37 research outputs found
Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry
Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gas- and particulate-phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at the Storm Peak Laboratory near Steamboat Springs, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh-resolution mass spectra of the samples after using a reversed-phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen-containing compounds (CHNO compounds), sulfur-containing compounds (CHOS and CHNOS compounds) and other oxygen-containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ∼0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of α-pinene, β-pinene, d-limonene, and β-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOxoxidation. Multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite were observed, indicating the significance of nitrate radical reactions on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur-containing compounds) were also observed; however further investigation is needed to determine the origin of the reduced sulfur-containing compounds. Overall, the molecular composition determined using ultrahigh-resolution Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry provides an unambiguous identification of the cloud water organic anion composition in the Rocky Mountain area that could help to improve the understanding of aqueous-phase processes
Mixed-phase orographic cloud microphysics during StormVEx and IFRACS
Wintertime mixed-phase orographic cloud (MPC) measurements were
conducted at the Storm Peak Laboratory (SPL) during the Storm Peak Lab Cloud
Property Validation Experiment (StormVEx) and Isotopic Fractionation in
Snow (IFRACS) programs in 2011 and 2014, respectively. The data include 92 h
of simultaneous measurements of supercooled liquid cloud droplet and
ice particle size distributions (PSDs). Average cloud droplet number
concentration (CDNC), droplet size (NMD), and liquid water content (LWC) were
similar in both years, while ice particle concentration (Ni) and ice water
content (IWC) were higher during IFRACS. The consistency of the liquid cloud
suggests that SPL is essentially a cloud chamber that produces a consistent
cloud under moist, westerly flow during the winter. A variable cloud
condensation nuclei (CCN)-related inverse relationship between CDNC and NMD
strengthened when the data were stratified by LWC. Some of this variation is
due to changes in cloud base height below SPL. While there was a weak
inverse correlation between LWC and IWC in the data as a whole, a stronger
relationship was demonstrated for a case study on 9 February 2014 during
IFRACS. A minimum LWC of 0.05 g m−3 showed that the cloud was not
completely glaciated on this day. Erosion of the droplet distribution at
high IWC was attributed to the Wegener–Bergeron–Findeisen process as the
high IWC was accompanied by a 10-fold increase in Ni. A relationship between
large cloud droplet concentration (25–35 µm) and small ice particles
(75–200 µm) under cold (<-8 ∘C) but not warm
(>-8 ∘C) conditions during IFRACS suggests primary
ice particle production by contact or immersion freezing. The effect of
blowing snow was evaluated from the relationship between wind speed and Ni
and by comparing the relative (percent) ice particle PSDs at high and low
wind speeds. These were similar, contrary to expectation for blowing snow.
However, the correlation between wind speed and ice crystal concentration
may support this explanation for high crystal concentrations at the surface.
Secondary processes could have contributed to high crystal concentrations
but there was no direct evidence to support this. Further experimental work
is needed to resolve these issues.</p
Atmospheric Radiation Measurements Aerosol Intensive Operating Period: Comparison of aerosol scattering during coordinated flights
Journal of Geophyshysical Research, Vol. 111, No. D5, D05S09The article of record as published may be located at http://dx.doi.org/10.1029/2005JD006250In May 2003, a Twin Otter airplane, equipped with instruments for making in situ
measurements of aerosol optical properties, was deployed during the Atmospheric
Radiation Measurements (ARM) Program’s Aerosol Intensive Operational Period in
Oklahoma. Several of the Twin Otter flights were flown in formation with an instrumented
light aircraft (Cessna 172XP) that makes routine in situ aerosol profile flights over the site.
This paper presents comparisons of measured scattering coefficients at 467 nm, 530 nm,
and 675 nm between identical commercial nephelometers aboard each aircraft. Overall,
the agreement between the two nephelometers decreases with longer wavelength. During
the majority of the flights, the Twin Otter flew with a diffuser inlet while the Cessna had a
1 mm impactor, allowing for an estimation of the fine mode fraction aloft. The fine mode
fraction aloft was then compared to the results of a ground-based nephelometer.
Comparisons are also provided in which both nephelometers operated with identical 1 mm
impactors. These scattering coefficient comparisons are favorable at the longer
wavelengths (i.e., 530 nm and 675 nm), yet differed by approximately 30% at 467 nm.
Mie scattering calculations were performed using size distribution measurements, made
during the level flight legs. Results are also presented from Cadenza, a new
continuous wave cavity ring-down (CW-CRD) instrument, which compared favorably
(i.e., agreed within 2%) with data from other instruments aboard the Twin Otter. With
this paper, we highlight the significant implications of coarse mode (larger than 1 mm)
aerosol aloft with respect to aerosol optical properties
Measurements of ice water content in tropopause region Arctic cirrus during
[1] A new instrument, the closed-path laser hygrometer (CLH), was flown on the NASA DC-8 aircraft during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) campaign in 1999-2000 to measure condensed-phase water. The ice water content (IWC) of Arctic cirrus was determined from in situ measurements of condensed-and gas-phase water. The IWC values obtained from the CLH observations are compared to those determined by integrating particle size distributions measured by a Forward Scattering Spectrometer Probe (FSSP) also flown on the DC-8. The considerably greater IWC seen by the CLH implies the presence of particles with diameters greater than the FSSP's upper limit of 20 mm. The evidence for and implications of the presence of large ice crystals in Arctic cirrus is discussed
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Optical and Physical Properties from Primary On-Road Vehicle ParticleEmissions And Their Implications for Climate Change
During the summers of 2004 and 2006, extinction and scattering coefficients of particle emissions inside a San Francisco Bay Area roadway tunnel were measured using a combined cavity ring-down and nephelometer instrument. Particle size distributions and humidification were also measured, as well as several gas phase species. Vehicles in the tunnel traveled up a 4% grade at a speed of approximately 60 km h{sup -1}. The traffic situation in the tunnel allows the apportionment of emission factors between light duty gasoline vehicles and diesel trucks. Cross-section emission factors for optical properties were determined for the apportioned vehicles to be consistent with gas phase and particulate matter emission factors. The absorption emission factor (the absorption cross-section per mass of fuel burned) for diesel trucks (4.4 {+-} 0.79 m{sup 2} kg{sup -1}) was 22 times larger than for light-duty gasoline vehicles (0.20 {+-} 0.05 m{sup 2} kg{sup -1}). The single scattering albedo of particles - which represents the fraction of incident light that is scattered as opposed to absorbed - was 0.2 for diesel trucks and 0.3 for light duty gasoline vehicles. These facts indicate that particulate matter from motor vehicles exerts a positive (i.e., warming) radiative climate forcing. Average particulate mass absorption efficiencies for diesel trucks and light duty gasoline vehicles were 3.14 {+-} 0.88 m{sup 2} g{sub PM}{sup -1} and 2.9 {+-} 1.07 m{sup 2} g{sub PM}{sup -1}, respectively. Particle size distributions and optical properties were insensitive to increases in relative humidity to values in excess of 90%, reinforcing previous findings that freshly emitted motor vehicle particulate matter is hydrophobic
A review of the anthropogenic influence on biogenic secondary organic aerosol
Because of the climate and air quality effects of organic aerosol, it is important to quantify the influence of anthropogenic emissions on the aerosol burden, both globally and regionally, and both in terms of mass and number. Methods exist with which the fractions of organic aerosol resulting directly from anthropogenic and biogenic processes can be estimated. However, anthropogenic emissions can also lead to an enhancement in secondary organic aerosol formation from naturally emitted precursors. We term this enhanced biogenic secondary organic aerosol (eBSOA). Here, we review the mechanisms through which such an effect may occur in the atmosphere and describe a work flow via which it may be quantified, using existing measurement techniques. An examination of published data reveals support for the existence of the enhancement effect
Molecular Variation at a Candidate Gene Implicated in the Regulation of Fire Ant Social Behavior
The fire ant Solenopsis invicta and its close relatives display an important social polymorphism involving differences in colony queen number. Colonies are headed by either a single reproductive queen (monogyne form) or multiple queens (polygyne form). This variation in social organization is associated with variation at the gene Gp-9, with monogyne colonies harboring only B-like allelic variants and polygyne colonies always containing b-like variants as well. We describe naturally occurring variation at Gp-9 in fire ants based on 185 full-length sequences, 136 of which were obtained from S. invicta collected over much of its native range. While there is little overall differentiation between most of the numerous alleles observed, a surprising amount is found in the coding regions of the gene, with such substitutions usually causing amino acid replacements. This elevated coding-region variation may result from a lack of negative selection acting to constrain amino acid replacements over much of the protein, different mutation rates or biases in coding and non-coding sequences, negative selection acting with greater strength on non-coding than coding regions, and/or positive selection acting on the protein. Formal selection analyses provide evidence that the latter force played an important role in the basal b-like lineages coincident with the emergence of polygyny. While our data set reveals considerable paraphyly and polyphyly of S. invicta sequences with respect to those of other fire ant species, the b-like alleles of the socially polymorphic species are monophyletic. An expanded analysis of colonies containing alleles of this clade confirmed the invariant link between their presence and expression of polygyny. Finally, our discovery of several unique alleles bearing various combinations of b-like and B-like codons allows us to conclude that no single b-like residue is completely predictive of polygyne behavior and, thus, potentially causally involved in its expression. Rather, all three typical b-like residues appear to be necessary
Current Status of a Model System: The Gene Gp-9 and Its Association with Social Organization in Fire Ants
The Gp-9 gene in fire ants represents an important model system for studying the evolution of social organization in insects as well as a rich source of information relevant to other major evolutionary topics. An important feature of this system is that polymorphism in social organization is completely associated with allelic variation at Gp-9, such that single-queen colonies (monogyne form) include only inhabitants bearing B-like alleles while multiple-queen colonies (polygyne form) additionally include inhabitants bearing b-like alleles. A recent study of this system by Leal and Ishida (2008) made two major claims, the validity and significance of which we examine here. After reviewing existing literature, analyzing the methods and results of Leal and Ishida (2008), and generating new data from one of their study sites, we conclude that their claim that polygyny can occur in Solenopsis invicta in the U.S.A. in the absence of expression of the b-like allele Gp-9b is unfounded. Moreover, we argue that available information on insect OBPs (the family of proteins to which GP-9 belongs), on the evolutionary/population genetics of Gp-9, and on pheromonal/behavioral control of fire ant colony queen number fails to support their view that GP-9 plays no role in the chemosensory-mediated communication that underpins regulation of social organization. Our analyses lead us to conclude that there are no new reasons to question the existing consensus view of the Gp-9 system outlined in Gotzek and Ross (2007)
Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry
Clouds alter the composition of atmospheric aerosol by acting as a medium
for interactions between gas- and particulate-phase substances. To determine
the cloud water atmospheric organic matter (AOM) composition and study the
cloud processing of aerosols, two samples of supercooled clouds were
collected at the Storm Peak Laboratory near Steamboat Springs, Colorado (3220 m a.s.l.).
Approximately 3000 molecular formulas were assigned to ultrahigh-resolution mass spectra of the samples after using a reversed-phase
extraction procedure to isolate the AOM components from the cloud water.
Nitrogen-containing compounds (CHNO compounds), sulfur-containing compounds
(CHOS and CHNOS compounds) and other oxygen-containing compounds (CHO
compounds) with molecular weights up to 700 Da were observed. Average
oxygen-to-carbon ratios of ∼0.6 indicate a slightly more
oxidized composition than most water-soluble organic carbon identified in
aerosol studies, which may result from aqueous oxidation in the clouds. The
AOM composition indicates significant influences from biogenic secondary
organic aerosol (SOA) and residential wood combustion. We observed 60% of
the cloud water CHO molecular formulas to be identical to SOA samples of
α-pinene, β-pinene, d-limonene, and β-caryophyllene
ozonolysis. CHNO compounds had the highest number frequency and relative
abundances and are associated with residential wood combustion and NO<sub>x</sub>
oxidation. Multiple nitrogen atoms in the assigned molecular formulas for
the nighttime cloud sample composite were observed, indicating the
significance of nitrate radical reactions on the AOM composition. Several
CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly
observed oxidized sulfur-containing compounds) were also observed; however
further investigation is needed to determine the origin of the reduced
sulfur-containing compounds. Overall, the molecular composition determined
using ultrahigh-resolution Fourier-transform ion cyclotron resonance
(FT-ICR) mass spectrometry provides an unambiguous identification of the
cloud water organic anion composition in the Rocky Mountain area that could
help to improve the understanding of aqueous-phase processes
Comparison of in situ aerosol extinction and scattering coefficient measurements made during the Aerosol Intensive Operating Period
Journal of Geophysical Research, Vol. 111, No. D5, D05S03The article of record as published may be located at http://dx.doi.org/10.1029/2005JD006056.In May 2003, the Department of Energy (DOE) Atmospheric Radiation Measurement
(ARM) Program sponsored the Aerosol Intensive Operating Period (AIOP) which was
conducted over the ARM Climate Research Facility (ACRF) in central Oklahoma. One
new instrument that flew in the AIOP, called Cadenza, employed a cavity ring-down
technique to measure extinction coefficient and a reciprocal nephelometer technique to
simultaneously measure scattering coefficient. This instrument is described in this paper,
and measurements are compared to those of conventional instrumentation. Agreement
between Cadenza extinction coefficient and that derived from combining nephelometer
scattering and PSAP absorption (Neph + PSAP) was excellent, about 2%. Agreement
between Cadenza scattering coefficient and TSI nephelometer scattering was also
excellent, about 2%, well within the uncertainty of the nephelometer and Cadenza
scattering measurements. Comparisons between these instruments, made for the special
case of plumes, showed that Cadenza measured extinction and scattering several percent
higher on average than the Neph + PSAP and nephelometer alone. This difference is
likely due to differences in the instrument response time: The response time for Cadenza
is 1 s while that for the nephelometer is a minimum of 8 s. Plumes, identified as
originating from Siberian biomass burning, are characterized. Composite size distributions
from wing-mounted probes showed that two of the plumes had significant large particle
modes that resulted in high values of the effective radius. The effect of the large
particle mode was not seen in the A ° ngstro¨m coefficient calculated from the in-cabin
scattering measurements because of the characteristics of the aircraft inlet