Within the framework of air quality studies at the megacity scale, highly time-resolved volatile organic compound (C2–C8) measurements were performed in downtown Paris (urban background sites) from ...January to November 2010. This unique dataset included non-methane hydrocarbons (NMHCs) and aromatic/oxygenated species (OVOCs) measured by a GC-FID (gas chromatograph with a flame ionization detector) and a PTR-MS (proton transfer reaction – mass spectrometer), respectively. This study presents the seasonal variability of atmospheric VOCs being monitored in the French megacity and their various associated emission sources. Clear seasonal and diurnal patterns differed from one VOC to another as the result of their different origins and the influence of environmental parameters (solar radiation, temperature). Source apportionment (SA) was comprehensively conducted using a multivariate mathematical receptor modeling. The United States Environmental Protection Agency's positive matrix factorization tool (US EPA, PMF) was used to apportion and quantify ambient VOC concentrations into six different sources. The modeled source profiles were identified from near-field observations (measurements from three distinct emission sources: inside a highway tunnel, at a fireplace and from a domestic gas flue, hence with a specific focus on road traffic, wood-burning activities and natural gas emissions) and hydrocarbon profiles reported in the literature. The reconstructed VOC sources were cross validated using independent tracers such as inorganic gases (NO, NO2, CO), black carbon (BC) and meteorological data (temperature). The largest contributors to the predicted VOC concentrations were traffic-related activities (including motor vehicle exhaust, 15 % of the total mass on the annual average, and evaporative sources, 10 %), with the remaining emissions from natural gas and background (23 %), solvent use (20 %), wood-burning (18 %) and a biogenic source (15 %). An important finding of this work is the significant contribution from wood-burning, especially in winter, where it could represent up to ∼ 50 % of the total mass of VOCs. Biogenic emissions also surprisingly contributed up to ∼ 30 % in summer (due to the dominating weight of OVOCs in this source). Finally, the mixed natural gas and background source exhibited a high contribution in spring (35 %, when continental air influences were observed) and in autumn (23 %, for home heating consumption).
Trends of long-term observations and emission inventories suggest that traffic emissions will no longer dominate the concentrations of monoaromatic compounds (i.e., TEX - toluene, xylenes, and ...ethylbenzene) in European urban areas. But the split limit between traffic and other emission sector contributions such as solvent use remains tenuous. Here long-term observations of an extensive set of hydrocarbons, including TEX, at traffic and urban background sites in London, Paris and Strasbourg were combined to estimate the relative importance of traffic emissions on TEX in every city. When analyzing the urban enhancement emission ratios of TEX-to-benzene on a seasonal basis, two potential source signatures other than traffic could be differentiated in all cities (1) summertime evaporation from fuel and/or solvent and (2) wintertime domestic heating. However, traffic emissions still unambiguously dominate the concentration levels of TEX in every city despite the reduction of their emissions at exhaust pipe over the last two decades. Traffic explains between 60% and 96% (at ±20%) of TEX levels while it is less clear for xylenes at some locations. Our results provide a basis to evaluate regional emission inventories. The method is applicable at any urban area where speciated hydrocarbon monitoring is available.
The mitochondrion is an organelle originating from an endosymbiotic event and playing a role in several fundamental processes such as energy production, metabolite syntheses, and programmed cell ...death. This organelle is delineated by two membranes whose synthesis requires an extensive exchange of phospholipids with other cellular organelles such as endoplasmic reticulum (ER) and vacuolar membranes in yeast. These transfers of phospholipids are thought to occur by a non-vesicular pathway at contact sites between two closely apposed membranes. In plants, little is known about the biogenesis of mitochondrial membranes. Contact sites between ER and mitochondria are suspected to play a similar role in phospholipid trafficking as in yeast, but this has never been demonstrated. In contrast, it has been shown that plastids are able to transfer lipids to mitochondria during phosphate starvation. However, the proteins involved in such transfer are still unknown. Here, we identified in Arabidopsis thaliana a large lipid-enriched complex called the mitochondrial transmembrane lipoprotein (MTL) complex. The MTL complex contains proteins located in the two mitochondrial membranes and conserved in all eukaryotic cells, such as the TOM complex and AtMic60, a component of the MICOS complex. We demonstrate that AtMic60 contributes to the export of phosphatidylethanolamine from mitochondria and the import of galactoglycerolipids from plastids during phosphate starvation. Furthermore, AtMic60 promotes lipid desorption from membranes, likely as an initial step for lipid transfer, and binds to Tom40, suggesting that AtMic60 could regulate the tethering between the inner and outer membranes of mitochondria.
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•AtMic60 is part of a mitochondrial transmembrane lipoprotein complex containing DGDG•AtMic60 is a key factor for mitochondria PE export and import of DGDG•AtMic60 could mediate mitochondria membrane contact site formation in the MTL complex•AtMic60 binds cardiolipin and destabilizes membranes
Mitochondria membrane biogenesis requires exchanges of lipids within mitochondria and with other organelles. Michaud et al. identify a mitochondrial transmembrane lipoprotein complex containing Mic60 in plants. They show that Mic60 plays a key role in mitochondria lipid trafficking, probably by acting on membrane destabilization and contact site.
As a part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) and
Cyprus Aerosols and Gas Precursors (ENVI-Med CyAr) programs, this study aims
primarily to provide an improved understanding ...of the sources and the fate of
volatile organic compounds (VOCs) in the eastern Mediterranean. More than 60
VOCs, including biogenic species (isoprene and eight monoterpenes) and
oxygenated VOCs, were measured during a 1-month intensive field campaign
performed in March 2015 at the Cyprus Atmospheric Observatory (CAO), a
regional background site in Cyprus. VOC measurements were conducted using
complementary online and offline techniques. Biogenic VOCs (BVOCs) were
principally imputed to local sources and characterized by compound-specific
daily cycles such as diurnal maximum for isoprene and nocturnal maximum for
α- and β-pinenes, in connection with the variability of emission
sources. The simultaneous study of pinene and isoprene temporal evolution and
meteorological parameters has shown that BVOC emissions were mainly
controlled by ambient temperature, precipitation and relative humidity. It
was found that isoprene daytime emissions at CAO depended on temperature and
solar radiation changes, whereas nocturnal BVOC concentrations (e.g., from
oak and pine forests) were more prone to the relative humidity and
temperature changes. Significant changes in monoterpene mixing ratios
occurred during and after rainfall. The second part of the study focused on
new particle formation (NPF) events at CAO. BVOCs are known to potentially
play a role in the growth as well as in the early stages of formation of new
atmospheric particles. Based on observations of the particle size
distribution performed with a differential mobility particle sizer (DMPS) and
the total number concentrations of particles larger than 1 nm diameter
measured by particle size magnifier (PSM), NPF events were found on 14 out of
20 days of the field campaign. For all possible proxy parameters
(meteorological parameters, calculated H2SO4 and measured gaseous
compounds) having a role in NPF, we present daily variations of different
classes during nucleation event and non-event days. NPF can occur at various
condensational sink (CS) values and both under polluted and clean atmospheric
conditions. High H2SO4 concentrations coupled with high BVOC
concentrations seemed to be one of the most favorable conditions to observe
NPF at CAO in March 2015. NPF event days were characterized by either
(1) a predominant anthropogenic influence (high concentrations of
anthropogenic source tracers observed), (2) a predominant biogenic influence
(high BVOC concentrations coupled with low anthropogenic tracer
concentrations), (3) a mixed influence (high BVOC concentrations coupled with
high anthropogenic tracer concentrations) and (4) a marine influence (both
low BVOC and anthropogenic tracer
concentrations). More pronounced NPF events were identified during mixed
anthropogenic–biogenic conditions compared to the pure anthropogenic or
biogenic ones, for the same levels of precursors. Analysis of a specific NPF
period of the mixed influence type highlighted that BVOC interactions with
anthropogenic compounds enhanced nucleation formation and growth of newly
formed particles. During this period, the nucleation-mode particles may be
formed by the combination of high H2SO4 and isoprene amounts, under
favorable meteorological conditions (high temperature and solar radiation and
low relative humidity) along with low CS. During the daytime, growth of the
newly formed particles, not only sulfate but also oxygen-like organic aerosol
(OOA) mass contributions, increased in the particle phase. High BVOC
concentrations were observed during the night following NPF events,
accompanied by an increase in CS and in semi-volatile OOA contributions,
suggesting further BVOC contribution to aerosol nighttime growth by
condensing onto pre-existing aerosols.
Arachidonic acid (C20: 4n-6, AA) plays a fundamental role in fish physiology, influencing growth, survival and stress resistance. However, imbalances in dietary AA can have detrimental effects on ...fish health and performance. Optimal AA requirements for rainbow trout have not been established. This study aimed to elucidate the effects of varying dietary AA levels on survival, growth, long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic capacity, oxylipin profiles, lipid peroxidation, and stress resistance of rainbow trout fry. Over a period of eight weeks, 4000 female rainbow trout fry at the resorptive stage (0.12 g) from their first feeding were fed diets with varying levels of AA (0.6%, 1.1% or 2.5% of total fatty acids) while survival and growth metrics were closely monitored. The dietary trial was followed by an acute confinement stress test. Notably, while the fatty acid profiles of the fish reflected dietary intake, those fed an AA-0.6% diet showed increased expression of elongase5, highlighting their inherent ability to produce LC-PUFAs from C18 PUFAs and suggesting potential AA or docosapentaenoic acid
(DPA
) biosynthesis. However, even with this biosynthetic capacity, the trout fed reduced dietary AA had higher mortality rates. The diet had no effect on final weight (3.38 g on average for the three diets). Conversely, increased dietary AA enhanced eicosanoid production from AA, suggesting potential inflammatory and oxidative consequences. This was further evidenced by an increase in non-enzymatic lipid oxidation metabolites, particularly in the AA-2.5% diet group, which had higher levels of phytoprostanes and isoprostanes, markers of cellular oxidative damage. Importantly, the AA-1.1% diet proved to be particularly beneficial for stress resilience. This was evidenced by higher post-stress turnover rates of serotonin and dopamine, neurotransmitters central to the fish's stress response. In conclusion, a dietary AA intake of 1.1% of total fatty acids appears to promote overall resilience in rainbow trout fry.
The ocean is a source of isoprene to the atmosphere. Although their global estimates are relatively low compared with the terrestrial source, these emissions have an influence on atmospheric ...chemistry. The lack of knowledge about the sources and sinks of isoprene in the ocean has hitherto precluded a precise assessment of when and where these emissions might be significant. Here we use the general circulation and biogeochemistry model Nucleus for European Modelling of the Ocean, Pelagic Interaction Scheme for Carbon and Ecosystem Studies (NEMO‐PISCES) to explore different parameterizations of the 3D oceanic sources and sinks of isoprene. In addition, we investigate a representation of the isoprene emission due to photoproduction in the sea surface microlayer. Our model estimates are complemented by a new data compilation of laboratory isoprene production rates and in situ isoprene concentrations. This study constitutes the first attempt to simulate isoprene in a global 3D ocean biogeochemical model. We find that sea surface temperature is an important driver modulating phytoplankton isoprene production and that light levels only play a secondary role at the scale of the global ocean. Furthermore, the use of a variable biochemical consumption rate improves the model‐data comparison. We show the importance of isoprene production below the mixed layer and, as a consequence, demonstrate that models based on 2D surface satellite chlorophyll‐a could miss up to 18.5% of oceanic isoprene emissions. The oceanic isoprene emissions to the atmosphere are estimated to 0.66 (0.43–0.82) Tg C yr−1 in the low range of previous estimates.
Key Points
We developed a mechanistic representation of the marine isoprene cycle in a 3D ocean biogeochemical model
The effect of temperature on biological production and the inclusion of a variable bacterial consumption rate are key to reproduce observed isoprene concentrations
The marine isoprene source to the atmosphere is estimated at 0.66 (0.43–0.82) Tg C yr−1, with a significant contribution from isoprene production below the mixed layer
Biogenesis of photosynthetic membranes depends on galactolipid synthesis, which relies on several cell compartments, notably the endoplasmic reticulum (ER) and the chloroplast envelope. Galactolipid ...synthesis involves lipid trafficking between both membrane compartments. In Arabidopsis, ALA10, a phospholipid flippase of the P 4 type-ATPase family, counteracts the limitation of monogalactosyldiacylglycerol (MGDG) production and has a positive effect on leaf development. ALA10 locates in distinct domains of the ER depending on the ALIS (ALA interacting subunit) subunit it interacts with: close to the plasma membrane with ALIS1, or next to chloroplasts with ALIS5. It interacts with FAD2 (Fatty acid desaturase 2) and prevents accumulation of linolenic (18:3) containing phosphatidylcholine (PC) stimulating an increase of MGDG synthesis. Here we report that ALA10 interacts with PUB11 (plant U-box type 11), an E3 protein ubiquitin ligase, in vitro and in vivo. ALA10 is however ubiquitinated and degraded by the 26S proteasome in a PUB11-independent process. In pub11 null mutant, the proteasome-dependent degradation of ALA10 is retained and ALA10 is still subject to ubiquitination although its ubiquitination profile appears different. In the absence of PUB11, ALA10 is constrained to the ER close to chloroplasts, which is the usual location when ALA10 is overexpressed. Additionally, in this condition, the decrease of 18:3 containing PC is no longer observed. Taken together these results suggest, that ALA10 contributes in chloroplast-distal ER interacting domains, to reduce the 18:3 desaturation of PC and that PUB11 is involved in reconditioning of ALA10 from chloroplast-proximal to chloroplast-distal ER interacting domains.
During the COVID-19 pandemic, the lockdown reduced anthropogenic emissions of NO2 in Paris. NO2 concentrations recorded in 2020 were the lowest they have been in the past 5 years. Despite these ...low-NO2 levels, Paris experienced PM2.5 pollution episodes, which were investigated here based on multi-species and multi-platform measurements. Ammonia (NH3) measurements over Paris, derived from a mini-DOAS (differential optical absorption spectroscopy) instrument and the Infrared Atmospheric Sounding Interferometer (IASI) satellite, revealed simultaneous enhancements during the spring PM2.5 pollution episodes. Using the IASI maps and the FLEXPART model, we show that long-range transport had a statistically significant influence on the degradation of air quality in Paris. In addition, concentrations of ammonium (NH4+) and PM2.5 were strongly correlated for all episodes observed in springtime 2020, suggesting that transport of NH3 drove a large component of the PM2.5 pollution over Paris. We found that NH3 was not the limiting factor for the formation of ammonium nitrate (NH4NO3), and we suggest that the conversion of ammonia to ammonium may have been the essential driver.
Portable sensors have emerged as a promising solution for personal exposure (PE) measurement. For the first time in Île-de-France, PE to black carbon (BC), particulate matter (PM), and nitrogen ...dioxide (NO
) was quantified based on three field campaigns involving 37 volunteers from the general public wearing the sensors all day long for a week. This successful deployment demonstrated its ability to quantify PE on a large scale, in various environments (from dense urban to suburban, indoor and outdoor) and in all seasons. The impact of the visited environments was investigated. The proximity to road traffic (for BC and NO
), as well as cooking activities and tobacco smoke (for PM), made significant contributions to total exposure (up to 34%, 26%, and 44%, respectively), even though the time spent in these environments was short. Finally, even if ambient outdoor levels played a role in PE, the prominent impact of the different environments suggests that traditional ambient monitoring stations is not a proper surrogate for PE quantification.
Airborne fungal spores (AFS) represent the major fraction of primary biological aerosol particles (PBAPs), and they are studied worldwide largely due to their important role within the Earth system. ...They have an impact on climate and human health, and they contribute to the propagation of diseases. As their presence in the air depends largely on studied ecosystems, a spore trap was used to monitor their atmospheric concentrations from 2014 to December 2018 in Saclay, a suburban area in the megacity of Paris. The main objective of this work was: (1) to understand the atmospheric variability of AFS in relation to different variables such as meteorological factors, agricultural practice, and (2) to identify their geographical origin by using a source receptor model. During our period of observation, 30 taxa have been identified under a light microscope. In order of importance, Ascospores, Cladosporium, Basidiospores, Tilletiopsis, Alternaria were found to be the most abundant types respectively (50.8%, 33.6%, 7.6%, 1.8%, and 1.3%) accounting for 95% of the atmospheric concentrations. We observed a general decrease associated with a strong interannual variability. A bimodal seasonal cycle was identified with a first maximum in July and a second in October. The main parameters driving the atmospheric concentration are temperature and precipitation. The daily variability is strongly activated by successive periods of hot weather and rainfall, multiplying the concentration by a factor of 1000 in less than 12 hours. Results from the source receptor model ZeFir point out unambiguous different origins of AFS due to specific sources impacting the observation site. Our study also indicated that a hydrological stress has a direct effect on the daily concentrations. This last point should be taken into account for every stressed ecosystem studied in a global warming context. This is particularly important for Mediterranean areas where water is a key control of the growth and dispersion of fungal spores.
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