Plume Chemistry Research Articles

On the Implications of Ground‐Based High‐Definition Imaging of Io's Surface

AbstractThe capability to observe temporal changes on Io's surface at optical wavelengths has recently been demonstrated by Conrad et al. (2024, https://doi.org/10.1029/2024GL108609) using new instrumentation at the Large Binocular Telescope. Monitoring of Io's surface morphology would be impactful since preexisting metrics of the degree, location and composition of Io's plume activities are severely limited. Relationships with external data sets appear especially fruitful. Comparisons with spatially resolved data on gas distributions and thermal hots spots would better characterize composition and chemistry in Io's volcanic plumes. Comparisons with measurements remote from Io are posed to advance our understanding of atmospheric escape and how eruptions connect to transient enhancements at disparate size and time scales in the extended neutral clouds and plasma torus.

Lastarria volcano, a major emitter of boron and chalcophiles in northern Chile and the Central Volcanic Zone

This study examines the trace element chemistry of fumarolic deposits and fumarolic plumes at Lastarria volcano, located in northern Chile. Fumarolic deposits were manually collected, while fumarolic plumes were sampled using the filter pack technique; after sample preparation, both sample types were analyzed by ICP-MS. The research focuses on chalcophile elements (As, Cd, Sb, Te, Cu, Zn, Tl, Pb, and Bi) and B, with the findings revealing significant enrichment of As and Pb in fumarolic deposit samples, especially in medium- and high-temperature fumarolic vents, respectively. On the other hand, filter pack measurements in the fumarolic plume indicate a notable enrichment in Te, B, As, and Tl, with Sc-normalized enrichment factors within the range of 104–106. From these elements, B, Tl, and Te appear to be less scavenged at the vent, presenting more significant enrichments in fumarolic plumes than in fumarolic deposits. By comparing our results with subduction-related volcanoes such as Etna, Stromboli, Lascar, Masaya, or La Soufrière de Guadeloupe, Lastarria fumarolic plume can be regarded as the one with the highest concentrations of B and As ever recorded. Moreover, Lastarria has chalcophile enrichments comparable to those volcanoes with shallower magma chambers and high-temperature magmatic emissions such as Stromboli. The higher abundance of chalcophiles suggests a significant magmatic influence feeding Lastarria fumaroles and the presence of ligands, such as Cl, which can transport significant amounts of chalcophiles at shallower levels of the crust during late-stage magma crystallization. Large amounts of chalcophiles released by Lastarria and Lascar volcanoes could be responsible for the naturally elevated concentrations of these elements in the Altiplano-Puna area. Future studies should focus on the lifetime of chalcophiles in the Central Andean atmosphere, where these elements could reside for a longer time given the dominant hyperarid environment.

Evolution and persistence of SiO emission in nanosecond laser ablation plumes

Abstract Analyzing laser-produced plasmas in a controlled oxygen-containing environment provides insight into the formation and evolution of molecular species through gas-phase oxidation. This study explores the role of ambient pressure and oxygen availability in forming SiO molecular species in laser ablation plumes. The self-emission emanating during the reactive ablation of Si targets was characterized by optical emission spectroscopy and optical time-of-flight techniques. Our results showed that the SiO species formation was greatly influenced by both the ambient pressure and oxygen availability. The intensity and the persistence of SiO emission bands are lower at higher oxygen concentrations, indicating they are depopulated by the formation of more complex silicon oxides. The oxygen partial pressure effects on plume chemistry showed that SiO formation is favored even with a minimal oxygen concentration in the environment.

End of the Cretaceous

Abstract The Cretaceous ended when the Chicxulub asteroid struck the Yucatán platform, and all deposits and landforms generated are earliest Paleocene in age. Drill core from the Cretaceous–Paleogene (K–Pg) boundary sequence deposited on top of the Chicxulub impact structure's peak ring paired with geophysical data within the crater and other well-preserved marine and terrestrial K–Pg boundary sites provide insight into impact processes and effects on Earth's ecosystems, in terms of extinction and recovery. Key findings as reviewed here are: (1) the confirmation of acoustic fluidization as a physical principle to explain impact structure formation; (2) the importance of the target rock properties and marine setting for impactite depositional processes and drivers of climate change; (3) the state of understanding of extinction mechanisms and ecological recovery; and (4) implications for impact-generated hydrothermal habitat creation. Areas highlighted for the next stages of discovery include: (1) physics and chemistry of impact vapour plumes and ejecta processes; (2) sampling of the K–Pg boundary deposit and impact melt sheet within the central basin of the impact structure; (3) examination of ecosystem recovery in an ‘Early Ocean’ scenario at a range of K–Pg boundary sites; and (4) experiments and observations of impact hydrothermal systems as habitats on Earth and other worlds.

Measuring Coupled Fire–Atmosphere Dynamics: The California Fire Dynamics Experiment (CalFiDE)

Abstract The social, economic, and ecological impacts of wildfires are increasing over much of the United States and globally, partially due to changing climate and build-up of fuels from past forest management practices. This creates a need to improve coupled fire–atmosphere forecast models. However, model performance is difficult to evaluate due to scarcity of observations for many key fire–atmosphere interactions, including updrafts and plume injection height, plume entrainment processes, fire intensity and rate-of-spread, and plume chemistry. Intensive observations of such fire–atmosphere interactions during active wildfires are rare due to the logistical challenges and scales involved. The California Fire Dynamics Experiment (CalFiDE) was designed to address these observational needs, using Doppler lidar, high-resolution multispectral imaging, and in situ air quality instruments on a NOAA Twin Otter research aircraft, and Doppler lidars, radar, and other instrumentation on multiple ground-based mobile platforms. Five wildfires were studied across northern California and southern Oregon over 16 flight days from 28 August to 25 September 2022, including a breadth of fire stages from large blow-up days to smoldering air quality observations. Missions were designed to optimize the observation of the spatial structure and temporal evolution of each fire from early afternoon until sunset during multiple consecutive days. The coordination of the mobile platforms enabled four-dimensional sampling strategies during CalFiDE that will improve understanding of fire–atmosphere dynamics, aiding in model development and prediction capability. Satellite observations contributed aerosol measurements and regional context. This article summarizes the scientific objectives, platforms and instruments deployed, coordinated sampling strategies, and presents first results.

Parameterizations of US wildfire and prescribed fire emission ratios and emission factors based on FIREX-AQ aircraft measurements

Abstract. Extensive airborne measurements of non-methane organic gases (NMOGs), methane, nitrogen oxides, reduced nitrogen species, and aerosol emissions from US wild and prescribed fires were conducted during the 2019 NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality campaign (FIREX-AQ). Here, we report the atmospheric enhancement ratios (ERs) and inferred emission factors (EFs) for compounds measured on board the NASA DC-8 research aircraft for nine wildfires and one prescribed fire, which encompass a range of vegetation types. We use photochemical proxies to identify young smoke and reduce the effects of chemical degradation on our emissions calculations. ERs and EFs calculated from FIREX-AQ observations agree within a factor of 2, with values reported from previous laboratory and field studies for more than 80 % of the carbon- and nitrogen-containing species. Wildfire emissions are parameterized based on correlations of the sum of NMOGs with reactive nitrogen oxides (NOy) to modified combustion efficiency (MCE) as well as other chemical signatures indicative of flaming/smoldering combustion, including carbon monoxide (CO), nitrogen dioxide (NO2), and black carbon aerosol. The sum of primary NMOG EFs correlates to MCE with an R2 of 0.68 and a slope of −296 ± 51 g kg−1, consistent with previous studies. The sum of the NMOG mixing ratios correlates well with CO with an R2 of 0.98 and a slope of 137 ± 4 ppbv of NMOGs per parts per million by volume (ppmv) of CO, demonstrating that primary NMOG emissions can be estimated from CO. Individual nitrogen-containing species correlate better with NO2, NOy, and black carbon than with CO. More than half of the NOy in fresh plumes is NO2 with an R2 of 0.95 and a ratio of NO2 to NOy of 0.55 ± 0.05 ppbv ppbv−1, highlighting that fast photochemistry had already occurred in the sampled fire plumes. The ratio of NOy to the sum of NMOGs follows trends observed in laboratory experiments and increases exponentially with MCE, due to increased emission of key nitrogen species and reduced emission of NMOGs at higher MCE during flaming combustion. These parameterizations will provide more accurate boundary conditions for modeling and satellite studies of fire plume chemistry and evolution to predict the downwind formation of secondary pollutants, including ozone and secondary organic aerosol.

Wildfire plume ageing in the Photochemical Large Aerosol Chamber (PHOTO-LAC).

Plumes from wildfires are transported over large distances from remote to populated areas and threaten sensitive ecosystems. Dense wildfire plumes are processed by atmospheric oxidants and complex multiphase chemistry, differing from processes at typical ambient concentrations. For studying dense biomass burning plume chemistry in the laboratory, we establish a Photochemical Large Aerosol Chamber (PHOTO-LAC) being the world's largest aerosol chamber with a volume of 1800 m3 and provide its figures of merit. While the photolysis rate of NO2 (jNO2) is comparable to that of other chambers, the PHOTO-LAC and its associated low surface-to-volume ratio lead to exceptionally low losses of particles to the walls. Photochemical ageing of toluene under high-NOx conditions induces substantial formation of secondary organic aerosols (SOAs) and brown carbon (BrC). Several individual nitrophenolic compounds could be detected by high resolution mass spectrometry, demonstrating similar photochemistry to other environmental chambers. Biomass burning aerosols are generated from pine wood and debris under flaming and smouldering combustion conditions and subsequently aged under photochemical and dark ageing conditions, thus resembling day- and night-time atmospheric chemistry. In the unprecedented long ageing with alternating photochemical and dark ageing conditions, the temporal evolution of particulate matter and its chemical composition is shown by ultra-high resolution mass spectrometry. Due to the spacious cavity, the PHOTO-LAC may be used for applications requiring large amounts of particulate matter, such as comprehensive chemical aerosol characterisation or cell exposures under submersed conditions.

Evaluation of atmospheric methane concentrations and growth trends in selected locations of Rivers State, Nigeria

The study addresses the increasing atmospheric methane mixing ratios in Rivers State, Nigeria, a pressing issue linked to global warming. The objective was to analyze the growth rate and sources of methane emissions in the region. Using a quantitative approach, ground-level methane measurements were collected from seven different locations between September 2021 and June 2022, complemented by data from the Tropospheric Monitoring Instrument satellite spanning January 2019 to June 2022. The methodology combined descriptive, comparative, and regression analyses with plume chemistry modeling using the U.S. EPA Atmospheric Dispersion Modeling System software. Results indicated significant spatial variance in methane concentrations, ranging from 9.76 ppm in Ogbogu to 21.5 ppm in Choba, with notable temporal fluctuations. Regression analysis revealed a correlation between atmospheric conditions and methane levels, while plume chemistry identified a landfill near Choba market as a major emission source, raising concerns about tropospheric ozone pollution and health risks. The study highlights the need for effective waste management in Rivers State and emphasizes the importance of continuous monitoring to address the challenges posed by methane emissions and tropospheric ozone pollution.

Analyzing the Impact of Evolving Combustion Conditions on the Composition of Wildfire Emissions Using Satellite Data

AbstractWildfires have become larger and more frequent because of climate change, increasing their impact on air pollution. Air quality forecasts and climate models do not currently account for changes in the composition of wildfire emissions during the commonly observed progression from more flaming to smoldering combustion. Laboratory measurements have consistently shown decreased nitrogen dioxide (NO2) relative to carbon monoxide (CO) over time, as they transitioned from more flaming to smoldering combustion, while formaldehyde (HCHO) relative to CO remained constant. Here, we show how daily ratios between column densities of NO2 versus those of CO and HCHO versus CO from the Tropospheric Monitoring Instrument (TROPOMI) changed for large wildfires in the Western United States. TROPOMI‐derived emission ratios were lower than those from the laboratory. We discuss reasons for the discrepancies, including how representative laboratory burns are of wildfires, the effect of aerosols on trace gas retrievals, and atmospheric chemistry in smoke plumes.

Satellite Evidence of HONO/NO2 Increase With Fire Radiative Power

AbstractWildfires are important sources of atmospheric reactive nitrogen. The reactive nitrogen species partitioning generally depends on fire characteristics. One reactive nitrogen compound, nitrous acid (HONO), is a source of hydroxyl radicals and nitric oxide, which can impact the oxidizing capacity of the atmosphere and fire plume chemistry and composition. We study the Australian wildfire season of 2019–2020, known as Black Summer, where numerous large and intense wildfires burned throughout the continent. We use HONO and nitrogen dioxide (NO2) from the TROPOspheric Monitoring Instrument (TROPOMI) and fire radiative power (FRP) from the Visible Infrared Imaging Radiometer Suite to investigate HONO and NO2 relationships with fire characteristics. The ratio of HONO to NO2 increases linearly with FRP both in Australia and globally. Both Australian and global fire relationships depend strongly on land cover type. These relationships can be applied to emission inventories to improve wildfire emission representation in models.

Insights into volcanic hazards and plume chemistry from multi-parameter observations: the eruptions of Fimmvörðuháls and Eyjafjallajökull (2010) and Holuhraun (2014–2015)

The eruptions of Eyjafjallajökull volcano in 2010 (including its initial effusive phase at Fimmvörðuháls and its later explosive phase from the central volcano) and Bárðarbunga volcano in 2014–2015 (at Holuhraun) were widely reported. Here, we report on complementary, interdisciplinary observations made of the eruptive gases and lavas that shed light on the processes and atmospheric impacts of the eruptions, and afford an intercomparison of contrasting eruptive styles and hazards. We find that (i) consistent with other authors, there are substantial differences in the gas composition between the eruptions; namely that the deeper stored Eyjafjallajökull magmas led to greater enrichment in Cl relative to S; (ii) lava field SO2 degassing was measured to be 5–20% of the total emissions during Holuhraun, and the lava emissions were enriched in Cl at both fissure eruptions—particularly Fimmvörðuháls; and (iii) BrO is produced in Icelandic plumes in spite of the low UV levels.

Quantifying BrO and SO2 distributions in volcanic plumes—Recent advances in imaging Fabry-Pérot interferometer correlation spectroscopy

Bromine monoxide (BrO) and sulphur dioxide (SO2) are two gases frequently observed in volcanic plumes by spectroscopic techniques capable of continuous gas monitoring like, e.g., Differential Optical Absorption Spectroscopy (DOAS). The spatio-temporal resolution of DOAS measurements, however, only allows to determine average gas fluxes (minutes to hours resolution). In particular, it is insufficient to record two-dimensional images of SO2 and BrO in real-time (seconds time resolution). Thus, it is impossible to resolve details of chemical conversions of reactive plume constituents. However, these details are vital for further understanding reactive halogen chemistry in volcanic plumes. Therefore, instruments that combine high spatio-temporal resolution and high gas sensitivity and selectivity are required. In addition, these instruments must be robust and compact to be suitable for measurements in harsh and remote volcanic environments. Imaging Fabry-Pérot interferometer (FPI) correlation spectroscopy (IFPICS) is a novel technique for atmospheric trace gas imaging. It allows measuring atmospheric gas column density (CD) distributions with a high spatial and temporal resolution, while at the same time providing selectivity and sensitivity comparable to DOAS measurements. IFPICS uses the periodic transmission spectrum of an FPI, that is matched to the periodic narrowband (vibrational) absorption features of the target trace gas. Recently, IFPICS has been successfully applied to volcanic SO2. Here we demonstrate the applicability of IFPICS to much weaker (about two orders of magnitude) trace gas optical densities, such as that of BrO in volcanic plumes. Due to its high reactivity, BrO is extremely difficult to handle in the laboratory. Thus, based on the similarity of the UV absorption cross sections, we used formaldehyde (HCHO) as a spectral proxy for BrO in instrument characterization measurements. Furthermore, we present recent advances in SO2 IFPICS measurements and simultaneous measurements of SO2 and BrO from a field campaign at Mt Etna in July 2021. We find photon shot-noise limited detection limits of 4.7 × 1017 molec s0.5 cm−2 for SO2 and of 8.9 × 1014 molec s0.5 cm−2 for BrO at a spatial resolution of 512 × 512 pixels and 200 × 200 pixels, respectively. Furthermore, an estimate for the BrO to SO2 ratio (around 10–4) in the volcanic plume is given. The prototype instrument presented here provides spatially resolved measurements of the reactive volcanic plume component BrO. The temporal resolution of our approach allows studies of chemical conversions inside volcanic plumes on their intrinsic timescale.

An investigation of petrochemical emissions during KORUS-AQ: Ozone production, reactive nitrogen evolution, and aerosol production

Emissions and secondary photochemical products from the Daesan petrochemical complex (DPCC), on the west coast of South Korea, were measured from the NASA DC-8 research aircraft during the Korea-United States Air Quality campaign in 2016. The chemical evolution of petrochemical emissions was examined utilizing near-source and downwind plume transects. Small alkenes, such as ethene (C2H4), propene (C3H6), and 1,3-butadiene (C4H6), dominated the hydroxyl (OH) radical reactivity near the source region. The oxidation of these alkenes in the petrochemical plumes led to efficient conversion of nitrogen oxides (NOx) to nitric acid (HNO3), peroxycarboxylic nitric anhydrides (PANs), and alkyl nitrates (ANs), where the sum of the speciated reactive nitrogen contributes more than 80% of NOy within a few hours. Large enhancements of short-lived NOx oxidation products, such as hydroxy nitrates (HNs) and peroxyacrylic nitric anhydride, were observed, in conjunction with high ozone levels of up to 250 ppb, which are attributed to oxidation of alkenes such as 1,3-butadiene. Instantaneous ozone production rates, P(O3), near and downwind of the DPCC ranged from 9 to 24 ppb h−1, which were higher than those over Seoul. Ozone production efficiencies ranged from 6 to 10 downwind of the DPCC and were lower than 10 over Seoul. The contributions of alkenes to the instantaneous secondary organic aerosol (SOA) production rate, P(SOA), were estimated to be comparable to those of more common SOA precursors such as aromatics at intermediate distances from the DPCC. A model case study constrained to an extensive set of observations provided a diagnostic of petrochemical plume chemistry. The simulated plume chemistry reproduced the observed evolution of ozone and short-lived reactive nitrogen compounds, such as PANs and HNs as well as the rate and efficiency of ozone production. The simulated peroxy nitrates (PNs) budget included large contributions (approximately 30%) from unmeasured PNs including peroxyhydroxyacetic nitric anhydride and peroxybenzoic nitric anhydride. The large, predicted levels of these PAN compounds suggest their potential importance in chemical evolution of petrochemical plumes. One unique feature of the DPCC plumes is the substantial contribution of 1,3-butadiene to ozone and potentially SOA production. This work suggests that reductions in small alkene, especially 1,3-butadiene, emissions from the DPCC should be a priority for reducing downwind ozone.

A Detailed View of Turbine Combustion

A new technique to image the chemistry of exhaust plumes has potential to radically improve our understanding of turbine combustion

Observing volcanoes with drones: studies of volcanic plume chemistry with ultralight sensor systems

The study of the chemical composition of volcanic emissions is an important method for obtaining information about volcanic systems and providing indirect and unique insights into magmatic processes. However, there is a non-negligible risk associated with sampling directly at volcanic craters or maintaining geochemical monitoring stations at such locations. Spectroscopic remote sensing methods, in turn, can measure only a few species. Here, drones offer the opportunity to bring measurement systems to the scene. Standard parameters that are commonly measured are SO2 and CO2 concentrations, as well as a number of meteorological parameters. The in-flight transmission of data by radio telemetry plays an important role, since visual localization of the volcanic plume from a distance of several kilometers is practically impossible. Until now, larger and quite cost-intensive drones have been used for this purpose, which must first be transported to the site of operation at great expense. Here, we present the development and successful deployment of a very small drone system (empty weight < 0.9 kg) for chemical characterization of volcanic plumes that can be easily transported on foot to difficult-to-access terrain and, moreover, requires only minimal flight and administrative preparations for operation as an aerial observation platform.

Reactive pulsed laser deposition of low particulate density and epitaxial TiN films on Si (100) for functional oxide integration

• Low particulate density epitaxial TiN on Si (100) is deposited via reactive PLD. • Plume chemistry (N/Ti) alters the structure and microstructure of the TiN film. • TiN films roughen in RPLD process under low N availability. • Edge mobility along ><˃˄110> TiN limits the lateral growth rates. • Ferroelectric BaTiO 3 is epitaxially integrated on reactive PLD TiN/Si. Epitaxial TiN films on (100) Si have been realized by reactive pulsed laser deposition (PLD). Their utility is demonstrated by subsequent growth of epitaxial BaTiO 3 . PLD geometry optimization has yielded TiN films with a low particulate density, ∼ 6 × 10 3 cm −2 , but with a growth rate, ∼1 μm/hr, comparable to the standard On-axis geometry. The method of heat up to growth temperatures yields oxide free epitaxial interface, (001) TiN ||(001) Si and <100> TiN ||<100> Si and ω-scan full width at half maximum of 1.2° in symmetric and asymmetric geometries. Repetition rate and fluence effect studies have resulted in films with a surface roughness of < 5 nm as required for device fabrication. Parameters that increase surface roughness also raise oxygen incorporation. A BaTiO 3 -TiN-Si stack, (001) BaTiO3 ||(001) TiN ||(001) Si and <100> BaTiO3 ||<100> TiN ||<100> Si , is demonstrated with switchable out of plane polarization.

Effect of gas flow on a helium/oxygen endoscopic plasma jet

This experimental study characterized the effect of carrier gas flow on an endoscopic plasma jet. This system generates and transports helium plasma in a tube over several meters, along with a separate channel transporting oxygen to enhance plasma reactivity on site. The resulting plasma plume exiting the tube allows treatment of tissue surfaces in an endoscopic setting with a view to perform therapeutic operations in the gastrointestinal tract. In a closed cavity simulating the tract, the carrier gas flow was studied by a combined approach investigating plasma plume chemistry, fluid dynamics, and plasma effects on the surface of a hydrogel tissue model reporting oxidation. These three aspects are shown to be closely inter-related. Plasma plume length, intensity, and shape strongly depend on helium content, velocity, turbulence, and environment. Optical emission spectroscopy was used to show that the helium gas flow rate increases the amount of helium and reactive oxygen species (ROS) in the plume. Schlieren imaging was used to visualize the transition of the fluid from buoyant to laminar and finally turbulent depending on flow rate, with a backflow in a closed cavity. Finally, the frontal and radial treatment of the cavity was assessed by measuring ROS delivery to a KI-starch agarose gel model. Helium flow rate had a noticeable effect on the treatment distribution profile and treatment intensity, with different maxima for frontal and radial treatments. This combined approach, in an accurate simulation of the target configuration (i.e. a closed, cylindrical cavity), is necessary to optimize treatment, as its outcome depends on a balance between ROS production, transport, and distribution.

Investigating laser ablated plume dynamics of carbon and aluminum targets

Recently acquired high-resolution images of nanosecond laser ablation plumes suggest a strong correlation between the internal plume structure and the type of material being ablated. However, the details of this relation are currently not well understood. In this work, we attempt to explore this correlation using a 2D radiation hydrodynamics model to study the dependence of internal plume structure formation on the ablation material. Spatio-temporal emission maps and plume expansion velocities from experimental measurements are compared with the model predictions, including synthetic emission maps. The shape and expansion rate of an outer air plume region are found to be in good agreement for both carbon and aluminum, as are the inner material plume dynamics for carbon ablation. The largest disagreement is observed in the case of a polished aluminum target, where the chaotic inner plume features seen in the experimental images are not observed in the model. The possible physical mechanisms responsible for this discrepancy are discussed. This effort constitutes a continued development toward a predictive model of ablation plume dynamics and chemistry for various materials in extreme environments.

Understanding the Evolution of Groundwater‐Contaminant Plume Chemistry Emanating from Legacy Contaminant Sources: An Example from a Long‐Term Crude Oil Spill

AbstractUnderstanding the evolution of plumes emanating from residual hydrocarbon contaminant sources requires evaluating how changes in source compositions over time cause changes in dissolved plume chemistry as residual sources age. This study investigates such changes at the site of a 1979 crude‐oil pipeline spill and is the first comprehensive look at groundwater chemistry associated with a residual hydrocarbon source zones in different stages of aging. The data show a direct relationship between concentrations of benzene and naphthalene in the residual oil and those measured in water samples collected below the oil. Groundwater associated with oil near the spill site had different chemical composition compared with water associated with oil that had spread downgradient from the spill zone, indicating a shift in biodegradation reactions. These results emphasize that source zone processes are spatially and temporally heterogeneous and should be accounted for in natural attenuation studies where residual source zones persist.

Photochemical evolution of the 2013 California Rim Fire: synergistic impacts of reactive hydrocarbons and enhanced oxidants

Abstract. Large wildfires influence regional atmospheric composition, but chemical complexity challenges model predictions of downwind impacts. Here, we elucidate key connections within gas-phase photochemistry and assess novel chemical processes via a case study of the 2013 California Rim Fire plume. Airborne in situ observations, acquired during the NASA Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) mission, illustrate the evolution of volatile organic compounds (VOCs), oxidants, and reactive nitrogen over 12 h of atmospheric aging. Measurements show rapid formation of ozone and peroxyacyl nitrates (PNs), sustained peroxide production, and prolonged enhancements in oxygenated VOCs and nitrogen oxides (NOx). Observations and Lagrangian trajectories constrain a 0-D puff model that approximates plume photochemical history and provides a framework for evaluating process interactions. Simulations examine the effects of (1) previously unmeasured reactive VOCs identified in recent laboratory studies and (2) emissions and secondary production of nitrous acid (HONO). Inclusion of estimated unmeasured VOCs leads to a 250 % increase in OH reactivity and a 70 % increase in radical production via oxygenated VOC photolysis. HONO amplifies radical cycling and serves as a downwind NOx source, although impacts depend on how HONO is introduced. The addition of initial HONO (representing primary emissions) or particulate nitrate photolysis amplifies ozone production, while heterogeneous conversion of NO2 suppresses ozone formation. Analysis of radical initiation rates suggests that oxygenated VOC photolysis is a major radical source, exceeding HONO photolysis when averaged over the first 2 h of aging. Ozone production chemistry transitions from VOC sensitive to NOx sensitive within the first hour of plume aging, with both peroxide and organic nitrate formation contributing significantly to radical termination. To simulate smoke plume chemistry accurately, models should simultaneously account for the full reactive VOC pool and all relevant oxidant sources.