Polycyclic aromatic hydrocarbons (PAHs) and their nitrated and oxygenated derivatives (NPAHs, OPAHs) are semivolatile air pollutants which may re-volatilise following atmospheric deposition to soil. Here, we determined polycyclic aromatic compounds' (PACs) concentrations in air, topsoil and air equilibrated with soil at a rural grassland site and a boreal forest site. The samples were analysed by GC-MS/MS and the flux was studied by fugacity calculations and a micrometeorological flux-gradient method. In soil at the boreal site, OPAH and NPAH contributed much higher fractions to PAC contamination of air and soil than at the rural site, reflecting the conversion of primary PACs during transport from sources. The same number of PACs in soil have reached equilibrium concentration with air, despite one site being in a polluted and PAC source region and the other in a much less polluted and PAC receptor region. The direction of air-soil exchange was found insensitive to the modest day-night temperature variation at both sites. Upward diffusive flux was observed for one PAH, triphenylene, at the rural grassland site, and for three 3-ring PAHs and naphthaldehyde at the boreal forest site. There, emission fluxes were quantified and ranged 0.5-12 ng m-2 h-1. The results indicate that low molecular weight PAH secondary emissions in a receptor region may be of same order of magnitude as domestic primary emissions.

Volatile chemical products (VCPs) in urban environments account for a significant portion of the volatile organic compounds (VOCs), enhancing the production of tropospheric ozone and secondary organic aerosols. Residential areas are an important source of VCPs in the urban environment, though few studies have examined the emission of VCPs in metropolitan areas from subtropical regions. To bridge the knowledge gap, this study aims to analyze the concentration and emission of D5-siloxane, a compound typically served as a tracer to characterize VCP emission from residential areas. The Texas A&M mobile laboratory, equipped with a Vocus 2R Chemical Ionization Mass Spectrometer (CIMS), and other gas and particle analyzers, continuously sampled the ambient gas phase concentration of D5-siloxane during a field deployment in a residential neighborhood near Houston, TX. A 0-D box model combining Planetary Boundary Layer Height (PBL) height, hourly D5-siloxane concentration, gas deposition velocities, and D5-siloxane reaction rate with hydroxyl radicals was constructed to represent emissions during our sampling period to derive the emission intensities of D5-siloxane. Monte Carlo statistical analysis was performed to gain insights into the emission profile of D5-siloxane, showing higher emission rates compared with other cities in North America but comparable to emissions of European cities. This study presents time-series concentrations and emissions of D5-siloxane in a subtropical residential area during the wintertime. The findings illustrate the temporal profile of D5-siloxane in a typical residential neighborhood in the Southeast United States and provide valuable data to enhance model parameterizations.

Per- and polyfluoroalkyl substances (PFAS) are prevalent in consumer products used indoors. However, few measurements of ionic PFAS exist for indoor air. We analyzed samples collected on PM2.5 quartz fiber filters (QFFs) in 11 North Carolina homes 1-3 times in living rooms (two QFFs in series), and immediately outside each home (single QFF), for 26 ionic PFAS as part of the 9 months Indoor PFAS Assessment (IPA) Campaign. All targeted PFAS, except for PFDS and 8:2 monoPAP, were detected indoors. PFBA, PFHpA, PFHxA, PFOA, PFOS, and 6:2 diPAP were detected in >50% of indoor samples. PFHxA, PFOA, and PFOS had the highest detection frequency (DF = 80%; medians = 0.5-0.7 pg m(-3)), while median PFBA concentrations (3.6 pg m(-3); DF = 67%) were highest indoors. Residential indoor air concentrations (sum of measured PFAS) were, on average, 3.4 times higher than residential outdoor air concentrations, and an order of magnitude higher than regional background concentrations. Indoor-to-outdoor emission rate estimates suggest that emissions from single unit homes could be a meaningful contributor to PFBA, PFOA, and PFOS emissions in populated areas far from major point sources. Backup QFFs were observed to adsorb some targeted PFAS from the gas-phase, making reported values upper-bounds for particle-phase and lower-bounds for total air (gas plus particle) concentrations. We found that higher concentrations of carbonaceous aerosol were associated with a shift in partitioning of short chain PFCAs and long chain PFSAs toward the particle phase.

Previous time-integrated (2 h to 4 h) measurements show that total gas-phase water-soluble organic carbon (WSOCg) is 10 to 20 times higher inside homes compared to outside. However, concentration dynamics of WSOCg and total particle phase WSOC (WSOCp)-are not well understood. During the Chemical Assessment of Surfaces and Air (CASA) experiment, we measured concentration dynamics of WSOCg and WSOCp inside a residential test facility in the house background and during scripted activities. A total organic carbon (TOC) analyzer pulled alternately from a particle-into-liquid sampler (PILS) or a mist chamber (MC). WSOCg concentrations (215 +/- 29 mu g-C m-3) were generally 36x higher than WSOCp (6 +/- 3 mu g-C m-3) and 20x higher than outdoor levels. A building-specific emission factor (Ef) of 31 mg-C h-1 maintained the relatively high house WSOCg background, which was dominated by ethanol (46 mu g-C m-3 to 82 mu g-C m-3). When we opened the windows, WSOCg decayed slower (2.8 h-1) than the air change rate (21.2 h-1) and Ef increased (243 mg-C h-1). The response (increased Ef) suggests WSOCg concentrations are regulated by large near surface reservoirs rather than diffusion through surface materials. Cooking and ozone addition had a small impact on WSOC, whereas surface cleaning, volatile organic compound (VOC) additions, or wood smoke injections had significant impacts on WSOC concentrations. WSOCg concentration decay rates from these activities (0.4 h-1 to 4.0 h-1) were greater than the normal operating 0.24 h-1 air change rate, which is consistent with an important role for surface removal. A system for semi-continuous real-time monitoring of gas- and particle-phase water soluble organic carbon (WSOC) was used to provide quantitative insights into the concentrations dynamics of WSOC in indoor air.

Redox-active substances in fine particulate matter (PM) contribute to inhalation health risks through their potential to generate reactive oxygen species in epithelial lung lining fluid (ELF). The ELF’s air–liquid interface (ALI) can play an important role in the phase transfer and multi-phase reactions of redox-active PM constituents. We investigated the influence of interfacial processes and properties by scrubbing of coated nano-particles with simulated ELF in a nebulizing mist chamber. Weakly water-soluble redox-active organics abundant in ambient fine PM were reproducibly loaded into ELF via ALI mixing. The resulting oxidative potential (OP) of selected quinones and other PAH derivatives were found to exceed the OP resulting from bulk mixing of the same amounts of redox-active substances and ELF. Our results indicate that the OP of PM components depends not only on the PM substance properties but also on the ELF interface properties and uptake mechanisms. OP measurements based on bulk mixing of phases may not represent the effective OP in the human lung.

Humidity plays an important role in the surface removal and concentrations of indoor pollutants such as ozone; however, the indoor surface dynamics and chemistry of organic peroxides is largely unknown. Organic hydroperoxides (ROOHs) are known to participate in the multiphase chemistry of outdoor aerosols and clouds, suggesting that reactive uptake in condensed grime on indoor surfaces is plausible, particularly in humid homes. Here, the effect of relative humidity (RH) on the deposition velocity (vd) and reaction probability (γ) of a model ROOH to naturally soiled indoor glass surfaces was investigated; specifically, by using authentic isoprene hydroxy hydroperoxide (1,2-ISOPOOH) as the model compound. Glass was soiled in 3 local homes for 1+ years and characterized. The removal of ISOPOOH by soiled and clean glass was measured under 5-6%, 56-58%, and 83-84% RH conditions using a novel flow reactor designed for indoor surfaces coupled to an iodide chemical ionization high-resolution time-of-flight mass spectrometer (I-HR-TOF-CIMS). The vd and γ increased with increasing RH, ranging from 0.001-0.059 cm s-1 and 0.4-4.6 (×10-6), respectively, on soiled glass surfaces. The vd and γ ranged from only 0.001-0.016 cm s-1 and 0.1-0.8 (×10-6), respectively, across RH conditions on clean glass, demonstrating a greater RH effect on soiled materials than clean. Loss rates calculated under humid conditions to soiled glass (∼1-6 h-1) were competitive in scale with ventilation rates in typical residences, indicating the importance of surface uptake for indoor ROOH concentrations. This work provides parameters for predictive modeling of indoor ROOHs. To our knowledge, these are the first direct measurements of the vd of an ROOH to naturally soiled indoor surfaces.

In addition to obvious negative effects on water quality in eutrophic aquatic ecosystems, recent work suggests that cyanobacterial harmful algal blooms (CHABs) also impact air quality via emissions carrying cyanobacterial cells and cyanotoxins. However, the environmental controls on CHAB-derived aerosol and its potential public health impacts remain largely unknown. Accordingly, the aims of this study were to 1) investigate the occurrence of microcystins (MC) and putatively toxic cyanobacterial communities in particulate matter ≤ 2.5 μm in diameter (PM2.5), 2) elucidate environmental conditions promoting their aerosolization, and 3) identify associations between CHABs and PM2.5 concentrations in the airshed of the Chowan River-Albemarle Sound, an oligohaline, eutrophic estuary in eastern North Carolina, USA. In summer 2020, during peak CHAB season, continuous PM2.5 samples and interval water samples were collected at two distinctive sites for targeted analyses of cyanobacterial community composition and MC concentration. Supporting air and water quality measurements were made in parallel to contextualize findings and permit statistical analyses of environmental factors driving changes in CHAB-derived aerosol. MC concentrations were low throughout the study, but a CHAB dominated by Dolichospermum occurred from late June to early August. Several aquatic CHAB genera recovered from Chowan River surface water were identified in PM2.5 during multiple time points, including Anabaena, Aphanizomenon, Dolichospermum, Microcystis, and Pseudanabaena. Cyanobacterial enrichment in PM2.5 was indistinctive between subspecies, but at one site during the early bloom, we observed the simultaneous enrichment of several cyanobacterial genera in PM2.5. In association with the CHAB, the median PM2.5 mass concentration increased to 8.97 μg m−3 (IQR = 5.15), significantly above the non-bloom background of 5.35 μg m−3 (IQR = 3.70) (W = 1835, p < 0.001). Results underscore the need for highly resolved temporal measurements to conclusively investigate the role that CHABs play in regional air quality and respiratory health risk.

Oxidation of isoprene, the biogenic volatile organic compound (BVOC) with the highest emissions globally, is a large source of secondary organic aerosol (SOA) in the atmosphere. Particulate organosulfates formed from acid-driven reactions of the oxidation products isoprene epoxydiol (IEPDX) isomers are important contributors to SOA mass. Most studies have focused on organosulfate formation on ammonium sulfate particles, often at low pH. However, recent work has shown that sea spray aerosol (SSA) in the accumulation mode (similar to 100 nm) is quite acidic (pH similar to 2) and undergoes further heterogeneous reactions with H2SO4 to form Na2SO4. Herein, we demonstrate that substantial SOA, including organosulfates, are formed on acidic sodium sulfate particles (pH = 1.4 +/- 0.1) via controlled laboratory experiments. Comparable organosulfate formation was observed for acidic sodium and ammonium sulfate particles even though acidic particles with sodium versus ammonium as the primary cation formed less SOA volume. Both exhibited core-shell morphology after the reactive uptake of IEPDX; however, organosulfates were identified with Raman microspectroscopy in the core and shell of ammonium sulfate SOA particles, but only in the core for sodium sulfate SOA. Key organosulfates were also identified in ambient samples from the Galkpagos Island. Our results suggest that isoprene-derived SOA formed on aged SSA is potentially an important, but underappreciated, source of SOA and organosulfates in marine and coastal regions that could modify SOA budgets.

Large fluoropolymer manufacturing facilities are major known sources of per- and polyfluoroalkyl substances (PFAS), many of which accumulate in groundwater, surface water, crops, wildlife, and people. Prior studies have measured high PFAS concentrations in groundwater, drinking water, soil, as well as dry and wet deposition near fluoropolymer facilities; however, much less is known about near-source PFAS air concentrations. We measured airborne PFAS on PM2.5 filters in close proximity to a major fluoropolymer manufacturing facility (Chemours' Fayetteville Works) located near Fayetteville, North Carolina, USA. Weekly PM2.5 filter samples collected over a six-month field campaign using high-volume air samplers at locations 3.7 km apart, north-northeast and south-southwest of the facility were analyzed for thirty-four targeted ionic PFAS species by liquid chromatography coupled to electrospray ionization tandem mass spectrometry. Twelve emerging and ten legacy PFAS compounds were detected. Thirteen PFAS were found at higher concentrations in these nearfield samples than at regional background sites, suggesting a local source for these compounds. Five emerging and five legacy PFAS compounds had maximum concentrations exceeding 1 pg m(-3). PFBA, PFHxA, PFHxDA, PFOS, PMPA, NVHOS, PFO5DoA, and Nafion BP1 contributed the most to the total (legacy + emerging) PFAS concentration (86%). Six PFAS, specifically PFBA, PFOS, PFO5DoA, Nafion BP1, Nafion BP2, and Nafion BP4, provide a consistent representative profile of elevated species across the two sites (with detection frequency >50%). To our knowledge, this is the first study to report both legacy and emerging ionic PFAS in air in close proximity to a U.S. fluoropolymer manufacturing facility.

Per- and polyfluoroalkyl substances (PFASs), with their water- and heat-resistant properties, have been widely used in industrial and consumer products, including floor waxes. Adverse health effects are associated with PFAS exposures (e.g., increased risk of cancer and immunotoxicity); however, exposures resulting from the use of PFAS-containing products are poorly understood. This study examines PFAS emissions during professional floor stripping/waxing and their potential for occupational exposures. We measured PFASs in dust and airborne particulate matter (PM, aerodynamic diameter ≤ 2.0 μm) before, during, and after floor stripping/waxing activities in three rooms in a university building. PM samples were analyzed for 34 targeted PFASs by ultra-high performance liquid chromatography coupled to electrospray ionization triple quadrupole mass spectrometer (UHPLC/ESI-MS/MS). In total, ten PFASs were detected in PM collected during floor waxing. Five were consistently higher during floor stripping/waxing compared to before (two with 95% confidence interval): perfluoro-2-methoxyacetic acid, perfluorobutanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, and perfluorooctane sulfonic acid. For these five, estimated exposures during floor stripping were 80.6, 320.5, 83.8, 29.6, and 157.7 pg m per hour of floor stripping, respectively, one order of magnitude greater than typical residential indoor and two orders of magnitude greater than ambient outdoor concentrations. Estimated emission rates were 3.0, 9.6, 3.4, 1.5, and 6.5 ng hm, respectively (34.6% uncertainty). Inhalation occupational exposures were in the range of 9.42-23.2 pg per kg body weight per hour of floor stripping across the five PFASs.

While carboxylic acids are important components in both particle and gas phases in the atmosphere, their sources and partitioning are not fully understood. In this study, we present real-time measurements of both particle- and gas-phase concentrations for five of the most common and abundant low-molecular-weight carboxylic acids (LMWCA) in a rural region in the southeastern U.S. in Fall 2016. Through comparison with secondary organic aerosol (SOA) tracers, we find that isoprene was the most important local precursor for all five LMWCA but via different pathways. We propose that monocarboxylic acids (formic and acetic acids) were mainly formed through gas-phase photochemical reactions, while dicarboxylic acids (oxalic, malonic, and succinic acids) were predominantly from aqueous processing. Unexpectedly high concentrations of particle-phase formic and acetic acids (in the form of formate and acetate, respectively) were observed and likely the components of long-range transport organic aerosol (OA), decoupled from their gas-phase counterparts. In addition, an extraordinarily strong correlation (R2 = 0.90) was observed between a particulate LMWCA and aged SOA, which we tentatively attribute to boundary layer dynamics.

Trace gases are commonly collected via accumulative sampling, employing sorbents and cryotraps that utilize passive (diffusive) or active sampling principles. For semivolatile substances such as ammonium salts as well as oxygenated and halogenated organics, the particulate and gas phases must be collected separately—either side by side or in a sample train. Aerosol particles are collected using a broad spectrum of samplers that rely on physical principles such as inertia-based particle sampling, diffusive particle transport and adsorption to surfaces, particle migration and deposition in external fields, and filter sampling. Dedicated inlet systems with minimized particle losses must be used to ensure that sampling gives representative results, particularly for the particle size distribution. Note that artifact-free sampling is not yet available for a number of target compounds.

Contamination of drinking water by per- and polyfluoroalkyl substances (PFASs) emitted from manufacturing plants, fire-fighting foams, and urban waste streams has received considerable attention due to concerns over toxicity and environmental persistence; however, PFASs in ambient air remain poorly understood, especially in the United States (US). We measured PFAS concentrations in ambient fine particulate matter (PM2.5) at 5 locations across North Carolina over a 1 year period in 2019. Thirty-four PFASs, including perfluoroalkyl carboxylic, perfluoroalkane sulfonic, perfluoroalkyl ether carboxylic and sulfonic acids were analyzed by UHPLC/ESI-MS/MS. Quarterly averaged concentrations ranged from <0.004-14.1 pg m-3. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) ranged from <0.18 to 14.1 pg m-3, comparable to previous PM2.5 measurements from Canada and Europe (<0.02-3.5 pg m-3). Concentrations above 1 pg m-3 were observed in July-September at Charlotte (14.1 pg m-3, PFOA), Wilmington (4.75 pg m-3, PFOS), and Research Triangle Park (1.37 pg m-3, PFOS). Notably, PM2.5 has a short atmospheric lifetime (<2 weeks), and thus, the presence of PFOS in these samples raises questions about their sources, since PFOS production was phased out in the US ∼20 years ago. This is the first US study to provide insights into ambient PFAS concentrations in PM2.5.

Wet deposition and dry deposition of legacy per- and polyfluoroalkyl substances (PFAS) and perfluoroalkyl ether carboxylic acids (PFECAs) were assessed on the southeastern coast of the United States, specifically, in Wilmington, NC, which is located 110 km from a fluorochemical manufacturer. Analytes were quantified by liquid chromatography coupled to electrospray ionization with triple-quadrupole mass spectrometry. Total concentrations of six PFAS compounds ranged from below the method quantification limit to 110 ng L-1 by wet deposition, and total fluxes of 0.3-29 ng m(-2) day(-1) by dry deposition were found. The estimated annual flux of all six PFAS was 30 mu g m(-2) by wet deposition and 1.4 mu g m(-2) by dry deposition, indicating that PFAS are more effectively removed from the atmosphere by wet deposition. There was a significant rainout/washout effect observed in our data, but there was no impact of the origin of the air mass on concentration or flux, suggesting that the incorporation of PFAS into rainwater is a relatively local phenomenon. This study shows the first direct evidence of PFECAs in wet and dry deposition. The data suggest that the particle-bound and gas-phase PFAS that may have undergone long-range transport can be incorporated into raindrops and removed rapidly.

The formation and evolution of secondary organic aerosol (SOA) were investigated at Yorkville, GA, in late summer (mid-August to mid-October 2016). The organic aerosol (OA) composition was measured using two online mass spectrometry instruments, the high-resolution time-of-flight aerosol mass spectrometer (AMS) and the Filter Inlet for Gases and AEROsols coupled to a high-resolution time-of-flight iodide-adduct chemical ionization mass spectrometer (FIGAERO-CIMS). Through analysis of speciated organics data from FIGAERO-CIMS and factorization analysis of data obtained from both instruments, we observed notable SOA formation from isoprene and monoterpenes during both day and night. Specifically, in addition to isoprene epoxydiol (IEPOX) uptake, we identified isoprene SOA formation from non-IEPOX pathways and isoprene organic nitrate formation via photooxidation in the presence of NOx and nitrate radical oxidation. Monoterpenes were found to be the most important SOA precursors at night. We observed significant contributions from highly oxidized acid-like compounds to the aged OA factor from FIGAERO-CIMS. Taken together, our results showed that FIGAERO-CIMS measurements are highly complementary to the extensively used AMS factorization analysis, and together they provide more comprehensive insights into OA sources and composition.

Anthropogenic emissions alter secondary organic aerosol (SOA) formation chemistry from naturally emitted isoprene. We use correlations of tracers and tracer ratios to provide new perspectives on sulfate, NOx, and particle acidity influencing isoprene-derived SOA in two isoprene-rich forested environments representing clean to polluted conditions-wet and dry seasons in central Amazonia and Southeastern U.S. summer. We used a semivolatile thermal desorption aerosol gas chromatograph (SV-TAG) and filter samplers to measure SOA tracers indicative of isoprene/HO2 (2-methyltetrols, C5-alkene triols, 2-methyltetrol organosulfates) and isoprene/NOx (2-methylglyceric acid, 2-methylglyceric acid organosulfate) pathways. Summed concentrations of these tracers correlated with particulate sulfate spanning three orders of magnitude, suggesting that 1 μg m-3 reduction in sulfate corresponds with at least ∼0.5 μg m-3 reduction in isoprene-derived SOA. We also find that isoprene/NOx pathway SOA mass primarily comprises organosulfates, ∼97% in the Amazon and ∼55% in Southeastern United States. We infer under natural conditions in high isoprene emission regions that preindustrial aerosol sulfate was almost exclusively isoprene-derived organosulfates, which are traditionally thought of as representative of an anthropogenic influence. We further report the first field observations showing that particle acidity correlates positively with 2-methylglyceric acid partitioning to the gas phase and negatively with the ratio of 2-methyltetrols to C5-alkene triols.

Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), a key isoprene oxidation product, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. Herein, we reveal that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate ratio (IEPOX:Sulfinorg), as determined by laboratory and field measurements. We further demonstrate that organosulfur greatly modifies critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights reveal that changes in SO2 emissions, especially in isoprene-dominated environments, will significantly alter biogenic SOA physicochemical properties. Consequently, IEPOX:Sulfinorg will play a central role in understanding historical climate and determining future impacts of biogenic SOA on global climate and air quality.

Gas-phase atmospheric concentrations of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and peroxymethacryloyl nitrate (MPAN) were measured on the ground using a gas chromatograph electron capture detector (GC-ECD) during the Southern Oxidants and Aerosols Study (SOAS) 2013 campaign (1 June to 15 July 2013) in Centreville, Alabama, in order to study biosphere–atmosphere interactions. Average levels of PAN, PPN, and MPAN were 169, 5, and 9 pptv, respectively, and the sum accounts for an average of 16 % of NOy during the daytime (10:00 to 16:00 local time). Higher concentrations were seen on average in air that came to the site from the urban NOx sources to the north. PAN levels were the lowest observed in ground measurements over the past two decades in the southeastern US. A multiple regression analysis indicates that biogenic volatile organic compounds (VOCs) account for 66 % of PAN formation during this study. Comparison of this value with a 0-D model simulation of peroxyacetyl radical production indicates that at least 50 % of PAN formation is due to isoprene oxidation. MPAN has a statistical correlation with isoprene hydroxynitrates (IN). Organic aerosol mass increases with gas-phase MPAN and IN concentrations, but the mass of organic nitrates in particles is largely unrelated to MPAN.

Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), key isoprene oxidation products, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur compounds. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. In this article, we demonstrate that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate concentration ratio (IEPOX/Sulfinorg), as determined by laboratory measurements. Characterization of the total sulfur aerosol observed at Look Rock, Tennessee, from 2007 to 2016 shows that organosulfur mass fractions will likely continue to increase with ongoing declines in anthropogenic Sulfinorg, consistent with our laboratory findings. We further demonstrate that organosulfur compounds greatly modify critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights demonstrate that changes in SO2 emissions, especially in isoprene-dominated environments, will significantly alter biogenic SOA physicochemical properties. Consequently, IEPOX/Sulfinorg will play an important role in understanding the historical climate and determining future impacts of biogenic SOA on the global climate and air quality.