The hydroxyl radical (OH) largely determines the atmosphere's oxidative capacity and, thus, the lifetimes of numerous trace gases, including methane (CH4). Hitherto, observation-based approaches for ...estimating the atmospheric oxidative capacity have primarily relied on using methyl chloroform (MCF), but as the atmospheric abundance of MCF has declined, the uncertainties associated with this method have increased. In this study, we examine the use of five hydrofluorocarbons (HFCs) (HFC-134a, HFC-152a, HFC-365mfc, HFC-245fa, and HFC-32) in multi-species inversions, which assimilate three HFCs simultaneously, as an alternative method to estimate atmospheric OH. We find robust estimates of OH regardless of which combination of the three HFCs are used in the inversions. Our results show that OH has remained fairly stable during our study period from 2004 to 2021, with variations of < 2 % and no significant trend. Inversions including HFC-32 and HFC-152a (the shortest-lived species) indicate a small reduction in OH in 2020 (1.6±0.9 % relative to the mean over 2004–2021 and 0.6±0.9 % lower than in 2019), but considering all inversions, the reduction was only 0.5±1.1 %, and OH was at a similar level to that in 2019.
Production and consumption of CFC-11 (trichlorofluoromethane, CCl3F), CFC-12 (dichlorodifluoromethane, CCl2F2) and CCl4 (carbon tetrachloride) are controlled under the regulations of the Montreal ...Protocol and have been phased out globally since 2010. Only CCl4 is still widely produced as a chemical feedstock. After 2010, emissions of CFC-11 and CFC-12 should therefore mostly originate from existing banks (e.g. from foams, mobile air conditioning units and refrigerators); however evidence has emerged of an increase in global emissions of CFC-11 in the last decade, some of which has not been fully accounted for. The motivation for this work was to assess the emissions of CFC-11, CFC-12 and CCl4 from western Europe. All countries in this region have been subject to the controls of the Montreal Protocol since the late 1980s and, as non-Article 5 Parties, have been prohibited from producing CFCs and CCl4 for dispersive use since 1996. Four different inverse modelling systems are used to estimate emissions of these gases from 2008 to 2021 using data from four atmospheric measurement stations: Mace Head (Ireland), Jungfraujoch (Switzerland), Monte Cimone (Italy) and Tacolneston (UK). The average of the four model studies found that western European emissions of CFC-11, CFC-12 and CCl4 between 2008 and 2021 were declining at 3.5 % yr-1 (2.7 % yr-1–4.8 % yr-1), 7.7 % yr-1 (6.3 % yr-1–8.0 % yr-1) and 4.4 % yr-1 (2.6 % yr-1–6.4 % yr-1), respectively. Even though the emissions were declining throughout the period, the area including northern France, Belgium, the Netherlands and Luxembourg showed consistently elevated emissions of CFC-11 compared with the surrounding regions. Emissions of CFC-12 were slightly elevated in the same region. CCl4 emissions were the highest in the south of France. France had the highest emissions of all three gases over the period 2008–2021. Emissions from western Europe (2008–2021) were on average 2.4 ± 0.4 Gg (CFC-11), 1.3 ± 0.3 Gg (CFC-12) and 0.9 ± 0.2 Gg (CCl4). Our estimated decline in emissions of CFC-11 is consistent with a western European bank release rate of 3.4 % (2.6 %–4.5 %). This study concludes that emissions of CFC-11, CFC-12 and CCl4 have all declined from 2008 to 2021 in western Europe. Therefore, no evidence is found that western European emissions contributed to the unexplained part of the global increase in atmospheric concentrations of CFC-11 observed in the last decade.
Impaired remyelination due to degeneration of both postmitotic oligodendrocytes and oligodendrocyte progenitors (OPs) is the major hallmark of inflammatory demyelination in multiple sclerosis (MS) ...lesions and experimental autoimmune encephalomyelitis (EAE). Here, we have demonstrated the potential of lovastatin, a HMG-CoA reductase inhibitor, for the restoration of impaired remyelination mediated through enhanced survival and differentiation of OPs in the spinal cord of treated EAE animals. Lovastatin treatment significantly increased the level of myelin lipids in the spinal cord of treated EAE animals, coinciding with the attenuation of disease severity and inflammatory demyelination as compared with untreated EAE animals. The increased expression of myelin proteins and transcription factors associated with differentiating oligodendrocytes along with the increase in number of NG2⁺/BrdU⁻ and NG2⁺/BrdU⁺ cells, and the expression of proliferating OP-specific proteins, demonstrated the restoration of remyelination in the spinal cord of lovastatin-treated EAE animals. Corresponding to this, in vitro studies further corroborated the increased survival and differentiation of OPs in lovastatin-treated activated mixed glial cells suggesting that lovastatin protects against the degeneration of OPs and enhances their differentiation through induction of a pro-remyelinating environment in the spinal cord of treated EAE animals. Together, these data demonstrate that lovastatin has the potential to augment remyelination in MS lesions and other neuroinflammatory diseases.-- Paintlia, A. S., Paintlia, M. K., Khan, M., Vollmer, T., Singh, A. K., Singh, I. HMG-CoA reductase inhibitor augments survival and differentiation of oligodendrocyte progenitors in animal model of multiple sclerosis.
This study assesses individual-vehicle molecular hydrogen (H
2) emissions in exhaust gas from current gasoline and diesel vehicles measured on a chassis dynamometer. Absolute H
2 emissions were found ...to be highest for motorcycles and scooters (141
±
38.6
mg km
−
1
), approximately 5 times higher than for gasoline-powered automobiles (26.5
±
12.1
mg km
−
1
). All diesel-powered vehicles emitted marginal amounts of H
2 (∼
0.1
mg km
−
1
). For automobiles, the highest emission factors were observed for sub-cycles subject to a cold-start (mean of 53.1
±
17.0
mg km
−
1
). High speeds also caused elevated H
2 emission factors for sub-cycles reaching at least 150
km h
−
1
(mean of 40.4
±
7.1
mg km
−
1
). We show that H
2/CO ratios (mol mol
−
1
) from gasoline-powered vehicles are variable (sub-cycle means of 0.44–5.69) and are typically higher (mean for automobiles 1.02, for 2-wheelers 0.59) than previous atmospheric ratios characteristic of traffic-influenced measurements. The lowest mean individual sub-cycle ratios, which correspond to high absolute emissions of both H
2 and CO, were observed during cold starts (for automobiles 0.48, for 2-wheelers 0.44) and at high vehicle speeds (for automobiles 0.73, for 2-wheelers 0.45). This finding illustrates the importance of these conditions to observed H
2/CO ratios in ambient air. Overall, 2-wheelers displayed lower H
2/CO ratios (0.48–0.69) than those from gasoline-powered automobiles (0.75–3.18). This observation, along with the lower H
2/CO ratios observed through studies without catalytic converters, suggests that less developed (e.g. 2-wheelers) and older vehicle technologies are largely responsible for the atmospheric H
2/CO ratios reported in past literature.
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering similar to 40 sq. deg in the far UV (FUV, lambda(eff) = 1539 angstrom, Delta lambda = 442 ...angstrom) and similar to 120 sq. deg in the near UV (NUV, lambda(eff) = 2316 angstrom, Delta lambda = 1060 angstrom). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared - submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early-and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (alpha similar to -1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference.
The 1,1,1,2‐tetrafluoroethane (HFC‐134a), an important alternative to CFC‐12 in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer, is a high global warming potential ...greenhouse gas. Here we evaluate variations in global and regional HFC‐134a emissions and emission trends, from 1995 to 2010, at a relatively high spatial and temporal (3.75° in longitude × 2.5° in latitude and 8 day) resolution, using surface HFC‐134a measurements. Our results show a progressive increase of global HFC‐134a emissions from 19 ± 2 Gg/yr in 1995 to 167 ± 5 Gg/yr in 2010, with both a slowdown in developed countries and a 20%/yr increase in China since 2005. A seasonal cycle is also seen since 2002, which becomes enhanced over time, with larger values during the boreal summer.
Key Points
New estimation of HFC‐134a emissions from 1995 to 2010
Seasonal cycle seen since 2002 during the boreal summer
Annual US budgets increasing after 2005, in disagreement with the EPA's estimates
Methyl chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. Large uncertainties in estimates of its source and sink ...magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of the surface fluxes of CH3Cl. The Model of Atmospheric Transport and Chemistry (MATCH), driven by NCEP interannually varying meteorological data, is then used to simulate CH3Cl mole fractions and quantify the time series of sensitivities of the mole fractions at each measurement site to the surface fluxes of various regional and global sources and sinks. We then implement the Kalman filter (with the unit pulse response method) to estimate the surface fluxes on regional/global scales with monthly resolution from January 2000 to December 2004. High frequency observations from the AGAGE, SOGE, NIES, and NOAA/ESRL HATS in situ networks and low frequency observations from the NOAA/ESRL HATS flask network are used to constrain the source and sink magnitudes. The inversion results indicate global total emissions around 4100 ± 470 Gg yr−1 with very large emissions of 2200 ± 390 Gg yr−1 from tropical plants, which turn out to be the largest single source in the CH3Cl budget. Relative to their a priori annual estimates, the inversion increases global annual fungal and tropical emissions, and reduces the global oceanic source. The inversion implies greater seasonal and interannual oscillations of the natural sources and sink of CH3Cl compared to the a priori. The inversion also reflects the strong effects of the 2002/2003 globally widespread heat waves and droughts on global emissions from tropical plants, biomass burning and salt marshes, and on the soil sink.
Perfluorocarbons (PFCs) are amongst the most potent greenhouse gases listed under the United Nations Framework Convention on Climate Change (UNFCCC). With atmospheric lifetimes on the order of ...thousands to tens of thousands of years, PFC emissions represent a permanent alteration to the global atmosphere on human timescales. While the industries responsible for the vast majority of these emissions – aluminium smelting and semi-conductor manufacturing – have made efficiency improvements and introduced abatement measures, the global mean mole fractions of three PFCs, namely tetrafluoromethane (CF4, PFC-14), hexafluoroethane (C2F6, PFC-116) and octafluoropropane (C3F8, PFC-218), continue to grow. In this study, we update baseline growth rates using in situ high-frequency measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and, using data from four European stations, estimate PFC emissions for northwest Europe. The global growth rate of CF4 decreased from 1.3 ppt yr−1 in 1979 to 0.6 ppt yr−1 around 2010 followed by a renewed steady increase to 0.9 ppt yr−1 in 2019. For C2F6, the growth rate grew to a maximum of 0.125 ppt yr−1 around 1999, followed by a decline to a minimum of 0.075 ppt yr−1 in 2009, followed by weak growth thereafter. The C3F8 growth rate was around 0.007 ppt yr−1 until the early 1990s and then quickly grew to a maximum of 0.03 ppt yr−1 in 2003–2004. Following a period of decline until 2012 to 0.015 ppt yr−1, the growth rate slowly increased again to ∼ 0.017 ppt yr−1 in 2019. We used an inverse modelling framework to infer PFC emissions for northwest Europe. No statistically significant trend in regional emissions was observed for any of the PFCs assessed. For CF4, European emissions in early years were linked predominantly to the aluminium industry. However, we link large emissions in recent years to a chemical manufacturer in northwest Italy. Emissions of C2F6 are linked to a range of sources, including a semi-conductor manufacturer in Ireland and a cluster of smelters in Germany's Ruhr valley. In contrast, northwest European emissions of C3F8 are dominated by a single source in northwest England, raising the possibility of using emissions from this site for a tracer release experiment.
The first atmospheric observations of octafluorooxolane
(octafluorotetrahydrofuran, c-C4F8O), a persistent greenhouse gas, are
reported. In addition, a complementary laboratory study of its most ...likely atmospheric
loss processes, its infrared absorption spectrum, and global warming potential (GWP) are
reported. First atmospheric measurements of c-C4F8O are provided from the
Cape Grim Air Archive (41∘ S, Tasmania, Australia, 1978–present), supplemented
by two firn air samples from Antarctica, in situ measurements of ambient air at
Aspendale, Victoria (38∘ S), and a few archived air samples from the Northern
Hemisphere. The atmospheric abundance in the Southern Hemisphere has monotonically grown
over the past decades and leveled at 74 ppq (parts per quadrillion, femtomole per mole
in dry air) by 2015–2018. The growth rate of c-C4F8O has decreased from a
maximum in 2004 of 4.0 to <0.25 ppq yr−1 in 2017 and 2018. Using a 12-box
atmospheric transport model, globally averaged yearly emissions and abundances of
c-C4F8O are calculated for 1951–2018. Emissions, which we speculate to
derive predominantly from usage of c-C4F8O as a solvent in the
semiconductor industry, peaked at 0.15 (±0.04, 2σ) kt yr−1 in 2004 and
have since declined to <0.015 kt yr−1 in 2017 and 2018. Cumulative emissions
over the full range of our record amount to 2.8 (2.4–3.3) kt, which correspond to 34 Mt
of CO2-equivalent emissions. Infrared and ultraviolet absorption spectra for
c-C4F8O as well as the reactive channel rate coefficient for the
O(1D) + c-C4F8O reaction were determined from laboratory
studies. On the basis of these experiments, a radiative efficiency of
0.430 W m−2 ppb−1 (parts per billion, nanomol mol−1) was determined,
which is one of the largest found for synthetic greenhouse gases. The global annually
averaged atmospheric lifetime, including mesospheric loss, is estimated to be
>3000 years. GWPs of 8975, 12 000, and 16 000 are estimated for the 20-, 100-, and
500-year time horizons, respectively.
Based on observations of the chlorofluorocarbons CFC-13 (chlorotrifluoromethane), ΣCFC-114 (combined measurement of both isomers of dichlorotetrafluoroethane), and CFC-115 (chloropentafluoroethane) ...in atmospheric and firn samples, we reconstruct records of their tropospheric histories spanning nearly 8 decades. These compounds were measured in polar firn air samples, in ambient air archived in canisters, and in situ at the AGAGE (Advanced Global Atmospheric Gases Experiment) network and affiliated sites. Global emissions to the atmosphere are derived from these observations using an inversion based on a 12-box atmospheric transport model. For CFC-13, we provide the first comprehensive global analysis. This compound increased monotonically from its first appearance in the atmosphere in the late 1950s to a mean global abundance of 3.18 ppt (dry-air mole fraction in parts per trillion, pmol mol−1) in 2016. Its growth rate has decreased since the mid-1980s but has remained at a surprisingly high mean level of 0.02 ppt yr−1 since 2000, resulting in a continuing growth of CFC-13 in the atmosphere. ΣCFC-114 increased from its appearance in the 1950s to a maximum of 16.6 ppt in the early 2000s and has since slightly declined to 16.3 ppt in 2016. CFC-115 increased monotonically from its first appearance in the 1960s and reached a global mean mole fraction of 8.49 ppt in 2016. Growth rates of all three compounds over the past years are significantly larger than would be expected from zero emissions. Under the assumption of unchanging lifetimes and atmospheric transport patterns, we derive global emissions from our measurements, which have remained unexpectedly high in recent years: mean yearly emissions for the last decade (2007–2016) of CFC-13 are at 0.48 ± 0.15 kt yr−1 (> 15 % of past peak emissions), of ΣCFC-114 at 1.90 ± 0.84 kt yr−1 (∼ 10 % of peak emissions), and of CFC-115 at 0.80 ± 0.50 kt yr−1 (> 5 % of peak emissions). Mean yearly emissions of CFC-115 for 2015–2016 are 1.14 ± 0.50 kt yr−1 and have doubled compared to the 2007–2010 minimum. We find CFC-13 emissions from aluminum smelters but if extrapolated to global emissions, they cannot account for the lingering global emissions determined from the atmospheric observations. We find impurities of CFC-115 in the refrigerant HFC-125 (CHF2CF3) but if extrapolated to global emissions, they can neither account for the lingering global CFC-115 emissions determined from the atmospheric observations nor for their recent increases. We also conduct regional inversions for the years 2012–2016 for the northeastern Asian area using observations from the Korean AGAGE site at Gosan and find significant emissions for ΣCFC-114 and CFC-115, suggesting that a large fraction of their global emissions currently occur in northeastern Asia and more specifically on the Chinese mainland.
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