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We present our study on the sub-seasonal variability of UTLS aerosols and CO that is a result of the variability induced by the sub-seasonal variability of the Asian summer monsoon dynamics. We use the NASA global model GEOS simulations that incorporates emissions from anthropogenic, biomass burning, volcanic, and other natural sources to simulate CO, aerosols and related gases and the model experiments separating source types (anthropogenic, biomass burning, volcanic) and source locations (East Asia, South Asia). With model results and observations from recent aircraft measurements (StratoClim, ACCLIP) in the UTLS over the Asian summer monsoon regions, we will discuss (1) the sub-seasonal variability of transport pathways of surface-generated pollutants to reach UTLS, and (2) sub-seasonal variation of aerosol composition that is determined by the variability of source type originating in different locations.

The NASA Earth Venture Suborbital (EVS-2) Atmospheric Tomography Mission (ATom) provided rich gas and aerosol measurements over the global oceans. In this study, we investigate the sulfur species of dimethyl sulfide (DMS), sulfur dioxide (SO2), methane sulfonic acid (MSA), and sulfate (SO4) that were measured during the ATom aircraft campaigns and simulated by five AeroCom models. This study focuses on remote regions over the Pacific, Atlantic, and Southern Oceans from near the surface to ~12 km altitude and covers all four seasons. We examine the vertical and seasonal variations of these sulfur species over tropical, mid-, and high latitude regions in both hemispheres. We identify their origins from land versus ocean and from anthropogenic versus natural sources with sensitivity studies by applying tagged tracers linking to emission types and regions. Using the GEOS model, we also investigate impact of cloud simulation (i.e., one-moment bulk cloud module, 1MOM vs two-moment cloud microphysics module, 2MOM) on the sulfur cycle and identify critical mechanisms of cloud impact by performing process-level budget analyses. Generally, SO4 has a better model-observation agreement than DMS, SO2 and MSA, and there are much larger DMS simulated concentrations close to the sea surface than measured, indicating all model DMS emissions may be too high. Anthropogenic emissions are the dominant source (44-60% of the total amount) for atmospheric SO4 simulated along ATom flight tracks in almost every altitude, followed by volcanic eruptions (18-33%) and oceanic sources (16-28%). GEOS SO4 simulations differ significantly between the 1MOM and 2MOM cloud schemes, with the sulfate chemical production via aqueous phase reactions seeming to be the critical process.

The 15 January 2022 eruption of the submarine Hunga Tonga-Hunga Ha'apai (HTHH) volcano (Tonga) ranks among the largest volcanic explosions of the satellite remote sensing era, and perhaps the last century. It shares many characteristics with the 1883 Krakatau eruption (Indonesia), including atmospheric pressure waves and tsunamis, and the phreatomagmatic interaction of magma and seawater likely played a major role in the dynamics of both events. A portion of the HTHH eruption column rose to lower mesospheric altitudes (~55 km) and the umbrella cloud extent (~500 km diameter at ~30-35 km altitude) rivalled that of the 1991 Pinatubo eruption, indicative of very high mass eruption rates. However, sulfur dioxide (SO2) emissions measured in the HTHH volcanic cloud (~0.4 Tg) were significantly lower than the post-Pinatubo SO2 loading (~10–15 Tg SO2), and on this basis we would expect minimal climate impacts from the HTHH event. Yet, in the aftermath of the eruption satellite observations show a persistent stratospheric aerosol layer with the characteristics of sulfate aerosol, along with a large stratospheric water vapor anomaly. At the time of writing, the origin, composition and eventual impacts of this stratospheric gas and aerosol veil are unclear. We present the preliminary results of a multi-disciplinary approach to understanding the HTHH eruption, including 1D- and 3D-modeling of the eruption column coupled to a 3D atmospheric general circulation model (NASA’s GEOS-5 model), volatile mass balance considerations involving potential magmatic, seawater and atmospheric volatile and aerosol sources, and an extensive suite of satellite observations. Analysis of the HTHH eruption will provide new insight into the dynamics and atmospheric impacts of large, shallow submarine eruptions. Such eruptions have likely occurred throughout Earth’s history but have never been observed with modern instrumentation.

The Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP) has been flying on the Suomi NPP satellite since October 2011. It is designed to produce ozone and aerosol vertical profiles at 1.6 km vertical resolution over the entire sunlit globe. The Version 1.5 (V1.5) aerosol extinction retrieval algorithm provides aerosol extinction profiles using observed radiances at 675 nm. The algorithm assumes Mie theory and a gamma function aerosol size distribution for the stratospheric aerosol that is derived from Community Aerosol and Radiation Model for Atmospheres (CARMA) calculated results and observations in April 2012. In this paper, we compare V1.5 LP aerosol profiles with SAGE III/ISS solar occultation observations for the period June 2017 – May 2019, when both measurements were available. Overall, LP extinction profiles agree with SAGE data to within ±25 % for the main aerosol layer between 19 and 27 km, even during periods perturbed by volcanic eruptions or intense forest fires. The slope parameter of linear fitting of LP extinctions with respect to SAGE measurements are close to 1.0, with Pearson's correlation coefficients of r ≥ 0.95, indicating that the LP aerosol data are reliable in that altitude range. Comparisons of extinction time series show a high degree of correlation between LP and SAGE, indicating that the LP retrieved extinction variability in time is robust. On the other hand, we find that LP retrieved extinction is systematically higher than SAGE observations at altitudes above 28 km and systematically lower below 19 km in the tropics. This is likely due in part to the fact that the actual aerosol size distribution is altitude dependent, while the assumed size distribution in the V1.5 retrieval is assumed to be altitude independent and so it may be less accurate for altitudes above 28 km and below 19 km where the size distribution is more variable. There are other reasons related to cloud contamination, wavelength limitations and the accuracy of both instruments at low aerosol loading.

Observations of multiwavelength Mie-Raman lidar taken during the SHADOW field campaign are used to analyze a smoke/dust episode over West Africa on 24–27 December 2015. For the case considered, the dust layer extended from the ground up to approximately 2000 m while the elevated smoke layer occurred in the 2500 m–4000 m range. The profiles of lidar measured backscattering, extinction coefficients and depolarization ratios are compared with the vertical distribution of aerosol parameters provided by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). The MERRA-2 model simulated the correct location of the near–surface dust and elevated smoke layers. The values of modeled and observed extinctions at both 355 nm and 532 nm are also rather close. Good coherence between measured and modeled extinction profiles provides an opportunity to test how well the model reproduces backscattering of dust particles at different wavelengths. The comparison shows good agreement of modeled and measured backscattering coefficients at 355 nm, meaning that the modeled dust lidar ratio of 65 sr in the near-surface layer is close to the observed value. At 532 nm however, the simulated lidar ratio is lower than measurements (about 40 sr and 50 sr respectively). The reason for this disagreement could be that the assumed imaginary part of the refractive index for dust (0.0025 at 532 nm) is too low, or that the particle size distribution in the model is too much weighted toward fine mode dust. The model predicts significant concentration of dust particles inside the smoke layer. This is supported by a high depolarization ratio of 15 % observed in the center of this layer. The backscattering Ångström exponent at 355/532 nm as well as both lidar ratios have a minimum in the center of the elevated layer, which can also be explained by the presence of dust.

Millions of tons of mineral dust are lifted by the wind from arid surfaces and transported around the globe every year. The physical and chemical properties of the mineral dust are needed to better constrain remote sensing observations and are of fundamental importance for the understanding of dust atmospheric processes. Ground-based in situ measurements and in situ filter collection of Saharan dust were obtained during the Fennec campaign in the central Sahara in 2011. This paper presents results of the absorption and scattering coefficients, and hence, single scattering albedo (SSA), of the Saharan dust measured in real time during the last period of the campaign, and subsequent laboratory analysis of the dust samples collected in two supersites, SS1 and SS2, in Algeria and in Mauritania, respectively. The samples were taken to the laboratory where their size and aspect ratio distributions, mean chemical composition, spectral mass absorption efficiency and spectral imaginary refractive index were obtained from the ultraviolet (UV) to the near infrared (NIR) wavelengths. At SS1 in Algeria, the time series of the scattering coefficients during the period of the campaign show dust events exceeding 3500 Mm−1 and a relatively high mean SSA of 0.995 at 670 nm was observed at this site. The laboratory results show for the fine distributions in both sites a spectral dependence of the imaginary part of the refractive index Im(m) with a bow-like shape, with increased absorption in ultraviolet and also in the shortwave infrared. The same signature was not observed, however, in the mixed size distribution in Algeria. Im(m) was found to range from 0.011 to 0.001i for dust collected in Algeria and 0.008 to 0.002i for dust collected in Mauritania over the wavelength range of 350–2500 nm. Differences in the mean elemental composition of the dust collected in the supersites in Algeria and in Mauritania and between fine and mixed modes distributions were observed from EDXRF measurements, although those differences cannot be used to explain the optical properties variability between the samples. Finally, particles with low-density typically larger than 10 μm in diameter were found in some of the samples collected at the supersite in Mauritania, but these low-density particles were not observed in Algeria.