35 research outputs found
Observed NO/NO_2 Ratios in the Upper Troposphere Imply Errors in NO-NO_2-O_3 Cycling Kinetics or an Unaccounted NO_x Reservoir
Observations from the SEAC^4RS aircraft campaign over the southeast United States in August–September 2013 show NO/NO_2 concentration ratios in the upper troposphere that are approximately half of photochemical equilibrium values computed from Jet Propulsion Laboratory (JPL) kinetic data. One possible explanation is the presence of labile NO_x reservoir species, presumably organic, decomposing thermally to NO_2 in the instrument. The NO_2 instrument corrects for this artifact from known labile HNO_4 and CH_3O_2NO_2 NO_x reservoirs. To bridge the gap between measured and simulated NO_2, additional unaccounted labile NO_x reservoir species would have to be present at a mean concentration of ~40 ppt for the SEAC^4RS conditions (compared with 197 ppt for NOx). An alternative explanation is error in the low‐temperature rate constant for the NO + O_3 reaction (30% 1‐σ uncertainty in JPL at 240 K) and/or in the spectroscopic data for NO_2 photolysis (20% 1‐σ uncertainty). Resolving this discrepancy is important for understanding global budgets of tropospheric oxidants and for interpreting satellite observations of tropospheric NO_2 columns
Observed NO/NO2 Ratios in the Upper Troposphere Imply Errors in NO-NO2-O3 Cycling Kinetics or an Unaccounted NOx Reservoir
Observations from the SEAC4RS aircraft campaign over the southeast United States in August-September 2013 show NO/NO2 concentration ratios in the upper troposphere that are approximately half of photochemical equilibrium values computed from Jet Propulsion Laboratory (JPL) kinetic data. One possible explanation is the presence of labile NOx reservoir species, presumably organic, decomposing thermally to NO2 in the instrument. The NO2 instrument corrects for this artifact from known labile HNO4 and CH3O2NO2 NOx reservoirs. To bridge the gap between measured and simulated NO2, additional unaccounted labile NOx reservoir species would have to be present at a mean concentration of ~40 ppt for the SEAC4RS conditions (compared with 197 ppt for NOx). An alternative explanation is error in the low-temperature rate constant for the NO + O3 reaction (30% 1-σ uncertainty in JPL at 240 K) and/or in the spectroscopic data for NO2 photolysis (20% 1-σ uncertainty). Resolving this discrepancy is important for understanding global budgets of tropospheric oxidants and for interpreting satellite observations of tropospheric NO2 columns
Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol
Thermodynamic models predict that sulfate aerosol (S(VI) ≡
H2SO4(aq) + HSO4−+ SO42−) should take up
available ammonia (NH3) quantitatively as ammonium (NH4+)
until the ammonium sulfate stoichiometry (NH4)2SO4 is close
to being reached. This uptake of ammonia has important implications for
aerosol mass, hygroscopicity, and acidity. When ammonia is in excess, the
ammonium–sulfate aerosol ratio R = [NH4+] ∕ [S(VI)] should approach
2, with excess ammonia remaining in the gas phase. When ammonia is in
deficit, it should be fully taken up by the aerosol as ammonium and no
significant ammonia should remain in the gas phase. Here we report that
sulfate aerosol in the eastern US in summer has a low ammonium–sulfate ratio
despite excess ammonia, and we show that this is at odds with thermodynamic
models. The ammonium–sulfate ratio averages only 1.04 ± 0.21 mol mol−1 in
the Southeast, even though ammonia is in large excess, as shown
by the ammonium–sulfate ratio in wet deposition and by the presence of
gas-phase ammonia. It further appears that the ammonium–sulfate aerosol
ratio is insensitive to the supply of ammonia, remaining low even as the wet
deposition ratio exceeds 6 mol mol−1. While the ammonium–sulfate ratio
in wet deposition has increased by 5.8 % yr−1 from 2003 to 2013 in the
Southeast, consistent with SO2 emission controls, the
ammonium–sulfate aerosol ratio decreased by 1.4–3.0 % yr−1.
Thus, the aerosol is becoming more acidic even as SO2 emissions decrease
and ammonia emissions stay constant; this is incompatible with
simple sulfate–ammonium thermodynamics. A tentative explanation is that
sulfate particles are increasingly coated by organic material, retarding the
uptake of ammonia. Indeed, the ratio of organic aerosol (OA) to sulfate in
the Southeast increased from 1.1 to 2.4 g g−1 over the 2003–2013 period
as sulfate decreased. We implement a simple kinetic mass transfer limitation
for ammonia uptake to sulfate aerosols in the GEOS-Chem chemical transport
model and find that we can reproduce both the observed ammonium–sulfate
aerosol ratios and the concurrent presence of gas-phase ammonia. If sulfate
aerosol becomes more acidic as OA ∕ sulfate ratios increase, then controlling
SO2 emissions to decrease sulfate aerosol will not have the co-benefit
of suppressing acid-catalyzed secondary organic aerosol (SOA) formation
Observed NO/NO_2 Ratios in the Upper Troposphere Imply Errors in NO-NO_2-O_3 Cycling Kinetics or an Unaccounted NO_x Reservoir
Observations from the SEAC^4RS aircraft campaign over the southeast United States in August–September 2013 show NO/NO_2 concentration ratios in the upper troposphere that are approximately half of photochemical equilibrium values computed from Jet Propulsion Laboratory (JPL) kinetic data. One possible explanation is the presence of labile NO_x reservoir species, presumably organic, decomposing thermally to NO_2 in the instrument. The NO_2 instrument corrects for this artifact from known labile HNO_4 and CH_3O_2NO_2 NO_x reservoirs. To bridge the gap between measured and simulated NO_2, additional unaccounted labile NO_x reservoir species would have to be present at a mean concentration of ~40 ppt for the SEAC^4RS conditions (compared with 197 ppt for NOx). An alternative explanation is error in the low‐temperature rate constant for the NO + O_3 reaction (30% 1‐σ uncertainty in JPL at 240 K) and/or in the spectroscopic data for NO_2 photolysis (20% 1‐σ uncertainty). Resolving this discrepancy is important for understanding global budgets of tropospheric oxidants and for interpreting satellite observations of tropospheric NO_2 columns
Cognitive and affective perspective-taking in conduct-disordered children high and low on callous-unemotional traits
<p>Abstract</p> <p>Background</p> <p>Deficits in cognitive and/or affective perspective-taking have been implicated in Conduct-Disorder (CD), but empirical investigations produced equivocal results. Two factors may be implicated: (a) distinct deficits underlying the antisocial conduct of CD subgroups, (b) plausible disjunction between cognitive and affective perspective-taking with subgroups presenting either cognitive or affective-specific deficits.</p> <p>Method</p> <p>This study employed a second-order false-belief paradigm in which the cognitive perspective-taking questions tapped the character's thoughts and the affective perspective-taking questions tapped the emotions generated by these thoughts. Affective and cognitive perspective-taking was compared across three groups of children: (a) CD elevated on Callous-Unemotional traits (<it>CD-high-CU</it>, <it>n </it>= 30), (b) CD low on CU traits (<it>CD-low-CU</it>, <it>n </it>= 42), and (c) a 'typically-developing' comparison group (<it>n </it>= 50), matched in age (7.5 – 10.8), gender and socioeconomic background.</p> <p>Results</p> <p>The results revealed deficits in <it>CD-low-CU </it>children for both affective and cognitive perspective-taking. In contrast <it>CD-high-CU </it>children showed relative competency in cognitive, but deficits in affective-perspective taking, a finding that suggests an affective-specific defect and a plausible dissociation of affective and cognitive perspective-taking in <it>CD-high-CU </it>children.</p> <p>Conclusion</p> <p>Present findings indicate that deficits in cognitive perspective-taking that have long been implicated in CD appear to be characteristic of a subset of CD children. In contrast affective perspective-taking deficits characterise both CD subgroups, but these defects seem to be following diverse developmental paths that warrant further investigation.</p
Stimulation of Microbially Mediated Arsenic Release in Bangladesh Aquifers by Young Carbon Indicated by Radiocarbon Analysis of Sedimentary Bacterial Lipids
The
sources of reduced carbon driving the microbially mediated
release of arsenic to shallow groundwater in Bangladesh remain poorly
understood. Using radiocarbon analysis of phospholipid fatty acids
(PLFAs) and potential carbon pools, the abundance and carbon sources
of the active, sediment-associated, in situ bacterial communities
inhabiting shallow aquifers (<30 m) at two sites in Araihazar,
Bangladesh, were investigated. At both sites, sedimentary organic
carbon (SOC) Δ<sup>14</sup>C signatures of −631 ±
54‰ (<i>n</i> = 12) were significantly depleted relative
to dissolved inorganic carbon (DIC) of +24 ± 30‰ and dissolved
organic carbon (DOC) of −230 ± 100‰. Sediment-associated
PLFA Δ<sup>14</sup>C signatures (<i>n</i> = 10) at
Site F (−167‰ to +20‰) and Site B (−163‰
to +21‰) were highly consistent and indicated utilization of
carbon sources younger than the SOC, likely from the DOC pool. Sediment-associated
PLFA Δ<sup>14</sup>C signatures were consistent with previously
determined Δ<sup>14</sup>C signatures of microbial DNA sampled
from groundwater at Site F indicating that the carbon source for these
two components of the subsurface microbial community is consistent
and is temporally stable over the two years between studies. These
results demonstrate that the utilization of relatively young carbon
sources by the subsurface microbial community occurs at sites with
varying hydrology. Further they indicate that these young carbon sources
drive the metabolism of the more abundant sediment-associated microbial
communities that are presumably more capable of Fe reduction and associated
release of As. This implies that an introduction of younger carbon
to as of yet unaffected sediments (such as those comprising the deeper
Pleistocene aquifer) could stimulate microbial communities and result
in arsenic release