these processes, and investigate uncertainties pertaining to indoor multiphase chemistry and chemical lifetimes. We find that multiphase reactions can play an important role in chemical fate indoors for reactive compounds with low volatility, i.e., octanol-air equilibrium partitioning ratios (Koa) above 108, with the impact of this chemistry dependent on chemical identity, oxidant type and concentration, and other parameters. This work highlights the need for further research into indoor chemical dynamics and multiphase chemistry to constrain human exposure to chemicals in the built environment

Ozonolysis Lifetime of Tetrahydrocannabinol in Thirdhand Cannabis Smoke

Thirdhand smoke (THS) describes the persistent contamination on indoor surfaces following smoking. Cannabis THS is a chemically distinct form of THS which remains poorly characterized, relative to tobacco. Understanding its fate is necessary to mitigate exposure to cannabis smoke components and potentially harmful transformation products. In this work, the heterogeneous reaction of surface-bound Δ9-tetrahydrocannabinol (THC), a component of cannabis smoke, with ozone was examined. Cannabis smoke deposits were collected inside a Teflon chamber on glass, cotton, and tile surfaces. Samples were exposed to high (100 ppb) and realistic indoor ozone concentrations (20 ppb) inside a flow tube and to low ozone levels (2 to 29 ppb) present in a genuine indoor environment. Chemical transformations were monitored by liquid chromatography-tandem mass spectrometry (LC-MS/MS), with epoxide and dicarbonyl products detected. Rapid initial loss of THC was observed on all surfaces, but a small fraction (5%–10%) persisted for extended time scales. A short loss lifetime (a few hours) was observed for THC deposited on glass and tile under typical indoor ozone exposures, leading to almost complete loss at longer times. THC decay on cotton was approximately five times longer than on glass, with up to 10% of THC remaining after 1 week of exposure

Reaction of HOCl with Wood Smoke Aerosol: Impacts on Indoor Air Quality and Outdoor Reactive Chlorine

High loadings of biomass burning (BB) aerosol particles from wildfire or residential heating sources can be present in both outdoor and indoor environments, where they deposit onto surfaces such as walls and furniture. These pollutants can interact with oxidants in both the aerosol and deposited forms. Hypochlorous acid (HOCl), a strong oxidant emitted during cleaning with chlorine-cleaning agents such as bleach, can attain mixing ratios of hundreds of ppbv indoors; moreover, lower mixing ratios are naturally present outdoors. Here, we report the heterogeneous reactivity of HOCl with wood smoke aerosol particles. After exposure to gas-phase HOCl, the particle chlorine content increased reaching chlorine-to-organic mass ratios of 0.07 with the chlorine covalently bound as organochlorine species, many of which are aromatic. Investigating individual potential BB components, we observed that unsaturated species such as coniferaldehyde and furfural react efficiently with HOCl. These observations indicate that organochlorine pollutants will form indoors when bleach cleaning a wildfire impacted space. The chlorine component of particles internally mixed with BB material and chloride initially increased, upon HOCl exposure, indicating that active chlorine recycling in the outdoor environment will be suppressed in the presence of BB emissions

When Does Multiphase Chemistry Influence Indoor Chemical Fate?

Human chemical exposure often occurs indoors, where large variability in contaminant concentrations and indoor chemical dynamics make assessments of these exposures challenging. A major source of uncertainty lies in the rates of chemical transformations which, due to high surface-to-volume ratios and rapid air change rates relative to rates of gas-phase reactions indoors, are largely gas-surface multiphase processes. It remains unclear how important such chemistry is in controlling indoor chemical lifetimes and, therefore, human exposure to both parent compounds and transformation products. We present a multimedia steady-state fugacity-based model to assess the importance of multiphase chemistry relative to cleaning and mass transfer losses, examine how the physicochemical properties of compounds and features of the indoor environment affect these processes, and investigate uncertainties pertaining to indoor multiphase chemistry and chemical lifetimes. We find that multiphase reactions can play an important role in chemical fate indoors for reactive compounds with low volatility, i.e., octanol-air equilibrium partitioning ratios (Koa) above 108, with the impact of this chemistry dependent on chemical identity, oxidant type and concentration, and other parameters. This work highlights the need for further research into indoor chemical dynamics and multiphase chemistry to constrain human exposure to chemicals in the built environment

When Does Multiphase Chemistry Influence Indoor Chemical Fate?

Human chemical exposure often occurs indoors, where large variability in contaminant concentrations and indoor chemical dynamics make assessments of these exposures challenging. A major source of uncertainty lies in the rates of chemical transformations which, due to high surface-to-volume ratios and rapid air change rates relative to rates of gas-phase reactions indoors, are largely gas-surface multiphase processes. It remains unclear how important such chemistry is in controlling indoor chemical lifetimes and, therefore, human exposure to both parent compounds and transformation products. We present a multimedia steady-state fugacity-based model to assess the importance of multiphase chemistry relative to cleaning and mass transfer losses, examine how the physicochemical properties of compounds and features of the indoor environment affect these processes, and investigate uncertainties pertaining to indoor multiphase chemistry and chemical lifetimes. We find that multiphase reactions can play an important role in chemical fate indoors for reactive compounds with low volatility, i.e., octanol-air equilibrium partitioning ratios (Koa) above 108, with the impact of this chemistry dependent on chemical identity, oxidant type and concentration, and other parameters. This work highlights the need for further research into indoor chemical dynamics and multiphase chemistry to constrain human exposure to chemicals in the built environment

A New Approach to Characterizing the Partitioning of Volatile Organic Compounds to Cotton Fabric

Chemical partitioning to surfaces can influence human exposure by various pathways, resulting in adverse health consequences. Clothing can act as a source, a barrier, or a transient reservoir for chemicals that can affect dermal and inhalation exposure rates. A few clothing-mediated exposure studies have characterized the accumulation of a select number of semi-volatile organic compounds (SVOCs), but systematic studies on the partitioning behavior for classes of volatile organic compounds (VOCs) and SVOCs are lacking. Here, the cloth–air equilibrium partition ratios (KCA) for carbonyl, carboxylic acid, and aromatic VOC homologous series were characterized for cellulose-based cotton fabric, using timed exposures in a real indoor setting followed by online thermal desorption and nontargeted mass spectrometric analysis. The analyzed VOCs exhibit rapid equilibration within a day. Homologous series generally show linear correlations of the logarithm of KCA with carbon number and the logarithms of the VOC vapor pressure and octanol–air equilibrium partition ratio (KOA). When expressed as a volume-normalized partition ratio, log KCA_V values are in a range of 5–8, similar to the values for previously measured SVOCs which have lower volatility. When expressed as surface area-normalized adsorption constants, KCA_S values suggest that equilibration corresponds to a saturated surface coverage of adsorbed species. Aqueous solvation may occur for the most water-soluble species such as formic and acetic acids. Overall, this new experimental approach facilitates VOC partitioning studies relevant to environmental exposure

Air Quality Data Approach for Defining Wildfire Influence: Impacts on PM_2.5, NO₂, CO, and O₃ in Western Canadian Cities

As the climate warms, it is recognized that wildfires are increasing in size and frequency. The negative effects of wildfires on air quality are well documented, especially on commonly monitored atmospheric pollutants such as PM2.5, NO2, CO, and O3. However, it is not clear how frequently wildfires influence urban air quality and the size of that influence relative to traffic and industrial pollutants. To understand the impact of wildfires on air quality, we have established an automated method to identify wildfire-influenced ambient air measurements. The trajectory-fire interception method (TFIM) compares hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) back-trajectories from an air quality monitoring station to satellite imagery of fire “hot-spots” to determine the number of trajectory-fire interceptions that occur. From the number of interceptions and local PM2.5 measurements, we have defined a wildfire-influenced period to occur if the interception count is ≥20. TFIM wildfire identification compares favorably with Environment and Climate Change Canada’s smoke forecast, FireWork, and with the BlueSky trajectory-based forecast. Using TFIM, we studied the impact of wildfire-influenced periods on PM2.5, NO2, CO, and O3 from 2001 to 2019 in Western Canadian urban areas. We show that wildfire-influenced periods have elevated concentrations of PM2.5, NO2, and CO but not O3. We show that a decreasing urban baseline of CO and NO2 over time results in a relatively greater impact of wildfires on these pollutants, which emphasizes the changing relative importance of wildfires on air quality

Gas- and Particle-Phase Amide Emissions from Cooking: Mechanisms and Air Quality Impacts

The high-temperature cooking of protein-rich foods represents an important but poorly constrained source of nitrogen-containing gases and particles to indoor and outdoor atmospheres. For example, panfrying meat may form and emit these nitrogen-containing compounds through complex chemistry occurring between heated proteins and cooking oils. Here, we simulate this cooking process by heating amino acids together with triglycerides. We explore their interactions across different temperatures, triglyceride types, and amino acid precursors to form amide-containing products. Ammonia, arising from the thermal degradation of amino acids, may react with a triglyceride’s ester linkages, forming amides and promoting de-esterification reactions that break the triglyceride into volatilizable products. Additionally, triglycerides may thermally oxidize and fragment as they are heated, and the resulting oxygenated breakdown products may react with ammonia to form amides. We observed evidence for amide formation through both of these pathways, including gas-phase emissions of C2‑11H5‑23NO species, whose emission factors ranged from 33 to 813 μg total gas-phase amides per gram of amino acid precursor. Comparable quantities of particle-phase oleamide (C18H35NO) were emitted, ranging from 45 to 218 μg/g. The observed amide products had variable predicted toxicities, highlighting the importance of understanding their emissions from cooking and their ultimate inhalation exposure risks

Avoiding Regrettable Replacements: Can the Introduction of Novel Functional Groups Move PFAS from Recalcitrant to Reactive?

Per- and polyfluoroalkyl substances (PFASs) are present in a range of commercial and consumer products. These chemicals are often high-performance surfactants or nonstick/water-repellant coatings due to their chemical stability; however, this stability leads to select PFAS being environmentally persistent. To facilitate degradation, new fluorosurfactant building blocks (F7C3–O–CHF-CF2–S-CH2–CH2–OH (FESOH), F3C–O–CHF-CF2–S-CH2–CH2–OH (MeFESOH), F7C3–O–CHF-CF2–O–CH2–CH2–OH (ProFdiEOH), F7C3–O–CHF-CF2–CH2–OH (ProFEOH), and F3C–O–CHF-CF2–O–CH2–CH2–OH (MeFdiEOH)) have been systematically developed with heteroatom linkages such as ethers, thioethers, and polyfluorinated carbons. The room temperature, gas-phase OH oxidation rate constants, and products of these chemicals were monitored in an atmospheric chamber to investigate their fate in the atmosphere. Analysis was performed using online high-resolution chemical ionization mass spectrometry (CIMS) using the iodide reagent ion and via offline UPLC-MS/MS. FESOH and MeFESOH, the thioether congeners, were observed to have the largest rate constants of kFESOH = 2.82 (±0.33) and kMeFESOH = 2.17 (±0.17) (×10–12 cm3 molecules–1 s–1, respectively). First-, second-, and third-generation products of OH oxidation were observed as a function of time, while product quantification yielded ultrashort perfluoropropionic acid (PFPrA) and short polyfluoroether acid species as the terminal products for FESOH and ProFdiEOH. There was evidence for MeFESOH being fully mineralized, demonstrating the potential benign chemical architecture