Volatile Organic Compounds in the Po Basin. Part A: Anthropogenic VOCs

Measurements of volatile organic compounds (VOCs) were performed in the Po Basin, northern Italy in early summer 1998 within the PIPAPO project as well as in summer 2002 and autumn 2003 within the FORMAT project. During the three campaigns, trace gases and meteorological parameters were measured at a semi-rural station, around 35 km north of the city center of Milan. Low toluene and benzene concentrations and lower toluene to benzene ratios on weekends, on Sundays, and in August enabled the identification of a ‘weekend' and a ‘vacation' effect when anthropogenic emissions were lower due to less traffic and reduced industrial activities, respectively. Recurrent nighttime cyclohexane peaks suggested a periodical short-term release of cyclohexane close to the semi-rural sampling site. A multivariate receptor model analysis resulted in the distinction of different characteristic concentration profiles attributed to natural gas, biogenic impact, vehicle exhaust, industrial activities, and a single cyclohexane sourc

Processes controlling the concentration of hydroperoxides at Jungfraujoch Observatory, Switzerland

International audienceAn automated, ground-based instrument was used to measure gas-phase hydroperoxides at the Jungfraujoch High Altitude Research Station as part of the Free Tropospheric EXperiment (FREETEX) during February/March 2003. A nebulising reflux concentrator sampled ambient air twice hourly, prior to on-site analysis by HPLC speciation, coupled with post-column peroxidase derivatisation and fluorescence detection. Hydrogen peroxide (H2O2) concentrations reached up to 1420 pptv over the 13-day period with a mean of 206±261 pptv (± one standard deviation). Methyl hydroperoxide (CH3OOH) reached up to 921 pptv with a mean of 76±96 pptv. No other organic hydroperoxides were detected. The lack of an explicit diurnal cycle suggests that hydroperoxide concentrations are chiefly influenced by transport processes rather than local photochemistry at this mountainous site. We find elevated concentrations of H2O2 in air masses originating from the south-west indicative of higher concentrations of HOx due to more active photochemistry. Air which has been recently polluted exhibits low H2O2 concentration due to a combination of suppression of HO2 by NOx and deposition. We also conclude that despite being at a high alpine site, the vast majority of the air observed was extensively influence by the boundary layer during our campaign (diagnosed from high CO concentrations and the high NOx to NOy ratio) resulting in deposition of H2O2 to the surface and hence reduced H2O2 concentrations. The concentrations of H2O2 sampled here are consistent with previous box modelling studies of hydroperoxides which invoked a depositional sink

The Dual Role of Zonula Occludens (ZO) Proteins

ZO (zonula occludens) proteins are scaffolding proteins providing the structural basis for the assembly of multiprotein complexes at the cytoplasmic surface of intercellular junctions. In addition, they provide a link between the integral membrane proteins and the filamentous cytoskeleton. ZO proteins belong to the large family of membrane-associated guanylate kinase (MAGUK)-like proteins comprising a number of subfamilies based on domain content and sequence similarity. Besides their structural function at cell-cell contacts, ZO proteins appear to participate in the regulation of cell growth and proliferation. Detailed molecular studies have shown that ZO proteins exhibit conserved functional nuclear localization and nuclear export motifs within their amino acid sequence. Further, ZO proteins interact with dual residency proteins localizing to the plasma membrane and the nucleus. Although the nuclear targeting of ZO proteins has well been described, many questions concerning the biological significance of this process have remained open. This review focuses on the dual role of ZO proteins, being indispensable structural components at the junctional site and functioning in signal transduction pathways related to gene expression and cell behavior

Volatile Organic Compounds in the Po Basin. Part B: Biogenic VOCs

Measurements of volatile organic compounds (VOCs) were performed in the Po Basin, northern Italy in early summer 1998, summer 2002, and autumn 2003. During the three campaigns, trace gases and meteorological parameters were measured at a semi-rural station, around 35 km north of the city center of Milan. Bimodal diurnal cycles of isoprene with highest concentrations in the morning and evening were found and could be explained by the interaction of emissions, chemical reactions, and vertical mixing. The diurnal cycle could be qualitatively reproduced by a three-dimensional Eulerian model. The nighttime decay of isoprene could be attributed mostly to reactions with NO3, while the decay of the isoprene oxidation products could not be explained with the considered chemical reactions. Methanol reached very high mixing ratios, up to 150 ppb. High concentrations with considerable variability occurred during nights with high relative humidities and low wind speeds. The origin of these nighttime methanol concentrations is most likely local and biogenic but the specific source could not be identifie

Continuous isotopic composition measurements of tropospheric CO₂ at Jungfraujoch (3580 m a.s.l.), Switzerland: real-time observation of regional pollution events

A quantum cascade laser based absorption spectrometer (QCLAS) is applied for the first time to perform in situ, continuous and high precision isotope ratio measurements of CO₂ in the free troposphere. Time series of the three main CO₂ isotopologue mixing ratios (¹²C¹⁶CO₂, ¹³C¹⁶CO₂ and ¹²C¹⁸O¹⁶O) have simultaneously been measured at one second time resolution over two years (from August 2008 to present) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l., Switzerland). This work focuses on periods in February 2009 only, when sudden and pronounced enhancements in the tropospheric CO₂ were observed. These short-term changes were closely correlated with variations in CO mixing ratios measured at the same site, indicating combustion related emissions as potential source. The analytical precision of 0.046‰ (at 50 s integration time) for both δ¹³C and δ¹⁸O and the high temporal resolution allowed the application of the Keeling plot method for source signature identification. The spatial origin of these CO₂ emission sources was then determined by backward Lagrangian particle dispersion simulations

Peroxy radicals in the summer free troposphere: seasonality and potential for heterogeneous loss

The sum of peroxy radicals (HO<sub>2</sub>+Σ<sub><i>i</i></sub>R<sub><i>i</i></sub>O<sub>2</sub>) and supporting trace gases were measured on the Jungfraujoch (3580 m a.s.l.) during the late summer of 2005. The period was marked by extended times of heavy snow which led to reduction in the observed peroxy radicals during the snowy periods that was greater than the concomitant reduction in <i>j</i>(O<sup>1</sup>D). In the limit a first order loss rate of 0.0063 s<sup>−1</sup> can be derived for the peroxy radical loss in the snowy conditions that could be potentially ascribed to a heterogenous loss process. On snow free days photolysis of HCHO is shown to be a significant peroxy radical source. The seasonal trends of the peroxy radical concentrations have been mapped from the winter to summer transition in line with previous experiments. Net ozone production in late summer at the Jungfraujoch was net neutral to marginally ozone destructive. A value of 28±4 pptv is calculated for the ozone compensation point for the snow free days

Investigations of residual stress distributions in retained austenite and martensite after carbonitriding of a low alloy steel

Abstract. Specimens of low alloy steel were carbonitrided under different conditions to attain varying levels of carbon and nitrogen contents. The residual stress depth distribution was evaluated in martensite and retained austenite by X-ray diffraction. Beside standard evaluations, triaxial residual stress states with σ 33 ≠0 in both phases were also considered. High values of residual stresses in both phases were observed. The sign, magnitude and location of maximum compressive residual stresses were greatly influenced by the level of carbon and nitrogen contents. Introduction The carbonitriding process is the modified form of carburizing [1] during which ammonia gas is added into the carburizing atmosphere. The main advantage of this process in comparison to carburizing is the rapid diffusion of carbon (C) and nitrogen (N) as well as the formation of high compressive residual stresses (RS) in the case. High compressive RS and hardness enhance the fatigue properties of components like shaft, gear and bearing and improves resistance to wear, bending fatigue, and rolling fatigue In the present work, carbonitrided specimens made of steel grade 18CrNiMo7-6 were investigated in terms of RS distribution in both martensite and RA phases according to the standard si

A new estimation of the recent tropospheric molecular hydrogen budget using atmospheric observations and variational inversion

This paper presents an analysis of the recent tropospheric molecular hydrogen (H2) budget with a particular focus on soil uptake and European surface emissions. A variational inversion scheme is combined with observations from the RAMCES and EUROHYDROS atmospheric networks, which include continuous measurements performed between mid-2006 and mid-2009. Net H2 surface flux, then deposition velocity and surface emissions and finally, deposition velocity, biomass burning, anthropogenic and N2 fixation-related emissions were simultaneously inverted in several scenarios. These scenarios have focused on the sensibility of the soil uptake value to different spatio-temporal distributions. The range of variations of these diverse inversion sets generate an estimate of the uncertainty for each term of the H2 budget. The net H2 flux per region (High Northern Hemisphere, Tropics and High Southern Hemisphere) varies between −8 and +8 Tg yr−1. The best inversion in terms of fit to the observations combines updated prior surface emissions and a soil deposition velocity map that is based on bottom-up and top-down estimations. Our estimate of global H2 soil uptake is −59±9 Tg yr−1. Forty per cent of this uptake is located in the High Northern Hemisphere and 55% is located in the Tropics. In terms of surface emissions, seasonality is mainly driven by biomass burning emissions. The inferred European anthropogenic emissions are consistent with independent H2 emissions estimated using a H2/CO mass ratio of 0.034 and CO emissions within the range of their respective uncertainties. Additional constraints, such as isotopic measurements would be needed to infer a more robust partition of H2 sources and sinks