Marine aerosol properties over the Southern Ocean in relation to the wintertime meteorological conditions

Given the vast expanse of oceans on our planet, marine aerosols (and sea salt in particular) play an important role in the climate system via multitude of direct and indirect effects. The efficacy of their net impact, however, depends strongly on the local meteorological conditions that influence their physical, optical and chemical properties. Understanding the coupling between aerosol properties and meteorological conditions is therefore important. It has been historically difficult to statistically quantify this coupling over larger oceanic areas due to the lack of suitable observations, leading to large uncertainties in the representation of aerosol processes in climate models. Perhaps no other region shows higher uncertainties in the representation of marine aerosols and their effects than the Southern Ocean. During winter the Southern Ocean boundary layer is dominated by sea salt emissions. Here, using 10 years of austral winter period (June, July and August, 2007–2016) space-based aerosol profiling by CALIOP-CALIPSO in combination with meteorological reanalysis data, we investigated the sensitivity of marine aerosol properties over the Southern Ocean (40–65∘ S) to various meteorological parameters, such as vertical relative humidity (RH), surface wind speed and sea surface temperature (SST) in terms of joint histograms. The sensitivity study is done for the climatological conditions and for the enhanced cyclonic and anticyclonic conditions in order to understand the impact of large-scale atmospheric circulation on the aerosol properties. We find a clear demarcation in the 532 nm aerosol backscatter and extinction at RH around 60 %, irrespective of the state of the atmosphere. The backscatter and extinction increase at higher relative humidity as a function of surface wind speed. This is mainly because of the water uptake by the wind-driven sea salt aerosols at high RH near the ocean surface resulting in an increase in size, which is confirmed by the decreased depolarization for the wet aerosols. An increase in aerosol backscatter and extinction is observed during the anticyclonic conditions compared to cyclonic conditions for the higher wind speeds and relative humidity, mainly due to aerosols being confined to the boundary layer, and their proximity to the ocean surface facilitates the growth of the particles. We further find a very weak dependency of aerosol backscatter on SSTs at lower wind speeds. However, when the winds are stronger than about 12 m s−1, the backscattering coefficient generally increases with SST. When aerosol properties are investigated in terms of aerosol verticality and in relation to meteorological parameters, it is seen that the aerosol backscatter values in the free troposphere (pressure <850 hPa) are much lower than in the boundary layer, irrespective of the RH and the three weather states. This indicates that the local emissions from the ocean surface make the dominant contribution to aerosol loads over the Southern Ocean. A clear separation of particulate depolarization is observed in the free and lower troposphere, more prominent in the climatological mean and the cyclonic states. For RH > 60 %, low depolarization values are noticeable in the lower troposphere, which is an indication of the dominance of water-coated and mostly spherical sea salt particles. For RH < 60 %, there are instances when the aerosol depolarization increases in the boundary layer; this is more prominent in the mean and anticyclonic cases, which can be associated with the presence of drier aerosol particles. Based on the joint histograms investigated here, we provide third-degree polynomials to obtain aerosol extinction and backscatter as a function of wind speed and relative humidity. Additionally, backscattering coefficient is also expressed jointly in terms of wind speed and sea surface temperature. Furthermore, depolarization is expressed as a function of relative humidity. These fitting functions would be useful to test and improve the parameterizations of sea salt aerosols in the climate models. We also note some limitations of our study. For example, interpreting the verticality of aerosol properties (especially depolarization) in relation to the meteorological conditions in the free and upper troposphere (pressure <850 hPa) was challenging. Furthermore, we do not see any direct evidence of sudden crystallization (efflorescence), deliquescence or hysteresis effects of the aerosols. Observing such effects will likely require a targeted investigation of individual cases considering tracer transport, rather than the statistical sensitivity study that entails temporally and geographically averaged large data sets.

Linking chemical composition and optical properties of biomass burning aerosols in Amazonia

Biomass burning emissions in Amazonia changes the atmospheric composition and aerosol properties during the dry season. We investigated fine-mode aerosol chemical composition and optical properties at an intensive field experiment...

Earth System Model Aerosol-Cloud Diagnostics Package (ESMAC Diags) Version 1: Assessing E3SM Aerosol Predictions Using Aircraft, Ship, and Surface Measurements

An Earth System Model (ESM) aerosol-cloud diagnostics package is developed to facilitate the routine evaluation of aerosols, clouds and aerosol-cloud interactions simulated by the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM). The first version focuses on comparing simulated aerosol properties with aircraft, ship, and surface measurements, most of them are measured in-situ. The diagnostics currently covers six field campaigns in four geographical regions: Eastern North Atlantic (ENA), Central U.S. (CUS), Northeastern Pacific (NEP) and Southern Ocean (SO). These regions produce frequent liquid or mixed-phase clouds with extensive measurements available from the Atmospheric Radiation Measurement (ARM) program and other agencies. Various types of diagnostics and metrics are performed for aerosol number, size distribution, chemical composition, CCN concentration and various meteorological quantities to assess how well E3SM represents observed aerosol properties across spatial scales. Overall, E3SM qualitatively reproduces the observed aerosol number concentration, size distribution and chemical composition reasonably well, but underestimates Aitken mode and overestimates accumulation mode aerosols over the CUS region, and underestimates aerosol number concentration over the SO region. The current version of E3SM struggles to reproduce new particle formation events frequently observed over both the CUS and ENA regions, indicating missing processes in current parameterizations. The diagnostics package is coded and organized in a way that can be easily extended to other field campaign datasets and adapted to higher-resolution model simulations. Future releases will include comprehensive cloud and aerosol-cloud interaction diagnostics.

Assessment of NAAPS-RA performance in Maritime Southeast Asia during CAMP²Ex

Monitoring and modeling aerosol particle lifecycle in Southeast Asia (SEA) is challenged by high cloud cover, complex meteorology, and the wide range of aerosol species, sources, and transformations found throughout the region. Satellite observations are limited, and there are few in situ observations of aerosol extinction profiles, aerosol properties, and environmental conditions. Therefore, accurate aerosol model outputs are crucial for the region. This work evaluates the Navy Aerosol Analysis and Prediction System Reanalysis (NAAPS-RA) aerosol optical thickness (AOT) and light extinction products using airborne aerosol and meteorological measurements from the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) in SEA. Modeled AOTs and extinction coefficients were compared to those retrieved with a High Spectral Resolution Lidar (HSRL-2). Correlations were highest for AOT in the mixed layer (AOTML; R2 = 0.83, bias = 0.00, root mean square error [RMSE] = 0.03) compared to total AOT (R2 = 0.68, bias = 0.01, RMSE = 0.14), although the correlations between the observations and 1° × 1° degree NAAPS-RA outputs were weaker in regions with strong gradients in aerosol properties, such as near areas of active convection. Correlations between simulated and retrieved aerosol extinction coefficients were highest from 145–500 m (R2 = 0.75, bias = 0.01 km−1, RMSE = 0.08 km−1) and decreased with increasing altitude (R2 = 0.69 and 0.26, bias = 0.00 and 0.00 km−1, RMSE = 0.09 and 0.00 km−1 for 500–1500 m and > 1500 m, respectively), which was likely a result of the use of bulk cloud mixing parameterizations. We also investigated the role of possible relative humidity (RH) errors in extinction simulations. Despite negative biases in modeled RH (−4.9, −7.7, and −2.3 % for altitudes < 500 m, 500–1500 m, and > 1500 m, respectively), AOT and extinction agreement with the HSRL-2 did not change significantly at any altitude when RHs from dropsondes were substituted into the model. Improvements may have been stunted due to errors in how NAAPS-RA modeled physics of particle hygroscopic growth, dry particle mass concentrations, and/or dry mass extinction efficiencies, especially when combined with AOT corrections from data assimilation. Specifically, the model overestimated the hygroscopicity of (i) smoke particles from biomass burning in the Maritime Continent (MC), and (ii) anthropogenic emissions transported from East Asia. This work provides insight into how certain environmental and microphysical properties influence AOT and extinction simulations, which can then be interpreted in the context of modeling global concentrations of particle mass and cloud condensation nuclei (CCN).

Dry Powders for Inhalation Containing Monoclonal Antibodies Made by Thin-Film Freeze-Drying

Thin-film freeze-drying (TFFD) is a rapid freezing and then drying technique used to prepare inhalable dry powders from the liquid form for drug delivery to the lungs. We report the preparation of aerosolizable dry powders of monoclonal antibodies (mAbs) by TFFD. We first formulated IgG with lactose/leucine (60:40 w/w) or trehalose/leucine (75:25). IgG 1% (w/w) formulated with lactose/leucine (60:40 w/w) in phosphate buffered saline (PBS) (IgG-1-LL-PBS) and processed by TFFD was found to produce the powder with the most desirable aerosol properties. We then replaced IgG with a specific antibody, anti-programmed cell death protein (anti-PD-1 mAb), to prepare a dry powder (anti-PD1-1-LL-PBS), which performed similarly to the IgG-1-LL-PBS powder. The aerosol properties of anti-PD1-1-LL-PBS were significantly better when TFFD was used to prepare the powder as compared to conventional shelf freeze-drying (shelf FD). The dry powder had a porous structure with nanoaggregates. The dry powder had a Tg value between 39-50 degree Celsius. When stored at room temperature, the anti-PD-1 mAb in the TFFD powder was more stable than that of the same formulation stored as a liquid. The addition of polyvinylpyrrolidone (PVP) K40 in the formulation was able to raise the Tg to 152 degree Celsius, which is expected to further increase the storage stability of the mAbs. The PD-1 binding activities of the anti-PD-1 mAbs before and after TFFD were not different. While protein loss, likely due to protein binding to glass or plastic vials and the TFF apparatus, was identified, we were able to minimize the loss by increasing mAb content in the powders. Lastly, we show that another mAb, anti-TNF-alpha;, can also be converted to a dry powder with a similar composition by TFFD. We conclude that TFFD can be applied to produce stable aerosolizable dry powders of mAbs for pulmonary delivery.

A novel method of identifying and analysing oil smoke plumes based on synergic satellite data

Black carbon aerosols are the second largest contributor to global warming while also being linked to respiratory and cardiovascular disease. These particles are generally found in smoke plumes originating from biomass burning and fossil fuel combustion. They are also heavily concentrated in smoke plumes originating from oil fires exhibiting the largest ratio of black carbon to organic carbon. In this study, we identified and analyzed oil smoke plumes derived from 30 major industrial events within a 12-year timeframe. To our knowledge, this is the first study of its kind that utilized a synergetic approach based on satellite remote sensing techniques. One objective of this study is to highlight the importance of satellite remote sensing techniques in identifying these types of events. As opposed to ground stations, satellite data offers access to remote areas all over the globe which would otherwise be very difficult to reach. Satellite data offers access to these events which, as seen in this study, are mainly located in war prone or hazardous areas. This study focuses on the use of MODIS (Moderate Resolution Imaging Spectroradiometer) and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) products regarding these types of aerosol while also highlighting their intrinsic limitations. By using data from both MODIS instruments onboard Terra and Aqua satellites we addressed the temporal evolution of the smoke plume while assessing Lidar specific properties and plume elevation using CALIPSO data. We present several aerosol properties in the form of plume specific averaged values. The MODIS ocean algorithms were successful in retrieving aerosol properties which, on average, ranged from −0.06 to 0.16 for plume specific AOD, −0.18 to 1.25 for Ångström exponent and 0.29 to 1.73 µm for the effective radius. CALIPSO measurements showed values of plume AOD ranging from 0 to 0.14 (532 nm) and 0 to 0.13 (1064 nm) except for one event where AOD values showed 1.52 (532 nm) and 1.42 (1064 nm). AE values ranged from 0.11 to 0.33 which were in agreeance with MODIS values. A large discrepancy can be found in one event where CALIPSO measured AOD values 5 times higher than MODIS. This event also produced the largest lidar ratio at 109 sr (532 nm) and 86 (1064 nm). Other lidar ratio values ranged from 37 to 55 sr however these unconstrained solutions were obtained for the entire layer of which the plumes were a part of and thus did not reflect specific plume conditions. Particulate backscatter values ranged from 0.002 to 0.0017 km−1 sr−1 while extinction coefficient values ranged from 0.10 to 1.65 km−1. On average backscatter and extinction coefficient values were 2 to 9 times higher than local background values. Particulate depolarization ratios ranged from 0.11 to 0.15 in 4 out of 6 cases while the remaining two ranged from 0.27 to 0.32 where dust was highly dominant. The values represented in this study are in good agreement with similar studies that used ground based and flight measurements. We believe that MODIS values are a conservative estimation of plume AOD since MODIS algorithms rely on general aerosol models and various atmospheric conditions within the look-up tables which do not reflect the highly absorbing nature of these smoke plumes. CALIPSO measurements are heavily dependent on lidar ratios which are not directly measured if plumes within the planetary boundary layer. We also believe that AOD values based on CALIPSO measurements are conservative in nature since heavy absorbing smoke would yield larger lidar ratios and AOD values. Based on this study we conclude that the MODIS land algorithms are not yet suited for retrieving aerosol properties for these types of smoke plumes due to the strong absorbing properties of these aerosols. We believe that these types of studies are a strong indicator for the need of improved aerosol models and retrieval algorithms.

New particle formation in coastal New Zealand with a focus on open ocean air masses

Even though oceans cover the majority of the Earth, most aerosol measurements are from continental sites. We measured aerosol particle number size distribution at Baring Head, in coastal New Zealand, over a total period of 10 months to study aerosol properties and new particle formation, with a special focus on aerosol formation in open ocean air masses. Particle concentrations were higher in land-influenced air compared to clean marine air in all size classes from sub-10 nm to cloud condensation nuclei sizes. When classifying the particle number size distributions with traditional methods designed for continental sites, new particle formation was observed at the station throughout the year with an average event frequency of 23 %. While most of these traditional event days had some land-influence, we also observed particle growth starting from nucleation mode during 16 % of the data in clean marine air and at least part of this growth was connected to nucleation in the marine boundary layer. Sub-10 nm particles accounted for 29 % of the total aerosol number concentration of particles larger than 1 nm in marine air during the spring. This shows that nucleation in marine air is frequent enough to influence the total particle concentration. Particle formation in land-influenced air was more intense and had on average higher growth rates than what was found for marine air. Particle formation and primary emissions increased particle number concentrations as a function of time spent over land during the first 1–2 days spent over land. After this, nucleation seems to start getting suppressed by the pre-existing particle population, but accumulation mode particle concentration keeps increasing, likely due to primary particle emissions. Further work showed that traditional NPF events were favoured by sunny conditions with low relative humidity and wind speeds. In marine air, formation of sub-10 nm particles was favoured by low temperatures, relative humidity, and wind speeds and could happen even during the night. Our future work will study the mechanisms responsible for particle formation at Baring Head with a focus on different chemical precursor species. This study sheds light on both new particle formation in open ocean air masses coming from the Southern Ocean and local aerosol properties in New Zealand.