Overshooting storms are convective systems with updrafts that penetrate through the tropopause into the overlying stratosphere. These storms can rapidly transport a wide variety of chemical species and aerosols from the boundary layer and free troposphere directly to the stratosphere. The central plains of the U.S. and the Sierra Madre Occidental of Mexico are two of the global hotspots for overshooting convection. While the existence of these storms has been known for several decades, the amount of tropospheric air, including water vapor, trace gases, and aerosols, transported across the tropopause is poorly understood, as is their impact on the dynamics, chemistry, and radiative balance of the stratosphere. Climate models suggest that as Earth’s climate continues to warm, overshooting convection over the U.S. may increase, potentially causing changes to stratospheric composition and transport. To address these scientific questions, the NASA ER-2 high-altitude research aircraft flew 31 missions during the summers of 2021 and 2022 to make observations of the outflow from overshooting storms in the stratosphere over North America and the eastern Pacific Ocean as part of the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) project. The ER-2 carried a payload of 12 instruments to measure meteorological parameters, water and its isotopologues, trace gases, and aerosol properties. Ozone, water vapor, and aerosol sondes were also launched on balloons during the field deployments. This paper describes the science goals of the DCOTSS project, the aircraft measurement strategy, the data produced by the project, and highlights of science results to date.

Ice nucleating particles (INPs) exert a substantial impact on radiative properties and lifetimes of mixed-phase clouds and can modulate their precipitation efficiency. Advancing our understanding of the abundance and properties of INPs is essential to elucidate how clouds change in a warming climate. We conducted INP measurements at the Storm Peak Laboratory (3200 m a.s.l.), in the Rocky Mountains (CO, USA) during two field campaigns in 2021/2022 and in 2025. INP concentrations were continuously measured with the Portable Ice Nucleation Experiment between-22 and-32 degrees C. INP concentrations were remarkably similar during the two campaigns and followed a seasonal pattern. Lowest concentrations were observed during winter, with median January values falling below 10 INP stdL(-1) at T >-26 degrees C. In spring, median INP concentrations increased by approximately one order of magnitude. Springtime is associated with increased dust concentrations in the Western United States, and back trajectories revealed regional and local dust regions as INP sources. As climate change is expected to intensify the influence of dust sources from deserts and semi-arid regions, this might impact INP concentrations. Moreover, INP sizes were investigated by ranked correlation coefficient analysis of parallel measurements of super-micrometer particles, and alternated INP measurements behind a 1 & micro;m impactor. In addition, for the first time, PINE was coupled to a pumped counterflow virtual impactor to analyze the sizes of ice residuals. Overall, super-micrometer particles were found to contribute significantly to the INP population throughout the entire campaign, with a reduced importance during winter.

The role of secondary organic aerosol (SOA) in atmospheric ice nucleation is not well understood, limiting accurate predictions of aerosol indirect effects in global climate simulations. This article details experiments performed to characterize the ice-nucleating properties of proxy SOA. Experimental techniques in conditioning aerosol to glass transition temperatures (T-g) as low as-70 degrees C using a pre-cooling unit are described. Ice nucleation measurements of proxy organosulfates (i.e., methyl, ethyl, and dodecyl sulfates) and citric acid were performed using the SPectrometer for ice nucleation (SPIN), operating at conditions relevant to upper-tropospheric cirrus temperatures (-45 degrees C, -40 degrees C, -35 degrees C) and ice saturation ratios (1.0 < S-ice < 1.6). Methyl, ethyl, and dodecyl sulfates did not nucleate ice, despite dodecyl sulfate possessing a T(g )higher than ambient temperature. Citric acid nucleated ice heterogeneously at-45 and-40 degrees C (1.2 < S-ice < 1.4) but required pre-cooling temperatures of-70 degrees C, notably colder than the lowest published T-g. A kinetic flux model was used to numerically estimate water diffusion timescales to verify experimental observations and predict aerosol phase state. Diffusion modeling showed rapid liquefaction of glassy methyl and ethyl sulfates due to high hygroscopicity, preventing heterogeneous ice nucleation. The modeling results suggest that citric acid nucleated ice heterogeneously via deposition freezing or immersion freezing after surface liquefaction. We conclude that Tg alone is not sufficient for predicting heterogeneous ice formation for proxy SOA using the SPIN.

The increasing size, severity, and frequency of wildfires have led to dramatic increases in particulate matter concentrations in the troposphere. Severe wildfires can generate intense convective systems capable of transporting large quantities of biomass burning organic aerosols (BBOA) to the upper troposphere and lower stratosphere (UTLS). Chemically complex organic matter and light-absorbing carbonaceous material is introduced into stratospheric regions that were historically isolated from direct surface emissions. In this study, stratospheric particles were sampled over North America during the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) campaign, an aircraft-based research project designed to characterize convective perturbation in the UTLS. Particle samples collected from six research flights during summer 2022 were analyzed using Computer-Controlled Scanning Electron Microscopy and Scanning Transmission X-ray Microscopy to investigate particle size distributions, morphology, chemical composition, and mixing state of stratospheric particles along transects across the continental United States and adjacent Pacific Ocean airspace. Analysis revealed that all sampled particles contained detectable levels of carbon, with most exhibiting organic volume fractions of 0.37 +/- 0.20. Notably, about 5% of the particles also contained soot inclusions, which indicates the presence of refractory black carbon transported to stratospheric altitudes and provides direct evidence of wildfire-derived black carbon reaching the UTLS. Typical particle morphology exhibits organic shells over soot and inorganic cores and suggests secondary processing and aging of BBOA during transport to and within the UTLS. These findings provide compelling evidence that wildfire emissions play a critical role in affecting the long-term composition and radiative properties of stratospheric particles.

Perchlorate is a toxic, regulated contaminant in drinking water. According to previous isotopic studies, much of the perchlorate deposited to the Earth's surface is formed in the atmosphere, with 36Cl suggesting a large contribution from the stratosphere. Here, we present measurements of perchlorate in stratospheric aerosol particles and confirm that the stratosphere is an important source of perchlorate, whereas we did not observe production in the troposphere. Mass mixing ratios of aerosol perchlorate in the stratosphere were 1 to 10 parts per trillion by mass (pptm), with the highest concentrations observed in summer and in the Southern Hemisphere. Almost all of the perchlorate is in biomass burning and nitrogen-rich particles, despite those types contributing only a few percent of the aerosol particles. Such particles are less acidic than the majority of sulfuric acid particles. If the formation of perchlorate is sensitive to acidity, then the injection of some materials for solar radiation modification might significantly increase the global production of perchlorate.

The third phase of the Fifth International Ice Nucleation Workshop (FIN-03) was conducted at the Storm Peak Laboratory in Steamboat Springs, Colorado, in September 2015 to facilitate the intercomparison of instruments measuring ice-nucleating particles (INPs) in the field. Instruments included two online and four offline measurement systems for INPs, which are a subset of those utilized in the laboratory study that comprised the second phase of FIN (FIN-02). The composition of the total aerosols was characterized using the Particle Analysis by Laser Mass Spectrometry (PALMS) and Wideband Integrated Bioaerosol Sensor (WIBS) instruments, and aerosol size distributions were measured by a laser aerosol spectrometer (LAS). The dominant total particle compositions present during FIN-03 were composed of sulfates, organic compounds, and nitrates, as well as particles derived from biomass burning. Mineral-dust-containing particles were ubiquitous throughout and represented 67 % of supermicron particles. Total WIBS fluorescing particle concentrations for particles with diameters of > 0.5 mu m were 0.04 +/- 0.02 cm-3 (0.1 cm-3 highest; 0.02 cm-3 lowest), typical of the warm season in this region and representing approximate to 9 % of all particles in this size range as a campaign average. The primary focus of FIN-03 was the measurement of INP concentrations via immersion freezing at temperatures > -33 degrees C. Additionally, some measurements were made in the deposition nucleation regime at these same temperatures, representing one of the first efforts to include both mechanisms within a field campaign. INP concentrations via immersion freezing agreed within factors ranging from nearly 1 to 5 times on average between matched (time and temperature) measurements, and disagreements only rarely exceeded 1 order of magnitude for sampling times coordinated to within 3 h. Comparisons were restricted to temperatures lower than -15 degrees C due to the limits of detection related to sample volumes and very low INP concentrations. Outliers of up to 2 orders of magnitude occurred between -25 and -18 degrees C; a better agreement was seen at higher and lower temperatures. Although the 5-10 factor agreement of INP measurements found in FIN-03 aligned with the results of the FIN-02 laboratory comparison phase, giving confidence in progress of this measurement field, this level of agreement still equates to temperature uncertainties of 3.5 to 5 degrees C that may not be sufficient for numerical cloud modeling applications that utilize INP information. INP activity in the immersion-freezing mode was generally found to be an order of magnitude or more, making it more efficient than in the deposition regime at 95 %-99 % water relative humidity, although this limited data set should be augmented in future efforts. To contextualize the study results, an assessment was made of the composition of INPs during the late-summer to early-fall period of this study inferred through comparison to existing ice nucleation parameterizations and through measurement of the influence of thermal and organic carbon digestion treatments on immersion-freezing ice nucleation activity. Consistent with other studies in continental regions, biological INPs dominated at temperatures of > -20 degrees C and sometimes colder, while arable dust-like or other organic-influenced INPs were inferred to dominate below -20 degrees C.

Organic aerosols (OAs) may serve as ice-nucleating particles (INPs), impacting the formation and properties of cirrus clouds when their phase state and viscosity are in the semisolid to glassy range. However, there is a lack of direct parameterization between aerosol viscosity and their ice nucleation capabilities. In this study, we experimentally measured the ice nucleation rate of 2-methyltetrols (2-MT) aerosols, a key component of isoprene-epoxydiol-derived secondary organic aerosols (IEPOX-SOA), at different viscosities. These results demonstrate that the phase state has a significant impact on the ice nucleation abilities of OA under typical cirrus cloud conditions, with the ice nucleation rate increasing by 2 to 3 orders of magnitude when the phase state changes from liquid to semisolid. An innovative parametric model based on classical nucleation theory was developed to directly quantify the impact of viscosity on the heterogeneous nucleation rate. This model accurately represents our laboratory measurement and can be implemented into climate models due to its simple, equation-based form. Based on data collected from the ACRIDICON-CHUVA field campaign, our model predicts that the INP concentration from IEPOX-SOA can reach the magnitude of 1 to tens per liter in the cirrus cloud region impacted by the Amazon rainforest, consistent with recent field observations and estimations. This novel parameterization framework can also be applied in regional and global climate models to further improve representations of cirrus cloud formation and associated climate impacts.

Large wildfires can generate pyrocumulonimbus (pyroCb) clouds that transport substantial amounts of smoke into the upper troposphere and lower stratosphere (UT/LS), perturbing aerosol budget and properties in these regions. Despite projections of increasing pyroCb events in the future, their climate impact, particularly the radiative forcing of smoke aerosols, remains poorly constrained, primarily due to limited direct measurements. Here we present aircraft measurements of aerosols and gases within 5-day-old pyroCb smoke plumes from a New Mexico wildfire, sampled at altitudes of 14-15 km. The aerosols, primarily organic biomass burning particles, exhibited an unusually large number-mode diameter of 500-600 nm. Microphysical simulations suggest that such large aerosols can form through combinations of cloud processing and coagulation in the relatively stable UT/LS environment. These large pyroCb aerosols increase outgoing radiation (aerosol-only perturbation) by 30-36% compared to typical non-pyroCb smoke aerosols with mode diameters of 200-300 nm, causing an instantaneous enhancement in cooling of the atmospheric column. Many climate models use smaller aerosol sizes for smoke than those observed for pyroCb aerosols, potentially underestimating the radiative cooling effects of pyroCb events. With a rising prevalence of pyroCb aerosols in a warming climate, accurately representing their size and optical properties in climate models is crucial.

An updated version of the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument, termed PALMS-NG (-Next Generation), has been designed to characterize particles in the troposphere and stratosphere. Two PALMS-NG instruments have been built: a Purdue University version, which has flown on the National Aeronautics and Space Administration (NASA) ER-2 and DC-8, and a National Oceanic and Atmospheric Administration (NOAA) version, which has flown on the NASA WB-57F. The general design and construction are nearly identical. New features and construction techniques are described here. These include a new inlet, optics for an extended size range of particle measurement, and a unique bipolar s-shape mass spectrometer with higher resolution. These make the -NG instrument a significant improvement over the original flight PALMS which was first flown 25 years ago.Copyright (c) 2024 American Association for Aerosol Research

Ice crystal formation in mixed-phase clouds is initiated by specific aerosol particles, termed ice-nucleating particles (INPs). Only a tiny fraction of all aerosol particles are INPs, providing a challenge for contemporary INP measurement techniques. Models have shown that the presence of INPs in clouds can impact their radiative properties and induce precipitation formation. However, for a qualified implementation of INPs in models, measurement techniques able to accurately detect the temperature-dependent INP concentration are needed. Here we present measurements of INP concentrations in ambient air under conditions relevant to mixed-phase clouds from a total of 10 INP methods over 2 weeks in October 2018 at the Puy de Dôme observatory in central France. A special focus in this intercomparison campaign was placed on having overlapping sampling periods. Although a variety of different measurement principles were used, the majority of the data show INP concentrations within a factor of 5 of one another, demonstrating the suitability of the instruments to derive model-relevant INP data. Lower values of comparability are likely due to instrument-specific features such as aerosol lamina spreading in continuous-flow diffusion chambers, demonstrating the need to account for such phenomena when interpreting INP concentration data from online instruments. Moreover, consistently higher INP concentrations were observed from aerosol filters collected on the rooftop at the Puy de Dôme station without the use of an aerosol inlet.

Knowledge of the chemical composition and mixing state of aerosols at a single-particle level is critical for gaining insights into atmospheric processes. One common tool to make these measurements is single-particle mass spectrometry. There remains a need to compare the performance of different single-particle mass spectrometers (SPMSs). An intercomparison of SPMSs was conducted at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber at the Karlsruhe Institute of Technology (KIT) in November 2014, as part of the first phase of the Fifth International Workshop on Ice Nucleation (FIN-01). In this paper we compare size distributions and mass spectra of atmospherically relevant particle types measured by five SPMSs. These include different minerals, desert and soil dusts, soot, bioaerosol (Snomax; protein granule), secondary organic aerosol (SOA), and SOA-coated mineral particles. Most SPMSs reported similar vacuum aerodynamic diameter (dva) within typical instrumental ranges from similar to 100-200 nm (lower limit) to similar to 2-3 mu m (upper limit). In general, all SPMSs exhibited a wide dynamic range (up to similar to 103) and high signal-to-noise ratio (up to similar to 104) in mass spectra. Common spectral features with small diversities in mass spectra were found with high average Pearson's correlation coefficients, i.e., for average positive spectra ravg-pos=0.74 +/- 0.12 and average negative spectra ravg-neg=0.67 +/- 0.22. We found that instrument-specific detection efficiency (DE) was more dependent on particle size than particle type, and particle identification favored the use of bipolar, rather than monopolar, instruments. Particle classification from "blind experiments" showed that all instruments differentiated SOA, soot, and soil dust and detected subtle changes in the particle internal mixing but had difficulties differentiating among specific mineral types and dusts. This study helps to further understand the capabilities and limitations of the single-particle mass spectrometry technique in general and the specific performance of the instrument in characterizing atmospheric aerosol particles.

Abstract. Aerosol particles have both natural and anthropogenic origins and are ubiquitous in the atmosphere. One particularly important type is carbonaceous aerosol, including a specific subset often termed “elemental carbon” chemically or “black carbon” (BC) radiatively. Carbonaceous aerosol particles have implications for atmospheric chemistry, human health, and climate, both directly and via their ability to act as sites of cloud droplet or ice crystal formation. Laboratory experiments and theory are needed to better understand these particles, specifically their radiative impact. Here we present laboratory measurements of scattering of visible radiation by analogs of atmospheric BC aggregates at scattering angles of 135±20∘ obtained using a depolarizing optical particle counter and accompanying theoretical calculations of scattering by compact and fractal theoretical BC aggregates. We show that, with random orientation, the theoretical calculations reproduce the qualitative behavior of the measurements but are unable to reproduce the highest values of the linear depolarization ratio; we are only able to obtain high values of the linear depolarization ratio using fixed orientation. Both our measurements and our theoretical calculations point to the possibility that fresh, unaged, bare, or uncoated BC aggregates, as opposed to the aged or coated BC or soot that was investigated in previous studies, can exhibit a higher back-scattering linear depolarization than previously assumed.

Large increases in the number of low earth orbit satellites are projected in the coming decades [L. Schulz, K.-H. Glassmeier, Adv. Space Res. 67, 1002-1025 (2021)] with perhaps 50,000 additional satellites in orbit by 2030 [GAO, Large constellations of satellites: Mitigating environmental and other effects (2022)]. When spent rocket bodies and defunct satellites reenter the atmosphere, they produce metal vapors that condense into aerosol particles that descend into the stratosphere. So far, models of spacecraft reentry have focused on understanding the hazard presented by objects that survive to the surface rather than on the fate of the metals that vaporize. Here, we show that metals that vaporized during spacecraft reentries can be clearly measured in stratospheric sulfuric acid particles. Over 20 elements from reentry were detected and were present in ratios consistent with alloys used in spacecraft. The mass of lithium, aluminum, copper, and lead from the reentry of spacecraft was found to exceed the cosmic dust influx of those metals. About 10% of stratospheric sulfuric acid particles larger than 120 nm in diameter contain aluminum and other elements from spacecraft reentry. Planned increases in the number of low earth orbit satellites within the next few decades could cause up to half of stratospheric sulfuric acid particles to contain metals from reentry. The influence of this level of metallic content on the properties of stratospheric aerosol is unknown.

A new inlet for studying the aerosol particles and hydrometeor residuals that compose mixed-phase clouds – the phaSe seParation Inlet for Droplets icE residuals and inteRstitial aerosol particles (SPIDER) – is described here. SPIDER combines a large pumped counterflow virtual impactor (L-PCVI), a flow tube evaporation chamber, and a pumped counterflow virtual impactor (PCVI) to separate droplets, ice crystals (∼3–25 µm), and interstitial aerosol particles for simultaneous sampling. Laboratory verification tests of each individual component and the composite SPIDER system were conducted. Transmission efficiency, evaporation, and ice crystals' survival were determined to show the capability of the system. The experiments show the SPIDER system can separate distinct cloud elements and interstitial aerosol particles for subsequent analysis. As a field instrument, SPIDER will help explore the properties of different cloud elements and interstitial aerosol particles in mixed-phase clouds.

Ice-nucleating particles (INPs) impact global climate by altering cloud formation and properties. The ability of aerosol particles to nucleate ice is in part determined by particle composition. Here, we demonstrate that the addition of common fluorinated pollutants to seawater can enhance the ice nucleation activity of resulting simulated sea spray particles, although we note that ambient sea spray will have additional organic components not considered here. We quantified the ice supersaturation at the onset of ice nucleation, fractional INP activation, and ice nucleation active site density for inorganic sea salt, assemblages of per- and poly-fluorinated alkyl substances (PFASs), and internally mixed particles. Particles composed solely of PFASs or sea salt mixed with PFASs nucleated ice heterogeneously in a temperature (-50 <= T <= -40 degrees C) and ice supersaturation (1.0 <= S-ice <= 1.5) range relevant to cirrus cloud formation. Conversely, the temperature and relative humidity trajectories considered here precluded heterogeneous ice nucleation of particles composed solely of inorganic sea salt. Our active site density calculations indicate that PFAS-containing sea salt aerosol exhibits ice nucleation activities similar to other effective INPs. Since the PFAS concentrations in our aerosolized solutions were similar to those observed in the ocean, our findings indicate that the addition of anthropogenic pollutants such as PFASs to seawater may enhance the ice-nucleating abilities of sea spray aerosols in the cirrus cloud regime. Further studies should investigate the interactions of PFASs with other marine organic matter to ascertain the impacts of particle composition on ambient sea spray's ice nucleation activity.

The term mineral dust encompasses a myriad of particle compositions from both fertile and arid regions. Due to this diversity, the quantitative understanding of mineral dust as Cloud Condensation Nuclei (CCN) and Ice Nucleating Particles (INPs) in the Earth's atmosphere demand further investigation. This study characterizes the CCN and INP activity of mineral dust particles from samples collected from one of the Earth's major arid regions, Saudi Arabia. Samples were size selected at particle diameters (Dp) of 300, 700, and 950 nm and introduced into a Cloud Condensation Nuclei Counter (CCNC) and a SPectrometer for Ice Nuclei (SPIN) chamber to investigate cloud nucleation activity. The chemical composition of the particles was analyzed with laser mass spectrometry and mineralogical information was provided by polarized light microscopy. Transmission electron microscopy was used to ascertain particle morphology. Each particle size was exposed to water supersaturations of 0.06-1.0% in the CCNC and to ice supersaturation ratios of 1.1 to 1.5 at temperatures from -25 to -42 degrees C in SPIN. The CCN activity ranged from hygroscopicity values (kappa) of 0.001 to 0.01. This is towards the lower range of critical supersaturations found for other mineral dust samples from e.g. the Sahara, North Africa, China and Asia. The INP activity, defined by fractional activation and supersaturation at the onset of ice nucleation was in the range of other natural mineral dusts (e.g., the Sahara, Canary Islands), and somewhat lower than industrially processed Arizona Test Dust. This study highlights the importance of considering size-resolved compositional data when interpreting the cloud-nucleation activity of natural mineral and soil dusts.