Enhanced radiative cooling by large aerosol particles from wildfire-driven thunderstorms

Yaowei Li; John A Dykema; David A Peterson; Xu Feng; Xiaoli Shen; Nicole A June; Michael D Fromm; Theodore M McHardy; Justin L Jacquot; Jasna V Pittman; Bruce C Daube; Steven C Wofsy; Jonathan Dean-Day; Anita D Rapp; Kenneth P Bowman; Daniel J Cziczo; Loretta J Mickley; Jeffrey R Pierce; Frank N Keutsch

doi:10.1126/sciadv.adw6526

. 2025 Dec 10;11(50):eadw6526. doi: 10.1126/sciadv.adw6526

Enhanced radiative cooling by large aerosol particles from wildfire-driven thunderstorms

Yaowei Li ^1,^*,^†, John A Dykema ¹, David A Peterson ², Xu Feng ¹, Xiaoli Shen ³, Nicole A June ⁴, Michael D Fromm ⁵, Theodore M McHardy ^2,⁶, Justin L Jacquot ^3,^‡, Jasna V Pittman ¹, Bruce C Daube ¹, Steven C Wofsy ¹, Jonathan Dean-Day ⁷, Anita D Rapp ⁸, Kenneth P Bowman ⁸, Daniel J Cziczo ³, Loretta J Mickley ¹, Jeffrey R Pierce ⁴, Frank N Keutsch ^1,^9,^10,^*

^¹School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.

^²Naval Research Laboratory, Monterey, CA, USA.

^³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA.

^⁴Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA.

^⁵Naval Research Laboratory, Washington, DC, USA.

^⁶American Society for Engineering Education, Washington, DC, USA.

^⁷Bay Area Environmental Research Institute, Moffett Field, CA, USA.

^⁸Department of the Atmospheric Sciences, Texas A&M University, College Station, TX, USA.

^⁹Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.

^¹⁰Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.

Corresponding author. Email: yaoweili@seas.harvard.edu (Y.L.);

Corresponding author. Email: keutsch@seas.harvard.edu (F.N.K.)

^†

Present address: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.

^‡

Present address: National Center for Atmospheric Research (NCAR), Research Aviation Facility/Earth Observing Laboratory (RAF/EOL), Broomfield, CO, USA.

Roles

Yaowei Li: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing

John A Dykema: Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Software, Supervision, Writing - original draft, Writing - review & editing

David A Peterson: Conceptualization, Data curation, Methodology, Resources, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing

Xu Feng: Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing - review & editing

Xiaoli Shen: Data curation, Formal analysis, Investigation, Resources, Visualization, Writing - review & editing

Nicole A June: Data curation, Formal analysis, Investigation, Methodology, Software, Visualization, Writing - original draft, Writing - review & editing

Michael D Fromm: Formal analysis, Investigation, Methodology, Visualization, Writing - review & editing

Theodore M McHardy: Visualization, Writing - review & editing

Justin L Jacquot: Investigation, Resources, Writing - review & editing

Jasna V Pittman: Conceptualization, Data curation, Investigation, Resources, Validation, Writing - review & editing

Bruce C Daube: Data curation, Investigation, Resources, Validation, Writing - review & editing

Steven C Wofsy: Conceptualization, Data curation, Funding acquisition, Investigation, Project administration, Resources, Supervision, Validation, Writing - review & editing

Jonathan Dean-Day: Formal analysis, Investigation, Writing - review & editing

Anita D Rapp: Investigation, Writing - review & editing

Kenneth P Bowman: Conceptualization, Funding acquisition, Project administration, Software

Daniel J Cziczo: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Validation, Writing - review & editing

Loretta J Mickley: Formal analysis, Funding acquisition, Investigation, Methodology, Resources, Supervision, Validation, Writing - review & editing

Jeffrey R Pierce: Conceptualization, Funding acquisition, Methodology, Resources, Software, Supervision, Writing - review & editing

Frank N Keutsch: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Validation, Writing - original draft, Writing - review & editing

PMCID: PMC12694039 PMID: 41370386

Abstract

Large wildfires can generate pyrocumulonimbus (pyroCb) clouds, injecting massive quantities of smoke aerosols into the upper troposphere and lower stratosphere (UT/LS), where they persist for months and affect climate. The radiative effects of pyroCb aerosols, however, remain poorly understood because of limited direct measurements. Here, we present in situ aircraft measurements of 5-day-old pyroCb smoke, addressing a critical observational gap in aerosol evolution from freshly emitted to weeks-to-months-aged states. The sampled smoke primarily contained unusually large aerosol particles (500 to 600 nanometers in diameter), formed through cloud processing and efficient coagulation in the UT/LS. Compared to smaller particles in typical non-pyroCb smoke, these large particles increase outgoing radiation by 30 to 36%, substantially enhancing atmospheric radiative cooling. Climate models may greatly underestimate this cooling effect by assuming smaller aerosol sizes for pyroCb smoke. As pyroCb events become more frequent, accurately representing their aerosol properties is essential for improving climate projections.

Smoke from wildfire-driven thunderstorms forms larger particles that enhance atmospheric cooling, challenging current models.

INTRODUCTION

Wildfires are a major source of atmospheric aerosols (1, 2), influencing climate, air quality, and human health (3–5). Notably, the frequency and intensity of wildfires are expected to increase with climate change (6, 7). Under specific meteorological conditions (8), large wildfires can generate thunderstorms known as pyrocumulonimbus (pyroCb), injecting vast amounts of smoke aerosols directly into the upper troposphere and lower stratosphere (UT/LS), broadly defined as ±5 km around the tropopause (9–11). This process substantially alters background aerosol properties in this region (12–14). Once in the UT/LS, these aerosols persist much longer than those in the lower troposphere, with lifetimes ranging from months to years (15), greatly increasing their climate impact.

Despite their prevalence and projected increase, the radiative effects of pyroCb aerosols in the UT/LS remain highly uncertain (16, 17), mainly due to poorly constrained microphysical and optical properties of these aerosols (18, 19). While remote sensing provides crucial data on aerosol extinction from pyroCb smoke, accurately quantifying radiative forcing requires detailed knowledge of aerosol size distributions and optical properties (20). Now, essential in situ measurements of pyroCb aerosol, such as size, composition, and optical properties, are notably scarce because of the episodic nature of pyroCb events and the challenges of rapidly deploying comprehensive airborne or balloon-borne instruments for detailed study (12, 21, 22).

Most research has focused on non-pyroCb wildfire aerosols in the lower and middle troposphere (23–26), where smoke aerosols typically exhibit number-mode diameters between 200 and 300 nm (27, 28). There is also evidence of dominant larger particles, with a volume-mode diameter near 600 nm, in smoke observed in the middle and upper troposphere, likely resulting from efficient coagulation under high-concentration plume conditions (29). In contrast, pyroCb aerosol size distributions in the UT/LS are likely more diverse and complex, shaped by two key factors: (i) cloud processing during vertical transport and (ii) coagulation in the stable UT/LS environment, where limited dilution sustains high aerosol concentrations. Both of these processes grow particles to larger sizes. For example, fresh pyroCb smoke (<2 hours old) has been observed with a primary number-mode aerosol diameter around 200 nm and a secondary mode between 250 and 300 nm (30). In contrast, weeks-to-months-old pyroCb aerosols in the UT/LS exhibit mode diameters exceeding 500 nm (12, 22, 31, 32). However, a critical knowledge gap remains in understanding the size evolution of these aerosols, particularly during the transition from freshly emitted to weeks-to-months-aged states.

Here, we present in situ measurements of young pyroCb smoke (a few days old), directly addressing this observational gap. Through targeted sampling of 5-day-old pyroCb smoke plumes during the National Aeronautics and Space Administration (NASA) Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) airborne mission, we provide aerosol size distribution and composition data, combined with aerosol microphysical modeling and radiative transfer calculations, to better constrain the microphysical evolution and radiative effects of pyroCb aerosols. Our findings highlight the characteristically large size of pyroCb aerosols in the UT/LS and their substantial role in modulating radiative forcing. As pyroCb events become more frequent in a warming climate (33, 34), accurately representing their aerosol properties in models is critical for assessing their role in Earth’s energy balance and improving climate projections.

RESULTS

Targeted in situ measurements of pyroCb smoke

Sampling pyroCb smoke in the UT/LS presents a formidable challenge because of its episodic nature and high altitude. In the DCOTSS mission, a flight plan was designed for the NASA ER-2 aircraft to intercept 5-day-old pyroCb smoke originating from a New Mexico wildfire, guided by satellite-based plume-tracking techniques. Figure 1 illustrates the identification and tracking of the pyroCb plumes by the Geostationary Operational Environmental Satellites (GOES); the plumes were injected into the UT/LS on 16 June 2022 from the active Calf Canyon and Hermits Peak fire complex in New Mexico (https://rb.gy/i9bh8r). Satellite imagery tracks the transport of plumes over Texas and Kansas 1 and 3 days after the pyroCb injection and eventually over Missouri 5 days postfire, where the ER-2 aircraft successfully sampled the smoke at ~14.5-km altitude (Fig. 2A). The initial injection height of the pyroCb smoke is estimated to have reached 14.7 km on the basis of data from Pueblo Colorado Next Generation Weather Radar (NEXRAD) maximum echo tops (fig. S1). In addition, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) detected the smoke 1 and 3 days postpyroCb within the 11- to 16-km altitude range over northwestern Texas (fig. S2).

Fig. 1. — (A) Active fire in New Mexico on 16 June 2022 and the resultant pyroCb event. Purple dots indicate active fire locations. (B to D) Day 1 smoke plumes shown in GOES Advanced Baseline Imager (ABI) True Color, OMPS Aerosol Index, and GOES Cirrus Channel imagery. The white contour lines in (B) outline the smoke regions where the aerosol index is ≥1, as shown in (C). (E and F) Smoke plumes 3 and 5 days after pyroCb injection in GOES Cirrus Channel imagery. The smoke plumes are highlighted within red ovals. The black square in (B) represents the area of the image where the pyroCb occurred on day 0 in (A). The aircraft’s launch location in Salina, Kansas, is denoted by a yellow star, and the flight track on day 5 is shown in blue in (F).

A substantial increase in aerosol number concentration was observed when the aircraft intercepted the pyroCb smoke plume in the UT (Fig. 2A), with smoke aerosols exhibiting a heterogeneous horizontal distribution. We categorized the three aerosol subplumes within the smoke, numbering them one through three in descending order of aerosol concentration. The composition-resolved volume size distribution within the smoke plumes (Fig. 2B) shows that ~85% of the aerosols by volume are biomass burning particles, serving as a clear indicator of the smoke encounter. Sulfate contributes less than 12% of the aerosol volume within the smoke. In contrast, background aerosols contain substantially fewer biomass burning particles (fig. S4). In addition, elevated concentrations of gas-phase biomass burning tracers, such as carbon monoxide [CO; ~120 versus ~60 ppbv (parts per billion by volume)] and carbon dioxide [CO₂; ~421 versus ~419.5 ppmv (parts per million by volume)], were observed inside the smoke plume compared to the background (fig. S5).

Characteristically large size of pyroCb aerosols

While the concentration of aerosols within the smoke plume is enhanced, it is more noteworthy that the size of these particles was substantially larger than that of background aerosols. Figure 2C offers a detailed examination of the aerosol size distributions inside the three pyroCb smoke plumes compared with the background conditions sampled just outside the smoke at the same altitude. The number size distribution reveals a distinctly large mode for aerosols within the smoke, ranging between 500 and 600 nm, which is even more evident in the volume size distribution (Fig. 2B and fig. S6). The particle sizes observed within this pyroCb smoke in the UT are more than double the size of typical non-pyroCb smoke aerosols sampled at lower altitudes, which have number-mode diameters between 200 and 300 nm (27, 28), as indicated by the gray-shaded area in Fig. 2C. These sizes are also much larger than the biomass burning aerosol sizes typically represented in regional or global climate models, which generally range from 100 to 400 nm in number-mode diameter, depending on the specific aerosol microphysical schemes (35–39).

Two potential (and complementary) mechanisms likely contribute to the formation of these large pyroCb aerosols: (i) cloud processing during transport within the pyroCb cloud, including in-cloud aqueous-phase chemistry and particle collision coalescence, and (ii) coagulation subsequent to aerosol detrainment from the cloud top. While condensation of secondary organic aerosol may also contribute to particle growth in smoke plumes, observations suggest that it can increase diameters by at most ~45% (40). Coagulation is therefore the dominant mechanism responsible for the very large diameter increases after detrainment (41). A direct measurement of fresh pyroCb aerosols just after cloud processing (<2 hours old) was obtained during the FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality) airborne mission (30). The aerosol size distribution of these fresh plumes revealed a primary number-mode diameter around 200 nm, with a second, larger number-mode diameter between 250 and 300 nm (fig. S7), likely resulting from cloud processing (42, 43).

Regardless of the initial size of the detrained smoke aerosols post–cloud processing, whether small (~100 to 200 nm) or medium (~200 to 400 nm), coagulation in the stable UT/LS environment, characterized by slow dilution, likely increases their size to the 500- to 600-nm range. As illustrated in Fig. 3A, simulations with a microphysical model (see Materials and Methods) (27) demonstrate that relatively small aerosols, with an initial mode diameter of 130 nm, can grow to 500 to 600 nm within 48 hours via coagulation in the stable UT/LS environment. Additional growth beyond this period is minimal under the conditions in our simulation. This limitation arises mainly because the coagulation rate scales with the square of the particle number concentration; as particles grow and the number concentration decreases, further coagulation becomes inefficient. To represent the effects of cloud processing on particle size, a bimodal simulation with a larger initial mode at 260 nm was also conducted. Similar to the unimodal simulation, coagulation growth within the first 48 hours shifts the aerosols to the large mode of 500 to 600 nm, with minimal growth thereafter (Fig. 3B). The modeled number concentrations on day 5 in both unimodal and bimodal simulations align closely with the DCOTSS measurements (Figs. 2C and 3). We note that the initial size distributions used in our simulations were derived from multiple fresh wildfire events, not from the New Mexico case, and were intended to represent plausible UT/LS injection conditions. The goal of the modeling was not to reproduce the specific New Mexico event but to evaluate whether coagulation after injection could plausibly explain the observed large particle mode under realistic UT/LS conditions.

Fig. 3. — (A) Growth of a unimodal size distribution with an initial size mode of 130 nm. (B) Growth of a bimodal size distribution with initial size modes at 130 and 260 nm. The second, larger size mode represents the effects of cloud processing on particle growth during convection. Both simulations were carried out for 5 days, and the figure depicts the evolution of the size distribution over this period. Both simulations also account for aerosol coagulation and dilution under upper tropospheric conditions using a realistic dilution rate for the UT/LS. Table S1 summarizes the parameters used in the simulations. All size distributions are under ambient conditions.

Our microphysical simulation and direct measurements of 5-day-old pyroCb smoke suggest the rapid coagulation growth of pyroCb aerosols in the UT/LS, with this larger size mode likely persisting in the UT/LS even after weeks to months of aging (12, 31). These findings do not downplay the role of cloud processing in particle growth. Instead, they demonstrate that different combinations of cloud processing and coagulation can produce large pyroCb aerosols (~500 to 600 nm) within a few days. Bringing together evidence from previously observed weeks-to-months-aged pyroCb aerosols (12, 31), the 5-day-old pyroCb aerosols sampled during DCOTSS, and the supporting microphysical analyses, we suggest that the observed unusually large aerosol size mode, with diameters ranging from 500 to 600 nm, is characteristic of pyroCb aerosols in the UT/LS.

Enhanced radiative cooling by large pyroCb aerosols

To assess the impact of the unusually large pyroCb aerosols on the atmospheric radiation balance, we first used an offline radiative transfer model to calculate their instantaneous direct radiative forcing. As demonstrated in Fig. 4A, calculated top-of-atmosphere (TOA) instantaneous shortwave radiative forcing (negative) substantially surpasses the longwave radiative forcing (positive) for all three pyroCb smoke plumes by nearly an order of magnitude, indicating that radiative cooling is the predominant effect. The observationally derived spectral complex refractive index (RI) data for biomass burning aerosols were taken from decadal climatology (2008 to 2017) of ambient smoke in the United States (44) and the high-resolution transmission (HITRAN) aerosol database (45). These RI scenarios cover a plausible range of absorption properties, accounting for contributions from black carbon (BC), brown carbon, and their mixing with organics and background aerosol components such as sulfate. Substantial uncertainties in shortwave radiative forcing arise from the wide range of shortwave RI scenarios associated with complex organic- and BC-containing biomass burning aerosols. However, only one measurement-based RI prescription for biomass burning aerosols is available that covers a wide range of longwave spectrum, so no error bar is shown for the longwave forcing. Values of RI scenarios used in this study can be found in fig. S8. The single scattering albedo (SSA) values for these RI scenarios, as shown in fig. S9, are consistent with the large ensemble of SSA values for biomass burning aerosols derived from various field measurements (37).

Fig. 4. — (A) TOA radiative forcing (shortwave and longwave) for the three measured pyroCb smoke plumes. Error bars on shortwave forcing reflect uncertainties across five different RI scenarios. The mass concentration is calculated assuming a particle density of 1400 kg m⁻³ (27). (B) Total (shortwave + longwave) TOA radiative forcing for the three pyroCb smoke plumes compared to typical non-pyroCb smoke aerosols with a 250-nm mode diameter and a modal width of 1.4. Non-pyroCb cases are adjusted to the same mass as the corresponding pyroCb cases (i.e., mass-equivalent). Error bars reflect uncertainties across five different RI scenarios (fig. S8). Dotted lines connect paired cases to aid comparison within the same RI scenario. The red “RF ratio” values show the ratio of the radiative forcing of pyroCb smoke to that of the corresponding non-pyroCb smoke, with the average displayed above and the range in brackets. (C) Total TOA radiative forcing for aerosol distributions with number-mode diameters of 100, 150, 200, 250, 300, 350, 400, and 600 nm (with corresponding modal widths of 1.55, 1.5, 1.45, 1.4, 1.35, 1.3, 1.25, and 1.2, respectively), as well as measured pyroCb smoke 1 with a 523-nm number-mode diameter. The progressively narrower widths with increasing diameter are consistent with coagulation being the dominant growth mechanism. The gray-shaded area shows the typical wildfire aerosol sizes in regional or global climate models (35–39), while the pink-shaded area represents the size range of pyroCb aerosols measured in this work and the hypothetical 600-nm case representing more extreme pyroCb conditions. Error bars reflect uncertainties from five RI scenarios. All radiative forcing results shown in this figure are derived from the offline radiative transfer calculations.

As previously noted, the aerosol size range of 200 to 300 nm is typical for smoke aerosols in the lower and middle troposphere. Figure 4B shows that the total TOA instantaneous radiative forcing derived from the measured pyroCb aerosol size is consistently more negative across all three smoke plumes compared to that calculated using a mass-equivalent size distribution of typical non-pyroCb smoke aerosols. This trend is observed not only in the comparison of mean values but also in all paired data comparisons calculated under the same RI scenarios, as represented by the error bars and further clarified in fig. S9. On average, the large pyroCb aerosols we measured increase outgoing radiation (aerosol-only perturbation) by 30 to 36% compared to typical non-pyroCb smoke aerosols with a 250-nm mode and equivalent mass concentrations, causing an instantaneous enhancement in the cooling of the atmospheric column. Although the observationally derived RI scenarios used here are expected to reflect mixing with background aerosol components such as sulfate, we conducted an additional sensitivity analysis assuming that 12% of the aerosols within the smoke are sulfate. As shown in fig. S10, the total radiative forcing becomes slightly less negative compared to that in fig. S9, primarily due to increased longwave absorption by sulfate. We also performed sensitivity tests on stronger absorption cases by varying the imaginary RI up to 0.05 over ultraviolet and visible wavelengths (350 to 750 nm), corresponding to SSA values from 0.97 to 0.80 (fig. S11). These cases span the range expected for smoke with increasing BC content, with the extreme absorption cases (SSA ~0.80) serving as upper bounds for plausible BC mass fractions in pyroCb smoke (estimated at 2 to 3%) (12, 13, 30, 37, 46). Nevertheless, the conclusion of substantially enhanced radiative cooling compared to typical non-pyroCb smoke aerosols remains robust.

Figure 4C further compares the TOA instantaneous radiative forcing calculated from the measured pyroCb aerosol size with that from the wildfire aerosol sizes typically represented in regional or global climate models, ranging from 100 to 400 nm in diameter (35–39). Across this range, the modeled aerosols show weaker negative radiative forcing compared to the measured pyroCb aerosols, with the largest differences occurring when smaller aerosol sizes are used in the models. The bias diminishes as the modeled diameter approaches 400 nm, at which point the instantaneous radiative forcing becomes more consistent with observations. We also include a hypothetical 600-nm case, representative of more extreme pyroCb conditions; this leads to a further enhancement of negative forcing, although the effect appears to plateau at larger sizes.

We also examined changes in aerosol optical depth (AOD) at a 600-nm wavelength and instantaneous TOA shortwave radiative forcing from large pyroCb aerosols using a regional model that couples the Weather Research and Forecasting (WRF) model with the GEOS-Chem (GC) chemical transport model, known as WRF-GC (47). This analysis allows us to explore the potential radiative effects of the 2022 New Mexico pyroCb event over a larger domain of the central United States, complementing the more localized analysis on the basis of aircraft observations and column-level radiative transfer calculations. Simulations using typical pyroCb aerosols (500-nm mode diameter, 1.3 modal width) increase the AOD by up to 0.0075 for plumes extending more than 800 km northeastward from the fire source (Fig. 5A) compared to control simulations with default wildfire aerosols (140-nm mode diameter, 1.6 modal width) (47). Unusually large smoke particles are also expected to modify the spectral slope of AOD, producing higher relative values at longer visible and near-infrared wavelengths compared to typical biomass burning aerosols (29), which may have important implications for the spectral dependence of radiative forcing. Consistent with the offline radiative transfer calculations in Fig. 4C, large pyroCb aerosols in the regional model enhance the negative instantaneous TOA shortwave radiative forcing by as much as 0.3 W m⁻² for far-field plumes (Fig. 5B), indicating enhanced radiative cooling effects across a wide region. Only clear-sky shortwave forcing is shown to avoid the complexities of aerosol-cloud interactions and longwave feedbacks because of temperature changes in this fully coupled model. We note that in the pyroCb experiment, all biomass burning aerosols are treated as pyroCb aerosols with a 500-nm mode diameter upon emission, representing an upper limit for their impacts on AOD and forcing within the study domain. Our results confirm that large pyroCb aerosols may lead to a substantial impact on the radiative cooling across a wide region, such as the broad central United States domain affected in this case.

Fig. 5. — Panels show the simulated differences in (A) AOD at a 600-nm wavelength and (B) instantaneous TOA clear-sky shortwave radiative forcing between pyroCb smoke aerosols (500-nm mode diameter, 1.3 modal width; pyroCb experiment) and default wildfire aerosols in the model (140-nm mode diameter, 1.6 modal width; control experiment), averaged over 16 to 21 June 2022. Simulations were performed using the WRF-GC model, an online two-way coupling of the WRF regional meteorological model and the GC chemical transport model (47). Both pyroCb and control experiments used the same biomass burning emissions from the Global Fire Assimilation System (GFAS) inventory. Emissions from the New Mexico fires contributed to 73% of the total fire emissions in the study domain from 16 to 21 June, with emissions on 16 June alone accounting for 67% of the total during that period (fig. S12). In the pyroCb experiment, all biomass burning aerosols are treated as pyroCb aerosols upon emission, providing an upper limit to the simulated differences.

DISCUSSION

We use airborne measurements within high-altitude (~14.5 km) 5-day-old smoke plumes from a 2022 New Mexico pyroCb event to examine the radiative effects of unusually large pyroCb aerosols. Although the pyroCb event we analyzed is not as intense as extreme events such as the 2019/20 Australian wildfires and the 2017 Pacific Northwest fires, it represents a more frequent type of moderate pyroCb event. Global records from 2013 to 2021 show that pyroCb activity is common, with a total of 546 recorded pyroCb events worldwide, more than 350 of which occurred in North America (48). More than half of these events involved smoke plumes injected into the UT (49), similar to the 2022 New Mexico case analyzed in this study. Even more notable is that the recent active Canadian wildfire season of 2023 is estimated to have generated more pyroCb events than any yearly global total since 2013, with most of these events resembling the moderate 2022 New Mexico pyroCb event described here (49, 50). Such pyroCb events are expected to become more frequent in a warming climate (33, 34).

Our results suggest that the unusually large pyroCb aerosols observed in the UT/LS can form through combinations of cloud processing and coagulation growth in this relatively stable environment. Determining the relative contributions of these two mechanisms, particularly cloud processing, remains challenging because of its complexity and the lack of detailed observational data. Furthermore, the extent of cloud processing, and consequently the size of detrained aerosols, can vary considerably across pyroCb events. These uncertainties highlight the need for further research and field studies in this area. Nevertheless, our microphysical modeling demonstrates that different combinations of cloud processing and efficient coagulation can reproduce the observed large pyroCb aerosols within a few days, providing a plausible explanation for this characteristic size feature.

We calculate only the instantaneous direct radiative forcing, which does not account for the diabatic influences on atmospheric dynamics or the indirect effects of aerosols on clouds (51). In addition, it does not account for the time-integrated radiative effects, which can be influenced by factors affecting the lifetime of pyroCb aerosols with different sizes, such as diabatic self-lofting (13, 52), settling velocities, and cloud scavenging efficiency. The self-lofting process substantially extends the residence time of smoke aerosols in the UT/LS by counteracting sedimentation and removal. Using the method from Ohneiser et al. (52) and radiative heating rates derived from offline radiative transfer calculations, we estimate lofting velocities for the sampled New Mexico pyroCb smoke to range from 17 to 88 m/day depending on the RI scenarios. This is an order of magnitude greater than the gravitational settling velocities of approximately a few meters per day for particles with diameters of 500 to 600 nm. Despite these uncertainties, our study represents a realistic scenario given the persistent injections of smoke aerosols into the UT/LS through pyroCb events during active wildfire seasons, such as the 2023 Canadian wildfire season from March to November (53).

As shown in Fig. 4, the RI prescription also plays an important role in determining the value of radiative forcing, emphasizing the need to better understand the chemical composition and aging processes that determine the RI of pyroCb aerosols in the UT/LS (20, 54, 55). While studies have highlighted compositional and optical differences between pyroCb and non-pyroCb smoke as a result of thicker organic coatings on BC in pyroCb aerosols (12, 56), constraints on the RI of pyroCb aerosols remain quite limited. Nevertheless, our sensitivity analysis demonstrates that enhanced radiative cooling resulting from large pyroCb particles is consistent across all plausible RI scenarios, including those derived from field measurements and bounding cases with high absorption (Fig. 4B and figs. S9 and S11). Brown et al. (37) suggested that biomass burning aerosols in most climate models are generally too absorbing, leading to underestimated cooling effects. Their updated treatment of optical properties resulted in a shift in the global mean TOA direct radiative forcing of biomass burning aerosols from +0.059 to −0.011 W m⁻². Similarly, Beeler et al. (56) showed that overestimated light absorption also applies to pyroCb plumes on the basis of analyses of fresh pyroCb smoke.

Our findings indicate that cooling effects from biomass burning may be even more pronounced if the larger size mode of pyroCb aerosols in the UT/LS is incorporated into climate models, as the larger pyroCb aerosol size enhances TOA direct radiative forcing by about one-third compared to typical non-pyroCb smoke with equivalent mass concentrations. Given that pyroCb events can contribute up to 25% of BC and organic aerosols in the present-day global lower stratosphere (12), and considering their distinct size and optical properties, pyroCb smoke may exert a nonnegligible influence on global aerosol radiative forcing—an effect that is underrepresented in current climate models.

MATERIALS AND METHODS

Satellite identification of pyroCb smoke

The 16 June 2022 pyroCb event generated over the Calf Canyon and Hermits Peak wildfire complex was automatically detected by the Naval Research Laboratory’s pyroCb detection algorithm (16). Peak pyroconvection occurred at approximately 18:50 UTC 16 June according to the Pueblo Colorado NEXRAD reflectivity (fig. S1). The injection height was constrained by associating GOES thermal infrared brightness temperature with the temperature profile measured by the Albuquerque radiosonde measurement undertaken nominally at 00:00 UTC 17 June. Independent pyroconvective cloud-top height was gleaned from National Oceanic and Atmospheric Administration NEXRAD radar reflectivity measurements from the Pueblo Colorado site. Echoes at 14.7 km above sea level were recorded at 18:51 UTC 16 June (fig. S1).

PostpyroCb smoke was tracked between 16 and 21 June with GOES visible and near-infrared reflectance and infrared brightness temperature data. Persistent brightness temperature signals (57) were present for more than 24 hours after the pyroCb over the Texas panhandle (fig. S2). Near-infrared reflectance imagery (Fig. 1) corroborates the infrared-based evidence of smoke transport over Texas and follows the smoke toward the NASA ER-2 encounter on 21 June during DCOTSS.

At two times postpyroCb, CALIOP intercepted the smoke as it drifted over northern Texas. On 17 June, 1 day after the pyroCb, CALIOP measurements were coincident with the ultraviolet absorbing aerosol index (UVAAI) enhancements measured by the Ozone Mapping and Profiler Suite (OMPS) aboard the Suomi National Polar-orbiting Partnership satellite (https://disc.gsfc.nasa.gov/datasets/OMPS_NPP_NMMIEAI_L2_2/summary) (Fig. 1C). Such UVAAI enhancements have been routinely used to identify nascent UT/LS smoke plumes (58). We used the UVAAI map (https://go.nasa.gov/3WbmLnX) and guidance from GOES imagery to ascertain a CALIOP intercept of the smoke between 11 and 16 km on ~21:10 UTC 17 June (fig. S2). Again, on 19 June, while a portion of the pyroCb smoke stalled over Texas, a nighttime CALIOP measurement (~10:00 UTC) detected aerosol features we attribute to smoke at 11 to 16 km, along with another suspected smoke layer farther north (fig. S2). Backward air-parcel trajectories from the 19 June CALIOP intercept were calculated. These show a close correspondence with the GOES plume history and end points near the pyroCb source at the time of the fire surge (fig. S3).

In situ aircraft measurements

The DCOTSS campaign, spanning June to August 2021 and May to July 2022 over North America, aimed to delve into the complex interactions between dynamical and chemical processes shaping the composition of the extratropical summer stratosphere (https://dcotss.org/). Using the NASA ER-2 high-altitude aircraft platform, the campaign entailed in situ sampling and analysis of aerosols and various trace gases in the UT/LS. The goal was to characterize both the baseline stratosphere and perturbations caused by overshooting convective events, volcanic eruptions, and wildfire injections. With its capability to cruise at altitudes up to 21 km and sustain flights lasting up to 8 hours, the ER-2 aircraft provided an ideal platform for the campaign’s objectives. Vertical profiling within the 13- to 21-km altitude range was consistently conducted throughout the DCOTSS missions.

The particle concentration and size distribution were measured using the DCOTSS portable optical particle spectrometer (DPOPS) instrument aboard the NASA ER-2 aircraft (59). DPOPS samples ambient particles isokinetically and measures particle number density as a function of size across a range of 140 to 2500 nm in diameter throughout the troposphere and lower stratosphere. It uses a 405-nm diode laser to count and size individual particles at a 1-Hz resolution (60). Campaign-wide calibrations for particle counting efficiency and size accuracy were performed in the lab with size-classified dioctyl sebacate (RI of 1.45 + 0i) particles and polystyrene latex (PSL; RI of 1.615 + 0.001i) beads. For pyroCb particles, a smoke-specific RI of 1.52 + 0.01i was used to perform the size calibration, instead of the RI of PSL or dioctyl sebacate, to reduce calibration bias. We assume spherical particles for size calibration following the standard practice (60). We therefore report optical diameters, which are used consistently in the radiative transfer calculations. After each flight, the instrument performance was routinely checked using 300-nm PSL beads. The size distribution data are binned into 36 nonuniformly spaced size bins. With careful calibration, the uncertainty of number concentration is estimated to be within 5%, and sizing uncertainty is estimated to be within 15% for particles smaller than 600 nm (60). A sensitivity analysis in the radiative transfer calculations, in which the full size distribution was perturbed by ±15%, confirms that the conclusion of enhanced radiative cooling compared to typical non-pyroCb smoke particles remains robust (fig. S13). The resulting distributions were used as input to the radiative transfer calculation, ensuring that size-distribution uncertainty is directly propagated to the TOA forcing.

The particle chemical composition and type were measured using the particle analysis by laser mass spectrometry-next generation (PALMS-NG) instrument (61) aboard the ER-2 aircraft. Ambient aerosols are sampled through a custom-designed aerodynamic lens inlet, after which they are ablated and ionized by a 193-nm pulse laser. The resulting ions are analyzed by two s-shaped time-of-flight mass spectrometers, producing bipolar mass spectra for individual particles. Particle identification is based on their mass spectra, allowing classification into types such as pure sulfate, sulfate-organic mixtures, biomass burning, mineral dust, sea salt, etc. The fractional abundance of particle types within a given size bin, measured by PALMS-NG, is multiplied by the absolute concentration in the same size bin from DPOPS to derive a quantitative composition-resolved volume size distribution, as shown in Fig. 2B. Details of the method can be found in the study of Froyd et al. (62). A full composition classification following this method was performed in this study. However, during the sampling period, several particle types had either zero or very few detections and were therefore grouped under the “others” category because of insufficient statistics for meaningful volume concentration estimates. The three particle types shown in Fig. 2B, including biomass burning, internally mixed sulfate and organics, and mineral dust, had sufficient statistics to support robust classification and quantification.

Trace gases of pollution, CO and CO₂, were measured by the Harvard University Picarro Cavity Ringdown Spectrometer (HUPCRS) (63). The instrument consists of a G2401-m Picarro gas analyzer (Picarro Inc., Santa Clara, CA) repackaged in a temperature-controlled pressure vessel, a calibration system with two multispecies gas standards, and an external pump and pressure control assembly that allow operations at a wide range of altitudes. Air enters the instrument through a rear-facing inlet, is initially filtered by a 2-μm Zeflour membrane, and is subsequently dehydrated by a multitube Nafion before entering the Picarro analyzer. Calibrations are performed periodically during the flight to monitor measurement accuracy and stability. HUPCRS reports concentrations of CO₂, CO, and methane (CH₄) every ~2.2 s, and data are averaged to 10 s. In-flight precision is 0.02 ppmv for CO₂ and 3.20 ppbv for CO in 10 s.

Meteorological parameters including static pressure and temperature and GPS (Global Positioning System) altitude, latitude, and longitude were measured by the Meteorological Measurement System (MMS) during the ER-2 flight. The MMS provides calibrated, high-resolution measurements of ambient meteorological parameters at 20 Hz, with accuracies of ±0.3 hPa for static pressure, ±0.3 K for static temperature, ±1 m/s for three-dimensional winds (horizontal and vertical combined), and ±15 m for GPS altitude (64).

Aerosol microphysical model

The aerosol microphysical box model (27) simulates coagulation and dilution processes under upper tropospheric conditions. The model parameters for temperature and pressure are consistently set at 207 K and 150 hPa to match the observations, respectively (fig. S5). The model is run for 5 days for both initial conditions, namely unimodal and bimodal distributions, to observe the evolution of particle size distribution.

The model simulates Brownian coagulation using the Fuchs form of the Brownian coagulation kernel (65). A particle density of 1400 kg m⁻³ is assumed for the coagulation kernel calculation. Dilution in the model is represented by assuming a first-order decay rate to determine the rate of number change as a result of dilution in each size bin.

Initial conditions for the unimodal simulation were determined through an iterative process of testing a range of realistic fresh smoke conditions (27, 28, 66) for number concentrations (10⁴ to 10⁶ cm⁻³), modal widths (1.2 to 2.1), and diameters (100 to 200 nm). A range of dilution rates (5 × 10⁻⁶ to 5 × 10⁻⁵ s⁻¹) was also assessed. From these tests of initial conditions, we found that the set of initial conditions with a single mode that best fit the observed distribution at 5 days was a number median diameter of 130 nm and a modal width of 1.5 with an initial concentration of 501,187 cm⁻³, with a dilution rate for this simulation of 1.143 × 10⁻⁵ s⁻¹ (table S1). This dilution rate is slower than the dilution rate of lower free tropospheric plumes but realistic for conditions in the UT/LS (27). We do not account for spatial variations in dilution, which could include more rapid mixing and entrainment at the edges of the plume than at its core.

For the bimodal distribution simulation, the smaller initial mode diameter and width were kept the same as the unimodal simulation to represent the fraction of smoke particles that did not undergo cloud processing, while the larger mode represents a fraction of smoke that experienced cloud processing. The same dilution rate as the unimodal simulation was used for testing of all bimodal initial conditions. An iterative process was used to test the initial diameter of the larger mode (200 to 300 nm), the modal width of the larger mode (1.2 to 2.1), the fraction of particles in the larger mode (0 to 0.5), and the total number of particles (3 × 10³ to 10⁶ cm⁻³) to determine initial conditions that best fit the observations at 5 days. The optimal scenario featured an initial larger mode diameter of 260 nm with a width of 1.4. A total of 40% of the total initial concentration of 160,700 cm⁻³ was located in the larger mode (table S1).

Offline radiative transfer calculation

The offline radiative transfer model used here is the Rapid Radiative Transfer Model for General Circulation Model Applications (RRTMG) developed by Clough et al. (67). RRTMG is an efficient, actively maintained, and freely accessible radiative transfer model that has been coupled to many climate models. It includes both shortwave and longwave radiation schemes that can be run separately. The shortwave scheme (RRTMG_SW) uses a two-stream algorithm to perform shortwave radiative flux calculations, and the longwave scheme (RRTMG_LW) calculates longwave radiative fluxes (excluding scattering) through the correlated k-distribution approach. The flux profiles are computed using the mid-latitude standard atmosphere profiles (68, 69) of temperature, water vapor, ozone, and five other radiatively active gaseous absorbers (carbon dioxide, nitrous oxide, methane, molecular oxygen, and carbon monoxide) and assuming cloud-free skies.

Shortwave extinction optical depth, SSA, and the asymmetry parameter are calculated by applying Mie theory (70) to an ensemble of biomass burning aerosol shortwave RI spectra. These spectra are estimated from long-term Aerosol Robotic Network (AERONET) column measurements (44, 71, 72), as well as airborne field measurements (73) that are included in the HITRAN database. AERONET and HITRAN RI datasets for smoke aerosols, while widely used, have limitations for pyroCb applications. AERONET retrievals reflect bulk column properties that may include higher fractions of nonbiomass components than pyroCb smoke, and the version 3 data (the latest available) used here may suppress the shortwave spectral variability associated with brown carbon absorption (74). HITRAN values are based on lower-tropospheric airborne measurements with potential retrieval biases (e.g., reliance on single-wavelength absorption extrapolation and spherical-particle assumptions). The HITRAN cases (RI4 and RI5 in fig. S8) show anomalous increases in absorption toward longer visible and near-infrared wavelengths, which likely reflect retrieval artifacts (73). We therefore treat RI4 and RI5 as bounding cases, not typical smoke spectra, and use them to test the robustness of our conclusions across a wide range of RI scenarios. Neither dataset directly represents pyroCb smoke. To address this, we extended our analyses to span a wide range of RI scenarios—including AERONET-derived values, HITRAN values, and additional high-absorption cases (up to SSA ~0.80, corresponding to upper bounds of plausible BC fractions). Across all cases, our central conclusion of enhanced TOA radiative cooling by large pyroCb aerosols remains robust. The longwave absorption optical depth is calculated from a biomass burning RI spectrum (75), also included in the HITRAN database and using Mie theory. Mie theory assumes spherical particles; while this may not fully represent the morphology of fresh biomass burning aerosols, aging processes tend to compact these particles into more spherical shapes (76). Given that both particle size measurement and radiative transfer calculation rely on this assumption, the use of Mie theory provides a consistent framework. The resulting uncertainty is partially captured through sensitivity tests using various RI datasets and perturbed size distributions, with the spread in radiative forcing estimates reflecting plausible variability as a result of both composition and morphology.

Aerosol concentrations and size distributions are taken from DPOPS measurements. The composition information from the PALMS-NG measurements is not included in the offline radiative transfer calculation. A 1-km-thick smoke layer with measured aerosol concentrations and size distributions is prescribed at the model level corresponding to ~150 hPa on the basis of rough estimates of the vertical extent from ER-2 plume encounters. A sensitivity analysis using thinner (0.5 km) and thicker (2 km) smoke layers demonstrates that while the absolute radiative forcing values vary with layer thickness, the conclusion of substantially enhanced radiative cooling by larger pyroCb aerosols remains robust across all tested scenarios (fig. S14). A Lambertian surface emissivity of 0.3 is used for all wavelengths. The shortwave radiative fluxes are calculated for a solar zenith angle of 60° to provide a representative, diurnally averaged value for instantaneous radiative forcing and to align with common practices in the aerosol radiative forcing literature. Instantaneous radiative forcing at the top of the atmosphere is derived as the difference between the net clear-sky radiative flux with and without the presence of pyroCb smoke.

WRF-GC regional meteorology-chemistry model

The WRF-GC model is an online two-way coupling of the WRF meteorological model and the GC chemical transport model, specifically designed for regional climate and atmospheric chemistry simulations (47, 77). Both WRF and GC are open-source community models. To simulate the aerosol radiative effects of the 2022 New Mexico pyroCb event, we conducted two experiments: a control experiment and a pyroCb experiment. In the control experiment, the number-mode diameter (μ) and modal width (σ) of the log-normal distributions for smoke aerosols, including organic carbon (OC) and BC, follow the model’s default aerosol size distributions (OC: μ = 140 nm, σ = 1.6; BC: μ = 40 nm, σ = 1.6). In the pyroCb experiment, the size distribution for all smoke OC was adjusted to better match the pyroCb aerosols sampled during DCOTSS, while that for BC was left unchanged (OC: μ = 500 nm, σ = 1.3; BC: μ = 40 nm, σ = 1.6). The purpose of the experiments is to show differences as a result of size only, not vertical location or compositional differences between pyroCb and non-pyroCb smoke. Brown carbon was not explicitly considered in our WRF-GC simulations, but in the offline radiative transfer calculations, we used bulk RI data from observation-based datasets, which account for the effects of brown carbon. Both pyroCb and control experiments relied on the same biomass burning emissions and injection heights from the Global Fire Assimilation System (GFAS) inventory and were simulated over the period from 11 to 21 June 2022. The first 5 days initialized the model. Emissions from the New Mexico fires contributed to 73% of the total fire emissions in the study domain from 16 to 21 June, with emissions on 16 June alone accounting for 67% of the total during that period (fig. S12). Given that the New Mexico fire on 16 June developed into a pyroCb, it is likely that most of the 67% of emissions on that day were carried aloft by pyroCb convection. In the WRF-GC model, plume heights reached 11 km, about 3 km lower than those observed in DCOTSS, but this underestimate should have little effect on the resulting estimates for AOD or shortwave forcing. The WRF-GC model diagnoses the AOD using static unimodal log-normal distributions for different aerosol types and compositions. The differences in AOD and clear-sky instantaneous shortwave radiative forcing between the two experiments reflect the radiative impacts of the large pyroCb aerosols. In these simulations, instantaneous shortwave radiative forcing is computed at each model time step using the local solar zenith angle, with output archived hourly and averaged over 16 to 21 June 2022. Given that all smoke OC aerosols in the pyroCb experiment were treated as pyroCb aerosols upon emission, our results represent an upper limit for the impacts of such aerosols on AOD and forcing within the study domain. We did not nudge the meteorology or pyroCb plume injection height using observations, and the simulation was intended to explore plausible regional-scale impacts rather than replicate observed plume structures in detail.

Acknowledgments

This work was supported by NASA under Earth Venture Suborbital-3 program awards for the DCOTSS mission. Additional support was provided by the Naval Research Laboratory, the National Science Foundation, and the Salata Institute for Climate and Sustainability at Harvard University. We thank the entire DCOTSS team, including NASA ER-2 flight crews, NASA Earth Science Project Office (ESPO) group, and science and engineering teams. We also thank J. Schwarz, Y. Zhang, J. Ding, and Q. Chen for valuable discussions.

Funding:

This work was supported by the following: National Aeronautics and Space Administration grant 80NSSC19K0326 (to Y.L., J.A.D., J.V.P., B.C.D., S.C.W., and F.N.K.), National Aeronautics and Space Administration grant 80NSSC19K1058 (to X.S., J.L.J., and D.J.C.), National Aeronautics and Space Administration grant 80NSSC19K0341 (to K.P.B. and A.D.R.), Naval Research Laboratory’s 6.2 Base Program (to D.A.P., M.D.F., and T.M.M.), National Aeronautics and Space Administration grant 80HQTR21T0099 (to D.A.P., M.D.F., and T.M.M.), National Science Foundation grant 2211153 (to J.R.P. and N.A.J.), and seed funding from the Salata Institute for Climate and Sustainability at Harvard University (to X.F. and L.J.M.).

Author contributions:

Conceptualization: Y.L., J.A.D., D.A.P., J.V.P., S.C.W., K.P.B., D.J.C., J.R.P., and F.N.K. Methodology: Y.L., J.A.D., D.A.P., X.F., N.A.J., M.D.F., D.J.C., L.J.M., J.R.P., and F.N.K. Software: Y.L., J.A.D., X.F., N.A.J., K.P.B., and J.R.P. Validation: Y.L., D.A.P., X.F., J.V.P., B.C.D., S.C.W., D.J.C., L.J.M., and F.N.K. Formal analysis: Y.L., J.A.D., X.F., X.S., N.A.J., M.D.F., J.D.-D., L.J.M., D.J.C., and F.N.K. Investigation: Y.L., J.A.D., X.F., X.S., N.A.J., M.D.F., J.L.J., J.V.P., B.C.D., S.C.W., J.D.-D., A.D.R., L.J.M., D.J.C., and F.N.K. Resources: Y.L., D.A.P., X.S., J.L.J., J.V.P., B.C.D., S.C.W., L.J.M., and J.R.P. Data curation: Y.L., D.A.P., X.F., X.S., N.A.J., J.V.P., B.C.D., S.C.W., and D.J.C. Writing—original draft: Y.L., J.A.D., D.A.P., N.A.J., and F.N.K. Writing—review and editing: Y.L., J.A.D., D.A.P., X.F., X.S., N.A.J., M.D.F., T.M.M., J.L.J., J.V.P., B.C.D., S.C.W., J.D.-D., A.D.R., D.J.C., L.J.M., J.R.P., and F.N.K. Visualization: Y.L., D.A.P., X.F., X.S., N.A.J., M.D.F., and T.M.M. Supervision: Y.L., J.A.D., D.A.P., S.C.W., D.J.C., L.J.M., J.R.P., and F.N.K. Project administration: Y.L., J.A.D., S.C.W., K.P.B., D.J.C., and F.N.K. Funding acquisition: S.C.W., K.P.B., D.J.C., L.J.M., J.R.P., and F.N.K.

Competing interests:

The authors declare that they have no competing interests.

Data and materials availability:

All aircraft measurement data from the DCOTSS mission are publicly available through the NASA Atmospheric Science Data Center (https://doi.org/10.5067/ASDC/DCOTSS-Aircraft-Data_1). The aerosol microphysical model code is archived on Zenodo (https://zenodo.org/records/15652684); the RRTMG offline radiative transfer code, developed and made publicly available by Atmospheric and Environmental Research (AER), is archived on Zenodo (https://zenodo.org/records/17088143); and the WRF-GC code is archived on Zenodo (https://zenodo.org/records/15654707).

Supplementary Materials

This PDF file includes:

Figs. S1 to S14

Table S1

References

sciadv.adw6526_sm.pdf^{(6.3MB, pdf)}

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Figs. S1 to S14

Table S1

References

sciadv.adw6526_sm.pdf^{(6.3MB, pdf)}

Data Availability Statement

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PERMALINK

Enhanced radiative cooling by large aerosol particles from wildfire-driven thunderstorms

Yaowei Li

John A Dykema

David A Peterson

Xu Feng

Xiaoli Shen

Nicole A June

Michael D Fromm

Theodore M McHardy

Justin L Jacquot

Jasna V Pittman

Bruce C Daube

Steven C Wofsy

Jonathan Dean-Day

Anita D Rapp

Kenneth P Bowman

Daniel J Cziczo

Loretta J Mickley

Jeffrey R Pierce

Frank N Keutsch

Roles

Abstract

INTRODUCTION

RESULTS

Targeted in situ measurements of pyroCb smoke

Fig. 1. Satellite observations of pyroCb activity and smoke plume transport.

Fig. 2. Size distribution of wildfire smoke aerosols from the 2022 New Mexico pyroCb event.

Characteristically large size of pyroCb aerosols

Fig. 3. Modeled coagulation growth of aerosols in the UT/LS.

Enhanced radiative cooling by large pyroCb aerosols

Fig. 4. TOA instantaneous radiative forcing of sampled pyroCb aerosols compared to typical non-pyroCb smoke and modeled wildfire aerosols.

Fig. 5. Changes in AOD at a 600-nm wavelength and instantaneous TOA shortwave radiative forcing from large pyroCb aerosols in regional meteorology-chemistry model simulations.

DISCUSSION

MATERIALS AND METHODS

Satellite identification of pyroCb smoke

In situ aircraft measurements

Aerosol microphysical model

Offline radiative transfer calculation

WRF-GC regional meteorology-chemistry model

Acknowledgments

Funding:

Author contributions:

Competing interests:

Data and materials availability:

Supplementary Materials

This PDF file includes:

REFERENCES AND NOTES

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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