Oxygenated organic molecules (OOMs) produced by the oxidation of aromatic compounds are key components of secondary organic aerosol (SOA) in urban environments. The steric effects of substitutions ...and rings and the role of key reaction pathways in altering the OOM distributions remain unclear because of the lack of systematic multi-precursor study over a wide range of OH exposure. In this study, we conducted flow-tube experiments and used the nitrate adduct time-of-flight chemical ionization mass spectrometer (NO3--TOF-CIMS) to measure the OOMs produced by the photooxidation of six key aromatic precursors under low-NOx conditions. For single aromatic precursors, the detected OOM peak clusters show an oxygen atom difference of one or two, indicating the involvement of multi-step auto-oxidation and alkoxy radical pathways. Multi-generation OH oxidation is needed to explain the diverse hydrogen numbers in the observed formulae. In particular, for double-ring precursors at higher OH exposure, multi-generation OH oxidation may have significantly enriched the dimer formulae. The results suggest that methyl substitutions in precursor lead to less fragmented OOM products, while the double-ring structure corresponds to less efficient formation of closed-shell monomeric and dimeric products, both highlighting significant steric effects of precursor molecular structure on the OOM formation. Naphthalene-derived OOMs however have lower volatilities and greater SOA contributions than the other-type of OOMs, which may be more important in initial particle growth. Overall, the OOMs identified by the NO3--TOF-CIMS may have contributed up to 30.0 % of the measured SOA mass, suggesting significant mass contributions of less oxygenated, undetected semi-volatile products. Our results highlight the key roles of progressive OH oxidation, methyl substitution and ring structure in the OOM formation from aromatic precursors, which need to be considered in future model developments to improve the model performance for organic aerosol.
Bromine radicals influence global tropospheric chemistry
by depleting ozone and by oxidizing elemental mercury and reduced sulfur
species. Observations typically indicate a 50 % depletion of sea salt
...aerosol (SSA) bromide relative to seawater composition, implying that SSA
debromination could be the dominant global source of tropospheric bromine.
However, it has been difficult to reconcile this large source with the
relatively low bromine monoxide (BrO) mixing ratios observed in the marine
boundary layer (MBL). Here we present a new mechanistic description of SSA
debromination in the GEOS-Chem global atmospheric chemistry model with a
detailed representation of halogen (Cl, Br, and I) chemistry. We show that
observed levels of SSA debromination can be reproduced in a manner
consistent with observed BrO mixing ratios. Bromine radical sinks from the
HOBr + S(IV) heterogeneous reactions and from ocean emission of
acetaldehyde are critical in moderating tropospheric BrO levels. The
resulting HBr is rapidly taken up by SSA and also deposited. Observations of SSA debromination at southern midlatitudes in summer suggest that model
uptake of HBr by SSA may be too fast. The model provides a successful
simulation of free-tropospheric BrO in the tropics and midlatitudes in summer,
where the bromine radical sink from the HOBr + S(IV) reactions is
compensated for by more efficient HOBr-driven recycling in clouds compared to
previous GEOS-Chem versions. Simulated BrO in the MBL is generally much
higher in winter than in summer due to a combination of greater SSA emission
and slower conversion of bromine radicals to HBr. An outstanding issue in
the model is the overestimate of free-tropospheric BrO in extratropical
winter–spring, possibly reflecting an overestimate of the HOBr∕HBr ratio
under these conditions where the dominant HOBr source is hydrolysis of
BrNO3.
Hockberger RS, Binder LS, Graber MA, Hoffman GL, Perina DG, Schneider SM, Sklar DP, Strauss RW, Viravec DR, Koenig WJ, Augustine JJ, Burdick WP, Henderson WV, Lawrence LL, Levy DB, McCall J, Parnell ...MA, Shoji KT. The model of the clinical practice of emergency medicine. Ann Emerg Med. June 2001;37:745-770.
We present an investigation of biomass burning (BB) plumes originating from
Africa and Madagascar based on measurements of a suite of volatile organic
compounds (VOCs), carbon monoxide (CO), ozone ...(O3) and nitrogen
dioxide (NO2) obtained during the dry season of 2018 and 2019 at the
high-altitude Maïdo observatory (21.1∘ S, 55.4∘ E,
2160 ma.s.l.), located on the remote island of La Réunion in
the south-west Indian Ocean (SWIO). Biomass burning plume episodes were
identified from increased acetonitrile (CH3CN) mixing
ratios. Enhancement ratios (EnRs) – relative to CO – were calculated from in
situ measurements for CH3CN, acetone (CH3COCH3), formic acid
(HCOOH), acetic acid (CH3COOH), benzene (C6H6), methanol
(CH3OH) and O3. We compared the EnRs to emission ratios (ERs)
– relative to CO – reported in the literature in order to estimate
loss or production of these compounds during transport. For CH3CN and
CH3COOH, the calculated EnRs are similar to the ERs. For C6H6
and CH3OH, the EnR is lower than the ER, indicating a net sink of
these compounds which was found to be in line with the expected atmospheric
lifetime. For CH3COCH3 and HCOOH, the calculated EnRs are larger than
the ERs. The discrepancy reaches an order of magnitude for HCOOH
(18–34 pptv ppbv−1 compared to
1.8–4.5 pptv ppbv−1). This points to significant secondary
production of HCOOH during transport. The Copernicus Atmospheric Monitoring
Service (CAMS) global model simulations reproduce the temporal variation
of CO mixing ratios well at the observatory but underestimate O3 and
NO2 mixing ratios in the plumes by on average 16 ppbv and
60 pptv respectively. This discrepancy between modelled and measured
O3 mixing ratios was attributed to (i) large uncertainties in VOC and
NOx (NO+NO2) emissions due to BB in CAMS and (ii)
misrepresentation of NOx recycling in the model during
transport. Finally, transport of pyrogenically emitted CO is calculated with
FLEXPART in order to (i) determine the mean plume age during the intrusions at
the observatory and (ii) estimate the impact of BB on the pristine marine
boundary layer (MBL). By multiplying the excess CO in the MBL with inferred
EnRs at the observatory, we calculated the expected impact of BB on
CH3CN, CH3COCH3, CH3OH and C6H6
concentrations in the MBL. These excesses constitute increases of ∼20 %–150 % compared to background measurements in the SWIO
MBL reported in the literature.
After tumor surgery or traumatic defects the anterior skull base needs sufficient closure in order to prevent rhinoliquorrhea, ascending infection and brain tissue prolaps. Small defects are ...sufficiently closed by non-vital tissue, e. g. mucosa, muscle, fat, fascia, bone, allogenic, xenogenic or alloplastic material. Larger defects of the skull base often require more extensive surgery, including transfer of local or distal vascularized flaps. The current article presents a stepwise tutorial for reconstruction of the skull base and by a large case series focuses on the interdisciplinary therapy of complex (size, recurrence, after radiotherapy) skull base defects.
Complex defects with small diameter, which can occur after extended sinus surgery, were permanently closed by local mucosa flaps of the lower turbinate or of the septum (n=31). Larger defects, e. g. after combined transcranial and endonasal tumor surgery, were closed by a 'sandwich technique' containing a galea periost flap and a calvarian split transfer (n=10). Reconstruction of the dura with fascia lata and local transfer of the temporal muscle were efficient for frontobasal defects with a more lateral location (n=4). Transfer of a distal desepithelialised vascularized forearm flap represents the ultimate procedure for reconstruction of large skull base defects, which was performed in 4 of our patients.
Successive escalation of the therapy and integra-tion of the entire repertoire of plastic-reconstructive surgery allows for durable closure of complex skull base defects. In every case, close cooperation between ENT- and neurosurgeons is necessary for planning and performance of a successful surgical procedure.
Smoke from wildfires is a significant source of air pollution, which can adversely impact air quality and ecosystems downwind. With the recently increasing intensity and severity of wildfires, the ...threat to air quality is expected to increase. Satellite-derived biomass burning emissions can fill in gaps in the absence of aircraft or ground-based measurement campaigns and can help improve the online calculation of biomass burning emissions as well as the biomass burning emissions inventories that feed air quality models. This study focuses on satellite-derived NOx emissions using the high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI) NO2 dataset. Advancements and improvements to the satellite-based determination of forest fire NOx emissions are discussed, including information on plume height and effects of aerosol scattering and absorption on the satellite-retrieved vertical column densities. Two common top-down emission estimation methods, (1) an exponentially modified Gaussian (EMG) and (2) a flux method, are applied to synthetic data to determine the accuracy and the sensitivity to different parameters, including wind fields, satellite sampling, noise, lifetime, and plume spread. These tests show that emissions can be accurately estimated from single TROPOMI overpasses. The effect of smoke aerosols on TROPOMI NO2 columns (via air mass factors, AMFs) is estimated, and these satellite columns and emission estimates are compared to aircraft observations from four different aircraft campaigns measuring biomass burning plumes in 2018 and 2019 in North America. Our results indicate that applying an explicit aerosol correction to the TROPOMI NO2 columns improves the agreement with the aircraft observations (by about 10 %–25 %). The aircraft- and satellite-derived emissions are in good agreement within the uncertainties. Both top-down emissions methods work well; however, the EMG method seems to output more consistent results and has better agreement with the aircraft-derived emissions. Assuming a Gaussian plume shape for various biomass burning plumes, we estimate an average NOx e-folding time of 2 ±1 h from TROPOMI observations. Based on chemistry transport model simulations and aircraft observations, the net emissions of NOx are 1.3 to 1.5 times greater than the satellite-derived NO2 emissions. A correction factor of 1.3 to 1.5 should thus be used to infer net NOx emissions from the satellite retrievals of NO2.
This study investigates the impact of reactive halogen species (RHS,
containing chlorine (Cl), bromine (Br) or iodine (I)) on atmospheric
chemistry in the tropical troposphere and explores the ...sensitivity to
uncertainties in the fluxes of RHS to the atmosphere and their chemical
processing. To do this, the regional chemistry transport model WRF-Chem has
been extended to include Br and I, as well as Cl chemistry for the first
time, including heterogeneous recycling reactions involving sea-salt aerosol
and other particles, reactions of Br and Cl with volatile organic compounds
(VOCs), along with oceanic emissions of halocarbons, VOCs and inorganic
iodine. The study focuses on the tropical east Pacific using field
observations from the Tropical Ocean tRoposphere Exchange of Reactive halogen
species and Oxygenated VOC (TORERO) campaign (January–February 2012) to
evaluate the model performance. Including all the new processes, the model does a reasonable job reproducing
the observed mixing ratios of bromine oxide (BrO) and iodine oxide (IO),
albeit with some discrepancies, some of which can be attributed to
difficulties in the model's ability to reproduce the observed halocarbons.
This is somewhat expected given the large uncertainties in the air–sea
fluxes of the halocarbons in a region where there are few observations of
their seawater concentrations. We see a considerable impact on the inorganic bromine (Bry)
partitioning when heterogeneous chemistry is included, with a greater
proportion of the Bry in active forms such as BrO, HOBr and
dihalogens. Including debromination of sea salt increases BrO slightly
throughout the free troposphere, but in the tropical marine boundary layer,
where the sea-salt particles are plentiful and relatively acidic,
debromination leads to overestimation of the observed BrO. However, it should
be noted that the modelled BrO was extremely sensitive to the inclusion of
reactions between Br and the oxygenated VOCs (OVOCs), which convert Br to
HBr, a far less reactive form of Bry. Excluding these
reactions leads to modelled BrO mixing ratios greater than observed. The
reactions between Br and aldehydes were found to be particularly important,
despite the model underestimating the amount of aldehydes observed in the
atmosphere. There are only small changes to the inorganic iodine
(Iy) partitioning and IO when the heterogeneous reactions,
primarily on sea salt, are included. Our model results show that tropospheric Ox loss due to
halogens ranges between 25 % and 60 %. Uncertainties in the
heterogeneous chemistry accounted for a small proportion of this range
(25 % to 31 %). This range is in good agreement with other estimates
from state-of-the-art atmospheric chemistry models. The upper bound is found
when reactions between Br and Cl with VOCs are not included and,
consequently, Ox loss by BrOx,
ClOx and IOx cycles is high (60 %).
With the inclusion of halogens in the troposphere, O3 is reduced by
7 ppbv on average. However, when reactions between Br and Cl with VOCs are
not included, O3 is much lower than observed. Therefore, the
tropospheric Ox budget is highly sensitive to the inclusion
of halogen reactions with VOCs and to the uncertainties in current
understanding of these reactions and the abundance of VOCs in the remote
marine atmosphere.
We present a parameterization retrieval of volume mixing ratios (VMRs) from differential slant column density (dSCD) measurements by Airborne Multi-AXis Differential Optical Absorption Spectroscopy ...(AMAX-DOAS). The method makes use of the fact that horizontally recorded limb spectra (elevation angle 0°) are strongly sensitive to the atmospheric layer at instrument altitude. These limb spectra are analyzed using reference spectra that largely cancel out column contributions from above and below the instrument, so that the resulting limb dSCDs, i.e., the column integrated concentration with respect to a reference spectrum, are almost exclusively sensitive to the atmospheric layers around instrument altitude. The conversion of limb dSCDs into VMRs is then realized by calculating box air mass factors (Box-AMFs) for a Rayleigh atmosphere and applying a scaling factor constrained by O4 dSCDs to account for aerosol extinction. An iterative VMR retrieval scheme corrects for trace gas profile shape effects. Benefits of this method are (1) a fast conversion that only requires the computation of Box-AMFs in a Rayleigh atmosphere; (2) neither local aerosol extinction nor the slant column density in the DOAS reference (SCDref) needs to be known; and (3) VMRs can be retrieved for every measurement point along a flight track, thus increasing statistics and adding flexibility to capture concentration gradients. Sensitivity studies are performed for bromine monoxide (BrO), iodine monoxide (IO) and nitrogen dioxide (NO2), using (1) simulated dSCD data for different trace gas and aerosol profiles and (2) field measurements from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) field experiment. For simulated data in a Rayleigh atmosphere, the agreement between the VMR from the parameterization method (VMRpara) and the true VMR (VMRtrue) is excellent for all trace gases. Offsets, slopes and R2 values for the linear fit of VMRpara over VMRtrue are, respectively (0.008 ± 0.001) pptv, 0.988 ± 0.001, 0.987 for BrO; (−0.0066 ± 0.0001) pptv, 1.0021 ± 0.0003, 0.9979 for IO; (−0.17 ± 0.03) pptv, 1.0036 ± 0.0001, 0.9997 for NO2. The agreement for atmospheres with aerosol shows comparable R2 values to the Rayleigh case, but slopes deviate a bit more from one: (0.093 ± 0.002) pptv, 0.933 ± 0.002, 0.907 for BrO; (0.0021 ± 0.0004) pptv, 0.887 ± 0.001, 0.973 for IO; (8.5 ± 0.1) pptv, 0.8302 ± 0.0006, 0.9923 for NO2. VMRpara from field data are further compared with optimal estimation retrievals (VMROE). Least orthogonal distance fit of the data give the following equations: BrOpara = (0.1 ± 0.2) pptv + (0.95 ± 0.14) × BrOOE; IOpara = (0.01 ± 0.02) pptv + (1.00 ± 0.12) × IOOE; NO2para = (3.9 ± 2.5) pptv + (0.87 ± 0.15) × NO2OE. Overall, we conclude that the parameterization retrieval is accurate with an uncertainty of 20 % for IO, 30 % for BrO and NO2, but not better than 0.05 pptv IO, 0.5 pptv BrO and 10 pptv NO2. The retrieval is applicable over a wide range of atmospheric conditions and measurement geometries and not limited to the interpretation of vertical profile measurements in the remote troposphere.
CONTEXT The value of assessing various emerging lipid-related markers for prediction of first cardiovascular events is debated. OBJECTIVE To determine whether adding information on apolipoprotein B ...and apolipoprotein A-I, lipoprotein(a), or lipoprotein-associated phospholipase A2 to total cholesterol and high-density lipoprotein cholesterol (HDL-C) improves cardiovascular disease (CVD) risk prediction. DESIGN, SETTING, AND PARTICIPANTS Individual records were available for 165 544 participants without baseline CVD in 37 prospective cohorts (calendar years of recruitment: 1968-2007) with up to 15 126 incident fatal or nonfatal CVD outcomes (10 132 CHD and 4994 stroke outcomes) during a median follow-up of 10.4 years (interquartile range, 7.6-14 years). MAIN OUTCOME MEASURES Discrimination of CVD outcomes and reclassification of participants across predicted 10-year risk categories of low (<10%), intermediate (10%-<20%), and high (≥20%) risk. RESULTS The addition of information on various lipid-related markers to total cholesterol, HDL-C, and other conventional risk factors yielded improvement in the model's discrimination: C-index change, 0.0006 (95% CI, 0.0002-0.0009) for the combination of apolipoprotein B and A-I; 0.0016 (95% CI, 0.0009-0.0023) for lipoprotein(a); and 0.0018 (95% CI, 0.0010-0.0026) for lipoprotein-associated phospholipase A2 mass. Net reclassification improvements were less than 1% with the addition of each of these markers to risk scores containing conventional risk factors. We estimated that for 100 000 adults aged 40 years or older, 15 436 would be initially classified at intermediate risk using conventional risk factors alone. Additional testing with a combination of apolipoprotein B and A-I would reclassify 1.1%; lipoprotein(a), 4.1%; and lipoprotein-associated phospholipase A2 mass, 2.7% of people to a 20% or higher predicted CVD risk category and, therefore, in need of statin treatment under Adult Treatment Panel III guidelines. CONCLUSION In a study of individuals without known CVD, the addition of information on the combination of apolipoprotein B and A-I, lipoprotein(a), or lipoprotein-associated phospholipase A2 mass to risk scores containing total cholesterol and HDL-C led to slight improvement in CVD prediction.
In this paper, we present a new version of the chemistry–climate model SOCOL-AERv2 supplemented by an iodine chemistry module. We perform three 20-year ensemble experiments to assess the validity of ...the modeled iodine and to quantify the effects of iodine on ozone. The iodine distributions obtained with SOCOL-AERv2-I agree well with AMAX-DOAS observations and with CAM-chem model simulations. For the present-day atmosphere, the model suggests that the iodine-induced chemistry leads to a 3 %–4 % reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30 ppbv less ozone at low latitudes and up to 100 ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5 %–10 % depending on geographical location. In the lower troposphere, 75 % of the modeled ozone reduction originates from inorganic sources of iodine, 25 % from organic sources of iodine. At 50 hPa, the results show that the impacts of iodine from both sources are comparable. Finally, we determine the sensitivity of ozone to iodine by applying a 2-fold increase in iodine emissions, as it might be representative for iodine by the end of this century. This reduces the ozone column globally by an additional 1.5 %–2.5 %. Our results demonstrate the sensitivity of atmospheric ozone to iodine chemistry for present and future conditions, but uncertainties remain high due to the paucity of observational data of iodine species.
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