Ascorbic acid is among the most abundant antioxidants in the lung, where it likely plays a key role in the mechanism by which particulate air pollution initiates a biological response. Because ...ascorbic acid is a highly redox active species, it engages in a far more complex web of reactions than a typical organic molecule, reacting with oxidants such as the hydroxyl radical as well as redox-active transition metals such as iron and copper. The literature provides a solid outline for this chemistry, but there are large disagreements about mechanisms, stoichiometries and reaction rates, particularly for the transition metal reactions. Here we synthesize the literature, develop a chemical kinetics model, and use seven sets of laboratory measurements to constrain mechanisms for the iron and copper reactions and derive key rate constants. We find that micromolar concentrations of iron(III) and copper(II) are more important sinks for ascorbic acid (both AH
and AH
) than reactive oxygen species. The iron and copper reactions are catalytic rather than redox reactions, and have unit stoichiometries: Fe(III)/Cu(II) + AH
/AH
+ O
→ Fe(III)/Cu(II) + H
O
+ products. Rate constants are 5.7 × 10
and 4.7 × 10
M
s
for Fe(III) + AH
/AH
and 7.7 × 10
and 2.8 × 10
M
s
for Cu(II) + AH
/AH
, respectively.
We analyse historical (1850–2014) atmospheric hydroxyl
(OH) and methane lifetime data from Coupled Model Intercomparison Project
Phase 6 (CMIP6)/Aerosols and Chemistry Model Intercomparison Project
...(AerChemMIP) simulations. Tropospheric OH changed little from 1850 up to
around 1980, then increased by around 9 % up to 2014, with an associated
reduction in methane lifetime. The model-derived OH trends from 1980 to 2005
are broadly consistent with trends estimated by several studies that infer
OH from inversions of methyl chloroform and associated measurements; most
inversion studies indicate decreases in OH since 2005. However, the model
results fall within observational uncertainty ranges. The upward trend in
modelled OH since 1980 was mainly driven by changes in anthropogenic
near-term climate forcer emissions (increases in anthropogenic nitrogen
oxides and decreases in CO). Increases in halocarbon emissions since 1950
have made a small contribution to the increase in OH, whilst increases in
aerosol-related emissions have slightly reduced OH. Halocarbon emissions
have dramatically reduced the stratospheric methane lifetime by about
15 %–40 %; most previous studies assumed a fixed stratospheric lifetime.
Whilst the main driver of atmospheric methane increases since 1850 is
emissions of methane itself, increased ozone precursor emissions have
significantly modulated (in general reduced) methane trends. Halocarbon and
aerosol emissions are found to have relatively small contributions to
methane trends. These experiments do not isolate the effects of climate
change on OH and methane evolution; however, we calculate residual terms that
are due to the combined effects of climate change and non-linear
interactions between drivers. These residual terms indicate that non-linear
interactions are important and differ between the two methodologies we use
for quantifying OH and methane drivers. All these factors need to be
considered in order to fully explain OH and methane trends since 1850; these
factors will also be important for future trends.
Calcidiol, the major circulating metabolite of vitamin D, supports induction of pleiotropic antimicrobial responses in vitro. Vitamin D supplementation elevates circulating calcidiol concentrations, ...and thus has a potential role in the prevention and treatment of infection. The immunomodulatory effects of administering vitamin D to humans with an infectious disease have not previously been reported. To characterize these effects, we conducted a detailed longitudinal study of circulating and antigen-stimulated immune responses in ninety-five patients receiving antimicrobial therapy for pulmonary tuberculosis who were randomized to receive adjunctive high-dose vitamin D or placebo in a clinical trial, and who fulfilled criteria for per-protocol analysis. Vitamin D supplementation accelerated sputum smear conversion and enhanced treatment-induced resolution of lymphopaenia, monocytosis, hypercytokinaemia, and hyperchemokinaemia. Administration of vitamin D also suppressed antigen-stimulated proinflammatory cytokine responses, but attenuated the suppressive effect of antimicrobial therapy on antigenstimulated secretion of IL-4, CC chemokine ligand 5, and IFN-α. We demonstrate a previously unappreciated role for vitamin D supplementation in accelerating resolution of inflammatory responses during tuberculosis treatment. Our findings suggest a potential role for adjunctive vitamin D supplementation in the treatment of pulmonary infections to accelerate resolution of inflammatory responses associated with increased risk of mortality.
Tropospheric ozone in CMIP6 simulations Griffiths, Paul T; Murray, Lee T; Zeng, Guang ...
Atmospheric chemistry and physics,
03/2021, Letnik:
21, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The evolution of tropospheric ozone from 1850 to 2100 has been studied using data from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We evaluate long-term changes using coupled ...atmosphere–ocean chemistry–climate models, focusing on the CMIP Historical and ScenarioMIP ssp370 experiments, for which detailed tropospheric-ozone diagnostics were archived. The model ensemble has been evaluated against a suite of surface, sonde and satellite observations of the past several decades and found to reproduce well the salient spatial, seasonal and decadal variability and trends. The multi-model mean tropospheric-ozone burden increases from 247 ± 36 Tg in 1850 to a mean value of 356 ± 31 Tg for the period 2005–2014, an increase of 44 %. Modelled present-day values agree well with previous determinations (ACCENT: 336 ± 27 Tg; Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP: 337 ± 23 Tg; Tropospheric Ozone Assessment Report, TOAR: 340 ± 34 Tg). In the ssp370 experiments, the ozone burden increases to 416 ± 35 Tg by 2100. The ozone budget has been examined over the same period using lumped ozone production (PO3) and loss (LO3) diagnostics. Both ozone production and chemical loss terms increase steadily over the period 1850 to 2100, with net chemical production (PO3-LO3) reaching a maximum around the year 2000. The residual term, which contains contributions from stratosphere–troposphere transport reaches a minimum around the same time before recovering in the 21st century, while dry deposition increases steadily over the period 1850–2100. Differences between the model residual terms are explained in terms of variation in tropopause height and stratospheric ozone burden.
The Montreal Protocol is successfully protecting the ozone layer. The main halogen gases responsible for stratospheric ozone depletion have been regulated under the Protocol, their combined ...atmospheric abundances are declining and ozone is increasing in some parts of the atmosphere1. Ozone depletion potentials2-4, relative measures of compounds' abilities to deplete stratospheric ozone, have been a key regulatory component of the Protocol in successfully guiding the phasing out in the manufacture ofthe most highly depleting substances. However, this latest, recovery phase in monitoring the success of the Protocol calls for further metrics. The 'delay in ozone return' has been widely used to indicate the effect of different emissions or phase-down strategies, but we argue here that it can sometimes be ambiguous or even of no use. Instead, we propose the use of an integrated ozone depletion (IOD) metric to indicate the impact of any new emission. The IOD measures the time-integrated column ozone depletion and depends only on the emission strength and the whole atmosphere and stratospheric lifetimes of the species considered. It provides a useful complementary metric of the impact of specific emissions of an ozone depleting substance for both the scientific and policy communities.
We present first observations of OH and (HO2 + RO2) carried out in Antarctica outside the summer season. Measurements were made over 23 days in spring at the coastal Antarctic station Halley. ...Increases in concentrations were evident during the measurement period due to rapidly increasing solar irradiance, and clear diurnal cycles were present throughout. There were also notable differences in air mass composition depending on wind direction. Air masses that had traversed the sea ice zone had both higher concentrations of OH and a larger OH:(HO2 + RO2) ratio. We use steady state kinetic arguments and a 0‐D box model to probe the chemical drivers. We find that differences in bromine chemistry, previously measured at Halley, are sufficient to account for the observed differences in OH concentration as well as the ratio. There is some evidence also that chlorine chemistry is influencing concentrations of RO2.
Plain Language Summary
The chemistry that goes on in the air is very sensitive to the presence of reactive trace gases, known as OH and the sum of HO2 + RO2. We have made the first measurements of these gases during the Antarctic spring, at the British Antarctic Survey station, Halley, in coastal Antarctica. We show that their concentrations vary regularly over the course of a day but generally increase over the 23 days of measurements as the Sun rises after the Antarctic winter. We also show that the concentrations of OH varied considerably from one day to the next, depending on the prevailing wind direction. At Halley, the wind tends to arrive at the station either after it has traveled over the continental snowpack (to the east of the station) or from over the sea ice zone (to the west/southwest of the station). When air has traveled over the sea ice zone, we know that it carries higher concentrations of halogen gases. We show that the higher concentrations of OH in air that has traversed the sea ice zone can be accounted for by the presence of bromine chemistry.
Key Points
First measurements of OH and HO2 + RO2 made in Antarctica outside of summer show dependence (concentration and ratio) on sea ice contact
Using a 0‐D model, we are able to reproduce OH concentrations and HOx partitioning by including bromine chemistry
This influence of sea ice‐derived halogens is another factor to be accounted for when considering impacts of changing polar sea ice
Stratospheric ozone and water vapour are key components of the Earth system, and past and future changes to both have important impacts on global and
regional climate. Here, we evaluate long-term ...changes in these species from the pre-industrial period (1850) to the end of the 21st century
in Coupled Model Intercomparison Project phase 6 (CMIP6)
models under a range of future emissions scenarios. There is good agreement between the CMIP multi-model mean and observations for total column
ozone (TCO), although there is substantial variation between the individual CMIP6 models. For the CMIP6 multi-model mean, global mean TCO has
increased from ∼ 300 DU in 1850 to ∼ 305 DU in 1960, before rapidly declining in the 1970s and 1980s following the
use and emission of halogenated ozone-depleting substances (ODSs). TCO is projected to return to 1960s values by the middle of the 21st century
under the SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0, and SSP5-8.5 scenarios, and under the SSP3-7.0 and SSP5-8.5 scenarios TCO values are projected to
be ∼ 10 DU higher than the 1960s values by 2100. However, under the SSP1-1.9 and SSP1-1.6 scenarios, TCO is not projected to
return to the 1960s values despite reductions in halogenated ODSs due to decreases in tropospheric ozone mixing ratios. This global pattern is
similar to regional patterns, except in the tropics where TCO under most scenarios is not projected to return to 1960s values, either through
reductions in tropospheric ozone under SSP1-1.9 and SSP1-2.6, or through reductions in lower stratospheric ozone resulting from an acceleration of
the Brewer–Dobson circulation under other Shared Socioeconomic Pathways (SSPs). In contrast to TCO, there is poorer agreement between the
CMIP6 multi-model mean and observed lower
stratospheric water vapour mixing ratios, with the CMIP6 multi-model mean underestimating observed water vapour mixing ratios by
∼ 0.5 ppmv at 70 hPa. CMIP6 multi-model mean stratospheric water vapour mixing ratios in the tropical lower stratosphere have
increased by ∼ 0.5 ppmv from the pre-industrial to the present-day period and are projected to increase further by the end of the 21st
century. The largest increases (∼ 2 ppmv) are simulated under the future scenarios with the highest assumed forcing pathway
(e.g. SSP5-8.5). Tropical lower stratospheric water vapour, and to a lesser extent TCO, shows large variations following explosive volcanic eruptions.
The nitrate radical (NO3) plays an important role in the chemistry of the lower troposphere, acting as the principle oxidant during the
night together with ozone. Previous model simulations suggest ...that the levels of NO3 have increased dramatically since the
preindustrial period. Here, we show projections of the evolution of the NO3 radical from 1850–2100 using the United Kingdom Earth
System Model (UKESM1) under
the Coupled Model Intercomparison Project Phase 6
(CMIP6) shared socioeconomic pathway (SSP) scenarios. Our model results highlight diverse trajectories for NO3, with some scenarios and regions undergoing rapid growth
of NO3 to unprecedented levels over the course of the 21st century and others seeing sharp declines. The local increases in NO3
(up to 40 ppt above the preindustrial base line) are driven not only by local changes in emissions of nitrogen oxides but have an important climate
component, with NO3 being favoured in warmer future climates. The changes in NO3 lead to changes in the oxidation of important
secondary organic aerosol precursors, with potential impacts on particulate matter pollution regionally and globally. This work highlights the
potential for substantial future growth in NO3 and the need to better understand the formation of secondary organic aerosol (SOA) from NO3 to accurately
predict future air quality and climate implications.
Large-scale epidemiological studies have shown a close correlation between adverse human health effects and exposure to ambient particulate matter (PM). The oxidative potential (OP) of ambient PM has ...been implicated in inducing toxic effects associated with PM exposure. In particular, reactive oxygen species (ROS), either bound to PM or generated by particulate components in vivo, substantially contribute to the OP and therefore toxicity of PM by lowering antioxidant concentrations in the lung, which can subsequently lead to oxidative stress, inflammation, and disease. Traditional methods for measuring aerosol OP are labor intensive and have poor time resolution, with significant delays between aerosol collection and ROS analysis. These methods may underestimate ROS concentrations in PM because of the potentially short lifetime of some ROS species; therefore, continuous online, highly time-resolved measurement of ROS components in PM is highly advantageous. In this work, we develop a novel online method for measuring aerosol OP based on ascorbic acid chemistry, an antioxidant prevalent in the lung, thus combining the advantages of continuous online measurement with a physiologically relevant assay. The method limit of detection is estimated for a range of atmospherically important chemical components such as Cu(II) 0.22 ± 0.03 μg m–3, Fe(II) 47.8 ± 5.5 μg m–3, Fe(III) 0.63 ± 0.05 μg m–3, and secondary organic aerosol 41.2 ± 6.9 μg m–3, demonstrating that even at this early stage of development, the online method is capable of measuring the OP of PM in polluted urban environments and smog chamber studies.
Infections acquired in hospital are an important cause of morbidity and mortality in very preterm infants. Several small trials have suggested that supplementing the enteral diet of very preterm ...infants with lactoferrin, an antimicrobial protein processed from cow's milk, prevents infections and associated complications. The aim of this large randomised controlled trial was to collect data to enhance the validity and applicability of the evidence from previous trials to inform practice.
In this randomised placebo-controlled trial, we recruited very preterm infants born before 32 weeks' gestation in 37 UK hospitals and younger than 72 h at randomisation. Exclusion criteria were presence of a severe congenital anomaly, anticipated enteral fasting for longer than 14 days, or no realistic prospect of survival. Eligible infants were randomly assigned (1:1) to receive either enteral bovine lactoferrin (150 mg/kg per day; maximum 300 mg/day; lactoferrin group) or sucrose (same dose; control group) once daily until 34 weeks' postmenstrual age. Web-based randomisation minimised for recruitment site, gestation (completed weeks), sex, and single versus multifetal pregnancy. Parents, caregivers, and outcome assessors were unaware of group assignment. The primary outcome was microbiologically confirmed or clinically suspected late-onset infection (occurring >72 h after birth), which was assessed in all participants for whom primary outcome data was available by calculating the relative risk ratio with 95% CI between the two groups. The trial is registered with the International Standard Randomised Controlled Trial Number 88261002.
We recruited 2203 participants between May 7, 2014, and Sept 28, 2017, of whom 1099 were assigned to the lactoferrin group and 1104 to the control group. Four infants had consent withdrawn or unconfirmed, leaving 1098 infants in the lactoferrin group and 1101 in the sucrose group. Primary outcome data for 2182 infants (1093 99·5% of 1098 in the lactoferrin group and 1089 99·0 of 1101 in the control group) were available for inclusion in the modified intention-to-treat analyses. 316 (29%) of 1093 infants in the intervention group acquired a late-onset infection versus 334 (31%) of 1089 in the control group. The risk ratio adjusted for minimisation factors was 0·95 (95% CI 0·86–1·04; p=0·233). During the trial there were 16 serious adverse events for infants in the lactoferrin group and 10 for infants in the control group. Two events in the lactoferrin group (one case of blood in stool and one death after intestinal perforation) were assessed as being possibly related to the trial intervention.
Enteral supplementation with bovine lactoferrin does not reduce the risk of late-onset infection in very preterm infants. These data do not support its routine use to prevent late-onset infection and associated morbidity or mortality in very preterm infants.
UK National Institute for Health Research Health Technology Assessment programme (10/57/49).
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