Direct measurement of NO3 radical reactivity in a boreal forest

We present the first direct measurements of NO3 reactivity (or inverse lifetime, s(-1))in the Finnish boreal forest. The data were obtained during the IBAIRN campaign (Influence of Biosphere-Atmosphere Interactions on the Reactive Nitrogen budget) which took place in Hyytiala, Finland during the summer/autumn transition in September 2016. The NO3 reactivity was generally very high with a maximum value of 0.94 s(-1) and displayed a strong diel variation with a campaign-averaged nighttime mean value of 0.11 s(-1) compared to a daytime value of 0.04 s(-1). The highest nighttime NO3 reactivity was accompanied by major depletion of canopy level ozone and was associated with strong temperature inversions and high levels of monoterpenes. The daytime reactivity was sufficiently large that reactions of NO3 with organic trace gases could compete with photolysis and reaction with NO. There was no significant reduction in the measured NO3 reactivity between the beginning and end of the campaign, indicating that any seasonal reduction in canopy emissions of reactive biogenic trace gases was offset by emissions from the forest floor. Observations of biogenic hydrocarbons (BVOCs) suggested a dominant role for monoterpenes in determining the NO3 reactivity. Reactivity not accounted for by in situ measurement of NO and BVOCs was variable across the diel cycle with, on average, approximate to 30% "missing" during nighttime and approximate to 60% missing during the day. Measurement of the NO3 reactivity at various heights (8.5 to 25 m) both above and below the canopy, revealed a strong nighttime, vertical gradient with maximum values closest to the ground. The gradient disappeared during the daytime due to efficient vertical mixing.Peer reviewe

Alkyl nitrates in the boreal forest : formation via the NO3-, OH- and O-3-induced oxidation of biogenic volatile organic compounds and ambient lifetimes

The formation of alkyl nitrates in various oxidation processes taking place throughout the diel cycle can represent an important sink of reactive nitrogen and mechanism for chain termination in atmospheric photo-oxidation cycles. The low-volatility alkyl nitrates (ANs) formed from biogenic volatile organic compounds (BVOCs), especially terpenoids, enhance rates of production and growth of secondary organic aerosol. Measurements of the NO3 reactivity and the mixing ratio of total alkyl nitrates (6 ANs) in the Finnish boreal forest enabled assessment of the relative importance of NO3-, O-3- and OH-initiated formation of alkyl nitrates from BVOCs in this environment. The high reactivity of the forest air towards NO3 resulted in reactions of the nitrate radical, with terpenes contributing substantially to formation of ANs not only during the night but also during daytime. Overall, night-time reactions of NO3 accounted for 49% of the local production rate of ANs, with contributions of 21 %, 18% and 12% for NO3, OH and O-3 during the day. The lifetimes of the gas-phase ANs formed in this environment were on the order of 2 h due to efficient uptake to aerosol (and dry deposition), resulting in the transfer of reactive nitrogen from anthropogenic sources to the forest ecosystem.Peer reviewe

Pyruvic acid in the boreal forest : gas-phase mixing ratios and impact on radical chemistry

Pyruvic acid (CH3C(O)C(O)OH, 2-oxopropanoic acid) is an organic acid of biogenic origin that plays a crucial role in plant metabolism, is present in tropospheric air in both gas-phase and aerosol-phase, and is implicated in the formation of secondary organic aerosols (SOAs). Up to now, only a few field studies have reported mixing ratios of gas-phase pyruvic acid, and its tropospheric sources and sinks are poorly constrained. We present the first measurements of gas-phase pyruvic acid in the boreal forest as part of the IBAIRN (Influence of Biosphere–Atmosphere Interactions on the Reactive Nitrogen budget) field campaign in Hyytiälä, Finland, in September 2016. The mean pyruvic acid mixing ratio during IBAIRN was 96 pptv, with a maximum value of 327 pptv. From our measurements we estimated the overall pyruvic acid source strength and quantified the contributions of isoprene oxidation and direct emissions from vegetation in this monoterpene-dominated forested environment. Further, we discuss the relevance of gas-phase pyruvic acid for atmospheric chemistry by investigating the impact of its photolysis on acetaldehyde and peroxy radical production rates. Our results show that, based on our present understanding of its photochemistry, pyruvic acid is an important source of acetaldehyde in the boreal environment, exceeding ethane and propane oxidation by factors of ∼10 and ∼20.Pyruvic acid (CH3C(O)C(O)OH, 2-oxopropanoic acid) is an organic acid of biogenic origin that plays a crucial role in plant metabolism, is present in tropospheric air in both gas-phase and aerosol-phase, and is implicated in the formation of secondary organic aerosols (SOAs). Up to now, only a few field studies have reported mixing ratios of gas-phase pyruvic acid, and its tropospheric sources and sinks are poorly constrained. We present the first measurements of gas-phase pyruvic acid in the boreal forest as part of the IBAIRN (Influence of Biosphere-Atmosphere Interactions on the Reactive Nitrogen budget) field campaign in Hyytiala, Finland, in September 2016. The mean pyruvic acid mixing ratio during IBAIRN was 96 pptv, with a maximum value of 327 pptv. From our measurements we estimated the overall pyruvic acid source strength and quantified the contributions of isoprene oxidation and direct emissions from vegetation in this monoterpene-dominated forested environment. Further, we discuss the relevance of gas-phase pyruvic acid for atmospheric chemistry by investigating the impact of its photolysis on acetaldehyde and peroxy radical production rates. Our results show that, based on our present understanding of its photochemistry, pyruvic acid is an important source of acetaldehyde in the boreal environment, exceeding ethane and propane oxidation by factors of similar to 10 and similar to 20.Peer reviewe

ClNO2 and nitrate formation via N2O5 uptake to particles: Derivation of N2O5 uptake coefficients from ambient datasets

Oral presentation abstract given at EGU General Assembly 2015.We present estimates of the uptake coefficient of N2O5 using ambient measurements of the trace gases N2O5 and ClNO2 and particle composition and surface area at the Kleiner Feldberg observatory, near Frankfurt, SW Germany, during the PARADE campaign (summer 2011). Three methods used to extract gamma(N2O5) from the datasets were found to be in reasonable agreement, generating values between 0.001 and 0.4. Gamma (N2O5) displayed a significant dependence on relative humidity (RH), the largest values obtained, as expected, at high RH. No significant dependence of gamma(N2O5) on particle organic content or sulphate-to-organic ratio was observed. The variability in gamma(N2O5) is however large, indicating that humidity is not the sole factor determining the uptake coefficient. There is also an indication that the yield of ClNO2 with respect to N2O5 uptake is larger with lower concentrations of PM1 total organics. Our results will be compared to existing uptake coefficients from laboratory studies and those derived from field observations.Max Planck Societ

Racial differences in systemic sclerosis disease presentation: a European Scleroderma Trials and Research group study

Objectives. Racial factors play a significant role in SSc. We evaluated differences in SSc presentations between white patients (WP), Asian patients (AP) and black patients (BP) and analysed the effects of geographical locations.Methods. SSc characteristics of patients from the EUSTAR cohort were cross-sectionally compared across racial groups using survival and multiple logistic regression analyses.Results. The study included 9162 WP, 341 AP and 181 BP. AP developed the first non-RP feature faster than WP but slower than BP. AP were less frequently anti-centromere (ACA; odds ratio (OR) = 0.4, P < 0.001) and more frequently anti-topoisomerase-I autoantibodies (ATA) positive (OR = 1.2, P = 0.068), while BP were less likely to be ACA and ATA positive than were WP [OR(ACA) = 0.3, P < 0.001; OR(ATA) = 0.5, P = 0.020]. AP had less often (OR = 0.7, P = 0.06) and BP more often (OR = 2.7, P < 0.001) diffuse skin involvement than had WP.AP and BP were more likely to have pulmonary hypertension [OR(AP) = 2.6, P < 0.001; OR(BP) = 2.7, P = 0.03 vs WP] and a reduced forced vital capacity [OR(AP) = 2.5, P < 0.001; OR(BP) = 2.4, P < 0.004] than were WP. AP more often had an impaired diffusing capacity of the lung than had BP and WP [OR(AP vs BP) = 1.9, P = 0.038; OR(AP vs WP) = 2.4, P < 0.001]. After RP onset, AP and BP had a higher hazard to die than had WP [hazard ratio (HR) (AP) = 1.6, P = 0.011; HR(BP) = 2.1, P < 0.001].Conclusion. Compared with WP, and mostly independent of geographical location, AP have a faster and earlier disease onset with high prevalences of ATA, pulmonary hypertension and forced vital capacity impairment and higher mortality. BP had the fastest disease onset, a high prevalence of diffuse skin involvement and nominally the highest mortality

Advances in High-Precision NO2 Measurement by Quantum Cascade Laser Absorption Spectroscopy

Nitrogen dioxide (NO2) is a major tropospheric air pollutant. Its concentration in the atmosphere is most frequently monitored indirectly by chemiluminescence detection or using direct light absorption in the visible range. Both techniques are subject to known biases from other trace gases (including water vapor), making accurate measurements at low concentration very challenging. Selective measurements of NO2 in the mid-infrared have been proposed as a promising alternative, but field deployments and comparisons with established techniques remain sparse. Here, we describe the development and validation of a quantum cascade laser-based spectrometer (QCLAS). It relies on a custom-made astigmatic multipass absorption cell and a recently developed low heat dissipation laser driving and a FPGA based data acquisition approach. We demonstrate a sub-pptv precision (1 σ) for NO2 after 150 s integration time. The instrument performance in terms of long-term stability, linearity and field operation capability was assessed in the laboratory and during a two-week inter-comparison campaign at a suburban air pollution monitoring station. Four NO2 instruments corresponding to three different detection techniques (chemiluminescence detection (CLD), cavity-attenuated phase shift (CAPS) spectroscopy and QCLAS) were deployed after calibrating them with three different referencing methods: gas-phase titration of NO, dynamic high-concentration cylinder dilution and permeation. These measurements show that QCLAS is an attractive alternative for high-precision NO2 monitoring. Used in dual-laser configuration, its capabilities can be extended to NO, thus allowing for unambiguous quantification of nitrogen oxides (NOx), which are of key importance in air quality assessments

Investigation of day- and night-time NOx/VOCs coupling using thermal dissociation cavity ring-down spectroscopy

Reactive nitrogen species, so called NOy, are a class of compounds involved in different atmospheric cycles that impact the global distribution of atmospheric trace gases. The NOz group of compoundswhose precursors are NOx (NO + NO2), includes short lived species like NO3, HONO, RO2NO2, ClNO2 and longer lived species like N2O5, HNO3, R(O)O2NO2 and RONO2. The fate of NOy (NOx + NOz) in the lowest layer of the atmosphere, the planetary boundary layer, has a strong influence on ozone levels, on HOx (OH + HO2 +RO2 ) species and on aerosol particles composition. The destruction of NOx through processes other than NO2 photolysis (which produces NO) like conversion to NOz and subsequent removal by dry or wet deposition, results in a decrease of the global ozone production. This thesis investigates atmospheric levels, lifetimes and production rates of different NOy species in the field using thermal dissociation cavity ring-down spectroscopy (abbreviated as TD-CRDS). Results using existing instruments and an instrument developed in the frame of this work are presented. The first chapter reports the current knowledge on NOy chemistry and describe the research objectives of this work. Chapter 2 describes the design and performances of a newly developed 5 channel TD-CRDS based instrument to measure NO2, NO3, N2O5, the sum peroxy nitrates (ƩRO2NO2, abbreviated as ƩPNs) and the sum of alkyl nitrates (ƩRONO2,abbreviated as ƩANs). We show that this method allows for precise measurement of those reactive nitrogen species at high time resolution and with a good accuracy. A number of design improvements compared to previously developed similar instruments which reduce the measurement uncertainties and facilitate field deployment are detailed. Chapter 3 reports field observations during two campaigns that took place in 2011 and 2015 on top of the “Kleiner Feldberg” mountain near Frankfurt am Main (Germany). NO3 mixing ratios and estimated lifetimes are analysed in regard to meteorological and chemical influences. It is demonstrated that the measurement site is occasionally sampling from the nocturnal residual layer which result in very high steady state NO3 lifetimes (up to 1 hour) which is unusual for ground based measurements. The estimated lifetimes assuming steady state are compared to the NO3 reactivity calculated using VOCs measurements (by GC-FID and GC-MS) and NO measurements (by CLD) and significant discrepancies are found. An unaccounted source of NO3 through the oxidation of NO2 by Stabilized Criegee Intermediates (SCIs) as well as the influence of the local topography are considered as the potential causes of the observed differences. In this chapter are also reported the measured mixing ratios and calculated production rates of organic nitrates during both campaign. The differences in lifetimes between OH and NO3 generated organic nitrates are discussed. The nitrogen partitioning ratio between organic nitrates (ƩPNs + ƩANs) and NOx is reported and found to depend on NOx and temperature and to be as high as 80 % in aged, warm air masses. Finally the effective yield of alkyl nitrates for the PARADE campaign is estimated using O3 and ƩANs mixing ratios and is found to match well the calculated yield based on VOCs measurements and individual alkyl nitrates yields reported in the literature. The general conclusions of this work are presented in Chapter 4.Reaktive Stickstoffverbindungen, sogenannte NOy, sind eine Klasse von Stoffen, die in verschiedenen atmosphärischen Kreisläufen die globale Verteilung von Spurengasen beeinflussen. Die Gruppe der NOz, gebildet aus NOx (NO+NO2), beinhaltet kurzlebige Verbindungen wie z.B. NO3, HONO, RO2NO2, ClNO2 aber auch langlebigere Verbindungen wie N2O5, HNO3, R(O)O2NO2 and RONO2. Das Schicksal von NOy (NOx+NOz) in der niedrigsten Schicht der Atmosphäre, der sogenannten Grenzschicht (boundary layer), hat einen starken Einfluss auf Ozon Mischverhältnisse, auf HOx Verbindungen (OH+HO2+RO2) und auf die Zusammensetzung von Aerosolen. Von der Photolyse von NO2 abgesehen, die zur Bildung von NO führt, führen die Zersetzung von NOx sowie die die Umwandlung zu NOz und der nachfolgende Entzug aus der Atmosphäre durch trockene oder nasse Ablagerung zu einem Absinken der globalen Ozon Produktion. Diese Doktorarbeit untersucht die atmosphärischen Konzentrationen, Lebenszeiten und Produktionsraten von verschiedenen NOy Verbindungen mit einer 5 Kanal, Laserabsorption Methode (Thermal Dissociation Cavity Ring-Down Spectroscopy (TD-CRDS)) in Feldmessungen. Die Ergebnisse unter Verwendung eines bereits existierenden, sowie eines neu entwickelten Instruments, werden im Rahmen dieser Arbeit präsentiert. Das erste Kapitel legt das derzeitige Wissen über NOy Chemie dar und beschreibt die Forschungsziele dieser Arbeit. Das zweite Kapitel beschreibt den Aufbau und die Leistung des neu entwickelten TD-CRDS um NO2, NO3, N2O5 sowie die Summe der Peroxynitrate (ƩRO2NO2) und die Summe der Alkylnitrate (ƩRONO2) zu messen. Wir demonstrieren, dass diese Methode genaue Messungen von reaktiven Stickstoffverbindugen mit guter Zeitauflösung und hoher Genauigkeit erlaubt. Weiterhin werden einige Verbesserungen zu bisher entwickelten Instrumenten aufgezeigt, welche Unsicherheiten in den Messungen reduzieren und gleichermaßen die Verwendung dieser Instrumente in Feldexperimenten erleichtern. In Kapitel 3 wird von 2 Feldmesskampagnen berichtet, die 2011 und 2015 auf dem Plateu des kleinen Feldbergs in der Nähe von Frankfurt (Deutschland) stattfanden. Im ersten Teil wird das Verhalten von NO3 Mischverhältnissen und Lebenszeiten mit Hinsicht auf meterologische und chemischen Einflüsse analysiert. Es wird gezeigt, dass dieser Messort gelegentlich Luftmassen aus der nächtlichen Restschicht (nocturnal residual layer) erhält, was zu sehr langen steady state NO3 Lebenszeiten (bis zu einer Stunde) führt, wie sie für bodenbasierte Messungen sehr ungewöhlich sind. Die steady state Lebenszeiten werden Reaktivitäten, berechnet aus VOC-Messungen (durch GC-FID und GC-MS) und NO Messungen (durch CLD), verglichen und es werden signifikante Unterschiede gefunden. Die Oxidation von NO2 durch stabilisierte Criegee Intermediate (SCIs) als Quelle von NO3 aber auch der Einfluss der lokalen Toopographie werden als mögliche Gründe für die beobachteten Unterschiede zwischen steady State und berechneten NO3 Lebenszeiten angenommen. In diesem Kapitel werden auch die gemessenen Mischverhältnisse und berechneten Produktionsraten von organischen Nitraten während der beiden Kampagnen beschrieben. Es werden zudem die unterschiedliche Lebensdauer dieser organischen Nitrate in Abhängigkeit ihrer Bildung durch OH oder NO3 diskutiert. Die Daten zeigen, dass die organische Nitrate bis 80 % der NOx Konzentration erreichen kann und dass die Partitionierung von [NOx] und von der Temperatur abhängig ist. Zuletzt wird die effektive Ausbeute von Alkylnitraten für die PARADE Kampagne, auf Grundlage der Ozon und RONO2 Mischverhältnisse, geschätzt. Diese steht in guter Übereinstimmung mit den berechneten Ausbeuten basierend auf den VOC Messungen und individuellen Alkylnitratausbeuten wie in der Literatur beschrieben. Die Schlussfolgerungen dieser Arbeit, sowie ein Ausblick und weitere mögliche Ansätze für zukünftige Arbeiten werden in Kapitel 4 beschrieben

Severe toxoplasmosis in immunocompetent hosts: be aware of atypical strains.

International audienc

A High-Precision Mid-Infrared Spectrometer for Ambient HNO₃ Measurements

Precise and accurate measurements of ambient HNO3 are crucial for understanding various atmospheric processes, but its ultra-low trace amounts and the high polarity of HNO3 have strongly hindered routine, widespread, direct measurements of HNO3 and restricted field studies to mostly short-term, localized measurement campaigns. Here, we present a custom field-deployable direct absorption laser spectrometer and demonstrate its analytical capabilities for in situ atmospheric HNO3 measurements. Detailed laboratory characterizations with a particular focus on the instrument response under representative conditions for tropospheric measurements, i.e., the humidity, spectral interference, changing HNO3 amount fractions, and air-sampling-related artifacts, revealed the key aspects of our method: (i) a good linear response (R2 > 0.98) between 0 and 25 nmol·mol−1 in both dry and humid conditions with a limit of detection of 95 pmol·mol−1; (ii) a discrepancy of 20% between the spectroscopically derived amount fractions and indirect measurements using liquid trapping and ion chromatography; (iii) a systematic spectral bias due to water vapor. The spectrometer was deployed in a three-week field measurement campaign to continuously monitor the HNO3 amount fraction in ambient air. The measured values varied between 0.1 ppb and 0.8 ppb and correlated well with the daily total nitrates measured using a filter trapping method

Impact of Three Different Algorithms for the Screening of SSc-PAH and Comparison with the Decisions of a Multidisciplinary Team

International audienceBackground: to compare three existing screening algorithms of pulmonary arterial hypertension (PAH) in systemic sclerosis (SSc) with the results of a multidisciplinary team (MDT) meeting from a tertiary center. Methods: we conducted a monocentric longitudinal study from 2015 to 2018. All patients with SSc according to LeRoy’s classification were eligible. Patients were excluded in the case of missing data required by any of the three screening algorithms. The algorithms were applied for each patient at inclusion. Right heart catheterization (RHC) was performed based on the MDT decision. MDT members were all blinded from the results of the three algorithms regarding RHC recommendations. The RHC recommendations of each algorithm were compared with the MDT decision, and the impact on diagnosis and management was evaluated. Results: 117 SSc patients were consecutively included in the study, and 99 had follow-up data over the three-year duration of the study (10 deaths). Among the 117 patients, the MDT suggested RHC for 16 patients (14%), DETECT algorithm for 28 (24%), ASIG for 48 (41%) and ESC/ERS 2015 for 20 (17%). Among the 16 patients who had RHC, SSc-PAH was diagnosed in seven. Among patients with an initial recommendation of RHC based on at least one algorithm but not according to the MDT meeting, no SSc-PAH was diagnosed during the three-year follow-up. Results were unchanged when the new 2018 definition of PAH was applied instead of the previous definition. Conclusion: a MDT approach appears interesting for the screening of SSc-PAH, with a significant reduction of RHC performed in comparison with dedicated algorithms. The specific relevance of a MDT for the management and follow-up of patients with RHC recommended by existing algorithms but with no PAH warrants further studies