Large RNA including mRNA (mRNA) has emerged as an important new class of therapeutics. Recently, this has been demonstrated by two highly efficacious vaccines based on mRNA sequences encoding for a ...modified version of the SARS-CoV-2 spike protein. There is currently significant demand for the development of new and improved analytical methods for the characterization of large RNA including mRNA therapeutics. In this study, we have developed an automated, high-throughput workflow for the rapid characterization and direct sequence mapping of large RNA and mRNA therapeutics. Partial RNase digestions using RNase T1 immobilized on magnetic particles were performed in conjunction with high-resolution liquid chromatography–mass spectrometry analysis. Sequence mapping was performed using automated oligoribonucleotide annotation and identifications based on MS/MS spectra. Using this approach, a >80% sequence of coverage of a range of large RNAs and mRNA therapeutics including the SARS-CoV-2 spike protein was obtained in a single analysis. The analytical workflow, including automated sample preparation, can be completed within 90 min. The ability to rapidly identify, characterize, and sequence map large mRNA therapeutics with high sequence coverage provides important information for identity testing, sequence validation, and impurity analysis.
Brown carbon (BrC) is an organic aerosol material that preferentially absorbs light of shorter wavelengths. Global‐scale radiative impacts of BrC have been difficult to assess due to the lack of BrC ...observational data. To address this, aerosol filters were continuously collected with near pole‐to‐pole latitudinal coverage over the Pacific and Atlantic basins in three seasons as part of the Atmospheric Tomography Mission. BrC chromophores in filter extracts were measured. We find that globally, BrC was highly spatially heterogeneous, mostly detected in air masses that had been transported from regions of extensive biomass burning. We calculate the average direct radiative effect due to BrC absorption accounted for approximately 7% to 48% of the top of the atmosphere clear‐sky instantaneous forcing by all absorbing carbonaceous aerosols in the remote atmosphere, indicating that BrC from biomass burning is an important component of the global radiative balance.
Plain Language Summary
Combustion produces light‐absorbing aerosols that can affect the global radiation balance. Black carbon, which absorbs light over a broad wavelength range, has been extensively studied, but recent work shows that a significant component of the light‐absorbing aerosol is brown, absorbing mostly in the lower end of the visible and into the ultraviolet (UV). Incomplete combustion, such as in wild fires, is known to produce substantial levels of brown carbon. Here we report direct measurements of brown carbon determined from filter samples collected from aircraft flights that extended from pole to pole over three seasons. We observed brown carbon in aerosols that had been transported long distances from regions of wild fires at various locations across the globe. A radiative transfer model indicated that this brown carbon can substantially contribute to the overall radiative forcing by light‐absorbing aerosols.
Key Points
Globally, biomass burning is a large source of light‐absorbing carbonaceous aerosol that directly affect the planetary radiation balance
Transported over long distances, brown carbon is a significant component of these aerosols, but its contribution was highly variable
Brown carbon contributed up to 48% of average clear‐sky instantaneous forcing by light absorption by carbonaceous aerosols
We present the first data on the concentration of sea-salt aerosol throughout
most of the depth of the troposphere and over a wide range of latitudes,
which were obtained during the Atmospheric ...Tomography (ATom) mission.
Sea-salt concentrations in the upper troposphere are very small, usually less
than 10 ng per standard m3 (about 10 parts per trillion by mass) and
often less than 1 ng m−3. This puts stringent limits on the
contribution of sea-salt aerosol to halogen and nitric acid chemistry in the
upper troposphere. Within broad regions the concentration of sea-salt aerosol
is roughly proportional to water vapor, supporting a dominant role for wet
scavenging in removing sea-salt aerosol from the atmosphere. Concentrations
of sea-salt aerosol in the winter upper troposphere are not as low as in the
summer and the tropics. This is mostly a consequence of less wet scavenging
in the drier, colder winter atmosphere. There is also a source of sea-salt
aerosol over pack ice that is distinct from that over open water. With a
well-studied and widely distributed source, sea-salt aerosol provides an
excellent test of wet scavenging and vertical transport of aerosols in
chemical transport models.
The size of aerosol particles has fundamental effects on their chemistry and radiative effects. We explore those effects using aerosol size and
composition data in the lowermost stratosphere along ...with calculations of light scattering. In the size range between about 0.1 and
1.0 µm diameter (accumulation mode), there are at least two modes of particles in the lowermost stratosphere. The larger mode consists
mostly of particles produced in the stratosphere, and the smaller mode consists mostly of particles transported from the troposphere. The
stratospheric mode is similar in the Northern and Southern Hemisphere, whereas the tropospheric mode is much more abundant in the Northern
Hemisphere. The purity of sulfuric acid particles in the stratospheric mode shows that there is limited production of secondary organic aerosol in
the stratosphere, especially in the Southern Hemisphere. Out of eight sets of flights sampling the lowermost stratosphere (four seasons and two
hemispheres) there were three with large injections of specific materials: volcanic, biomass burning, or dust. The stratospheric and tropospheric
modes have very different roles for radiative effects on climate and for heterogeneous chemistry. Because the larger particles are more efficient at
scattering light, most of the radiative effect in the lowermost stratosphere is due to stratospheric particles. In contrast, the tropospheric
particles can have more surface area, at least in the Northern Hemisphere. The surface area of tropospheric particles could have significant
implications for heterogeneous chemistry because these particles, which are partially neutralized and contain organics, do not correspond to the
substances used for laboratory studies of stratospheric heterogeneous chemistry. We then extend the analysis of size-dependent properties to
particles injected into the stratosphere, either intentionally or from volcanoes. There is no single size that will simultaneously maximize the
climate impact relative to the injected mass, infrared heating, potential for heterogeneous chemistry, and undesired changes in direct sunlight. In
addition, light absorption in the far ultraviolet is identified as an issue requiring more study for both the existing and potentially modified
stratosphere.
Cloud condensation nuclei (CCN) can affect cloud properties and therefore the Earth’s radiative balance. New particle formation (NPF) from condensable vapours in the free troposphere has been ...suggested to contribute to CCN, especially in remote, pristine atmospheric regions, but direct evidence is sparse, and the magnitude of this contribution is uncertain. Here we use in-situ aircraft measurements of vertical profiles of aerosol size distributions to present a global-scale survey of NPF occurrence. We observed intense NPF occurring at high altitude in tropical convective regions over both the Pacific and Atlantic Oceans. Together with the results of chemical-transport models, our findings indicate that NPF persists at all longitudes as a global-scale band in the tropical upper troposphere, covering about 40% of the Earth’s surface. Furthermore, we find that this NPF in the tropical upper troposphere is a globally important source of CCN in the lower troposphere, where they can affect cloud properties. Our findings suggest that the production of CCN, as these new particles descend towards the surface, is currently not adequately captured in global models, because they tend to underestimate both the magnitude of tropical upper tropospheric NPF and the subsequent growth to CCN sizes. This has potential implications for cloud albedo and the global radiative balance.
Single-particle mass spectrometry (SPMS) instruments characterize the composition of individual aerosol particles in real time. Their fundamental ability to differentiate the externally mixed ...particle types that constitute the atmospheric aerosol population enables a unique perspective into sources and transformation. However, quantitative measurements by SPMS systems are inherently problematic. We introduce a new technique that combines collocated measurements of aerosol composition by SPMS and size-resolved absolute particle concentrations on aircraft platforms. Quantitative number, surface area, volume, and mass concentrations are derived for climate-relevant particle types such as mineral dust, sea salt, and biomass burning smoke. Additionally, relative ion signals are calibrated to derive mass concentrations of internally mixed sulfate and organic material that are distributed across multiple particle types.
Global observations and model studies indicate that new particle formation (NPF) in the upper troposphere (UT) and subsequent particles supply 40 %-60 % of cloud condensation nuclei (CCN) in the ...lower troposphere, thus affecting the Earth's radiative budget. There are several plausible nucleation mechanisms and precursor species in this atmospheric region, which, in the absence of observational constraints, lead to uncertainties in modeled aerosols. In particular, the type of nucleation mechanism and concentrations of nucleation precursors, in part, determine the spatial distribution of new particles and resulting spatial distribution of CCN from this source. Although substantial advances in understanding NPF have been made in recent years, NPF processes in the UT in pristine marine regions are still poorly understood and are inadequately represented in global models.
While formation and growth of particles in the troposphere have been extensively studied in the past two decades, very limited efforts have
been devoted to understanding these in the stratosphere. ...Here we use both
Cosmics Leaving OUtdoor Droplets (CLOUD) laboratory measurements taken under
very low temperatures (205–223 K) and Atmospheric Tomography Mission (ATom) in situ observations of particle number size distributions (PNSDs) down to 3 nm to constrain nucleation mechanisms and to evaluate
model-simulated particle size distributions in the lowermost stratosphere (LMS). We show that the binary homogenous nucleation (BHN) scheme used in most of the existing stratospheric aerosol injection (a proposed method of solar
radiation modification) modeling studies overpredicts the nucleation rates by
3–4 orders of magnitude (when compared to CLOUD data) and particle number
concentrations in the background LMS by a factor ∼ 2–4 (when
compared to ATom data). Based on a recently developed kinetic nucleation
model, which gives rates of both ion-mediated nucleation (IMN) and BHN at
low temperatures in good agreement with CLOUD measurements, both BHN and IMN
occur in the stratosphere. However, IMN rates are generally more than 1
order of magnitude higher than BHN rates and thus dominate nucleation in the
background stratosphere. In the Southern Hemisphere (SH) LMS with minimum
influence of anthropogenic emissions, our analysis shows that ATom-measured
PNSDs generally have four apparent modes. The model captures reasonably well
the two modes (Aitken mode and the first accumulation mode) with the highest
number concentrations and size-dependent standard deviations. However,
the model misses an apparent second accumulation mode peaking around
300–400 nm, which is in the size range important for aerosol direct
radiative forcing. The bimodal structure of accumulation mode particles has
also been observed in the stratosphere well above tropopause and in the
volcano-perturbed stratosphere. We suggest that this bimodal structure may
be caused by the effect of charges on coagulation and growth, which is not
yet considered in any existing models and may be important in the
stratosphere due to high ionization rates and the long lifetime of aerosols.
Considering the importance of accurate PNSDs for projecting a realistic
radiation forcing response to stratospheric aerosol injection (SAI), it is
essential to understand and incorporate such potentially important processes
in SAI model simulations and to carry out further research to find out what
other processes the present models might have missed.
In situ measurements of aerosol microphysical, chemical, and optical properties were made during global-scale flights from 2016-2018 as part of the Atmospheric Tomography Mission (ATom). The NASA ...DC-8 aircraft flew from â¼ 84.sup." N to â¼ 86.sup." S latitude over the Pacific, Atlantic, Arctic, and Southern oceans while profiling nearly continuously between altitudes of â¼ 160 m and â¼ 12 km. These global circuits were made once each season. Particle size distributions measured in the aircraft cabin at dry conditions and with an underwing probe at ambient conditions were combined with bulk and single-particle composition observations and measurements of water vapor, pressure, and temperature to estimate aerosol hygroscopicity and hygroscopic growth factors and calculate size distributions at ambient relative humidity. These reconstructed, composition-resolved ambient size distributions were used to estimate intensive and extensive aerosol properties, including single-scatter albedo, the asymmetry parameter, extinction, absorption, Ãngström exponents, and aerosol optical depth (AOD) at several wavelengths, as well as cloud condensation nuclei (CCN) concentrations at fixed supersaturations and lognormal fits to four modes. Dry extinction and absorption were compared with direct in situ measurements, and AOD derived from the extinction profiles was compared with remotely sensed AOD measurements from the ground-based Aerosol Robotic Network (AERONET); this comparison showed no substantial bias.
The details of aerosol processes and size distributions
in the stratosphere are important for both heterogeneous chemistry and
aerosol–radiation interactions. Using in situ, global-scale measurements ...of
the size distribution of particles with diameters > 3 nm from the
NASA Atmospheric Tomography Mission (ATom), we identify a mode of aerosol
smaller than 12 nm in the lowermost stratosphere (LMS) at mid- and high
latitudes. This mode is substantial only in the Northern Hemisphere (NH)
and was observed in all four seasons. We also observe elevated SO2, an
important precursor for new particle formation (NPF) and growth, in the NH
LMS. We use box modelling and thermodynamic calculations to show that NPF
can occur in the LMS conditions observed on ATom. Aircraft emissions are
shown as likely sources of this SO2, as well as a potential source of
nucleation mode particles directly emitted by or formed in the plume of the
engines. These nucleation mode particles have the potential to grow to
larger sizes and to coagulate with larger aerosol, affecting heterogeneous
chemistry and aerosol–radiation interactions. Understanding all sources and
characteristics of stratospheric aerosols is important in the context of
anthropogenic climate change as well as proposals for climate intervention
via stratospheric sulfur injection. This analysis not only adds to the,
currently sparse, observations of the global impact of aviation, but also
introduces another aspect of climate influence, namely a size distribution
shift of the background aerosol distribution in the LMS.
PDF
