The composition and prevalence of microorganisms in the middle-to-upper troposphere (8–15 km altitude) and their role in aerosol-cloud-precipitation interactions represent important, unresolved ...questions for biological and atmospheric science. In particular, airborne microorganisms above the oceans remain essentially uncharacterized, as most work to date is restricted to samples taken near the Earth’s surface. Here we report on the microbiome of low- and high-altitude air masses sampled onboard the National Aeronautics and Space Administration DC-8 platform during the 2010 Genesis and Rapid Intensification Processes campaign in the Caribbean Sea. The samples were collected in cloudy and cloud-free air masses before, during, and after two major tropical hurricanes, Earl and Karl. Quantitative PCR and microscopy revealed that viable bacterial cells represented on average around 20% of the total particles in the 0.25- to 1-μm diameter range and were at least an order of magnitude more abundant than fungal cells, suggesting that bacteria represent an important and underestimated fraction of micrometer-sized atmospheric aerosols. The samples from the two hurricanes were characterized by significantly different bacterial communities, revealing that hurricanes aerosolize a large amount of new cells. Nonetheless, 17 bacterial taxa, including taxa that are known to use C1–C4 carbon compounds present in the atmosphere, were found in all samples, indicating that these organisms possess traits that allow survival in the troposphere. The findings presented here suggest that the microbiome is a dynamic and underappreciated aspect of the upper troposphere with potentially important impacts on the hydrological cycle, clouds, and climate.
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. The NOAA Particle Analysis by Laser Mass Spectrometry (PALMS) instrument
measures size-resolved aerosol chemical composition from aircraft. We
describe the identification and quantification of nine major atmospheric
particle classes, including sulfate–organic–nitrate mixtures, biomass
burning, elemental carbon, sea salt, mineral dust, meteoric material, alkali
salts, heavy fuel oil combustion, and a remainder class. Classes can be
sub-divided as necessary based on chemical heterogeneity, accumulated
secondary material during aging, or other atmospheric processing.
Concentrations are derived for sizes that encompass the accumulation and
coarse size modes. A statistical error analysis indicates that particle
class concentrations can be determined within a few minutes for abundances
above ∼10 ng m−3. Rare particle types require longer
sampling times. We explore the instrumentation requirements and the limitations of the
method for airborne measurements. Reducing the size resolution of the
particle data increases time resolution with only a modest increase in
uncertainty. The principal limiting factor to fast time response
concentration measurements is statistically relevant sampling across the
size range of interest, in particular, sizes D < 0.2 µm for
accumulation-mode studies and D > 2 µm for coarse-mode
analysis. Performance is compared to other airborne and ground-based
composition measurements, and examples of atmospheric mineral dust
concentrations are given. The wealth of information afforded by
composition-resolved size distributions for all major aerosol types
represents a new and powerful tool to characterize atmospheric aerosol
properties in a quantitative fashion.
Brown carbon in the continental troposphere Liu, Jiumeng; Scheuer, Eric; Dibb, Jack ...
Geophysical research letters,
28 March 2014, Letnik:
41, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Little is known about the optical significance of light absorbing particulate organic compounds (i.e., brown carbon, BrC), including the importance relative to black carbon (BC) and influence on ...direct radiative forcing by aerosols. The vertical profile of BrC affects its radiative forcing, yet the distribution of BrC in the free troposphere is largely unknown. In this study, BrC absorption was directly measured in solvent extracts of particulate filters obtained from aircraft sampling over the continental USA. Excluding biomass burning plumes, BrC was observed throughout the tropospheric column (<13 km), and its prevalence increased relative to BC with increasing altitude, indicating contributions from secondary sources. Closure analysis showed good agreement between light absorption from BC plus BrC relative to measured total aerosol absorption. A radiative transfer model indicated that BrC absorption reduced top of atmosphere aerosol forcing by ~20%, suggesting that it is an important component of direct aerosol radiative forcing.
Key Points
BrC is prevalent in the troposphere and increases relative to BC with altitude
Optical closure is obtained between BrC plus BC and total absorption at 365nm
BrC contributes 20% to top of atmosphere absorbing aerosol forcing
Biogenic sources contribute to cloud condensation nuclei (CCN) in the clean marine atmosphere, but few measurements exist to constrain climate model simulations of their importance. The chemical ...composition of individual atmospheric aerosol particles showed two types of sulfate-containing particles in clean marine air masses in addition to mass-based Estimated Salt particles. Both types of sulfate particles lack combustion tracers and correlate, for some conditions, to atmospheric or seawater dimethyl sulfide (DMS) concentrations, which means their source was largely biogenic. The first type is identified as New Sulfate because their large sulfate mass fraction (63% sulfate) and association with entrainment conditions means they could have formed by nucleation in the free troposphere. The second type is Added Sulfate particles (38% sulfate), because they are preexisting particles onto which additional sulfate condensed. New Sulfate particles accounted for 31% (7 cm
) and 33% (36 cm
) CCN at 0.1% supersaturation in late-autumn and late-spring, respectively, whereas sea spray provided 55% (13 cm
) in late-autumn but only 4% (4 cm
) in late-spring. Our results show a clear seasonal difference in the marine CCN budget, which illustrates how important phytoplankton-produced DMS emissions are for CCN in the North Atlantic.
Aviation-related aerosol emissions contribute to the formation of contrail cirrus clouds that can alter upper tropospheric radiation and water budgets, and therefore climate. The magnitude of ...air-traffic-related aerosol-cloud interactions and the ways in which these interactions might change in the future remain uncertain. Modelling studies of the present and future effects of aviation on climate require detailed information about the number of aerosol particles emitted per kilogram of fuel burned and the microphysical properties of those aerosols that are relevant for cloud formation. However, previous observational data at cruise altitudes are sparse for engines burning conventional fuels, and no data have previously been reported for biofuel use in-flight. Here we report observations from research aircraft that sampled the exhaust of engines onboard a NASA DC-8 aircraft as they burned conventional Jet A fuel and a 50:50 (by volume) blend of Jet A fuel and a biofuel derived from Camelina oil. We show that, compared to using conventional fuels, biofuel blending reduces particle number and mass emissions immediately behind the aircraft by 50 to 70 per cent. Our observations quantify the impact of biofuel blending on aerosol emissions at cruise conditions and provide key microphysical parameters, which will be useful to assess the potential of biofuel use in aviation as a viable strategy to mitigate climate change.
We evaluate the sensitivity of the size calibrations of
two commercially available, high-resolution optical particle sizers to
changes in aerosol composition and complex refractive index (RI). The
...Droplet Measurement Technologies Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) and the TSI, Inc. Laser Aerosol Spectrometer (LAS) are
two commonly used instruments for measuring the portion of the aerosol size
distribution with diameters larger than nominally 60–90 nm. Both instruments
illuminate particles with a laser and relate the single-particle light
scattering intensity and count rate measured over a wide range of angles to
the size-dependent particle concentration. While the optical block geometry
and flow system are similar for each instrument, a significant difference
between the two models is the laser wavelength (1054 nm for the UHSAS and
633 nm for the LAS) and intensity (about 100 times higher for the UHSAS), which
may affect the way each instrument sizes non-spherical or absorbing
aerosols. Here, we challenge the UHSAS and LAS with laboratory-generated,
mobility-size-classified aerosols of known chemical composition to quantify
changes in the optical size response relative to that of ammonium sulfate
(RI of 1.52+0i at 532 nm) and NIST-traceable polystyrene latex spheres
(PSLs with RI of 1.59+0i at 589 nm). Aerosol inorganic salt species are
chosen to cover the real refractive index range of 1.32 to 1.78, while
chosen light-absorbing carbonaceous aerosols include fullerene soot,
nigrosine dye, humic acid, and fulvic acid standards. The instrument
response is generally in good agreement with the electrical mobility
diameter. However, large undersizing deviations are observed for the
low-refractive-index fluoride salts and the strongly absorbing nigrosine dye and fullerene soot particles. Polydisperse size distributions for both fresh
and aged wildfire smoke aerosols from the recent Fire Influence on Regional
to Global Environments Experiment and Air Quality (FIREX-AQ) and the Cloud,
Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex)
airborne campaigns show good agreement between both optical sizers and
contemporaneous electrical mobility sizing and particle time-of-flight mass
spectrometric measurements. We assess the instrument uncertainties by
interpolating the laboratory response curves using previously reported RIs
and size distributions for multiple aerosol type classifications. These
results suggest that, while the optical sizers may underperform for strongly
absorbing laboratory compounds and fresh tailpipe emissions measurements,
sampling aerosols within the atmospherically relevant range of refractive
indices are likely to be sized to better than ±10 %–20 % uncertainty over the submicron aerosol size range when using instruments calibrated with
ammonium sulfate.
Aerosols over Earth's remote and spatially extensive ocean surfaces have important influences on planetary climate. However, these aerosols and
their effects remain poorly understood, in part due to ...the remoteness and limited observations over these regions. In this study, we seek to
understand factors that shape marine aerosol size distributions and composition in the northwest Atlantic Ocean region. We use the GEOS-Chem model with the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm
model to interpret measurements collected from ship and aircraft during the four seasonal campaigns of the North Atlantic Aerosols and Marine
Ecosystems Study (NAAMES) conducted between 2015 and 2018. Observations from the NAAMES campaigns show enhancements in the campaign-median number of
aerosols with diameters larger than 3 nm in the lower troposphere (below 6 km), most pronounced during the phytoplankton bloom
maxima (May/June) below 2 km in the free troposphere. Our simulations, combined with NAAMES ship and aircraft measurements, suggest several
key factors that contribute to aerosol number and size in the northwest Atlantic lower troposphere, with significant regional-mean
(40–60∘ N and 20–50∘ W) cloud-albedo aerosol indirect effect (AIE) and direct radiative effect (DRE) processes during the phytoplankton
bloom. These key factors and their associated simulated radiative effects in the region include the following: (1) particle formation near and above the marine
boundary layer (MBL) top (AIE: −3.37 W m−2, DRE: −0.62 W m−2); (2) particle growth due to marine secondary organic
aerosol (MSOA) as the nascent particles subside into the MBL, enabling them to become cloud-condensation-nuclei-sized particles (AIE:
−2.27 W m−2, DRE: −0.10 W m−2); (3) particle formation and growth due to the products of dimethyl sulfide, above and within the
MBL (−1.29 W m−2, DRE: −0.06 W m−2); (4) ship emissions (AIE: −0.62 W m−2, DRE: −0.05 W m−2);
and (5) primary sea spray emissions (AIE: +0.04 W m−2, DRE: −0.79 W m−2). Our results suggest that a synergy of particle
formation in the lower troposphere (particularly near and above the MBL top) and growth by MSOA contributes strongly to
cloud-condensation-nuclei-sized particles with significant regional radiative effects in the northwest Atlantic. To gain confidence in radiative
effect magnitudes, future work is needed to understand (1) the sources and temperature dependence of condensable marine vapors forming MSOA, (2) primary sea spray emissions, and (3) the species that can form new particles in the lower troposphere and grow these particles as they descend into
the marine boundary layer.
We couple airborne, ground‐based, and satellite observations; conduct regional simulations; and develop and apply an inversion technique to constrain hourly smoke emissions from the Rim Fire, the ...third largest observed in California, USA. Emissions constrained with multiplatform data show notable nocturnal enhancements (sometimes over a factor of 20), correlate better with daily burned area data, and are a factor of 2–4 higher than a priori estimates, highlighting the need for improved characterization of diurnal profiles and day‐to‐day variability when modeling extreme fires. Constraining only with satellite data results in smaller enhancements mainly due to missing retrievals near the emissions source, suggesting that top‐down emission estimates for these events could be underestimated and a multiplatform approach is required to resolve them. Predictions driven by emissions constrained with multiplatform data present significant variations in downwind air quality and in aerosol feedback on meteorology, emphasizing the need for improved emissions estimates during exceptional events.
Key Points
Hourly smoke emissions from a wildfire are constrained with multiplatform data
Diurnal profiles for modeling extreme fire events need to be improved
Only a multiplatform approach allows to fully resolve emissions for these events
The Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) field campaign provides accurate data for aerosol characterization and trace gas profiles, and establishes ...knowledge of the relationships between aerosols and water. The dropsonde dataset provides an in situ characterization of the vertical thermodynamic structure of the atmosphere during 165 research flights by NASA Langley's King Air research aircraft between February 2020 and June 2022 and four test flights between December 2019 and November 2021. The research flights covered the western North Atlantic region, off the coast of the Eastern United States and around Bermuda and covered all seasons. The dropsonde profiles provide observations of temperature, pressure, relative humidity, and horizontal and vertical winds between the surface and about 9 km. 801 dropsondes were released, of which 796 were processed and 788 provide complete profiles of all parameters between the flight level and the surface with normal parachute performance. Here, we describe the dataset, the processing of the measurements, general statistics, and applications of this rich dataset.
Chloride (Cl−) displacement from sea salt particles is an extensively studied phenomenon with implications for human health, visibility, and the global radiation budget. Past works have investigated ...Cl− depletion over the northwest Atlantic (NWA); however, an updated, multi-seasonal, and geographically expanded account of sea salt reactivity over the region is needed. This study uses chemically resolved mass concentrations and meteorological data from the airborne Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) to quantify seasonal, spatial, and meteorological trends in Cl− depletion and to explore the importance of quantifying (1) non-sea salt sources of Na+ and (2) mass concentrations of lost Cl− (instead of relative amounts displaced). Lost Cl− mass concentrations are lowest in December–February and March, moderate around Bermuda in June, and highest in May (median losses of 0.04, 0.04, 0.66, and 1.76 µg m−3, respectively), with losses in May that are high enough to potentially accelerate tropospheric oxidation rates. Inorganic acidic species can account for all Cl− depletion in December–February, March, and June near Bermuda but none of the lost Cl− in May, suggesting that organic acids may be of importance for Cl− displacement in certain months. Contributions of dust to Na+ are not important seasonally but may cause relevant overestimates of lost Cl− in smoke and dust plumes. Higher percentages of Cl− depletion often do not correspond to larger mass concentrations of lost Cl−, so it is highly recommended to quantify the latter to place depletion reactions in context with their role in atmospheric oxidation and radiative forcing.
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