New particle formation is an important source of Arctic atmospheric particles and cloud condensation nuclei, yet their precursor sources and molecular-level mechanisms remain poorly understood. Here we report comprehensive ship-based observations from 19 May to 26 June 2022 from southeastern to western Greenland and into the Davis Strait's marginal ice zone to investigate sources and processes controlling atmospheric particles and cloud condensation nuclei. Our observations provide field evidence of frequent nucleation events driven by the multicomponent iodine oxoacid and sulfuric acid mechanism recently identified in laboratory studies. Newly formed particles grew rapidly beyond 20 nm on 8 out of 13 nucleation days, mainly driven by oxygenated organic molecules from aldehyde and monoterpene oxidation. We also report a previously unobserved class of iodine-containing oxygenated organic molecules that contributed to particle growth and enhanced cloud condensation nuclei formation. We show that marginal sea ice zone produces precursors that drive rapid new particle formation and enhance cloud condensation nuclei concentrations by up to 50-fold. Our findings demonstrate that Arctic iodine, sulfur and organic precursors can enhance cloud condensation nuclei abundance through new particle formation, highlighting a potential but unquantified pathway for influencing cloud cover, radiative balance and the hydrological cycle.

Abstract. Secondary organic aerosol (SOA) makes up much of the particulate matter in the troposphere and impacts global climate and human health, though uncertainties regarding the sources and properties of SOA limit our understanding of these effects. New analytical techniques are required to better characterize the molecular composition of SOA, including methods that can identify isomeric compounds that may have different contributions to SOA properties such as hygroscopicity or volatility. We present a method for isomer-resolved analysis of SOA using a commercially available chemical ionization ion-mobility time-of-flight mass spectrometer (CI-IMS-TOF) and a Vaporization Inlet for Aerosols (VIA). The compatibility of the VIA and the CI-IMS-TOF was assessed through the analysis of 10 carboxylic acid standards across a large temperature range (30 - 170 °C). Ion drift times were found to be stable to within 0.075% of their initial values after drift time calibration. The VIA-CI-IMS-TOF was also used to collect real-time ion mobility and mass spectra of SOA constituents during an α-pinene ozonolysis chamber experiment. Several reaction products were identified in the SOA using synthetic standards, including structural isomers of C8H12O4 and C9H14O4. Temporal evolution of reaction products was used to assess formation timescales and determine the generation of oxidation for individual isomers. Both iodide and bromide reagent ions were used in the VIA-CI-IMS-TOF to achieve a more comprehensive analysis of SOA. This study demonstrates the performance of the VIA-CI-IMS-TOF for online, isomer-resolved analysis of organic aerosol and its potential for improving the current understanding of SOA composition.

The COVID-19 pandemic led to heightened interest in germicidal ultraviolet (GUV) lamps, which can deactivate bacteria and viruses in infectious aerosols. Recently, lamps using 222 nm (GUV222) light to disinfect occupied spaces have become more popular and available, as that wavelength is safer for human exposure compared to 254 nm lamps. However, GUV222 produces ozone, which drives the formation of other pollutants. Previous work in a controlled Teflon chamber with GUV222 has shown the production of ozone, followed by the formation of secondary organic aerosol (SOA) from limonene ozonolysis, and developed a model of this process. This work adapts that model to newly obtained measurements in an unoccupied office. The model is able to accurately predict SOA formation and yield given a continuous source of limonene, and we use it here to show how GUV222 lamps increase SOA exposure in indoor spaces. SOA yields from limonene in the office were found to be similar to those measured in a Teflon chamber. However, SOA formation resulting from briefly emitted limonene was harder to capture in the model. Typically, these limonene injections led to the formation of many ultrafine particles, which did not result in a significant increase in SOA mass, although they can still pose a risk to human health. GUV222 also had other impacts on room chemistry; concentrations of most VOCs increased under GUV222, potentially driven by gas and surface-phase ozone reactions as well as direct surface emissions.

Volatility and viscosity are important parameters affecting the formation, reaction, and fate of atmospheric organic aerosols. In this study, a Vaporization Inlet for Aerosol (VIA) coupled with a Vocus chemical ionization mass spectrometer (Vocus-CIMS) using NH4 + adduct ionization is employed to simultaneously detect and quantify the molecular composition and volatility of organic aerosols through a program-controlled temperature ramp, thereby providing viscosity information. Volatility calibration was conducted with a series of reference aerosol particles with different chemical compositions, covering a vapor pressure range from 10-1 to 10-8 Pa. Secondary organic aerosols (SOA) produced from the potential aerosol mass reactor were analyzed by the VIA-CIMS. Chemical species ranging from semivolatile to low-volatility, including highly oxygenated dimers, were identified. Individual ions from the collected mass spectra were fitted and grouped by volatility basis sets to yield the volatility distribution of the SOA, allowing for the quantification of the glass transition temperatures and viscosities. Results show that β-caryophyllene ozonolysis SOA has lower volatility and is more viscous than the α-pinene SOA. This approach enables the online quantification of SOA particle chemical composition and volatility distribution, while simultaneously characterizing particle phase state, such as viscosity and water diffusion time, providing crucial insights into their chemical processes and climate impacts.

Weighted positive matrix factorization (PMF) has been used by scientists to find small sets of underlying factors in environmental data. However, as the size of the data has grown, increasing computational costs have made it impractical to use traditional methods for this factorization. In this paper, we present a new weighting method to dramatically decrease computational costs for these traditional algorithms. We then apply this weighting method with the Randomized Hierarchical Alternating Least Squares (RHALS) algorithm to a large environmental dataset, where we show that interpretable factors can be reproduced using these methods. We show this algorithm results in a computational speedup of 38, 67, and 634 compared to the Multiplicative Update (MU), deterministic Hierarchical Alternating Least Squares (HALS), and non-negative Alternating Least Squares (ALS) algorithms, respectively. We also investigate rotational ambiguity in the solution, and present a simple ``pulling'' method to rotate a set of factors. This method is shown to find alternative solutions, and in some cases, lower the weighted residual error of the algorithm.

Long-term measurements of the composition and mass concentration of particulate matter (PM) are important for source apportionment, epidemiological studies, and trends in atmospheric chemistry. The Aerosol Chemical Speciation Monitor (ACSM) has been widely used for in situ, real time measurements of PM. However, ACSMs provide unit mass resolution data, meaning isobaric ions (same unit mass, different exact m/z) cannot be separated, which can impact detection limits and separation and identification of different organic ions (e.g., C2H3O+ vs C3H7+). Here, we present a new Time-of-Flight ACSM with eXtended resolution (TOF-ACSM-X). With a mass resolving power of similar to 2000 m/Delta m, the TOF-ACSM-X enables higher-resolution, multi-peak fitting of individual ions compared to the two other existing ACSM models, namely the Time-of-Flight ACSM (TOF-ACSM) and quadrupole ACSM (Q-ACSM). This improved resolution leads to a factor of 25 improvement in ammonium detection limits, from similar to 0.200 to similar to 0.008 mu g m-3 (TOF-ACSM versus TOF-ACSM-X, respectively), for 10-minute integration times, allows for elemental analysis (O/C and H/C) of organic aerosol, and enables improved mass spectral separation of the CH2O+ and NO+ signals at m/z = 30 for improved quantification of organic and inorganic particle nitrate. Comparisons of the TOF-ACSM-X with ambient measurements from two separate instruments show that the TOF-ACSM-X agrees quantitatively and that the TOF-ACSM-X provides unconstrained positive matrix factorization results for the organic aerosol that would not be possible with the unit mass resolution TOF-ACSM. Finally, we are now recommending a more direct and unifying calculation of nitrate mass concentration for both AMS and ACSM ionization efficiency calibrations.

Chlorinated paraffins (CPs) are synthetic polychlorinated n-alkanes produced as mixtures of a range of C x Cl y H2x-y+2 formulas. CPs have numerous industrial applications but are toxic, long-lived, and environmentally ubiquitous with environmental releases occurring throughout their production, use, and disposal. Short-chain chlorinated paraffins (SCCPs, C10-13) have been regulated by the United States Environmental Protection Agency since 2009 and by the Stockholm Convention since 2017. SCCP regulation is expected to cause increased production of medium-chain chlorinated paraffins (MCCPs; C14-17), which are currently under consideration for Stockholm Convention regulations. Thus, there is a need to improve the understanding of MCCP environmental transport, distribution, and fate. Existing measurements are limited in their spatial and temporal coverage. Measurements of CP atmospheric loading are particularly scarce. Historically, these measurements have required long sampling times, obscuring the temporal behavior of atmospheric CPs. We report real-time in situ measurements of 18 gas-phase MCCPs. These measurements were made in the United States Southern Great Plains with nitrate ion chemical ionization mass spectrometry (NO3-CIMS). The estimated average lower-limit concentration of MCCPs is on the order of single-digit ng/m3. MCCP diel behavior is partially explained by gas-particle partitioning with implications for MCCP transport and lifetimes.

BACKGROUND:Cumulative risk assessment (CRA) is key to characterizing health risks in fenceline and disadvantaged communities, which face environmental pollution and challenging socioeconomic conditions. Traditional approaches for inclusion of mixtures in CRA are limited and only assess the most sensitive target organ system for each chemical. METHODS:We developed an expanded approach to cumulative risk assessment that considers all known target organ systems associated with a chemical. Specifically, we created a multi-effects toxicity database by a) compiling toxicological and epidemiological data from the Agency for Toxic Substances and Disease Registry's (ATSDR) Toxicological Profiles and the Environmental Protection Agency (US EPA) CompTox Chemicals Dashboard; b) developing a tiering system to prioritize identified data for use in developing toxicity values; and c) accounting for uncertainty to create toxicity values for additional target organ systems. We demonstrated differences between the traditional approach and our expanded approach by using state-of-the-art mobile monitoring data from our Southeastern Pennsylvania Hazardous Air Pollutant Monitoring and Assessment Project (SEPA HAP-MAP) to conduct a cumulative risk assessment. RESULTS:Of the 32 chemicals quantified in SEPA HAP-MAP, 28 were represented in our multi-effects toxicity database, whereas only 16 were included using a traditional approach. In total, we derived toxicity values for 172 chemical-target organ system combinations. Our expanded approach found neurological, renal, respiratory, endocrine, and systemic risks (hazard index >1) in SEPA HAP-MAP fenceline communities, whereas no risks were identified using a traditional approach limited to the most sensitive target organ systems only. CONCLUSION:Our results suggest that traditional approaches to CRA underestimate health risks in fenceline and other highly exposed communities and highlight the need for improved methods to inform health-protective and just risk management decisions. https://doi.org/10.1289/EHP14696.

Non-traditional VOC emissions, including emerging pollutants, air toxics, and volatile chemical products (VPCs) span a range of volatilities and molecular structures that impact their reactivity in the atmosphere and eventual fate. However, little is known their source apportionment, temporal behavior, and relative importance to health impacts along with ozone and SOA formation. With the need to characterize these emissions, comprehensive measurement techniques that capture the unexpected but are also highly specific to detail molecular structure and provide compound quantification are needed. The work presented in this study uses chemical ionization (CI) techniques (H3O+, NH4+, NO+, O2+) for the direct detection and quantification of VOCs considered to be hazardous air pollutants (HAPs). With our work, we show that the ionization patterns for these classes of compounds within each ionization scheme can be used to expand these methods to interpret unknown signals in complex environments. This detailed characterization was conducted by coupling in-situ gas chromatography (GC) to the CI-TOF-MS for pre-separation of the complex mixture. Our results show how the speciated data can be used to deconvolve the complexities of chemical ionization detection (including the presence of fragmentation, cluster formation, and mixed ionization schemes e.g. proton transfer, charge transfer, dehydration). To apply these methods to ambient atmospheric measurements we need to reconcile the need for both continuous isomer specific quantification and high time resolution data. To accomplish this, we simultaneously coupled the in-situ GC with both CI and electron ionization (EI) TOF-MS. Resulting in the generation of three data sets (GC-EI, GC-CI, and direct-CI data) that offer continuous GC quantification, universal detection of speciated organics (EI), speciated CI data to constrain interferences, and direct-CI data for high time resolution data. This instrument combination was deployed in Spring 2023 for a 4-week mobile laboratory campaign in a region of southeast Louisiana, US that is dense with petrochemical production and industrial activity, to quantify hazardous air pollutants to gauge exposure for the local population. The combination of the in-situ GC, EI-TOF-MS, PTR-TOF-MS was used to provide highly specific, quantitative data on VOCs considered to be air toxics in the area, while also acquiring high time resolution PTR-TOF data that allowed the characterization of different point sources and their variability over time-of-day and day-of-week.

Organic species in the atmosphere originate from a wide range of sources and processes. While real time chemical ionization mass spectrometry (CIMS) has improved our capability to characterize individual organic species in the atmosphere, the selectivity of CIMS reagent ions can limit the range of species that can be measured. In this work the need to detect a broader range of species with a single CIMS instrument is addressed. A fast-switching bipolar time-of-flight CIMS that switches between four different reagent ions, including positive and negative ions, is demonstrated. The performance and utility of this instrument is demonstrated by measurements obtained on board a ship in Antarctica during the PolarChange field campaign and from New York City during the AEROMMA campaign. During both campaigns the instrument cycled through iodide (I-), benzene (C6H6+), and acetone dimer ((C3H6O)2H+) reagent ions at a 2 second data acquisition rate per cycle. In the case of PolarChange, this combination of ions enabled simultaneous detection of trends in primary marine biological emissions such as dimethyl sulfide, nucleating species such as ammonia and methyl amine, and acids, such as nitric acid. During AEROMMA, the fast bipolar switching capability enabled Eddy Correlation measurements of primary biogenic and urban emissions (i.e. monoterpenes and aromatics), secondary products of atmospheric oxidation (i.e. highly oxidized organics and organic nitrates), and reduced nitrogen species. Preliminary results from this dataset, including positive matrix analyses of the combined multi-reagent ion datasets, are discussed. Simultaneous gas and aerosol composition measurements obtained by coupling this mass spectrometer with aerosol inlets are also described.

To quantify the volatility of organic aerosols (OA), a comprehensive campaign was conducted in the Chinese megacity. Volatility distributions of OA and particle-phase organic nitrate (pON) were estimated based on five methods: (a) empirical method and (b) kinetic model based on the measurement of a thermodenuder (TD) coupled with an aerosol mass spectrometer; (c) Formula-based SIMPOL model-driven method; (d) Element-based estimations using molecular formula measurements of OA; and (e) gas/particle partitioning. Our results demonstrate that the ambient OA volatility distribution shows good agreement between the two heating methods and the formula-based method when assuming ambient OA was mainly composed of organic nitrate (pON), organic sulfate and acid groups using the SIMPOL model. However, the element-based method tends to overestimate the volatility of OA compared to the above three methods, suggesting large uncertainties in the parameterizations or in the representativeness of the molecular measurements that need further refinement. The volatility of ambient OA is generally lower than that of the laboratory-derived secondary OA, emphasizing the impact of aging. A large fraction at the higher and lower volatility ranges (approximately log C* <= -9 and >= 2 mu g m-3) was found for pON, implying the importance of both extremely low volatile and semi-volatile species. Overall, this study evaluates different methods for volatility estimation and gives new insight into the volatility of OA and pON in urban areas. Volatility, which controls the gas/particle partitioning of organic compounds, is one of most the important physiochemistry properties of organic aerosols (OA). Multiple methods have been used to estimate OA volatility, whereas the accuracy of each method is still unclear. The purpose of this study is to verify the volatility of ambient OA and its key component (i.e., particulate organic nitrate, pON) in urban areas by comparing the estimated results using different methods. With the help of state-of-art mass spectrometers, the estimation methods, including two heating methods, one formula-based method, one element-based method, and one gas/particle partitioning method, were achieved. In general, we found the heating methods show good agreement with the formula-based method with a reasonable assumption of functional groups contained in OA and pON. In general, we observed a large faction of extremely low volatile compounds exist in OA (30%-40%), and both extremely low volatile and semi-volatile species exist in pON, suggesting the complex evolution of atmospheric particles. The results provide a better understanding of the volatility of OA and pON in urban areas and benefit accurate volatility estimation that facilitates the model simulations of OA. The volatility of ambient organic aerosols (OA) and organic nitrate (pON) estimated from five methods were systematically compared The OA volatility from SIMPOL-driven model under organic sulfate, pON and acid assumption are consistent with those from heating method The volatility distribution of pON indicates both extremely low volatility compounds as oligomers and semi-volatile species exist in pON

Ethylene oxide ("EtO") is an industrially made volatile organic compound and a known human carcinogen. There are few reliable reports of ambient EtO concentrations around production and end-use facilities, however, despite major exposure concerns. We present in situ, fast (1 Hz), sensitive EtO measurements made during February 2023 across the southeastern Louisiana industrial corridor. We aggregated mobile data at 500 m spatial resolution and reported average mixing ratios for 75 km of the corridor. Mean and median aggregated values were 31.4 and 23.3 ppt, respectively, and a majority (75%) of 500 m grid cells were above 10.9 ppt, the lifetime exposure concentration corresponding to 100-in-one million excess cancer risk (1 x 10(-4)). A small subset (3.3%) were above 109 ppt (1000-in-one million cancer risk, 1 x 10(-3)); these tended to be near EtO-emitting facilities, though we observed plumes over 10 km from the nearest facilities. Many plumes were highly correlated with other measured gases, indicating potential emission sources, and a subset was measured simultaneously with a second commercial analyzer, showing good agreement. We estimated EtO for 13 census tracts, all of which were higher than EPA estimates (median difference of 21.3 ppt). Our findings provide important information about EtO concentrations and potential exposure risks in a key industrial region and advance the application of EtO analytical methods for ambient sampling and mobile monitoring for air toxics.

Lamps emitting at 222 nm have attracted recent interest for germicidal ultraviolet disinfection ("GUV222"). Their impact on indoor air quality is considered negligible. In this study, ozone formation is observed for eight different lamps from five manufacturers, in amounts an order-of-magnitude larger than previous reports. Most lamps produce O3 in amounts close to the first-principles calculation, with e.g. a generation rate of 22 ppb h-1 for Ushio B1 modules in a 21 m3 chamber. Much more O3 is produced by lamps when optical filters were removed for tests, and by an undesired internal electrical discharge. A test in an office shows an increase of ~6.5 ppb during lamp-on periods, consistent with a simple model with the O3 generation rate, ventilation and O3 losses. We demonstrate the use of a photolytic tracer to quantify the averaged GUV222 fluence rate in a room. Low-cost electrochemical O3 sensors were not useful below 100 ppb. Formation of O3 increases indoor particulate matter (PM), which is ~10-30 times more deadly than O3 per unit mass, and which is ignored when only considering O3 threshold limit values. To limit GUV222-created indoor pollution, lower fluence rates should be used if possible, especially under low-ventilation conditions.

Reduced nitrogen (N) is central to global biogeochemistry, yet there are large uncertainties surrounding its sources and rate of cycling. Here, we present observations of gas-phase urea (CO(NH2)2) in the atmosphere from airborne high-resolution mass spectrometer measurements over the North Atlantic Ocean. We show that urea is ubiquitous in the lower troposphere in the summer, autumn, and winter but was not detected in the spring. The observations suggest that the ocean is the primary emission source, but further studies are required to understand the responsible mechanisms. Urea is also observed aloft due to long-range transport of biomass-burning plumes. These observations alongside global model simulations point to urea being an important, and currently unaccounted for, component of reduced-N to the remote marine atmosphere. Airborne transfer of urea between nutrient-rich and -poor parts of the ocean can occur readily and could impact ecosystems and oceanic uptake of carbon dioxide, with potentially important climate implications.

Long-term measurements of the composition and mass concentration of particulate matter (PM) are essential for source apportionment, epidemiological studies, and air quality trends. Over the past ten years, the Aerosol Chemical Speciation Monitor (ACSM) has been widely used for long-term, in situ, high time resolution measurements. However, to date there are limited measurements with these instruments in Africa and South/Southeast Asia. The measurements that have been made in these regions suggest the presence of varied and complex sources. Current ACSMs have unit mass resolution (UMR), which impacts detection limits and separation and identification of ions, limiting source apportionment. Here, we present a new instrument, the Time-of-Flight ACSM with eXtended resolution (TOF-ACSM-X) with updated analysis software (Tofware) to allow for high-resolution peak fitting. The TOF-ACSM-X has a mass resolution of ~2000 m/Δm, which is approximately an order of magnitude higher than the other versions of the ACSM. This enhanced resolution improves ammonium detection limits by approximately 2-orders of magnitude, from ~0.200 μg m-3 to ~0.008 μg m-3 (TOF-ACSM versus TOF-ACSM-X, respectively), for 15-minute integration times. Intercomparisons of the TOF-ACSM-X with other measurements show improved performance in source apportionment and elemental analysis.

In the lower troposphere, rapid collisions between ions and trace gases result in the transfer of positive charge to the highest proton affinity species and negative charge to the lowest proton affinity species. Measurements of the chemical composition of ambient ions thus provide direct insight into the most acidic and basic trace gases and their ion–molecule clusters – compounds thought to be important for new particle formation and growth. We deployed an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF) to measure ambient ion chemical composition during the 2016 Holistic Interactions of Shallow Clouds, Aerosols, and Land Ecosystems (HI-SCALE) campaign at the United States Department of Energy Atmospheric Radiation Measurement facility in the Southern Great Plains (SGP), an agricultural region. Cations and anions were measured for alternating periods of ∼ 24 h over 1 month. We use binned positive matrix factorization (binPMF) and generalized Kendrick analysis (GKA) to obtain information about the chemical formulas and temporal variation in ionic composition without the need for averaging over a long timescale or a priori high-resolution peak fitting. Negative ions consist of strong acids including sulfuric and nitric acid, organosulfates, and clusters of NO3- with highly oxygenated organic molecules (HOMs) derived from monoterpene (MT) and sesquiterpene (SQT) oxidation. Organonitrates derived from SQTs account for most of the HOM signal. Combined with the diel profiles and back trajectory analysis, these results suggest that NO3 radical chemistry is active at this site. SQT oxidation products likely contribute to particle growth at the SGP site. The positive ions consist of bases including alkyl pyridines and amines and a series of high-mass species. Nearly all the positive ions contained only one nitrogen atom and in general support ammonia and amines as being the dominant bases that could participate in new particle formation. Overall, this work demonstrates how APi-ToF measurements combined with binPMF analysis can provide insight into the temporal evolution of compounds important for new particle formation and growth.

Organic aerosol in the atmosphere has an impact on climate, visibility, and human health. Oxidation of biogenic volatile organic compounds forms secondary organic aerosols by lowering the volatility of the product molecules and thus enhancing partitioning to the particle phase. The NO3-initiated oxidation of Delta-3-carene was studied because it connects the interaction between biogenic and anthropogenic emissions to form aerosols. This work characterized the first-generation gas-phase products of the NO3- initiated oxidation of Delta-3-carene in a 7.4 m3 Teflon FEP chamber using a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus) and a high-resolution time-of-flight chemical ionization mass spectrometer (CIMS) using iodide adducts. The mass spectra not only show the presence of most of the expected products, including dicarbonyl, hydroxy nitrate, carbonyl nitrate, hydroxy dicarbonyl, and dicarbonyl nitrate but also show significant fragmentation of the parent ions in the Vocus through the loss of water and/or nitric acid and other neutral fragments. Parent and fragment ions were grouped together, taking advantage of gas-wall interactions in Teflon tubing, which separate the molecules by their inlet delay time. After grouping product ions, the Vocus signals were used to determine the gas-phase product yields for the NO3 + Delta-3-carene reaction. A comparison between the Vocus and iodide CIMS data allowed the sensitivity of the iodide CIMS to be investigated. Understanding the mechanism of the oxidation of Delta-3-carene by NO3 radicals allows for a better understanding of the sources of organic nitrate in the atmosphere and can improve the interpretation of field data and the representation of this chemistry in models.