Halocarbons contained in equipment such as air conditioners, fire extinguishers, and foams continue to be emitted after production has ceased. These ‘banks’ within equipment and applications are thus ...potential sources of future emissions, and must be carefully accounted for in order to evaluate nascent production versus banked emissions. Here, we build on a probabilistic Bayesian model, previously developed to quantify CFC-11, 12 and 113 banks and their emissions. We extend this model to a suite of the major banked chemicals regulated under the Montreal Protocol (HCFC-22, HCFC-141b, and HCFC-142b, halon-1211, and halon-1301, and CFC-114 and CFC-115) along with CFC-11, 12 and 113 in order to quantify a fuller range of ozone-depleting substance banks by chemical and equipment type. We show that if atmospheric lifetime and prior assumptions are accurate, banks are very likely larger than previous international assessments suggest, and that total production has been very likely higher than reported. We identify that banks of greatest climate-relevance, as determined by global warming potential weighting, are largely concentrated in CFC-11 foams and CFC-12 and HCFC-22 non-hermetic refrigeration. Halons, CFC-11, and 12 banks dominate the banks weighted by ozone depletion potential. Thus, we identify and quantify the uncertainties in substantial banks whose future emissions will contribute to future global warming and delay ozone hole recovery if left unrecovered.
The lifetime of nitrous oxide, the third‐most‐important human‐emitted greenhouse gas, is based to date primarily on model studies or scaling to other gases. This work calculates a semiempirical ...lifetime based on Microwave Limb Sounder satellite measurements of stratospheric profiles of nitrous oxide, ozone, and temperature; laboratory cross‐section data for ozone and molecular oxygen plus kinetics for O(1D); the observed solar spectrum; and a simple radiative transfer model. The result is 116 ± 9 years. The observed monthly‐to‐biennial variations in lifetime and tropical abundance are well matched by four independent chemistry‐transport models driven by reanalysis meteorological fields for the period of observation (2005–2010), but all these models overestimate the lifetime due to lower abundances in the critical loss region near 32 km in the tropics. These models plus a chemistry‐climate model agree on the nitrous oxide feedback factor on its own lifetime of 0.94 ± 0.01, giving N2O perturbations an effective residence time of 109 years. Combining this new empirical lifetime with model estimates of residence time and preindustrial lifetime (123 years) adjusts our best estimates of the human‐natural balance of emissions today and improves the accuracy of projected nitrous oxide increases over this century.
Key Points
Nitrous oxide lifetime is computed empirically from MLS satellite data
Empirical N2O lifetimes compared with models including interannual variability
Results improve values for present anthropogenic and preindustrial emissions
Aged soybean seeds show widespread cleavage of long mRNA transcripts with no particular relationship to transcript function, consistent with extant hypotheses of aging mechanisms.
Abstract
Seeds ...exist in the vulnerable state of being unable to repair the chemical degradation all organisms suffer, which slowly ages seeds and eventually results in death. Proposed seed aging mechanisms involve all classes of biological molecules, and degradation of total RNA has been detected contemporaneously with viability loss in dry-stored seeds. To identify changes specific to mRNA, we examined the soybean (Glycine max) seed transcriptome, using new, whole-molecule sequencing technology. We detected strong evidence of transcript fragmentation in 23-year-old, compared with 2-year-old, seeds. Transcripts were broken non-specifically, and greater fragmentation occurred in longer transcripts, consistent with the proposed mechanism of molecular fission by free radical attack at random bases. Seeds died despite high integrity of short transcripts, indicating that functions encoded by short transcripts are not sufficient to maintain viability. This study provides an approach to probe the asymptomatic phase of seed aging, namely by quantifying transcript degradation as a function of storage time.
The reduction of iron is an essential step in the transferrin (Tf) cycle, which is the dominant pathway for iron uptake by red blood cell precursors. A deficiency in iron acquisition by red blood ...cells leads to hypochromic, microcytic anemia. Using a positional cloning strategy, we identified a gene, six-transmembrane epithelial antigen of the prostate 3 (Steap3), responsible for the iron deficiency anemia in the mouse mutant nm1054. Steap3 is expressed highly in hematopoietic tissues, colocalizes with the Tf cycle endosome and facilitates Tf-bound iron uptake. Steap3 shares homology with F420H2:NADP+ oxidoreductases found in archaea and bacteria, as well as with the yeast FRE family of metalloreductases. Overexpression of Steap3 stimulates the reduction of iron, and mice lacking Steap3 are deficient in erythroid ferrireductase activity. Taken together, these findings indicate that Steap3 is an endosomal ferrireductase required for efficient Tf-dependent iron uptake in erythroid cells.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Concerns for ozone recovery Liang, Qing; Strahan, Susan E.; Fleming, Eric L.
Science (American Association for the Advancement of Science),
12/2017, Letnik:
358, Številka:
6368
Journal Article
Recenzirano
Climate change mitigation and compliance with the Montreal Protocol are crucial for ozone layer recovery
Reactive halogen gases containing chlorine (Cl) or bromine (Br) can destroy stratospheric ...ozone via catalytic cycles. The main sources of atmospheric reactive halogen are the long-lived synthetic chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), carbon tetrachloride (CCl
4
), methyl chloroform (CH
3
CCl
3
), and bromine-containing halons, all of which persist in the atmosphere for years. These ozone-depleting substances are now controlled under the Montreal Protocol and its amendments. Natural methyl bromide (CH
3
Br) and methyl chloride (CH
3
Cl) emissions are also important long-lived sources of atmospheric reactive halogen. Rising concentrations of very-short-lived substances (VSLSs) with atmospheric lifetimes of less than half a year may also contribute to future stratospheric ozone depletion. A greater concern for ozone layer recovery is incomplete compliance with the Montreal Protocol, which will impact stratospheric ozone for many decades, as well as rising natural emissions as a result of climate change.
Proteins with iron–sulfur (Fe–S) clusters participate in multiple metabolic pathways throughout the cell. The mitochondrial ABC half-transporter Abcb7, which is mutated in X-linked sideroblastic ...anemia with ataxia in humans, is a functional ortholog of yeast Atm1p and is predicted to export a mitochondrially derived metabolite required for cytosolic Fe–S cluster assembly. Using an inducible Cre/loxP system to delete exons 9 and 10 of the Abcb7 gene, we examined the phenotype of mice deficient in Abcb7. We found that Abcb7 was essential in extra-embryonic tissues early in gestation and that the mutant allele exhibits an X-linked parent-of-origin lethality effect. Furthermore, using X-chromosome inactivation assays and tissue-specific deletions, Abcb7 was found to be essential for the development and function of numerous other cell types and tissues. A notable exception to this was liver, where loss of Abcb7 impaired cytosolic Fe–S cluster assembly but was not lethal. In this situation, control of iron regulatory protein 1, a key cytosolic modulator of iron metabolism, which is responsive to the availability of cytosolic Fe–S clusters, was impaired and contributed to the dysregulation of hepatocyte iron metabolism. Altogether, these studies demonstrate the essential nature of Abcb7 in mammals and further substantiate a central role for mitochondria in the biogenesis of cytosolic Fe–S proteins.
The invasive aquatic plant Eurasian watermilfoil (
L.) can hybridize with the related North American native species northern watermilfoil (
Kom.). Hybrid watermilfoil (
×
) populations have higher ...fitness and reduced sensitivity to some commonly used aquatic herbicides, making management more difficult. There is growing concern that management practices using herbicides in lakes with mixed populations of watermilfoil species may further select for hybrid individuals due to the difference in herbicide sensitivity. Accurate and cost-effective identification of rare hybrid individuals within populations is therefore critical for herbicide management decisions. Here we describe KASP assays for three SNPs in the ITS region to genotype individuals from both parental watermilfoil species and their hybrid, using synthesized plasmids containing the respective sequences as positive controls. Using KASP we genotyped 16 individuals from one lake and 23 individuals from a second lake, giving a highly accurate picture of
species distribution dynamics. We identified one hybrid individual among 16 samples from one lake, a discovery rate of <10%. Discriminant analysis showed that while a single SNP was generally sufficient for genotyping an individual, using multiple SNPs increased the reliability of genotyping. In the future, the ability to genotype many samples will provide the ability to identify the presence of rare individuals, such as a less common parental species or the inter-specific hybrid. Lakes with complex species distribution dynamics, such as a low proportion of hybrids, are where herbicide application must be carefully chosen so as not to select for the more vigorous and less herbicide-sensitive hybrid individuals.
The Whole Atmosphere Community Climate Model (WACCM3) has been used to study the long‐term (more than a few months) effects of solar proton events (SPEs). Extremely large solar proton events occurred ...in 1972, 1989, 2000, 2001, and 2003 and caused some longer‐lasting atmospheric changes. The highly energetic solar protons produced odd hydrogen (HOx) and odd nitrogen (NOy), which then led to ozone variations. Some statistically significant long‐term effects on mesospheric ozone were caused by the HOx increases due to a very active time period for SPEs (years 2000–2004), even though the HOx increases were short‐lived (days). The long‐term stratospheric ozone effects were caused by the NOy enhancements. Very large NOy enhancements lasted for months in the middle and lower stratosphere after a few of the largest SPEs. SPE‐caused NOy increases computed with WACCM3 were statistically significant at the 95% level throughout much of the polar stratosphere and mesosphere in the recent solar maximum 5‐year period (2000–2004). WACCM3‐computed SPE‐caused polar stratospheric ozone decreases of >10% continued for up to 5 months past the largest events; however, statistically significant ozone decreases were computed for only a relatively small fraction of this time in relatively limited altitudes in the lower mesosphere and upper stratosphere. Annually averaged model output showed statistically significant (to 95%) stratospheric ozone loss in the polar Northern Hemisphere for years 2000–2002. The computed annually averaged temperature and total ozone change in these years were not statistically significant.
Ozone depletion by hydrofluorocarbons Hurwitz, Margaret M.; Fleming, Eric L.; Newman, Paul A. ...
Geophysical research letters,
28 October 2015, Letnik:
42, Številka:
20
Journal Article
Recenzirano
Odprti dostop
Atmospheric concentrations of hydrofluorocarbons (HFCs) are projected to increase considerably in the coming decades. Chemistry climate model simulations forced by current projections show that HFCs ...will impact the global atmosphere increasingly through 2050. As strong radiative forcers, HFCs increase tropospheric and stratospheric temperatures, thereby enhancing ozone‐destroying catalytic cycles and modifying the atmospheric circulation. These changes lead to a weak depletion of stratospheric ozone. Simulations with the NASA Goddard Space Flight Center 2‐D model show that HFC‐125 is the most important contributor to HFC‐related atmospheric change in 2050; its effects are comparable to the combined impacts of HFC‐23, HFC‐32, HFC‐134a, and HFC‐143a. Incorporating the interactions between chemistry, radiation, and dynamics, ozone depletion potentials (ODPs) for HFCs range from 0.39 × 10−3 to 30.0 × 10−3, approximately 100 times larger than previous ODP estimates which were based solely on chemical effects.
Key Points
HFCs are weak ozone‐depleting substances
HFCs warm the troposphere and stratosphere and modify atmospheric circulation
In 2050, HFC‐125 is projected to be the largest HFC contributor to atmospheric change
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