Browsing by Author "Carlton, Annmarie G."
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Item Investigating the evolution of water-soluble organic carbon in evaporating cloud water(Royal Society of Chemistry, 2020-12-22) Pratap, Vikram; Christiansen, Amy E.; Carlton, Annmarie G.; Lance, Sara; Casson, Paul; Dukett, Jed; Hassan, Hesham; Schwab, James J.; Hennigan, Christopher J.Cloud cycling plays a key role in the evolution of atmospheric particles and gases, producing secondary aerosol mass and transforming the optical properties and impacts of aerosols globally. In this study, bulk cloud water samples collected at Whiteface Mountain (Wilmington, NY) in the summer of 2017 were aerosolized, dried to 50% RH, and analyzed for the evaporative loss of water soluble organic carbon (WSOC) and for brown carbon (BrC) formation. Systematic WSOC evaporation occurred in all cloud water samples, while no evidence for drying induced BrC formation was observed. On average, 11% (±3%) of WSOC evaporated when the aerosolized cloud droplets were dried to 50% RH, though this represents a lower bound on the WSOC reversibly partitioned to clouds due to experimental constraints. To our knowledge, this represents the first direct measurements of organic evaporation from actual cloud water undergoing drying. Formate and acetate contributed 19%, on average, to the evaporated WSOC, while no oxalate evaporation occurred. GECKO-A model simulations were carried out to predict the production of WSOC compounds that reversibly partition to cloud water from photooxidation of an array of VOCs. The model results suggest that precursor VOC identity and oxidation regime (VOC:NOx) have a dramatic effect on the reversible partitioning of WSOC to cloud water and the abundance of aqSOA precursors, though the higher abundance of reversibly partitioned WSOC predicted by the model may be due to aqueous production of low-volatility material in the actual cloud samples. This study underscores the importance of the large fraction of unidentified compounds that contribute to WSOC in cloud water and their aqueous processing.Item On Aerosol Liquid Water and Sulfate Associations: The Potential for Fine Particulate Matter Biases(MDPI, 2020-02-12) Babila, Jonathon E.; Carlton, Annmarie G.; Hennigan, Christopher J.; Ghate, Virendra P.In humid locations of the Eastern U.S., sulfate is a surrogate for aerosol liquid water (ALW), a poorly measured particle constituent. Regional and seasonal variation in ALW–sulfate relationships offers a potential explanation to reconcile epidemiology and toxicology studies regarding particulate sulfur and health endpoints. ALW facilitates transfer of polar species from the gas phase to the particle phase and affects particle pH and metal oxidation state. Though abundant and a potential indicator of adverse health endpoints, ALW is largely removed in most particulate matter measurement techniques, including in routine particulate matter (PM₂.₅) networks that use federal reference method (FRM) monitors, which are used in epidemiology studies. We find that in 2004, a typical year in the available record, ambient ALW mass is removed during sampling and filter equilibration to standard laboratory conditions at most (94%) sites, up to 85% of the ambient water mass. The removal of ALW can induce the evaporation of other semi-volatile compounds present in PM₂.₅, such as ammonium nitrate and numerous organics. This produces an artifact in the PM mass measurements that is, importantly, not uniform in space or time. This suggests that PM₂.₅ epidemiology studies that exclude ALW are biased. This work provides a plausible explanation to resolve multi-decade discrepancies regarding ambient sulfate and health impacts in some epidemiological and toxicological studies.Item Urban aerosol chemistry at a land-water transition site during summer – Part 1: Impact of agricultural and industrial ammonia emissions(Copernicus Publications, 2021-05-18) Balasus, Nicholas; Battaglia, Michael A.; Ball, Katherine; Caicedo, Vanessa; Delgado, Ruben; Carlton, Annmarie G.; Hennigan, Christopher J.This study characterizes the impact of the Chesapeake Bay and associated meteorological phenomena on aerosol chemistry during the second Ozone Water-Land Environmental Transition Study (OWLETS-2) field campaign during summer 2018. Measurements of inorganic PM₂.₅ composition, gas-phase ammonia (NH₃), and an array of meteorological parameters were undertaken at Hart-Miller Island (HMI), a land-water transition site just east of downtown Baltimore on the Chesapeake Bay. The observations at HMI were characterized by abnormally high NH₃ concentrations (maximum of 19.3 μg m⁻³, average of 3.83 μg m⁻³), which were more than a factor of three higher than NH₃ levels measured at the closest Atmospheric Ammonia Network (AMoN) site (approximately 45 km away). While sulfate concentrations at HMI agreed quite well with those measured at a regulatory monitoring station 45 km away, aerosol ammonium and nitrate concentrations were significantly higher, due to the ammonia-rich conditions that resulted from the elevated NH₃. The high NH₃ concentrations were largely due to regional agricultural emissions, including dairy farms in southeastern Pennsylvania and poultry operations in the Delmarva Peninsula (Delaware-Maryland-Virginia). Reduced NH₃ deposition during transport over the Chesapeake Bay likely contributed to enhanced concentrations at HMI compared to the more inland AMoN site. Several peak NH₃ events were recorded, including the maximum NH₃ observed during OWLETS-2, that appear to originate from a cluster of industrial sources near downtown Baltimore. Such events were all associated with nighttime emissions and advection to HMI under low 15 wind speeds (< 1 m s⁻¹) and stable atmospheric conditions. Our results demonstrate the importance of industrial sources, including several that are not represented in the emissions inventory, on urban air quality. Together with our companion paper, which examines aerosol liquid water and pH during OWLETS-2, we highlight unique processes affecting urban air quality of coastal cities that are distinct from continental locations.Item Urban aerosol chemistry at a land-water transition site during summer – Part 2: Aerosol pH and liquid water content(Copernicus Publications, 2021-05-28) Battaglia, Michael A. Jr.; Balasus, Nicholas; Ball, Katherine; Caicedo, Vanessa; Delgado, Ruben; Carlton, Annmarie G.; Hennigan, Christopher J.Particle acidity (aerosol pH) is an important driver of atmospheric chemical processes and the resulting effects on human and environmental health. Understanding the factors that control aerosol pH is critical when enacting control strategies targeting specific outcomes. This study characterizes aerosol pH at a land-water transition site near Baltimore, MD during summer 2018 as part of the second Ozone Water-Land Environmental Transition Study (OWLETS-2) field campaign. Inorganic fine mode aerosol composition, gas-phase NH₃ measurements, and all relevant meteorological parameters were used to characterize the effects of temperature, aerosol liquid water (ALW), and composition on predictions of aerosol pH. Temperature, the factor linked to the control of NH₃ partitioning, was found to have the most significant effect on aerosol pH during OWLETS-2. Overall, pH varied with temperature at a rate of −0.047 K⁻¹ across all observations, though the sensitivity was −0.085 K⁻¹ for temperatures > 293 K. ALW had a minor effect on pH, except at the lowest ALW levels (< 1 µg m⁻³) which caused a significant increase in aerosol acidity (decrease in pH). Aerosol pH was generally insensitive to composition (SO₄²⁻ , SO₄²⁻:NH₄⁺ , Tot-NH₃ = NH₃ ⁺ NH₄⁺), consistent with recent studies in other locations. In a companion paper, the sources of episodic NH₃ events (95th percentile concentrations, NH₃ > 7.96 µg m⁻³) during the study are analyzed; aerosol pH was higher by only ~0.1–0.2 pH units during these events compared to the study mean. A case study was analyzed to characterize the response of aerosol pH to nonvolatile cations (NVCs) during a period strongly influenced by primary Chesapeake Bay emissions. Depending on the method used, aerosol pH was estimated to be either weakly (~0.1 pH unit change based on NH₃ partitioning calculation) or strongly (~1.4 pH unit change based on ISORROPIA thermodynamic model predictions) affected by NVCs. The case study suggests a strong pH gradient with size during the event and underscores the need to evaluate assumptions of aerosol mixing state applied to pH calculations. Unique features of this study, including the urban land-water transition site and the strong influence of NH₃ emissions from both agricultural and industrial sources, add to the understanding of aerosol pH and its controlling factors in diverse environments.