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The budget of reactive nitrogen species, which play a central role in atmospheric chemistry (e.g. in photochemical O3 production), is poorly understood in forested regions. In this study, through observations of NO, NO2, NOy, and O3 in the Rambouillet Forest near Paris, France, we have examined nighttime processes controlling NOx in an anthropogenically impacted forest environment. The O3 mixing ratios displayed a strong diel profile at the site that was driven by a variable but generally rapid deposition to soil and foliar surfaces. The O3 diel profile was strongly influenced by relative humidity and temperature inversion. Only when the O3 mixing ratio was sufficiently low (and thus the NO lifetime sufficiently long) were sustained NO peaks observed above the instrumental detection limit, enabling the derivation of average NO emission rates of ∼1.4 ppbv h−1 from the soil. Observations of the lack of increase in NO2 at night, despite a significant production rate from the reaction of NO with O3, enabled an effective lifetime of NO2 of ∼0.5–3 h to be derived. As the loss of NO2 was not compensated for by the formation of gas- or particle-phase reactive nitrogen species, it was presumably either driven by deposition to soil and foliar surfaces or any products formed were themselves short-lived with respect to deposition. By comparison, the daytime lifetime of NO2 with respect to loss by reaction with OH is about 1 d. Our results indicate that the nighttime deposition of NO2 is a major sink of boundary layer NOx in this temperate forest environment.

We present direct measurements of biogenic volatile organic compound (BVOC)-induced nitrate radical (NO3) reactivity (kVOC) through the diel cycle in the suburban, temperate forest of Rambouillet near Paris (France). The data were obtained in a 6-week summer period in 2022 as part of the Atmospheric ChemistRy Of the Suburban foreSt (ACROSS) campaign. kVOC was measured in a small (700 m2) clearing mainly at a height of 5.5 m above ground level but also at 40 m (for 5 d and nights). At nighttime, mean values (and 25th–75th percentile ranges) of knightVOC(5.5m) = (0.24-0.06+0.32) s−1 and knightVOC(40m) = (0.016-0.007+0.018) s−1 indicate a significant vertical gradient and low NO3 reactivity above the canopy, whereas knightVOC(5.5 m) showed peak values of up to 2 s−1 close to the ground. The strong vertical gradient in NO3 reactivity could be confirmed by measurements between 0 and 24 m on one particular night characterized by a strong temperature inversion and is a result of the decoupling of air masses aloft from the ground- and canopy-level sources of BVOCs (and nitric oxide, NO). No strong vertical gradient was observed in the mean daytime NO3 reactivity, with kdayVOC(5.5m) = (0.12 ± 0.04) s−1 for the entire campaign and kdayVOC(40m) = (0.07 ± 0.02) s−1 during the 5 d period. Within the clearing, the fractional contribution of VOCs to the total NO3 loss rate coefficient (ktot, determined by photolysis, reaction with NO and VOCs) was 80 %–90 % during the night and ∼ 50 % during the day. In terms of chemical losses of α-pinene below canopy height in the clearing, we find that at nighttime hydroxyl radicals (OH) and ozone (O3) dominate, with NO3 contributing “only” 17 %, which decreases further to 8.5 % during the day. Based on measured OH, measured O3, and calculated NO3 concentrations, the chemical lifetime of BVOCs at noon is about 1 h and is likely to be longer than timescales of transport out of the canopy (typically of the order of minutes), thus significantly reducing the importance of daytime in-canopy processing. Clearly, in forested regions where sufficient nitric oxide and nitrogen dioxide (NOx) is available, the role of NO3 and OH as initiators of BVOC oxidation is not strictly limited to nighttime and daytime, respectively, as often implied in e.g. atmospheric chemistry textbooks.

The residual stress state in the subsurface is a key element of surface integrity. It is well known to have a significant impact on a component's properties in terms of fatigue behavior and resistance to wear and corrosion. For this reason, adjusting residual stresses during manufacturing is a major challenge in modern production engineering, to improve and ensure a component's fatigue strength. In this context, hydrostatic deep rolling of the workpiece surface using adapted parameters enables the targeted induction of compressive residual stresses into subsurface layers. Due to specific properties regarding subsurface and topography for functional components in tribological applications, a further machining operation by microfinishing following deep rolling seems to be purposeful. In particular with regard to the production of components exposed to periodic load changes when used, the process combination can enable a substitution of the typically required conventional subsurface zone hardening. With the aim of economical process design, the corresponding parts can be manufactured with significantly reduced time and costs. Efficient and well-founded methods for monitoring the resulting influence on the subsurface zone properties are essential for a reproducible and target-oriented process design. The prevailing method for the non-destructive assessment of residual stresses in both academia and industry is X-ray diffractometry using the sin2 ψ-method. However, this method is time-intensive and requires complex instrumentation. Thus, efforts have been undertaken in past decades to develop alternative methods for the efficient and reliable characterization of residual stresses. In this research, the applicability of the cos α-method in X-ray diffractometry and a micromagnetic approach for residual stress assessment was investigated, analyzing deep rolled and microfinished AISI 4140 specimen conditions. In addition to the diffractometric and micromagnetic measurements, metallographic and topographic analyses of machined surfaces were carried out. Deep rolling was found to induce significant compressive residual stresses of up to −1100 MPa. After microfinishing of the deep rolled surfaces, favorable compressive residual stresses remain in the subsurface, reaching approximately up to −750 MPa. Based on this, the production of tailored surfaces with respect to a suitable combination of topography and subsurface is possible. For all surface states investigated, a good agreement between the two approaches in X-ray diffraction was found. Magnetic Barkhausen noise (MBN) measurements prove to be well applicable for an efficient and holistic assessment of surface integrity in the subsurface of deep rolled and microfinished AISI 4140 specimens.

We present direct measurements of biogenic volatile organic compound (BVOC)-induced nitrate radical (NO3) reactivity (kVOC) through the diel cycle in the suburban, temperate forest of Rambouillet near Paris (France). The data were obtained in a 6-week summer period in 2022 as part of the Atmospheric ChemistRy Of the Suburban foreSt (ACROSS) campaign. kVOC was measured in a small (700 m2) clearing mainly at a height of 5.5 m above ground level but also at 40 m (for 5 d and nights). At nighttime, mean values (and 25th–75th percentile ranges) of knightVOC(5.5m) = (0.24-0.06+0.32) s-1 and knightVOC(40m) = (0.016-0.007+0.018) s-1 indicate a significant vertical gradient and low NO3 reactivity above the canopy, whereas knightVOC (5.5 m) showed peak values of up to 2 s-1 close to the ground. The strong vertical gradient in NO3 reactivity could be confirmed by measurements between 0 and 24 m on one particular night characterized by a strong temperature inversion and is a result of the decoupling of air masses aloft from the ground- and canopy-level sources of BVOCs (and nitric oxide, NO). No strong vertical gradient was observed in the mean daytime NO3 reactivity, with kdayVOC(5.5m) = (0.12±0.04) s-1 for the entire campaign and kdayVOC(40m) = (0.07±0.02) s-1 during the 5 d period. Within the clearing, the fractional contribution of VOCs to the total NO3 loss rate coefficient (ktot , determined by photolysis, reaction with NO and VOCs) was 80 %–90 % during the night and ∼ 50 % during the day. In terms of chemical losses of α -pinene below canopy height in the clearing, we find that at nighttime hydroxyl radicals (OH) and ozone (O3) dominate, with NO3 contributing "only" 17 %, which decreases further to 8.5 % during the day. Based on measured OH, measured O3 , and calculated NO3 concentrations, the chemical lifetime of BVOCs at noon is about 1 h and is likely to be longer than timescales of transport out of the canopy (typically of the order of minutes), thus significantly reducing the importance of daytime in-canopy processing. Clearly, in forested regions where sufficient nitric oxide and nitrogen dioxide (NOx) is available, the role of NO3 and OH as initiators of BVOC oxidation is not strictly limited to nighttime and daytime, respectively, as often implied in e.g. atmospheric chemistry textbooks. [ABSTRACT FROM AUTHOR]

Reaction of stabilized Criegee intermediates (SCIs) with SO2 was proposed as an additional pathway of gaseous sulfuric acid (H2SO4) formation in the atmosphere, supplementary to the conventional mechanism of H2SO4 production by oxidation of SO2 in reaction with OH radicals. However, because of a large uncertainty in mechanism and rate coefficients for the atmospheric formation and loss reactions of different SCIs, the importance of this additional source is not well established. In this work, we present an estimation of the role of SCIs in H2SO4 formation at a western Mediterranean (Cape Corsica) remote site, where comprehensive field observations including gas-phase H2SO4, OH radicals, SO2, volatile organic compounds (VOCs) and aerosol size distribution measurements were performed in July–August 2013 as a part of the project ChArMEx (Chemistry-Aerosols Mediterranean Experiment). The measurement site was under strong influence of local emissions of biogenic volatile organic compounds, including monoterpenes and isoprene generating SCIs in reactions with ozone, and, hence, presenting an additional source of H2SO4 via SO2 oxidation by the SCIs. Assuming the validity of a steady state between H2SO4 production and its loss by condensation on existing aerosol particles with a unity accommodation coefficient, about 90 % of the H2SO4 formation during the day could be explained by the reaction of SO2 with OH. During the night the oxidation of SO2 by OH radicals was found to contribute only about 10 % to the H2SO4 formation. The accuracy of the derived values for the contribution of OH + SO2 reaction to the H2SO4 formation is limited mostly by a large, at present factor of 2, uncertainty in the OH + SO2 reaction rate coefficient. The contribution of the SO2 oxidation by SCIs to the H2SO4 formation was evaluated using available measurements of unsaturated VOCs and steady-state SCI concentrations estimated by adopting rate coefficients for SCI reactions based on structure–activity relationships (SARs). The estimated concentration of the sum of SCIs was in the range of (1–3) × 103 molec. cm−3. During the day the reaction of SCIs with SO2 was found to account for about 10 % and during the night for about 40 % of the H2SO4 production, closing the H2SO4 budget during the day but leaving unexplained about 50 % of the H2SO4 formation during the night. Despite large uncertainties in used kinetic parameters, these results indicate that the SO2 oxidation by SCIs may represent an important H2SO4 source in VOC-rich environments, especially during nighttime.

The objective of designing a biocompatible and mechanically stable scaffold for hard tissue regeneration was achieved by fabricating diopside/forsterite composites. Superior mechanical strength, slow degradation, excellent antibacterial activity and good cell viability were attained with the increase in forsterite ratio in the composites whereas apatite deposition ability got enhanced as the diopside content was increased. The variation in the rate of apatite deposition on the surface of composites exhibited different surface topography such as nano-structured interconnected fibrous network and globular morphology. The scaffolds after one-month immersion in a physiological environment exhibited good Young’s modulus and compressive strength. Clear and distinguishable prevention of bacterial growth confirms that composites have the potential to inhibit microbial colony formation of nine different clinical pathogens. The composite containing major diopside content was more effective toward S. aureus while the growth of E. coli was inhibited more by the composite containing a higher ratio of forsterite. The interaction of composites with MG-63 cells showed an enhancement in cell viability as the content of forsterite was increased. MTS assay confirmed the cytocompatibility of samples with negligible toxicity effects.

We present direct measurements of BVOC-induced nitrate radical (NO3) reactivity (kVOC) through the diel cycle in the suburban, temperate forest of Rambouillet near Paris (France). The data were obtained in a six-week summer period in 2022 as part of the ACROSS campaign (Atmospheric ChemistRy Of the Suburban foreSt). kVOC was measured in a small (700 m²) clearing mainly at a height of 5.5 m above ground level, but also at 40 m (for 5 days/nights). At nighttime, mean values of kVOCnight (5.5 m) = (0.24 ± 0.27) s-1 and kVOCnight (40 m) = (0.016 ± 0.007) s-1 indicate a significant vertical gradient and low NO3 reactivity above the canopy, whereas kVOCnight (5.5 m) showed peak values of up to 2 s-1 close to the ground. The strong vertical gradient in NO3 reactivity could be confirmed by measurements between 0 and 24 m on one particular night characterised by a strong temperature inversion, and is a result of the decoupling of air masses aloft from the ground- and canopy-level sources of BVOCs (and NO). No strong vertical gradient was observed in the mean daytime NO3 reactivity with kVOCnight(5.5 m) = (0.12 ± 0.04) s-1 for the entire campaign and kVOCnight(40 m) = (0.07 ± 0.02) s-1 during the 5-day period. Within the clearing, the fractional contribution of VOCs to the total NO3 loss rate (LNO3, determined by photolysis, reaction with NO and VOCs) was 80-90 % during the night and ~50 % during the day. In terms of chemical losses of α-pinene below canopy height in the clearing, we find that at nighttime OH and O3 dominate with NO3 contributing "only" 17 %, which decreases further to 8.5 % during the day. Based on OH, O3 and NO3 concentrations, the chemical lifetime of BVOCs at noon is about one hour and is likely to be longer than timescales of transport out of the canopy (typically in the order of minutes), thus significantly reducing the importance of daytime, in-canopy processing. Clearly, in forested regions where sufficient NOX is available, the role of NO3 and OH as initiators of BVOC oxidation are not strictly limited to the night and to the day, respectively, as often implied in e.g. atmospheric chemistry text-books. [ABSTRACT FROM AUTHOR]

Methylglyoxal (MGLY) is an important atmospheric α-dicarbonyl species for which photolysis acts as a significant source of peroxy radicals, contributing to the oxidizing capacity of the atmosphere and, as such, the formation of secondary pollutants such as organic aerosols and ozone. However, despite its importance, only a few techniques exhibit time resolutions and detection limits that are suitable for atmospheric measurements.This study presents the first field measurements of MGLY by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) performed during the ChArMEx SOP2 field campaign. This campaign took place at a Mediterranean site characterized by intense biogenic emissions and low levels of anthropogenic trace gases. Concomitant measurements of MGLY were performed using the 2,4-dinitrophenylhydrazine (DNPH) derivatization technique and high performance liquid chromatography (HPLC) with UV detection. PTR-ToF-MS and DNPH–HPLC measurements were compared to determine whether these techniques can perform reliable measurements of MGLY.Ambient time series revealed levels of MGLY ranging from 28 to 365 pptv, with a clear diurnal cycle due to elevated concentrations of primary biogenic species during the daytime, and its oxidation led to large production rates of MGLY. A scatter plot of the PTR-ToF-MS and DNPH–HPLC measurements indicates a reasonable correlation (R2 = 0.48) but a slope significantly lower than unity (0.58±0.05) and a significant intercept of 88.3±8.0 pptv. A careful investigation of the differences between the two techniques suggests that this disagreement is not due to spectrometric interferences from H3O+(H2O)3 or methyl ethyl ketone (or butanal) detected at m∕z 73.050 and m∕z 73.065, respectively, which are close to the MGLY m∕z of 73.029. The differences are more likely due to uncorrected sampling artifacts such as overestimated collection efficiency or loss of MGLY into the sampling line for the DNPH–HPLC technique or unknown isobaric interfering compounds such as acrylic acid and propanediol for the PTR-ToF-MS.Calculations of MGLY loss rates with respect to OH oxidation and direct photolysis indicate similar contributions for these two loss pathways.

Through observations of NO, NO2, NOY and O3 in the Rambouillet forest near Paris, France, (as part of the ACROSS campaign, 2022) we have gained insight into nighttime processes controlling NOX in an anthropogenically impacted forest environment. O3 mixing ratios displayed a strong diel profile at the site, which was driven by a variable but generally rapid deposition to soil and foliar surfaces. The O3 diel profile was strongly influenced by relative humidity, which impacted the surface resistance to uptake, and temperature inversion, which influenced the rate of entrainment of O3 from above the canopy. Only when the O3 mixing ratio was sufficiently low (and thus the NO lifetime sufficiently long), were sustained NO peaks observed above the instrumental detection limit, enabling derivation of average NO emission rates from the soil of ~1.4 ppbv h‑1. Observations of the lack of increase in NO2 at night, despite a significant production rate from the reaction of NO with O3, enabled an effective lifetime of NO2 of ⁓0.5–3 h to be derived. As the loss of NO2 was not compensated by the formation of gas- or particle-phase reactive nitrogen species it was presumably driven by deposition to soil and foliar surfaces, or any products formed were themselves short-lived with respect to deposition. By comparison, the daytime lifetime of NO2 with respect to loss by reaction with OH is about 1 day. We conclude that the nighttime deposition of NO2 is a major sink of boundary layer NOX in this temperate forest environment. [ABSTRACT FROM AUTHOR]

Through observations of NO, NO2, NOY and O3 in the Rambouillet forest near Paris, France, (as part of the ACROSS campaign, 2022) we have gained insight into nighttime processes controlling NOX in an anthropogenically impacted forest environment. O3 mixing ratios displayed a strong diel profile at the site, which was driven by a variable but generally rapid deposition to soil and foliar surfaces. The O3 diel profile was strongly influenced by relative humidity, which impacted the surface resistance to uptake, and temperature inversion, which influenced the rate of entrainment of O3 from above the canopy. Only when the O3 mixing ratio was sufficiently low (and thus the NO lifetime sufficiently long), were sustained NO peaks observed above the instrumental detection limit, enabling derivation of average NO emission rates from the soil of -1.4 ppbv h-1. Observations of the lack of increase in NO2 at night, despite a significant production rate from the reaction of NO with O3, enabled an effective lifetime of NO2 of -0.5-3 h to be derived. As the loss of NO2 was not compensated by the formation of gas- or particle-phase reactive nitrogen species it was presumably driven by deposition to soil and foliar surfaces, or any products formed were themselves short-lived with respect to deposition. By comparison, the daytime lifetime of NO2 with respect to loss by reaction with OH is about 1 day. We conclude that the nighttime deposition of NO2 is a major sink of boundary layer NOX in this temperate forest environment. [ABSTRACT FROM AUTHOR]

Indigenous peoples, including Native Hawaiians and Pacific Islanders (NHPIs), experience significant cardiometabolic health disparities arising in large part from rapid changes to their diets and food systems. Innovative food sovereignty initiatives led by NHPIs are needed to address these disparities. This article describes a community-based participatory research study that incorporates social and biological measures to examine the impact of an Indigenous-led land-based food sovereignty youth leadership program on health disparities among NHPI youth in Hawaiʻi. Grounded in the Indigenous knowledge that holistic health and wellbeing of people is inseparable from that of the environment and to counter rampant food insecurity in their community of Waiʻanae, Oʻahu, MAʻO Organic Farms developed a Youth Leadership Training (YLT) program that offers education, nutrition, physical activity, and access to health care. The program also engages YLT interns and their social networks in health education and research in the ongoing Mauli Ola study. Preliminary data from this study affirm the need to address the disproportionately high rates of obesity, type 2 diabetes mellitus (T2D), and poor mental health conditions among young NHPIs in the Waiʻanae community, and how the YLT program may provide an effective approach to address this need. Our unique academic-community partnership underscores the importance of social and biomedical research to understand health disparities in the NHPI population, which present novel avenues to enable disease prevention. The outcomes of the Mauli Ola study may serve as a valuable model for health disparities research while leveraging ongoing social programs that support Indigenous food sovereignty. [ABSTRACT FROM AUTHOR]

Ice sheet exerts a force on the hydraulic structures and vessels with developing and transporting hydrocarbons in the offshore waters of the Arctic causing to strengthen their design and/or provide additional measures against ice loads. The risk of ice impacts on objects of offshore oil and gas fields of the Arctic region determines the existence of the problem of ensuring the sustainability of these objects in terms of iceberg danger and ice formations. Reducing these risks involves the development of organizational and technical measures for improving the sustainability of the facilities in terms of iceberg danger through the use of international experience and development of advanced technologies to prevent dangerous effects of ice formations. Based on the fact that ice management is a specific activity that requires special effort and funds which as part of the rescue security (RS) forces at sea are missing, as well as on the basis of the fact that the system of RS at sea is not assigned to prevent accidents and to ensure the smooth operation of offshore facilities, an ice management is seen as an independent kind of ensuring the proper functioning objects of hydrocarbons production and marine transportation. The paper considers the analysis and synthesis of domestic and foreign experience of ice and iceberg management. A system of security measures for functioning marine oil and gas facilities in icy conditions on the basis of technology of preventing dangerous effects of ice formations has been worked out. It has been shown that the system of ice and iceberg management of marine objects of hydrocarbon production and marine transportation should be a practical mechanism for reducing deposits' operation risks in ice conditions. The work relates to the safe operation of mining platforms in the Arctic seas, and more particularly, to methods and means of influence on the icebergs in order to prevent collisions with fixed or floating production units.

Surface ozone has been measured since 2004 at the coastal East Antarctic site of Dumont d'Urville (DDU), and since 2007 at the Concordia station located on the high East Antarctic plateau. This paper discusses long-term changes, seasonal and diurnal cycles, as well as inter-annual summer variability observed at these two East Antarctic sites. At Concordia, near-surface ozone data were complemented by balloon soundings and compared to similar measurements done at the South Pole. The DDU record is compared to those obtained at the coastal site of Syowa, also located in East Antarctica, as well as the coastal sites of Neumayer and Halley, both located on the coast of the Weddell Sea in West Antarctica. Surface ozone mixing ratios exhibit very similar seasonal cycles at Concordia and the South Pole. However, in summer the diurnal cycle of ozone is different at the two sites with a drop of ozone in the afternoon at Concordia but not at the South Pole. The vertical distribution of ozone above the snow surface also differs. When present, the ozone-rich layer located near the ground is better mixed and deeper at Concordia (up to 400 m) than at the South Pole during sunlight hours. These differences are related to different solar radiation and wind regimes encountered at these two inland sites. DDU appears to be the coastal site where the impact of the late winter/spring bromine chemistry is the weakest, but where the impact of elevated ozone levels caused by NOx snow emissions from the high Antarctic plateau is the highest. The highest impact of the bromine chemistry is seen at Halley and Neumayer, and to a lesser extent at Syowa. These three sites are only weakly impacted by the NOx chemistry and the net ozone production occurring on the high Antarctic plateau. The differences in late winter/spring are attributed to the abundance of sea ice offshore from the sites, whereas those in summer are related to the topography of East Antarctica that promotes the katabatic flow bringing oxidant-rich inland air masses to the site. There appears to be a decreasing change in summer surface ozone at the two East Antarctic sites of Concordia and DDU over the most recent period (2004–2014 and 2007–2014). Further research, including continued monitoring, is needed at these two sites to better separate the effect of synoptic transport from possible change of NOx snow emissions in response to recovery of the stratospheric ozone layer leading to penetration of more UV radiation to the surface.

Variations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO2 = NOx). The unique and distinctive 17O excess (Δ17O = δ17O − 0.52 × δ18O) of ozone, which is transferred to NOx via oxidation, is a particularly useful isotopic fingerprint in studies of NOx transformations. Constraining the propagation of 17O excess within the NOx cycle is critical in polar areas, where there exists the possibility of extending atmospheric investigations to the glacial–interglacial timescale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic Plateau) during the austral summer of 2011/2012. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NOx, O3, OH, HO2, RO2, etc.) and direct observations of the transferrable Δ17O of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO2 pathway and using concurrent measurements of OH and NO2, we calculated a Δ17O signature for nitrate on the order of (21–22 ± 3) ‰. These values are lower than the measured values that ranged between 27 and 31 ‰. This discrepancy between expected and observed Δ17O(NO3−) values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this East Antarctic region. However, systematic errors or false isotopic balance transfer functions are not totally excluded.

Mixing ratios of the atmospheric nitrogen oxides NO and NO2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands & Export) campaign at Dome C, East Antarctica (75.1° S, 123.3° E, 3233 m), during December 2011 to January 2012. Profiles of NOx mixing ratios of the lower 100 m of the atmosphere confirm that, in contrast to the South Pole, air chemistry at Dome C is strongly influenced by large diurnal cycles in solar irradiance and a sudden collapse of the atmospheric boundary layer in the early evening. Depth profiles of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO2 and is a sink of gas-phase ozone (O3). First-time observations of bromine oxide (BrO) at Dome C show that mixing ratios of BrO near the ground are low, certainly less than 5 pptv, with higher levels in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO2 radicals are too low to explain the large NO2 : NO ratios found in ambient air, possibly indicating the existence of an unknown process contributing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011–2012, NOx mixing ratios and flux were larger than in 2009–2010, consistent with also larger surface O3 mixing ratios resulting from increased net O3 production. Large NOx mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mixing height and significant NOx emissions by surface snow (FNOx). During 23 December 2011–12 January 2012, median FNOx was twice that during the same period in 2009–2010 due to significantly larger atmospheric turbulence and a slightly stronger snowpack source. A tripling of FNOx in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO3− concentrations in the snow skin layer, and only to a secondary order by decrease of total column O3 and associated increase in NO3− photolysis rates. A source of uncertainty in model estimates of FNOx is the quantum yield of NO3− photolysis in natural snow, which may change over time as the snow ages.

During the 2011/12 and 2012/13 austral summers, HCHO was investigated for the first time in ambient air, snow, and interstitial air at the Concordia site, located near Dome C on the East Antarctic Plateau, by deploying an Aerolaser AL-4021 analyzer. Snow emission fluxes were estimated from vertical gradients of mixing ratios observed at 1 cm and 1 m above the snow surface as well as in interstitial air a few centimeters below the surface and in air just above the snowpack. Typical flux values range between 1 and 2 × 1012 molecules m−2 s−1 at night and 3 and 5 × 1012 molecules m−2 s−1 at noon. Shading experiments suggest that the photochemical HCHO production in the snowpack at Concordia remains negligible compared to temperature-driven air–snow exchanges. At 1 m above the snow surface, the observed mean mixing ratio of 130 pptv and its diurnal cycle characterized by a slight decrease around noon are quite well reproduced by 1-D simulations that include snow emissions and gas-phase methane oxidation chemistry. Simulations indicate that the gas-phase production from CH4 oxidation largely contributes (66%) to the observed HCHO mixing ratios. In addition, HCHO snow emissions account for ~ 30% at night and ~ 10% at noon to the observed HCHO levels.

Concentrations of OH radicals and the sum of peroxy radicals, RO2, were measured in the boundary layer for the first time on the East Antarctic Plateau at the Concordia Station (Dome C, 75.10° S, 123.31° E) during the austral summer 2011/2012. The median concentrations of OH and RO2 radicals were 3.1 × 106 molecule cm−3 and 9.9 × 106 molecule cm−3, respectively. These values are comparable to those observed at the South Pole, confirming that the elevated oxidative capacity of the Antarctic atmospheric boundary layer found at the South Pole is not restricted to the South Pole but common over the high Antarctic plateau. At Concordia, the concentration of radicals showed distinct diurnal profiles with the median maximum of 5.2 × 106 molecule cm−3 at 11:00 and the median minimum of 1.1 × 106 molecule cm−3 at 01:00 for OH radicals and 1.7 × 108 molecule cm−3 and 2.5 × 107 molecule cm−3 for RO2 radicals at 13:00 and 23:00, respectively (all times are local times). Concurrent measurements of O3, HONO, NO, NO2, HCHO and H2O2 demonstrated that the major primary source of OH and RO2 radicals at Dome C was the photolysis of HONO, HCHO and H2O2, with the photolysis of HONO contributing ~75% of total primary radical production. However, photochemical modelling with accounting for all these radical sources overestimates the concentrations of OH and RO2 radicals by a factor of 2 compared to field observations. Neglecting the net OH production from HONO in the photochemical modelling results in an underestimation of the concentrations of OH and RO2 radicals by a factor of 2. To explain the observations of radicals in this case an additional source of OH equivalent to about (25–35)% of measured photolysis of HONO is required. Even with a factor of 5 reduction in the concentrations of HONO, the photolysis of HONO represents the major primary radical source at Dome C. To account for a possibility of an overestimation of NO2 observed at Dome C the calculations were also performed with NO2 concentrations estimated by assuming steady-state NO2 / NO ratios. In this case the net radical production from the photolysis of HONO should be reduced by a factor of 5 or completely removed based on the photochemical budget of OH or 0-D modelling, respectively. Another major factor leading to the large concentration of OH radicals measured at Dome C was large concentrations of NO molecules and fast recycling of peroxy radicals to OH radicals.

During the austral summer 2011/2012 atmospheric nitrous acid (HONO) was investigated for the second time at the Concordia site (75°06' S, 123°33' E), located on the East Antarctic Plateau, by deploying a long-path absorption photometer (LOPAP). Hourly mixing ratios of HONO measured in December 2011/January 2012 (35 ± 5.0 pptv) were similar to those measured in December 2010/January 2011 (30.4 ± 3.5 pptv). The large value of the HONO mixing ratio at the remote Concordia site suggests a local source of HONO in addition to weak production from oxidation of NO by the OH radical. Laboratory experiments demonstrate that surface snow removed from Concordia can produce gas-phase HONO at mixing ratios half that of the NOx mixing ratio produced in the same experiment at typical temperatures encountered at Concordia in summer. Using these lab data and the emission flux of NOx from snow estimated from the vertical gradient of atmospheric concentrations measured during the campaign, a mean diurnal HONO snow emission ranging between 0.5 and 0.8 × 109 molecules cm−2 s−1 is calculated. Model calculations indicate that, in addition to around 1.2 pptv of HONO produced by the NO oxidation, these HONO snow emissions can only explain 6.5 to 10.5 pptv of HONO in the atmosphere at Concordia. To explain the difference between observed and simulated HONO mixing ratios, tests were done both in the field and at lab to explore the possibility that the presence of HNO4 had biased the measurements of HONO.

The formation, abundance and distribution of organic nitrates are relevant for determining the production efficiency and resident mixing ratios of tropospheric ozone (O3) on both regional and global scales. Here we investigate the effect of applying the recently measured direct chemical production of methyl nitrate (CH3ONO2) during NOx recycling involving the methyl-peroxy radical on the global tropospheric distribution of CH3ONO2 and the perturbations introduced towards tropospheric NOx and O3 using the TM5 global chemistry transport model. By comparisons against numerous observations, we show that the global surface distribution of CH3ONO2 can be largely explained by introducing the chemical production mechanism using a branching ratio of 0.3%, when assuming a direct oceanic emission source of ~0.15 Tg N yr−1. On a global scale, the chemical production of CH3ONO2 converts 1 Tg N yr−1 from nitrogen oxide for this branching ratio. The resident mixing ratios of CH3ONO2 are found to be highly sensitive to the dry deposition velocity that is prescribed, where more than 50% of the direct oceanic emission is lost near the source regions, thereby mitigating the subsequent effects due to long-range and convective transport out of the source region. For the higher alkyl nitrates (RONO2) we find improvements in the simulated distribution near the surface in the tropics (10° S–10° N) when introducing direct oceanic emissions equal to ~0.17 Tg N yr−1 . In terms of the vertical profile of CH3ONO2, there are persistent overestimations in the free troposphere and underestimations in the upper troposphere across a wide range of latitudes and longitudes when compared against data from measurement campaigns. This suggests either a missing transport pathway or source/sink term, although measurements show significant variability in resident mixing ratios at high altitudes at global scale. For the vertical profile of RONO2, TM5 performs better at tropical latitudes than at mid-latitudes, with similar features in the comparisons to those for CH3ONO2. Comparisons of CH3ONO2 with a wide range of surface measurements shows that further constraints are necessary regarding the variability in the deposition terms for different land surfaces in order to improve on the comparisons presented here. For total reactive nitrogen (NOy) ~20% originates from alkyl nitrates in the tropics and subtropics, where the introduction of both direct oceanic emissions and the chemical formation mechanism of CH3ONO2 only makes a ~5% contribution to the total alkyl nitrate content in the upper troposphere when compared with aircraft observations. We find that the increases in tropospheric O3 that occur due oxidation of CH3ONO2 originating from direct oceanic emission is negated when accounting for the chemical formation of CH3ONO2, meaning that the impact of such oceanic emissions on atmospheric lifetimes becomes marginal when a branching ratio of 0.3% is adopted.

Nitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NOx, O3, photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity, wind speed and wind direction), black carbon concentration, total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h−1 and 0.25 ppb h−1, during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J(NO2) and the product between J(NO2) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground.

Chemical Ionisation Mass Spectrometer measurements of hydroxyl radical (OH) and the sum of hydroperoxy and organic peroxy (HO2+RO2) radicals were conducted during the MEGAPOLI summer field campaign at the SIRTA observatory near Paris, France, in July 2009. OH and (HO2+RO2) showed a typical diurnal variation with averaged daytime maxima values around 5×106 and 1.2×108 molecule cm−3, respectively. Simultaneously, a large number of ancillary measurements, such as NOx, O3, HONO, HCHO and other VOCs were also conducted. These data provide an opportunity to assess our understanding of the radical chemistry in a suburban environment by comparing the radical observations to calculations. First, OH mixing ratios were estimated by a simple Photo Stationary State (PSS) calculation. PSS calculations overestimate the OH mixing ratio by 50%, especially at NOx mixing ratios lower than 10 ppb, suggesting that some loss processes were missing in the calculation at low NOx. Then, a photochemical box model simulation based on the Master Chemical Mechanism (MCM) and constrained by ancillary measurements was run to calculate radical concentrations. Three different modelling procedures were tested, varying the way the unconstrained secondary species were estimated, to cope with the unavoidable lack of their measurements. They led to significant differences in simulated radical concentrations. OH and (HO2+RO2) concentrations estimated by two selected model version were compared with measurements. These versions of the model were chosen because they lead, respectively, to the higher and lower simulated radical concentrations and are thus the two extremes versions. The box model showed better results than PSS calculations, with a slight overestimation of 12% and 5%, for OH and (HO2+RO2) respectively, in average for the reference model, and an overestimation of approximately 20% for OH and an underestimation for (HO2+RO2) for the other selected model version. Thus, we can conclude from our study that OH and (HO2+RO2) radical levels agree on average with observations within the uncertainty range. Finally, an analysis of the radical budget, on a daily basis (06:00–18:00 UTC), indicates that HONO photolysis (~35%), O3 photolysis (~23%), and aldehydes and ketones photolysis (~16% for formaldehyde and 18% for others) are the main radical initiation pathways. According to the MCM modelling, the reactions of RO2 with NO2 (~19%), leading mainly to PAN formation, is a significant termination pathway in addition to the main net loss via reaction of OH with NO2 (~50%).

The main results of changing of high-strength antipenetration coatings in the result of development of the potentialities of their main component – refractory filler are given.

The technological aspects of processing and remelting of dispersed metal scrap, generated during polishing and grinding of tools made from high speed steel and carbide and lump scrap for the manufacture of drilling equipment and mining equipment are investigated.

It is shown that for improvement of physical and chemical properties of cast products, exploited inconditions of intensive contact with the abrasive environment, boron carbide of great interest.

The African Monsoon Multidisciplinary Analyses (AMMA) fourth airborne campaign was conducted in July–August 2006 to study the chemical composition of the middle and upper troposphere in West Africa with the major objective to better understand the processing of chemical emissions by the West African Monsoon (WAM) and its associated regional-scale and vertical transports. In particular, the french airborne experiment was organized around two goals. The first was to characterize the impact of Mesoscale Convective Systems (MCSs) on the ozone budget in the upper troposphere and the evolution of the chemical composition of these convective plumes as they move westward toward the Atlantic Ocean. The second objective was to discriminate the impact of remote sources of pollution over West Africa, including transport from the middle east, Europe, Asia and from southern hemispheric fires. Observations of O3, CO, NOx, H2O and hydroperoxide above West Africa along repeated meridional transects were coupled with transport analysis based on the FLEXPART lagrangian model. The cross analysis of trace gas concentrations and transport pathways revealed 5 types of air masses: convective uplift of industrial and urban emissions, convective uplift of biogenic emissions, slow advection from Cotonou polluted plumes near the coast, meridional transport of upper tropospheric air from the subtropical barrier region, and meridional transport of Southern Hemisphere (SH) biomass burning emissions. O3/CO correlation plots and the correlation plots of H2O2 with a OH proxy revealed not only a control of the trace gas variability by transport processes but also significant photochemical reactivity in the mid- and upper troposphere. The study of four MCSs outflow showed contrasted chemical composition and air mass origins depending on the MCSs lifetime and latitudinal position. Favorables conditions for ozone production were found for MCSs with increased MCS lifetime (>1.5 days), which allowed for more H2O2 formation, and with trajectories crossing the 10° N latitude, which increased CO transport to the upper troposphere. The upper tropospheric concentrations sampled in the MCS outflow regions showed mixed origins including local vertical convective transport, and uplifting of air from the low troposphere over the middle-east related to the summer Asian low pressure system or from the southern hemispheric fires.

We have studied the impact of the recently observed reaction NO+HO2→HNO3 on atmospheric chemistry. A pressure and temperature-dependent parameterisation of this minor channel of the NO+HO2→NO2+OH reaction has been included in both a 2-D stratosphere-troposphere model and a 3-D tropospheric chemical transport model (CTM). Significant effects on the nitrogen species and hydroxyl radical concentrations are found throughout the troposphere, with the largest percentage changes occurring in the tropical upper troposphere (UT). Including the reaction leads to a reduction in NOx everywhere in the troposphere, with the largest decrease of 25% in the tropical and Southern Hemisphere UT. The tropical UT also has a corresponding large increase in HNO3 of 25%. OH decreases throughout the troposphere with the largest reduction of over 20% in the tropical UT. The mean global decrease in OH is around 13%, which is very large compared to the impact that typical photochemical revisions have on this modelled quantity. This OH decrease leads to an increase in CH4 lifetime of 5%. Due to the impact of decreased NOx on the OH:HO2 partitioning, modelled HO2 actually increases in the tropical UT on including the new reaction. The impact on tropospheric ozone is a decrease in the range 5 to 12%, with the largest impact in the tropics and Southern Hemisphere. Comparison with observations shows that in the region of largest changes, i.e. the tropical UT, the inclusion of the new reaction tends to degrade the model agreement. Elsewhere the model comparisons are not able to critically assess the impact of including this reaction. Only small changes are calculated in the minor species distributions in the stratosphere.