The stratosphere is often considered to be dynamically stable with limited vertical exchange; however, episodic deep convection can even transport tropospheric air masses into the upper troposphere (UT) and even across the tropopause into lower stratosphere (LS). We deployed a newly developed airborne single particle mass spectrometer, Particle Analysis by Laser Mass Spectrometry – Next Generation (PALMS-NG), aboard a NASA ER-2 stratospheric aircraft to characterize aerosol particles in the UTLS during the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission. Here, we present observations revealing substantial perturbations of the stratospheric aerosol layer during an active convection and wildfire season in 2022.We show that carbonaceous–sulfate particles of tropospheric origin account for up to 90% of stratospheric particles with physical diameters between 0.1 and 1.5 µm within an approximately 4 km layer above the tropopause. Approximately 43% of these stratospheric carbonaceous–sulfate particles are directly attributed to biomass burning. The injected particles are chemically complex and organic-rich, and some exhibit internally mixed signatures containing both tropospheric and stratospheric components.Our observations further demonstrate that biomass-burning-related aerosols do not remain chemically unchanged following injections into the stratosphere. Instead, they undergo chemical mixing with stratospheric components, indicating a pronounced perturbation of the stratospheric aerosol layer driven by convective transport.These results highlight the coupling between dynamics and chemistry in modulating UTLS aerosol populations. As wildfire frequency and intensity increase alongside enhanced deep convection in a warming climate, convective delivery of biomass-burning products to the stratosphere may become increasingly important, with implications for ozone chemistry and radiative forcing.

We present direct measurements of the asymmetry parameter ( g ) from biomass burning aerosol at two wavelengths using the Laser Imaging Nephelometer. We compare the measurements with Mie theory calculations based on optically measured size distributions and with g values derived from hemispheric backscatter ( b ) measurements using both an integrating and an imaging nephelometer. During the FIREX‐AQ field mission, we measured the optical and microphysical properties of smoke plumes that had been emitted between 0.5 and 8.5 hr earlier. We find that the measured g can only be reproduced from particle size distribution measurements using a higher refractive index than is typically retrieved from remote measurements and assumed in some models. Retrievals performed using the GRASP algorithm suggest the refractive index is wavelength‐dependent with n = 1.55 ± 0.03 at λ = 660 nm and (1.63 ± 0.04) at λ = 405 nm. Using a simple radiative transfer equation, we show that the instantaneous aerosol cooling of the planet by fresh smoke is increased by 20% when evaluated using the measured g values instead of assuming n = 1.52. Besides improving model representations of radiative cooling by fresh smoke, using a more accurate aerosol optical model can improve retrievals of aerosol microphysical properties from remote sensing techniques. Better retrievals will provide a more accurate constraint on the emissions inventories used in global and regional models. This will ultimately reduce the uncertainty in radiative forcing associated with the increasing frequency and magnitude of wildfires.

Reactive halogens catalytically destroy O3 and therefore affect (1) stratospheric O3 depletion and (2) the oxidative capacity of the troposphere. Reactive halogens also partition into the aerosol phase, but what governs halogen-aerosol partitioning is poorly constrained in models. In this work, we present global-scale measurements of non-sea-salt aerosol (nSSA) bromine and iodine taken during the NASA Atmospheric Tomography Mission (ATom). Using the Particle Analysis by Laser Mass Spectrometry instrument, we found that bromine and iodine are present in 8 %–26 % (interquartile range, IQR) and 12 %–44 % (IQR) of accumulation-mode nSSA, respectively. Despite being commonly found in nSSA, the concentrations of bromine and iodine in nSSA were low but potentially important, at 0.11–0.57 pmol mol−1 (IQR) and 0.04–0.24 pmol mol−1 (IQR), respectively. In the troposphere, we find two distinct sources of bromine and iodine for nSSA: (1) a primary source from biomass burning and (2) a pervasive secondary source. In the stratosphere, nSSA bromine and iodine concentrations increased with increasing O3 concentrations; however, higher concentrations of stratospheric nSSA bromine and iodine were found in organic-rich particles that originated in the troposphere. Finally, we compared our ATom nSSA iodine measurements to the global chemical transport model GEOS-Chem (Goddard Earth Observing System); nSSA bromine concentrations could not be compared because they were not tracked in the model. We found that the model compared well to our ATom nSSA iodine measurements in the background atmosphere but not in the marine boundary layer, biomass burning plumes, or stratosphere.

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.

Understanding the viscosity and phase state of biomass-burning organic aerosol (BBOA) from wildfires and pyrocumulonimbus (pyroCb) events in the stratosphere is critical for predicting their role in stratospheric multiphase chemistry and ozone depletion. However, the viscosity and phase state of BBOA under stratospheric conditions, including interactions with sulfuric acid (H₂SO₄), remain largely unquantified. In this study, we combine laboratory data with a thermodynamic model to predict the viscosity and phase state of BBOA under stratospheric conditions. Our results suggest that BBOA with a H₂SO₄-to-BBOA mass ratio of 0.37—an estimated upper limit for pyroCb smoke in the lower stratosphere after two months of aging— is highly viscous and frequently exists in a glassy state. Even at a higher H₂SO₄-to-BBOA mass ratio of 0.79 – an estimated upper limit after nine months of aging – BBOA can still transition to a glassy state under certain stratospheric conditions. In the glassy state, bulk reactions are suppressed, and multiphase chemistry may be limited to the particle surfaces. We also highlight key areas for future research needed to better constrain the viscosity and phase state of BBOA in the stratosphere and its subsequent impact on ozone.

The stratospheric aerosol layer plays an essential role in stratospheric chemical and radiative processes. Emissions of SO2 from small-to-midsized volcanic eruptions are typically introduced into the lower stratosphere, where a background aerosol already exists. The radiative and chemical consequences of these eruptive emissions depend in part upon the characteristics of these background particles, whose number originates from the troposphere. In-situ observations of sub-0.1 µm diameter particles in the upper troposphere/lower stratosphere are rare, but are of particular importance in understanding the contribution of upwelling ultrafine particles formed near the tropical tropopause and their subsequent evolution in the stratospheric (Brewer-Dobson) circulation. In the Stratospheric Aerosol processes, Budget and Radiative Effects (SABRE) mission from January to March 2023, we used three particle sizing instruments on the NASA WB-57 high-altitude aircraft to measure the size distribution of aerosol particles in the size range from 0.003 to ~4.0 μm in the lower stratosphere from middle to high latitudes at altitudes up to 19.6 km. The composition of individual aerosol particles >0.1 µm was also measured, along with O3, N2O, SF6 and OCS. Together, these measurements were used to investigate dynamical and chemical processes in the stratosphere that determine the evolution of the stratospheric aerosol as a function of stratospheric age up to several years. We observed a clear bimodal size distribution structure, with a small mode (< 0.1 μm diameter) originating from the troposphere and a larger mode (>0.2 µm diameter) originating from the photolysis of OCS (the classic Junge, or stratospheric, aerosol layer). These two modes evolve as a function of stratospheric age in a manner consistent with coagulation, condensation, and sedimentation. These are the first reported observations of the presence and evolution of this bimodal aerosol structure deep into the stratosphere. The small (tropospheric) particle mode provides a significant condensation sink at young stratospheric ages. SO2 from modest volcanic eruptions emitted into the lower stratosphere may condense on these smaller particles, reducing the amount of light scattering per unit mass. Proposed geoengineering efforts must also account for this tropospheric mode of particles. Models simulating aerosol processes in the stratosphere need to accurately represent tropospheric particles in the lower stratosphere and their evolution with stratospheric age.

The very large pyrocumulonimbus events that occurred during the Australian summer of 2019–2020 caused extremely unusual partitioning of stratospheric chlorine in the Southern Hemisphere midlatitude and Antarctic regions not only in 2020 but also in 2021. This was likely caused by enhanced HCl solubility in organic species that increased heterogeneous chemistry. Here, we show that observed HCl and ClONO2 values remain outside the pre-wildfire satellite range, measured from 2005 until just prior to the event, in both the Southern Hemisphere midlatitude and Antarctic regions in 2021. Through model simulations, we replicate this prolonged multiyear chemical perturbation, in good agreement with observations. This was achieved by calculating the HCl solubility in mixed wildfire and sulfate aerosols consistent with assumptions of (1) liquid–liquid phase separation and (2) linear dependence on organic and sulfate composition. The model simulations also suggest that the Australian pyrocumulonimbus organic aerosols contributed to low midlatitude ozone values in 2020 and 2021. A marked, photochemically controlled seasonality of the chemical perturbations and ozone depletion is also observed and simulated, and its underlying chemical drivers are identified. This work highlights that lower concentrations of smoke still had profound effects on stratospheric heterogeneous chemistry more than a year after the 2019–2020 wildfire event.

Each year, commercial ships emit over 1.67 Tg of particulate matter (PM) pollution into the atmosphere. These ships rely on the combustion of heavy fuel oil, which contains high levels of sulfur, large aromatic organic compounds, and metals. Vanadium is one of the metals most commonly associated with heavy fuel oil and is often used as a tracer for PM from ship exhaust. Previous studies have suggested that vanadium-containing PM has impacts on human health and climate due to its toxicological and cloud-formation properties, respectively; however, its distribution in the atmosphere is not fully understood, which limits our ability to quantify the environmental implications of PM emitted by ships. Here, we present data obtained from a Particle Analysis by Laser Mass Spectrometry (PALMS) instrument on the NASA DC-8 aircraft during the 2016–2018 Atmospheric Tomography Mission (ATom) and show that ∼ 1 % of the accumulation mode particles measured in the marine boundary layer of the central Pacific and Atlantic oceans contain vanadium. These measurements, which were made without targeting ship plumes, suggest that PM emitted by ships is widespread in the atmosphere. Furthermore, we observed vanadium-containing ship exhaust particles at altitudes up to 13 km, which demonstrates that not all ship exhaust particles are immediately removed via wet deposition processes. In addition, using laboratory calibrations, we determined that most vanadium-containing ship exhaust particles can contain up to a few weight percent of vanadium. This study furthers our understanding of both the chemical composition and distribution of PM emitted by ships, which will allow us to better constrain the climate, health, and air quality implications of these particle types in the future. We note that these data were collected prior to the 2020 International Maritime Organization (IMO) sulfur regulation and stand as a reference for understanding how ship emissions have evolved in light of these regulations.

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

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. Reactive halogens catalytically destroy O3 and therefore affect (1) stratospheric O3 depletion, and (2) the oxidative capacity of the troposphere. Reactive halogens also partition into the aerosol phase, but what governs halogen-aerosol partitioning is poorly constrained in models. In this work, we present global-scale measurements of non-sea-salt aerosol (nSSA) bromine and iodine taken during the NASA Atmospheric Tomography Mission (ATom). Using the Particle Analysis by Laser Mass Spectrometry instrument, we found that bromine and iodine are present in 8–26 % (interquartile range, IQR) and 12–44 % (IQR) of accumulation-mode nSSA, respectively. Despite being commonly found in nSSA, the mass concentrations of bromine and iodine in nSSA were low, 0.11–0.57 pmol mol-1 (IQR) and 0.04–0.24 pmol mol-1 (IQR), respectively. In the troposphere, we find two distinct sources of bromine and iodine to nSSA: (1) a primary source from biomass burning, and (2) a pervasive secondary source. In the stratosphere, nSSA bromine and iodine mass increased with increasing O3 concentrations; however, higher concentrations of stratospheric nSSA bromine and iodine were found in organic-rich particles that originated in the troposphere. Finally, we compared our ATom nSSA iodine measurements to the global chemical transport model GEOS-Chem; nSSA bromine concentrations could not be compared because they were not tracked in the model. We found that the model compared well to our ATom nSSA iodine measurements in the background atmosphere, but not in the marine boundary layer, biomass burning plumes, or in the stratosphere.

AbstractBiogenic organic compounds in the surface ocean may significantly alter the cloud‐forming ability of sea spray aerosol and thereby affect the amount of solar radiation reaching the ocean surface. Estimates of the organic mass fraction of sea spray vary widely, and some results show a significant dependence on biological activity in the source seawater. We present airborne observations of the organic mass fraction of individual sea spray particles measured using the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument during the Atmospheric Tomography (ATom) mission, which sampled a wide range of latitudes and altitudes over the remote Atlantic and Pacific Oceans across four seasons, from the marine boundary layer to the upper troposphere. The measured sea spray particles of about 0.15–0.7 μm dry diameter showed higher average organic mass fractions at smaller sizes, but values were low overall, with regional integrated submicron means almost always <10%. Atmospheric aging adds organics to sea spray particles, leading to higher mean organic mass fractions (sometimes exceeding 50%) in the free troposphere than in the marine boundary layer. The average submicron sea spray organic mass fractions are on the low end of previously reported values and show weak seasonal variability for most regions. These results imply that recent biological activity in the surface ocean has only weak control over how much organic matter is in nascent submicron sea spray particles over the remote oceans, in contrast to findings from some observational studies and global numerical simulations.

Pyrocumulonimbus (pyroCb) are wildfire-generated convective clouds that can inject smoke directly into the stratosphere. PyroCb have been tracked for years, yet their apparent rarity and episodic nature lead to highly uncertain climate impacts. In situ measurements of pyroCb smoke reveal its distinctive and exceptionally stable aerosol properties and define the long-term influence of pyroCb activity on the stratospheric aerosol budget. Analysis of 13 years of airborne observations shows that pyroCb are responsible for 10 to 25% of the black carbon and organic aerosols in the "present-day" lower stratosphere, with similar impacts in both the North and South Hemispheres. These results suggest that, should pyroCb increase in frequency and/or magnitude in future climates, they could generate dominant trends in stratospheric aerosol.

&lt;p&gt;The Asian Summer Monsoon Anticyclone (AMA) is known to bring ground-level pollutants up to the stratosphere. Aerosols in the AMA often form what is known as the Asian Tropopause Aerosol Layer (ATAL), with modelling studies suggesting that the ATAL can provide up to 15 % of the stratospheric aerosol in the Northern Hemisphere. In this work, we present single-particle mass spectrometry measurements of aerosol composition in the AMA outflow and in the North American upper troposphere/lower stratosphere (UTLS) during the same season. Measurements were taken by the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument and made during the Asian Summer Monsoon Chemical &amp; CLimate Impact Project (ACCLIP). We find that the dominant aerosol type found in the ATAL and those found in the UTLS over North America are chemically different. Despite high concentrations of ground-level gas phase pollutants, particles in the ATAL are dominated by secondary nitrate particles. The organic content of these particles is low, which precludes them from being organic-nitrate aerosol; thus, we believe that these particles are either nitric/sulfuric acid solutions, or they are mixtures of partially neutralized ammonium nitrate/sulfate. Finally, we present the mass concentrations of nitrate particles, dust, and sulfate-organic particles in the ATAL, and estimate each particle type&amp;#8217;s influence on the aerosol composition over the North American continent.&lt;/p&gt;

Remarkable perturbations in the stratospheric abundances of chlorine species and ozone were observed over Southern Hemisphere mid-latitudes following the 2020 Australian wildfires1,2. These changes in atmospheric chemical composition suggest that wildfire aerosols affect stratospheric chlorine and ozone depletion chemistry. Here we propose that wildfire aerosol containing a mixture of oxidized organics and sulfate3-7 increases hydrochloric acid solubility8-11 and associated heterogeneous reaction rates, activating reactive chlorine species and enhancing ozone loss rates at relatively warm stratospheric temperatures. We test our hypothesis by comparing atmospheric observations to model simulations that include the proposed mechanism. Modelled changes in 2020 hydrochloric acid, chlorine nitrate and hypochlorous acid abundances are in good agreement with observations1,2. Our results indicate that wildfire aerosol chemistry, although not accounting for the record duration of the 2020 Antarctic ozone hole, does yield an increase in its area and a 3-5% depletion of southern mid-latitude total column ozone. These findings increase concern2,12,13 that more frequent and intense wildfires could delay ozone recovery in a warming world.

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.

Abstract. Dust aerosols affect the radiative and energy balance at local and global scales by scattering and absorbing sunlight and infrared light. Parameterizations of dust lifting, microphysics, as well as physical and radiative properties of dust in climate models are still subject to large uncertainty. Here we use a sectional aerosol model (CARMA) coupled with a climate model (CESM1) to investigate the global distribution of dust aerosols, with an emphasis on the vertical distribution of dust. Consistent with observations at locations remote from source regions, simulated dust mass size distributions peak at around 2–3 micrometres in diameter and increase by 4 orders of magnitude from 0.1 μm to 2 µm. The size distribution above 2 µm is highly variable depending on distance from the source, and subject to uncertainty due to possible size dependent changes in physical properties such as shape and density. Simulated annual mean dust mass concentrations are within one order of magnitude of those found by the surface measurement network around the globe. Simulated annual mean aerosol optical depths are ~10 % lower than AERONET observations near the dust source regions. Both simulations and in-situ measurements during the NASA ATom field campaign suggest that dust mass concentrations over the remote ocean drop by two to three orders of magnitude from the surface to the upper troposphere (200 hPa). The model suggests that Saharan, Middle Eastern, and Asian dust accounts for ~59.7 %, 12.5 %, and 13.3 % of the global annual mean dust emissions, with the remaining 14.5 % originating from scattered smaller dust sources. Although Saharan dust dominates global dust mass loading at the surface, the relative contribution of Asian dust increases with altitude and becomes dominant in the upper troposphere. The simulations show that Asian dust contributes ~60.9 % to the global and annual mean dust concentration between 266 hPa and 160 hPa. Asian dust is mostly lifted in the spring by mid-latitude frontal systems. However, deep convection during the Asian summer monsoon (ASM) favours the vertical transport of local dust to the upper atmosphere. Simulated dust accumulates in the ASM anticyclone and forms a local maximum; however, the simulated dust mass concentration is only ~0.04 % of the total aerosols in the Asian Tropopause Aerosol Layer (ATAL), which are dominated by organics, sulfates and nitrates.

. 11 Dust aerosols affect the radiative and energy balance at local and global scales by 12 scattering and absorbing sunlight and infrared light. Previous study suggests dust size 13 distribution is one of the major sources of uncertainty in modelling the dust global 14 distribution. Climate models overestimates the fine dust (≤ 5 µm) by an order of 15 magnitude, while underestimates the coarse dust (≥5µm) ranges between half to one- 16 and-a-half orders of magnitude compared with the global observations. Here we 17 improved the simulated size distribution of dust aerosol using a sectional aerosol 18 model coupled with the Community Earth System Model (CESM1/CARMA). 19 Simulated dust mass size distributions peak at around 2-3 micrometers in diameter 20 and increase by 4 orders of magnitude from 0.1 μm to 2 µm. Our model demonstrates 21 that North African, Middle Eastern, and Asian dust accounts for ~59.7%, 12.5%, and 22 13.3% to the global annual mean dust emissions, with the remaining 14.5% 23 originating from scattered smaller dust sources. The model dust vertical distributions 24 are validated against the NASA Atmospheric Tomography (ATom) field campaign 25 datasets. Both simulations and ATom in-situ measurements during ATom field 26 campaign suggest that dust mass concentrations over the remote ocean drop by two to 27 three orders of magnitude from the surface to the upper troposphere (200 hPa). Our 28 model suggests that Asian dust contributes to more than 40% of annual mean dust 29 mass abundances in the global upper troposphere and lower stratosphere (UTLS). 30 Model suggests that the Asian dust dominates the dust mass budget in the UTLS of 31 the Asian summer monsoon (ASM) region, with a relative contribution 1-2 orders of 32 magnitude higher than the dust originated from North African and Middle Eastern 33 deserts.

The global Flow-following finite-volume Icosahedral Model (FIM), which was developed in the Global Systems Laboratory (GSL) of NOAA, has been coupled inline with aerosol and gas-phase chemistry schemes of different complexity using the chemistry and aerosol packages from WRF-Chem v3.7, named FIM-Chem v1. The three chemistry schemes include (1) the simple aerosol modules from the Goddard Chemistry Aerosol Radiation and Transport model that includes only simplified sulfur chemistry, black carbon (BC), organic carbon (OC), and sectional dust and sea salt modules (GOCART); (2) the photochemical gas phase of the Regional Atmospheric Chemistry Mechanism (RACM) coupled to GOCART to determine the impact of more realistic gas-phase chemistry on the GOCART aerosol simulations (RACM_GOCART); and (3) a further sophistication within the aerosol modules by replacing GOCART with a modal aerosol scheme that includes secondary organic aerosols (SOAs) based on the volatility basis set (VBS) approach (RACM_SOA_VBS). FIM-Chem is able to simulate aerosol, gas-phase chemical species, and SOA at various spatial resolutions with different levels of complexity and quantify the impact of aerosol on numerical weather prediction (NWP). We compare the results of RACM_GOCART and GOCART schemes which use the default climatological model fields for OH, H2O2, and NO3. We find significant reductions of sulfate that are on the order of 40% to 80% over the eastern US and are up to 40% near the Beijing region over China when using the RACM_GOCART scheme. We also evaluate the model performance by comparing it with the Atmospheric Tomography Mission (ATom-1) aircraft measurements in the summer of 2016. FIM-Chem shows good performance in capturing the aerosol and gas-phase tracers. The model-predicted vertical profiles of biomass burning plumes and dust plumes off western Africa are also reproduced reasonably well.