Drew R. Gentner

High Resolution Image Download MS PowerPoint Slide Ammonia (NH 3 ) influences indoor air and surface chemistry. Its temporal dynamics and sources during early occupancy of new homes is not well characterized. As part of the New Home Air Quality Study (NHAQS), temporal changes in indoor reduced nitrogen, especially NH 3, from preoccupancy through 12 months was quantified in 48 new homes with nonsmoking residents in the Ottawa-Gatineau area from 2019 to 2024. Passive samplers collected target analytes quantified by ion chromatography and liquid chromatography with mass spectrometry. Indoor NH 3 mixing ratios decreased from pre- to postoccupancy and remained relatively stable over 12 months following, consistent with reduced emissions from new materials and increased partitioning surface area upon occupancy. The NH 3 indoor-to-outdoor ratio indicated indoor sources dominated. Indoor NH 3 levels were higher in warmer months, likely due to temperature-driven repartitioning. A generalized linear mixed model identified glass cleaners and resident presence ≥18 h day –1 as significant positive predictors of elevated NH 3, while oven cleaner use decreased indoor NH 3 levels. A case study of five homes found reduced nitrogen fate depends on surface chemistry, with potential pathways such as carbonyl condensation, and amide and N-heteroaromatic formation shaping household-specific patterns. This work provides new insights on how homeowners may recognize and reduce NH 3 sources to improve indoor air quality.

Ammonia (NH₃) influences indoor air and surface chemistry. Its temporal dynamics and sources during early occupancy of new homes is not well characterized. As part of the New Home Air Quality Study (NHAQS), temporal changes in indoor reduced nitrogen, especially NH₃, from preoccupancy through 12 months was quantified in 48 new homes with nonsmoking residents in the Ottawa-Gatineau area from 2019 to 2024. Passive samplers collected target analytes quantified by ion chromatography and liquid chromatography with mass spectrometry. Indoor NH₃ mixing ratios decreased from pre- to postoccupancy and remained relatively stable over 12 months following, consistent with reduced emissions from new materials and increased partitioning surface area upon occupancy. The NH₃ indoor-to-outdoor ratio indicated indoor sources dominated. Indoor NH₃ levels were higher in warmer months, likely due to temperature-driven repartitioning. A generalized linear mixed model identified glass cleaners and resident presence ≥18 h day^–1 as significant positive predictors of elevated NH₃, while oven cleaner use decreased indoor NH₃ levels. A case study of five homes found reduced nitrogen fate depends on surface chemistry, with potential pathways such as carbonyl condensation, and amide and N-heteroaromatic formation shaping household-specific patterns. This work provides new insights on how homeowners may recognize and reduce NH₃ sources to improve indoor air quality.

Ammonia (NH₃) influences indoor air and surface chemistry. Its temporal dynamics and sources during early occupancy of new homes is not well characterized. As part of the New Home Air Quality Study (NHAQS), temporal changes in indoor reduced nitrogen, especially NH₃, from preoccupancy through 12 months was quantified in 48 new homes with nonsmoking residents in the Ottawa-Gatineau area from 2019 to 2024. Passive samplers collected target analytes quantified by ion chromatography and liquid chromatography with mass spectrometry. Indoor NH₃ mixing ratios decreased from pre- to postoccupancy and remained relatively stable over 12 months following, consistent with reduced emissions from new materials and increased partitioning surface area upon occupancy. The NH₃ indoor-to-outdoor ratio indicated indoor sources dominated. Indoor NH₃ levels were higher in warmer months, likely due to temperature-driven repartitioning. A generalized linear mixed model identified glass cleaners and resident presence ≥18 h day^–1 as significant positive predictors of elevated NH₃, while oven cleaner use decreased indoor NH₃ levels. A case study of five homes found reduced nitrogen fate depends on surface chemistry, with potential pathways such as carbonyl condensation, and amide and N-heteroaromatic formation shaping household-specific patterns. This work provides new insights on how homeowners may recognize and reduce NH₃ sources to improve indoor air quality.

Ammonia (NH₃) influences indoor air and surface chemistry. Its temporal dynamics and sources during early occupancy of new homes is not well characterized. As part of the New Home Air Quality Study (NHAQS), temporal changes in indoor reduced nitrogen, especially NH₃, from preoccupancy through 12 months was quantified in 48 new homes with nonsmoking residents in the Ottawa-Gatineau area from 2019 to 2024. Passive samplers collected target analytes quantified by ion chromatography and liquid chromatography with mass spectrometry. Indoor NH₃ mixing ratios decreased from pre- to postoccupancy and remained relatively stable over 12 months following, consistent with reduced emissions from new materials and increased partitioning surface area upon occupancy. The NH₃ indoor-to-outdoor ratio indicated indoor sources dominated. Indoor NH₃ levels were higher in warmer months, likely due to temperature-driven repartitioning. A generalized linear mixed model identified glass cleaners and resident presence ≥18 h day^–1 as significant positive predictors of elevated NH₃, while oven cleaner use decreased indoor NH₃ levels. A case study of five homes found reduced nitrogen fate depends on surface chemistry, with potential pathways such as carbonyl condensation, and amide and N-heteroaromatic formation shaping household-specific patterns. This work provides new insights on how homeowners may recognize and reduce NH₃ sources to improve indoor air quality.

High Resolution Image Download MS PowerPoint Slide Oil sands operations in Alberta, Canada, are a large source of secondary organic aerosol (SOA) with unknown health impacts. As a first step in closing this knowledge gap, the oxidative potential (OP), an established metric linking particle exposure to toxicological effects, of oil sands-derived SOA was investigated via OH-initiated oxidation. Experiments used a mixture of gas-phase precursors emitted from oil sands ore that is expected to be representative of mine-face emissions and three relevant single precursors ( n -decane, m -xylene, and naphthalene) for comparison. The OP of the formed SOA in all cases was found to increase rapidly at short simulated photochemical ages (<1.5 days), followed by a decrease upon further oxidation (>2.5 days). This was driven by dynamic changes in SOA composition, particularly organic peroxides, quinones, and unsaturated carbonyls. The measured OP of oil sand ore SOA (OP OS ) ranged from 38.0 to 60.3 pmol min –1 μg –1 over photochemical ages of 0.4–4.6 days. This range of OP OS is considerably higher than those reported for other types of aerosol particles typically present in the oil sands region, including the natural background (e.g., α-pinene and isoprene SOA). The results not only provide the first OP measurements of oil sands-derived SOA but also emphasize the importance of accounting for atmospheric aging when evaluating the oxidative potential of SOA.

Oil sands operations in Alberta, Canada, are a large source of secondary organic aerosol (SOA) with unknown health impacts. As a first step in closing this knowledge gap, the oxidative potential (OP), an established metric linking particle exposure to toxicological effects, of oil sands-derived SOA was investigated via OH-initiated oxidation. Experiments used a mixture of gas-phase precursors emitted from oil sands ore that is expected to be representative of mine-face emissions and three relevant single precursors (<i>n</i>-decane, <i>m</i>-xylene, and naphthalene) for comparison. The OP of the formed SOA in all cases was found to increase rapidly at short simulated photochemical ages (<1.5 days), followed by a decrease upon further oxidation (>2.5 days). This was driven by dynamic changes in SOA composition, particularly organic peroxides, quinones, and unsaturated carbonyls. The measured OP of oil sand ore SOA (OP_OS) ranged from 38.0 to 60.3 pmol min^–1 μg^–1 over photochemical ages of 0.4–4.6 days. This range of OP_OS is considerably higher than those reported for other types of aerosol particles typically present in the oil sands region, including the natural background (e.g., α-pinene and isoprene SOA). The results not only provide the first OP measurements of oil sands-derived SOA but also emphasize the importance of accounting for atmospheric aging when evaluating the oxidative potential of SOA.

Understanding the impact of biomass burning, including wildfires, on air quality requires accurate quantification of associated surface-level pollution, which is often underpredicted due to chemical aging and variable confounding sources. Using methodology that incorporates decades of aerosol spectroscopy and isolates biomass burning across wood combustion types and fire sizes, we find that biomass burning contributes over 40% of organic 5 particulate matter across a majority of 43 measurement sites in the Northeastern U.S. We differentiate substantial contributions from wildfires, prescribed burns, and other anthropogenic activities, while finding that half of smoke originates from minor events that often go undetected. With biomass burning comprising an increasing fraction of pollution, transferable approaches to routinely estimate its impacts are critical to informing science and policy in a changing world.

ABSTRACT Low‐cost air pollution sensor networks are increasingly being deployed globally, supplementing sparse regulatory monitoring with localized air quality data. In some areas, like Baltimore, Maryland, there are only a few regulatory (reference) devices but multiple low‐cost sensor networks. There are many available methods to calibrate data from each network individually, including the recently proposed Gaussian process filter (GP filter) method, which mitigates the underestimation issue of other calibration methods, models spatial correlation, and yields a dynamic calibration equation. However, separate calibration of each network using a GP filter or any other calibration approach leads to conflicting air quality predictions. In this manuscript, we extend the GP filter to jointly model data from multiple low‐cost networks and reference devices. The approach provides dynamic calibrations (informed by the latest reference data) and unified predictions (combining information from all available low‐cost and reference sensors) for the entire region. This method accounts for network‐specific bias and noise, as different networks can use different types of sensors, and uses a Gaussian process to capture spatial correlations. We apply the method to calibrate PM data from Baltimore in June and July 2023 ‐ a period including days of hazardous concentrations due to wildfire smoke. Our method helps mitigate the effects of preferential sampling of one low‐cost sensor network in Baltimore, resulting in better predictions and more precise credible intervals. Our approach can be used to calibrate low‐cost air pollution sensor data in Baltimore and other areas with multiple low‐cost networks.

The fin-and-tube heat exchangers from air conditioning (AC) units are known locations of microbial growth within the built environment. Prior studies have documented the presence of potentially harmful fungal taxa on AC coils and noted the association of AC use and elevated respiratory symptoms in building occupants. This study aims to determine the rate at which fungi can be aerosolized from AC coils during normal operation. We investigated five AC units in commercial buildings in Southern CT, USA. At the end of the cooling season, we measured size-resolved aerosol concentrations (total, biological, fungal) upstream and downstream of the coils and applied ecological analysis to determine if fungal taxa on coil surfaces were emitted into downstream air. Coils were net sinks for a broad range of total aerosol sizes (0.4 to 20 μm). However, three of the five units were net emitters of bioaerosols with average emission rates of 5.6 × 10 7 to 7.2 × 10 7 biological particles hr -1 and 1.1 × 10 4 to 6.6 × 10 5 fungal spore equivalents hr -1 . Considering only measurements indicating the units as net sources, these AC units contributed approximately 34% of biological particle and 72% of airborne fungi in the downstream air. The two net sink coils were characterized by the presence of Leotiomycetes fungi , while the emitting coils had high abundance of Cladosporium , Penicillium, Aspergillus, Stachybotrys and Malassezia fungi. While most particles were found to deposit onto these coils, there is evidence that they can become net emitters of bioaerosols into air supplied indoors. • AC Coils were net sinks for a broad range of total aerosols in the upstream air. • 60% of the investigated AC units were net emitters of bioaerosols and fungi. • The non-emitting coils were characterized by Leotiomycetes and an elevated cooling load. • The emitting coil surfaces were abundant in Cladosporium , Penicillium, Aspergillus.

In collaboration with Yale University, scientists and engineers from NOAA conducted ground-based atmospheric NH3 concentration measurements from April 27 to October 24, 2023. In this field study, continuous and high-temporal resolution measurements of atmospheric NH3 concentrations and meteorological variables were collected at the Yale Coastal Field Station (YCFS) in Guilford, CT as part of the Atmospheric Emissions and Reactions Observed from Megacities to Marine Area (AEROMMA) campaign. The objectives of this study were to characterize the magnitude and the seasonal variability of atmospheric NH3 concentrations, as well as to evaluate the effect of wind direction in order to analyze the influence of emission sources of NH3 upwind at the YCFS located in the Long Island Sound region, which often experiences poor air quality.

m), optical photothermal infrared (O-PTIR). We compare O-PTIR to existing microspectroscopy methods [Raman, fluorescence, and energy dispersive X-ray (EDX)] to study sources and aging of the complex NYC aerosol based on functional group and elemental information, which we also relate to bulk mass spectrometry methods. Single particle data shows submicron aerosol composition dominated by carbonaceous particles that fluoresce mixed with ammonium and sulfate, with a range of oxidized organic functional groups observed. At larger sizes, more primary sources (salts, dust, and biological) were observed, with nitrate being the dominant secondary anion. Collectively, the results from OPTIR and other instruments across case-study days reveal variations in sources and aging, with greater variability at larger diameters. Demonstrating the potential of O-PTIR when combined with the other methods to provide data that is important for improving air quality in urban megacities.

Asphalt-related emissions are an understudied source of reactive organic compounds with the potential to form organic aerosol (OA). Ambient aerosol mass spectrometry (AMS) measurements of asphalt-related aerosols near a month-long road paving project showed enhanced ambient OA concentrations with a mix of primary and secondary OA signatures. For comparison, gas-phase emissions from real-world road asphalt samples at application (e.g., 140 °C) and in-use (e.g., 60 °C) temperatures were injected into an environmental chamber and an oxidation flow reactor to simulate varying degrees of oxidative aging while measuring their gas- and aerosol-phase oxidation products. Secondary OA formation was observed via both self-nucleation and condensation, with chemical properties dependent on asphalt temperature and reaction conditions. The chemical composition of less-aged asphalt-related OA observed in outdoor and laboratory measurements was similar to OA from other petrochemical-based sources and hydrocarbon-like OA source factors observed via AMS in previous urban studies. The composition of aged OA varied with the degree of oxidation, similar to oxidized OA factors observed in ambient air. Taken together, these field and laboratory observations suggest that contributions to urban OA during and after application may be challenging to deconvolve from other traditional sources in ambient measurements.

Despite well over a half century of research, gaps remain in our understanding of ozone formation chemistry. Net ozone formation results from the oxidation of NO to NO2 by peroxy radicals (HO2 and RO2) followed by photolysis of NO2. Measurements of peroxy radicals made by several analytical methods over the past decade in numerous locations across the world have revealed discrepancies under high NOx conditions ([NO] &gt; 1 ppb), with zero-dimensional models apparently underestimating peroxy radical concentrations and ozone production rates (P(O3)) by up to a factor of eight. These findings suggest that models may misidentify when ozone formation is NOx-limited vs. NOx-saturated (VOC-limited) and that our knowledge of the relevant reactions is incomplete. To investigate these anomalously high P(O3) values at high NOx, we used the Drexel University Ethane Chemical AMPlifier (ECHAMP) instrument to measure total peroxy radicals at a roof-top site in Manhattan (NYC) as part of the NOAA AEROMMA/NYC-METS project. &amp;#160;A wide assortment of other measurements were made by spectroscopic and mass spectrometric methods. We will present results from this field project with special emphasis on our measurements during a few &amp;#8220;high-NOx&amp;#8221; periods (roughly defined as daytime periods with NO mixing ratios greater than 1 ppb).

Abstract Aqueous‐phase uptake and processing of water‐soluble organic compounds can promote secondary organic aerosol (SOA) production. We evaluated the contributions of aqueous‐phase chemistry to summertime urban SOA at two sites in New York City. The relative role of aqueous‐phase processing varied with chemical and environmental conditions, with evident daytime SOA enhancements (e.g., &gt;1 μg/m 3 ) during periods with relative humidities (RH) exceeding 65% and often higher temperatures. Oxygenated organic aerosol (OOA) production was also sensitive to secondary inorganic aerosols, in part through their influence on aerosol liquid water. On average, high‐RH periods exhibited a 69% increase in less‐oxidized OOA production in Queens, NY. These enhancements coincided with southerly backward trajectories and greater inorganic aerosol concentrations, yet showed substantial intra‐city variability between Queens and Manhattan. The observed aqueous‐phase SOA production, even with historically low sulfate and nitrate aerosol loadings, highlights both opportunities and challenges for continued reductions in summertime PM 2.5 in urban communities.

The importance of nitrate radicals (NO 3 ) as an atmospheric oxidant is well-established. For decades, laboratory studies of multiphase NO 3 chemistry have used the same methods – either NO 2 + O 3 reactions or N 2 O 5 thermal decomposition – to generate NO 3 as it occurs in the atmosphere. These methods, however, come with limitations, especially for N 2 O 5, which must be produced and stored under cold and dry conditions until its use. Recently, we developed a new photolytic source of gas-phase NO 3 by irradiating aqueous solutions of ceric ammonium nitrate and nitric acid. In this study, we adapted the method to maintain stable NO 3 concentrations for over 24 h. We applied the method in laboratory oxidation flow reactor (OFR) experiments to measure the yield and chemical composition of oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) formed from NO 3 oxidation of volatile organic compounds (VOCs) emitted by biogenic sources (isoprene, β-pinene, limonene, and β-caryophyllene) and biomass burning sources (phenol, guaiacol, and syringol). SOA yields and elemental ratios were typically within a factor of 2 and 10%, respectively, of those obtained in studies using conventional NO 3 sources. Maximum SOA yields obtained in our studies ranged from 0.02 (isoprene/NO 3 ) to 0.96 (β-caryophyllene/NO 3 ). The highest SOA oxygen-to-carbon ratios (O/C) ranged from 0.48 (β-caryophyllene/NO 3 ) to 1.61 (syringol/NO 3 ). Additionally, we characterized novel condensed-phase oxidation products from syringol/NO 3 reactions. Overall, the use of irradiated aqueous cerium nitrate as a source of gas-phase NO 3 may enable more widespread studies of NO 3 -initiated oxidative aging, which has been less explored compared to that of hydroxyl radical chemistry.

Dry deposition is an important yet poorly constrained process that removes reactive organic carbon from the atmosphere, making it unavailable for airborne chemical reactions and transferring it to other environmental systems. Using an aircraft-based measurement method, we provide large-scale estimates of total gas-phase organic carbon deposition rates and fluxes. Observed deposition rates downwind of large-scale unconventional oil operations reached up to 100 tC hour −1 , with fluxes exceeding 0.1 gC m −2 hour −1 . The observed deposition lifetimes (τ dep ) were short enough (i.e., 4 ± 2 hours) to compete with chemical oxidation processes and affect the fate of atmospheric reactive carbon. Yet, much of this deposited organic carbon cannot be accounted for using traditional gas-phase deposition algorithms used in regional air quality models, signifying underrepresented, but influential, chemical-physical surface properties and processes. Furthermore, these fluxes represent a major unaccounted contribution of reactive carbon to downwind freshwater ecosystems that outweigh terrestrial sources, necessitating the inclusion of dry deposition in aquatic carbon balances and models.

High Resolution Image Download MS PowerPoint Slide Fine-mode particulate matter (PM 2.5 ) is a highly detrimental air pollutant, regulated without regard for chemical composition and a chief component of wildfire smoke. As wildfire activity increases with climate change, its growing continental influence necessitates multidisciplinary research to examine smoke’s evolving chemical composition far downwind and connect chemical composition-based source apportionment to potential health effects. Leveraging advanced real-time speciated PM 2.5 measurements, including an aerosol chemical speciation monitor in conjunction with source apportionment and health risk assessments, we quantified the stark pollution enhancements during peak Canadian wildfire smoke transport to New York City over June 6–9, 2023. Interestingly, we also observed lower-intensity, but frequent, multiday wildfire smoke episodes during May–June 2023, which risk exposure misclassification as generic aged organic PM 2.5 via aerosol mass spectrometry given its extensive chemical transformations during 1 to 6+ days of transport. Total smoke-related organic PM 2.5 showed significant associations with asthma exacerbations, and estimates of in-lung oxidative stress were enhanced with chemical aging, collectively demonstrating elevated health risks with increasingly frequent smoke episodes. These results show that avoiding underestimated aged biomass burning PM 2.5 contributions, especially outside of peak episodes, necessitates real-time chemically resolved PM 2.5 monitoring to enable next-generation health studies, models, and policy under far-reaching wildfire impacts in the 21st century.

Aerosols mediate the radiative fluxes in clear and cloudy skies and dominate the uncertainty in the radiative forcing of climate. Relatively dense networks of aerosol optical depth measurements have been used to effectively constrain simulated aerosol optical properties, but model diversity of aerosol microphysical properties is much larger (Mann et al. 2014, Myhre et al. 2009). A better understanding of aerosol microphysics is essential as they are the fundamental pieces of information required to convert aerosol emissions information to radiative and cloud-nucleating properties that drive radiative effects and forcing of climate. Model representation of aerosol microphysical properties has lagged in part due to their inherently greater spatial variability, but also due to a lack of available observations. This project – the Printed Optical Particle Spectrometer Network (POPSnet)-Southern Great Plains (SGP) Pilot – launched the first spatially dense network of aerosol size distribution measurements over an area the size of a global model grid cell and demonstrated its use in providing valuable information regarding the spatial variability of aerosol microphysical properties and its drivers for improving model constraints.

When studying the impact of policy interventions or natural experiments on air pollution, such as new environmental policies or the opening or closing of an industrial facility, careful statistical analysis is needed to separate causal changes from other confounding factors. Using COVID-19 lockdowns as a case study, we present a comprehensive framework for estimating and validating causal changes from such perturbations. We propose using flexible machine learning-based comparative interrupted time series (CITS) models for estimating such a causal effect. We outline the assumptions required to identify causal effects, showing that many common methods rely on strong assumptions that are relaxed by machine learning models. For empirical validation, we also propose a simple diagnostic criterion, guarding against false effects in baseline years when there was no intervention. The framework is applied to study the impact of COVID-19 lockdowns on atmospheric nitrogen dioxide (NO2) levels in the eastern United States. The machine learning approaches guard against false effects better than common methods and suggest decreases in NO2 levels in 4 US cities (Boston, Massachusetts; New York, New York; Baltimore, Maryland; and Washington, DC) during the pandemic lockdowns. The study showcases the importance of our validation framework in selecting a suitable method and the utility of a machine learning-based CITS model for studying causal changes in air pollution time series. This article is part of a Special Collection on Environmental Epidemiology.

<strong class="journal-contentHeaderColor">Abstract.</strong> Biogenic volatile organic compounds (BVOCs) are the largest source of secondary organic aerosols (SOA) globally. However, the complex interactions between marine and terrestrial BVOCs remain unclear, inhibiting our in-depth understanding of the SOA formation in the coastal areas and its environmental impacts. Here, we performed smog chamber experiments with mixed <em>&alpha;</em>-pinene (a typical monoterpene) and dimethyl sulfide (DMS, a typical marine emission BVOC) to investigate their possible interactions and subsequent SOA formation. It is found that DMS has a non-linear effect on SOA generation: the mass concentration and yield of SOA show an increasing and then decreasing trend with the increase of the initial concentration of DMS. The increasing trend can be attributed to OH regeneration together with acid-catalyzed heterogeneous reactions by the oxidation of DMS, while the decreasing trend is explained by the high OH reactivity that inhibits the formation of low volatility products. The results from infrared spectra and mass spectra together reveal the contribution of sulfur-containing molecules in the mixed system. Moreover, the mass spectra results indicate that acidic products generated by DMS photooxidation enhance the O:C ratio, while organosulfates are produced to contribute to the formation of mixed SOA. In addition, the trends in relative abundance of highly oxygenated organic molecules (HOMs) with C₈-C₁₀ multiple functional groups in different mixed systems agree well with the turning point of the SOA yield. The findings of this study have significant implications for understanding binary or more complex systems in the atmosphere in the coastal areas.

Fine-mode particulate matter (PM2.5) is a highly detrimental air pollutant produced in large quantities from wildfires, which are increasing with climate change. Leveraging advanced chemical measurements in conjunction with source apportionment and health risk assessments, we quantified the stark pollution enhancements during Canadian wildfire smoke transport to New York City at its peak over June 6-9, 2023. Interestingly, we also observed lower-intensity, but frequent, multi-day wildfire smoke episodes during May-June 2023, which risk exposure misclassification as generic aged organic PM2.5 given its extensive chemical transformations during 1-6+ days of transport. This smoke-related organic PM2.5 showed significant associations with asthma exacerbations, and estimates of in-lung oxidative stress demonstrate the health risks of increasingly-frequent smoke episodes and potential enhancements with chemical aging. Avoiding underestimated contributions of aged biomass burning PM2.5, especially outside of peak pollution episodes, necessitates real-time chemically-resolved monitoring to enable next-generation health studies, models, and policy under far-reaching wildfire impacts.

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.&amp;#160; 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.&amp;#160; 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.&amp;#160; 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. &amp;#160;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.&amp;#160; 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. &amp;#160;Preliminary results from this dataset, including positive matrix analyses of the combined multi-reagent ion datasets, are discussed.&amp;#160; Simultaneous gas and aerosol composition measurements obtained by coupling this mass spectrometer with aerosol inlets are also described.

Abstract. Cooking is an important but understudied source of urban anthropogenic fine particulate matter (PM2.5). Using a mobile laboratory, we measured PM size and composition in urban restaurant plumes. Size distribution measurements indicate that restaurants are a source of urban ultrafine particles (UFPs, particles &lt;100 nm mobility diameter), with a mode diameter &lt;50 nm across sampled restaurants and particle number concentrations (PNCs, a proxy for UFPs) that were substantially elevated relative to the urban background. In our observations, PM mass emitted from restaurants was almost entirely organic aerosol (OA). Aerosol mass spectra show that while emissions from most restaurants were similar, there were key mass spectral differences. All restaurants emit OA at m/z 41, 43, and 55, though the composition (e.g., the ratio of oxygenated to reduced ions at specific m/z) varied across locations. All restaurant emissions included reduced-nitrogen species detected as CxHyN+ fragments, making up ∼15 % of OA mass measured in plumes, with reduced molecular functionalities (e.g., amines, imides) that were often accompanied by oxygen-containing functional groups. The largest reduced-nitrogen emissions were observed from a commercial bread bakery (i.e., 30 %–50 % of OA mass), highlighting the marked differences between restaurants and their importance for emissions of both urban UFPs and reduced nitrogen.

Anthropogenic organic carbon emissions reporting has been largely limited to subsets of chemically speciated volatile organic compounds. However, new aircraft-based measurements revealed total gas-phase organic carbon emissions that exceed oil sands industry-reported values by 1900% to over 6300%, the bulk of which was due to unaccounted-for intermediate-volatility and semivolatile organic compounds. Measured facility-wide emissions represented approximately 1% of extracted petroleum, resulting in total organic carbon emissions equivalent to that from all other sources across Canada combined. These real-world observations demonstrate total organic carbon measurements as a means of detecting unknown or underreported carbon emissions regardless of chemical features. Because reporting gaps may include hazardous, reactive, or secondary air pollutants, fully constraining the impact of anthropogenic emissions necessitates routine, comprehensive total organic carbon monitoring as an inherent check on mass closure.

As part of the summer 2022 NYC-METS (New York City metropolitan Measurements of Emissions and TransformationS) campaign and the ASCENT (Atmospheric Science and Chemistry mEasurement NeTwork) observational network, speciated particulate matter was measured in real time in Manhattan and Queens, NY, with additional gas-phase measurements. Largely due to observed reductions in inorganic sulfate aerosol components over the 21st century, summertime aerosol composition in NYC has become predominantly organic (80–83%). Organic aerosol source apportionment via positive matrix factorization showed that this is dominated by secondary production as oxygenated organic aerosol (OOA) source factors comprised 73–76% of OA. Primary factors, including cooking-related organic aerosol (COA) and hydrocarbon-like organic aerosol (HOA) comprised minor fractions of OA, only 13–15% and 10–11%, respectively. The two sites presented considerable spatiotemporal variations in OA source factor concentrations despite similar average PM 2.5 concentrations. The less- and more-oxidized OOA factors exhibited clear temperature dependences at both sites with increased concentrations and greater degrees of oxidation at higher temperatures, including during a heatwave. With strong temperature sensitivity and minimal changes in summertime concentrations since 2001, secondary OA poses a particular challenge for air quality policy in NYC that will very likely be exacerbated by continued climate change and extreme heat events.

Abstract Furans are a major class of volatile organic compounds emitted from biomass burning. Their high reactivity with atmospheric oxidants leads to the formation of secondary organic aerosol (SOA), including secondary brown carbon (BrC) that can affect global climate via interactions with solar radiation. Here, we investigate the optical properties and chemical composition of SOA generated via photooxidation of furfural, 2‐methylfuran, and 3‐methylfuran under dry (RH &lt; 5%) and humid (RH ∼ 50%) conditions in the presence of nitrogen oxides (NO x ) and ammonium sulfate seed aerosol. Dry furfural oxidation has the greatest BrC formation, including reduced nitrogen‐containing organic compounds (NOCs) in SOA, which are dominated by amines and amides formed from reactions between carbonyls and ammonia/ammonium. Based on the products detected, we propose novel formation pathways of NOCs in furfural photooxidation, which can contribute to BrC via accretion reactions during the photochemical aging of biomass burning plumes.

Abstract. We present a novel photolytic source of gas-phase NO3 suitable for use in atmospheric chemistry studies that has several advantages over traditional sources that utilize NO2 + O3 reactions and/or thermal dissociation of dinitrogen pentoxide (N2O5). The method generates NO3 via irradiation of aerated aqueous solutions of ceric ammonium nitrate (CAN, (NH4)2Ce(NO3)6) and nitric acid (HNO3) or sodium nitrate (NaNO3). We present experimental and model characterization of the NO3 formation potential of irradiated CAN / HNO3 and CAN / NaNO3 mixtures containing [CAN] = 10−3 to 1.0 M, [HNO3] = 1.0 to 6.0 M, [NaNO3] = 1.0 to 4.8 M, photon fluxes (I) ranging from 6.9 × 1014 to 1.0 × 1016 photons cm−2 s−1, and irradiation wavelengths ranging from 254 to 421 nm. NO3 mixing ratios ranging from parts per billion to parts per million by volume were achieved using this method. At the CAN solubility limit, maximum [NO3] was achieved using [HNO3] ≈ 3.0 to 6.0 M and UVA radiation (λmax⁡ = 369 nm) in CAN / HNO3 mixtures or [NaNO3] ≥ 1.0 M and UVC radiation (λmax⁡ = 254 nm) in CAN / NaNO3 mixtures. Other reactive nitrogen (NO2, N2O4, N2O5, N2O6, HNO2, HNO3, HNO4) and reactive oxygen (HO2, H2O2) species obtained from the irradiation of ceric nitrate mixtures were measured using a NOx analyzer and an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). To assess the applicability of the method for studies of NO3-initiated oxidative aging processes, we generated and measured the chemical composition of oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) from the β-pinene + NO3 reaction using a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to the HR-ToF-CIMS.

High Resolution Image Download MS PowerPoint Slide Asphalt is ubiquitous across cities and a source of organic compounds spanning a wide range of volatility and may be an overlooked source of urban organic aerosols. The emission rate and composition depend strongly on temperature, but emissions have been observed at both application temperatures and surface temperatures during warm sunny days. Here we report primary organic aerosol (POA) emissions and secondary organic aerosol (SOA) production from asphalt. We reheated real-world asphalt samples to application-relevant temperatures (∼130 °C) and typical summertime road-surface temperatures (∼55 °C) and then flushed the emitted vapors into an environmental oxidation chamber containing ammonium sulfate seed particles. SOA was then formed following the photo-oxidation of emissions under high-NO x conditions typical of urban atmospheres. We find that POA only forms at application temperature as it does not require further oxidation, whereas SOA forms under both conditions; with the resulting POA and SOA both being semi-volatile. While total OA formation rates were substantially greater under the limited time spent under application conditions, SOA formation from passive asphalt heating presents a potential long-term source, as heating continues for the lifetime of the road surface. This suggests that persistent asphalt solar heating is likely a considerable and continued source of summertime SOA in urban environments.

Low-cost air pollution sensors, offering hyperlocal characterization of pollutant concentrations, are becoming increasingly prevalent in environmental and public health research. However, low-cost air pollution data can be noisy, biased by environmental conditions, and usually need to be field-calibrated by collocating low-cost sensors with reference-grade instruments. We show, theoretically and empirically, that the common procedure of regression-based calibration, using collocated data, systematically underestimates high air pollution concentrations, which are critical to diagnose from a health perspective. Current calibration practices also often fail to utilize the spatial correlation in pollutant concentrations. We propose a novel spatial filtering approach to collocation-based calibration of low-cost networks that mitigates the underestimation issue by using an inverse regression. The inverse regression also allows for incorporating spatial correlations by a second-stage model for the true pollutant concentrations using a conditional Gaussian process. Our approach works with one or more collocated sites in the network and is dynamic, leveraging spatial correlation with the latest available reference data. Through extensive simulations, we demonstrate how the spatial filtering substantially improves estimation of pollutant concentrations and measures peak concentrations with greater accuracy. We apply the methodology for calibration of a low-cost PM2.5 network in Baltimore, Maryland, and diagnose air pollution peaks that are missed by the regression-calibration.

Mobile sources are responsible for a substantial controllable portion of the reactive organic carbon (ROC) emitted to the atmosphere, especially in urban environments of the United States. We update existing methods for calculating mobile source organic particle and vapor emissions in the United States with over a decade of laboratory data that parameterize the volatility and organic aerosol (OA) potential of emissions from on-road vehicles, nonroad engines, aircraft, marine vessels, and locomotives. We find that existing emission factor information from Teflon filters combined with quartz filters collapses into simple relationships and can be used to reconstruct the complete volatility distribution of ROC emissions. This new approach consists of source-specific filter artifact corrections and state-of-the-science speciation including explicit intermediate-volatility organic compounds (IVOCs), yielding the first bottom-up volatility-resolved inventory of US mobile source emissions. Using the Community Multiscale Air Quality model, we estimate mobile sources account for 20 %-25 % of the IVOC concentrations and 4.4 %-21.4 % of ambient OA. The updated emissions and air quality model reduce biases in predicting fine-particle organic carbon in winter, spring, and autumn throughout the United States (4.3 %-11.3 % reduction in normalized bias). We identify key uncertain parameters that align with current state-of-the-art research measurement challenges.

High Resolution Image Download MS PowerPoint Slide Exposure to ambient fine particulate matter (PM 2.5 ) is associated with millions of premature deaths annually. Oxidative stress through overproduction of reactive oxygen species (ROS) is a possible mechanism for PM 2.5 -induced health effects. Organic aerosol (OA) is a dominant component of PM 2.5 worldwide, yet its role in PM 2.5 toxicity is poorly understood due to its chemical complexity. Here, through integrated cellular ROS measurements and detailed multi-instrument chemical characterization of PM in urban southeastern United States, we show that oxygenated OA (OOA), especially more-oxidized OOA, is the main OA type associated with cellular ROS production. We further reveal that highly unsaturated species containing carbon–oxygen double bonds and aromatic rings in OOA are major contributors to cellular ROS production. These results highlight the key chemical features of ambient OA driving its toxicity. As more-oxidized OOA is ubiquitous and abundant in the atmosphere, this emphasizes the need to understand its sources and chemical processing when formulating effective strategies to mitigate PM 2.5 health impacts.

<strong class="journal-contentHeaderColor">Abstract.</strong> We present a novel photolytic source of gas-phase NO₃ suitable for use in atmospheric chemistry studies that has several advantages over traditional sources that utilize NO₂ + O₃ reactions and/or thermal dissociation of dinitrogen pentoxide (N₂O₅). The method generates NO₃ via irradiation of aerated aqueous solutions of ceric ammonium nitrate ((NH₄)₂Ce(NO₃)₆, &ldquo;CAN&rdquo;) and nitric acid (HNO₃) or sodium nitrate (NaNO₃). We present experimental and model characterization of the NO₃ formation potential of irradiated CAN/HNO₃ and CAN/NaNO₃ mixtures containing [CAN] = 10^&minus;3 to 1.0 M, [HNO₃] = 1.0 to 6.0 M, [NaNO₃] = 1.0 to 4.8 M, photon fluxes (<em>I</em>) ranging from 6.9&times;10¹⁴ to 1.0&times;10¹⁶ photons cm^&minus;2 s^&minus;1, and irradiation wavelengths ranging from 254 to 421 nm. NO₃ mixing ratios ranging from parts per billion to parts per million by volume were achieved using this method. At the CAN solubility limit, maximum [NO₃] was achieved using [HNO₃] &asymp; 3.0 to 6.0 M and UVA radiation (&lambda;_max = 369 nm) in CAN/HNO₃ mixtures or [NaNO₃] &ge; 1.0 M and UVC radiation (&lambda;_max = 254 nm) in CAN/NaNO₃ mixtures. Other reactive nitrogen (NO₂, N₂O₄, N₂O₅, N₂O₆, HNO₂, HNO₃, HNO₄) and reactive oxygen (HO₂, H₂O₂) species obtained from the irradiation of ceric nitrate mixtures were measured using a NO_x analyzer and an iodide adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). To assess the applicability of the method for studies of NO₃-initiated oxidative aging processes, we generated and measured the chemical composition of oxygenated volatile organic compounds and secondary organic aerosols from the <em>&beta;</em>-pinene + NO₃ reaction using a Filter Inlet for Gases and Aerosols (FIGAERO) coupled to the HR-ToF-CIMS.

Abstract. We present a novel photolytic source of gas-phase NO3 suitable for use in atmospheric chemistry studies that has several advantages over traditional sources that utilize NO2 + O3 reactions and/or thermal dissociation of dinitrogen pentoxide (N2O5). The method generates NO3 via irradiation of aerated aqueous solutions of ceric ammonium nitrate ((NH4)2Ce(NO3)6, “CAN”) and nitric acid (HNO3) or sodium nitrate (NaNO3). We present experimental and model characterization of the NO3 formation potential of irradiated CAN/HNO3 and CAN/NaNO3 mixtures containing [CAN] = 10−3 to 1.0 M, [HNO3] = 1.0 to 6.0 M, [NaNO3] = 1.0 to 4.8 M, photon fluxes (I) ranging from 6.9×1014 to 1.0×1016 photons cm−2 s−1, and irradiation wavelengths ranging from 254 to 421 nm. NO3 mixing ratios ranging from parts per billion to parts per million by volume were achieved using this method. At the CAN solubility limit, maximum [NO3] was achieved using [HNO3] ≈ 3.0 to 6.0 M and UVA radiation (λmax = 369 nm) in CAN/HNO3 mixtures or [NaNO3] ≥ 1.0 M and UVC radiation (λmax = 254 nm) in CAN/NaNO3 mixtures. Other reactive nitrogen (NO2, N2O4, N2O5, N2O6, HNO2, HNO3, HNO4) and reactive oxygen (HO2, H2O2) species obtained from the irradiation of ceric nitrate mixtures were measured using a NOx analyzer and an iodide adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). To assess the applicability of the method for studies of NO3-initiated oxidative aging processes, we generated and measured the chemical composition of oxygenated volatile organic compounds and secondary organic aerosols from the β-pinene + NO3 reaction using a Filter Inlet for Gases and Aerosols (FIGAERO) coupled to the HR-ToF-CIMS.

Low-cost air quality monitors are growing in popularity among both researchers and community members to understand variability in pollutant concentrations. Several studies have produced calibration approaches for these sensors for ambient air. These calibrations have been shown to depend primarily on relative humidity, particle size distribution, and particle composition, which may be different in indoor environments. However, despite the fact that most people spend the majority of their time indoors, little is known about the accuracy of commonly used devices indoors. This stems from the fact that calibration data for sensors operating in indoor environments are rare. In this study, we sought to evaluate the accuracy of the raw data from PurpleAir fine particulate matter monitors and for published calibration approaches that vary in complexity, ranging from simply applying linear corrections to those requiring co-locating a filter sample for correction with a gravimetric concentration during a baseline visit. Our data includes PurpleAir devices that were co-located in each home with a gravimetric sample for 1-week periods (265 samples from 151 homes). Weekly-averaged gravimetric concentrations ranged between the limit of detection (3 μg/m3) and 330 μg/m3. We found a strong correlation between the PurpleAir monitor and the gravimetric concentration (R>0.91) using internal calibrations provided by the manufacturer. However, the PurpleAir data substantially overestimated indoor concentrations compared to the gravimetric concentration (mean bias error ≥ 23.6 μg/m3 using internal calibrations provided by the manufacturer). Calibrations based on ambient air data maintained high correlations (R ≥ 0.92) and substantially reduced bias (e.g. mean bias error = 10.1 μg/m3 using a US-wide calibration approach). Using a gravimetric sample from a baseline visit to calibrate data for later visits led to an improvement over the internal calibrations, but performed worse than the simpler calibration approaches based on ambient air pollution data. Furthermore, calibrations based on ambient air pollution data performed best when weekly-averaged concentrations did not exceed 30 μg/m3, likely because the majority of the data used to train these models were below this concentration.

<strong class="journal-contentHeaderColor">Abstract.</strong> Mobile sources are responsible for a substantial controllable portion of the reactive organic carbon (ROC) emitted to the atmosphere, especially in urban environments of the United States (U.S.). We update existing methods for calculating mobile source organic particle and vapor emissions in the U.S. with over a decade of laboratory data that parameterize the volatility and organic aerosol (OA) potential of emissions from onroad vehicles, nonroad engines, aircraft, marine vessels, and locomotives. We find that existing emission factor information from teflon filters combined with quartz filters collapses into simple relationships and can be used to reconstruct the complete volatility distribution of ROC emissions. This new approach consists of source-specific filter artifact corrections and state-of-the-science speciation including explicit intermediate volatility organic compounds (IVOCs), yielding the first bottom-up volatility-resolved inventory of U.S. mobile source emissions. Using the Community Multiscale Air Quality model, we estimate mobile sources account for 20&ndash;25 % of the IVOC concentrations and 4.4&ndash;21.4 % of ambient OA. The updated emissions and air quality model reduce biases in predicting fine-particle organic carbon in winter, spring, and autumn throughout the U.S. (4.3&ndash;11.3 % reduction in normalized bias). We identify key uncertain parameters that align with current state-of-the-art research measurement challenges.

<strong class="journal-contentHeaderColor">Abstract.</strong> Cooking is an important but understudied source of urban anthropogenic fine particulate matter (PM_2.5). Using a mobile laboratory, we measured PM size and composition in urban restaurant&nbsp; plumes. Size distribution measurements indicate that restaurants are a source of urban ultrafine particles (UFPs, particles &lt;100 nm diameter), with a mode diameter &lt;50 nm across sampled restaurants and particle number concentrations (PNC, a proxy for UFPs) that were substantially elevated relative to the urban background. The majority of observed PM was organic aerosol (OA) by mass. Aerosol mass spectra show that while emissions from most restaurants were similar, there were key mass spectral differences. All restaurants emit OA at <em>m/z</em> 41, 43, and 55, though the composition (e.g., the ratio of oxygenated to reduced ions at specific <em>m/z</em>) varied across locations. All restaurant emissions included reduced nitrogen species detected as C_xH_yN⁺ fragments, making up ~15 % of OA mass measured in plumes, with reduced molecular functionalities (e.g., amines, imides) that were often accompanied by oxygen-containing functional groups. The largest reduced nitrogen emissions were observed from a commercial bread bakery (i.e., 30&ndash;50 % of OA mass), highlighting the marked differences between restaurants and their importance for emissions of both urban UFPs and reduced nitrogen.

Air quality policies have made substantial gains by reducing pollutant emissions from the transportation sector. In March 2020, New York City's activities were severely curtailed in response to the COVID-19 pandemic, resulting in 60-90% reductions in human activity. We continuously measured major volatile organic compounds (VOCs) during January-April 2020 and 2021 in Manhattan. Concentrations of many VOCs decreased significantly during the shutdown with variations in daily patterns reflective of human activity perturbations, resulting in a temporary ∼28% reduction in chemical reactivity. However, the limited effect of these dramatic measures was outweighed by larger increases in VOC-related reactivity during the anomalously warm spring 2021. This emphasizes the diminishing returns from transportation-focused policies alone and the risk of increased temperature-dependent emissions undermining policy-related gains in a warming climate.

<strong class="journal-contentHeaderColor">Abstract.</strong> <span>Brunia is a distinctive crustal block within the European Variscides, composed of a late Neoproterozoic arc complex overlain by Ediacaran&ndash;early Cambrian cover sequences. Sparse preservation of early Paleozoic strata obscures its pre-Variscan paleogeography. Proposed models suggest Brunia either shared a crustal domain with adjacent parts of the Bohemian Massif, represented a far-eastern extension of Avalonia accreted to Baltica in the early Paleozoic, or maintained long-term connections to Baltica since the late Ediacaran.</span> <span>To address these uncertainties, we present the first systematic study of detrital zircons (both U&ndash;Pb and Lu&ndash;Hf isotopic data) from Devonian strata overlying Brunia&rsquo;s Neoproterozoic basement. Two distinct age-spectral patterns are identified. Type-1, widespread across Brunia, exhibit a near-unimodal late Neoproterozoic peak corresponding to locally preserved arc magmatism. Type-2, display a multimodal spectrum with significant Late Ordovician&ndash;Silurian and Paleoproterozoic&ndash;early Neoproterozoic age peaks, and only minor late Neoproterozoic input.</span> <span>The Type-1 pattern reflects predominant recycling of local Brunia sources. Nearly-uniformly positive &epsilon;Hf(t) values in Neoproterozoic zircons contrast with the wide isotopic range typical of other Variscan terranes in Central and Western Europe, but are comparable with values from Avalonian strata in Newfoundland, supporting a Neoproterozoic link between West Avalonia and Brunia.</span> <span>The Type-2 pattern broadly matches Devonian detrital zircon signatures from the British Isles, the Rhenish and Harz Mountains, Dobrogea, and NW Turkey delineating the northern margin of the Rheic Ocean. Strong similarity to Ordovician&ndash;Silurian Scandinavian datasets suggests original derivation from the Caledonides and confirms an Early Devonian connection between Brunia and Baltica.</span>

Abstract. Cooking is an important but understudied source of urban anthropogenic fine particulate matter (PM2.5). Using a mobile laboratory, we measured PM size and composition in urban restaurant plumes. Size distribution measurements indicate that restaurants are a source of urban ultrafine particles (UFPs, particles &lt;100 nm diameter), with a mode diameter &lt;50 nm across sampled restaurants and particle number concentrations (PNC, a proxy for UFPs) that were substantially elevated relative to the urban background. The majority of observed PM was organic aerosol (OA) by mass. Aerosol mass spectra show that while emissions from most restaurants were similar, there were key mass spectral differences. All restaurants emit OA at m/z 41, 43, and 55, though the composition (e.g., the ratio of oxygenated to reduced ions at specific m/z) varied across locations. All restaurant emissions included reduced nitrogen species detected as CxHyN+ fragments, making up ~15 % of OA mass measured in plumes, with reduced molecular functionalities (e.g., amines, imides) that were often accompanied by oxygen-containing functional groups. The largest reduced nitrogen emissions were observed from a commercial bread bakery (i.e., 30–50 % of OA mass), highlighting the marked differences between restaurants and their importance for emissions of both urban UFPs and reduced nitrogen.