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Plake D.,Max Planck Institute for Chemistry | Plake D.,UCL Umwelt Control Labor GmbH | Stella P.,Max Planck Institute for Chemistry | Stella P.,French National Institute for Agricultural Research | And 8 more authors.
Agricultural and Forest Meteorology

Nowadays, eddy covariance is the state-of-the-art method to quantify turbulent exchange fluxes in the surface boundary layer. In the absence of instruments suitable for high-frequency measurements, fluxes can also be determined using e.g., chamber techniques. However, up to date fluxes of depositing compounds were rarely determined using chamber techniques, mainly due to a modification of the aerodynamic conditions for the trace gas transport within the chamber. In this study, we present ozone (O3) deposition fluxes measured by the dynamic chamber technique and validate them against the eddy covariance (EC) method for a natural grassland site in Germany. The chamber system presented in Pape et al. (2009) was used and optimized to (i) reduce the likelihood of non-stationarities, (ii) yield 30min averages of flux measurements, and (iii) supply simultaneous profile measurements. The raw O3 fluxes of the dynamic chamber were corrected for gas-phase chemistry in the chamber volume and for the modification of the aerodynamic and boundary layer resistances. Simultaneously measured carbon dioxide and water vapor fluxes by both methods compared well during daytime documenting an equal vegetation activity inside and outside the chambers. The final corrected O3 deposition fluxes of both methods deviated on average by only 11% during daytime. The findings demonstrate the capability of the dynamic chamber method to capture representative O3 deposition fluxes for grassland ecosystems, even when the canopy height is similar to the chamber height. The canopy resistance to O3 was assessed by both methods and showed a characteristic diurnal cycle with minimum hourly median values of 180sm-1 (chambers) and 150sm-1 (EC) before noon. During nighttime the fluxes and resistances showed a higher uncertainty for both methods due to frequent low wind associated with non-stationary conditions at the experimental site. Canopy resistances for nitrogen dioxide (NO2) deposition were determined analogously with the chambers and were on average 86% higher than for O3. © 2015 Elsevier B.V. Source

Libra J.A.,Acatech German Academy of Science and Engineering | Ro K.S.,U.S. Department of Agriculture | Kammann C.,Justus Liebig University | Funke A.,TU Berlin | And 7 more authors.

The carbonization of biomass residuals to char has strong potential to become an environmentally sound conversion process for the production of a wide variety of products. In addition to its traditional use for the production of charcoal and other energy vectors, pyrolysis can produce products for environmental, catalytic, electronic and agricultural applications. As an alternative to dry pyrolysis, the wet pyrolysis process, also known as hydrothermal carbonization, opens up the field of potential feedstocks for char production to a range of nontraditional renewable and plentiful wet agricultural residues and municipal wastes. Its chemistry offers huge potential to influence product characteristics on demand, and produce designer carbon materials. Future uses of these hydrochars may range from innovative materials to soil amelioration, nutrient conservation via intelligent waste stream management and the increase of carbon stock in degraded soils. © 2011 Future Science Ltd. Source

Bonn B.,Goethe University Frankfurt | Bonn B.,Institute for Advanced Sustainability Studies | Bourtsoukidis E.,Goethe University Frankfurt | Bourtsoukidis E.,Max Planck Institute for Chemistry | And 15 more authors.
Atmospheric Chemistry and Physics

It has been claimed for more than a century that atmospheric new particle formation is primarily influenced by the presence of sulfuric acid. However, the activation process of sulfuric acid related clusters into detectable particles is still an unresolved topic. In this study we focus on the PARADE campaign measurements conducted during August/September 2011 at Mt Kleiner Feldberg in central Germany. During this campaign a set of radicals, organic and inorganic compounds and oxidants and aerosol properties were measured or calculated. We compared a range of organic and inorganic nucleation theories, evaluating their ability to simulate measured particle formation rates at 3 nm in diameter (J3) for a variety of different conditions. Nucleation mechanisms involving only sulfuric acid tentatively captured the observed noon-time daily maximum in J3, but displayed an increasing difference to J3 measurements during the rest of the diurnal cycle. Including large organic radicals, i.e. organic peroxy radicals (RO2) deriving from monoterpenes and their oxidation products, in the nucleation mechanism improved the correlation between observed and simulated J3. This supports a recently proposed empirical relationship for new particle formation that has been used in global models. However, the best match between theory and measurements for the site of interest was found for an activation process based on large organic peroxy radicals and stabilised Criegee intermediates (sCI). This novel laboratory-derived algorithm simulated the daily pattern and intensity of J3 observed in the ambient data. In this algorithm organic derived radicals are involved in activation and growth and link the formation rate of smallest aerosol particles with OH during daytime and NO3 during night-time. Because the RO2 lifetime is controlled by HO2 and NO we conclude that peroxy radicals and NO seem to play an important role for ambient radical chemistry not only with respect to oxidation capacity but also for the activation process of new particle formation. This is supposed to have significant impact of atmospheric radical species on aerosol chemistry and should be taken into account when studying the impact of new particles in climate feedback cycles. © Author(s) 2014. Source

Bourtsoukidis E.,Max Planck Institute for Chemistry | Bourtsoukidis E.,Goethe University Frankfurt | Bonn B.,Goethe University Frankfurt | Dittmann A.,Goethe University Frankfurt | And 3 more authors.

Sesquiterpenes (C15H24) are semi-volatile organic compounds emitted by vegetation and are of interest in atmospheric research because they influence the oxidative capacity of the atmosphere and contribute to the formation of secondary organic aerosols. However, little is known about their emission pattern and no established parameterisation is available for global emission models. The aim of this study is to investigate a Central European spruce forest and its emission response to meteorological and environmental parameters, looking for a parameterisation that incorporates heat and oxidative stress as the main driving forces of the induced emissions. Therefore, a healthy ca. 80 yr old Norway spruce (Picea abies) tree was selected and a dynamical vegetation enclosure technique was applied from April to November 2011. The emissions clearly responded to temperature changes with small variations in the β-factor along the year (βspring =0.09±0.01, βsummer =0.12±0.02, βautumn =0.11±0.02). However, daily calculated values revealed a vast amount of variability in temperature dependencies ((0.02±0.002)< β < (0.27±0.04)) with no distinct seasonality. By separating the complete dataset in 10 different ozone regimes, we found that in moderately or less polluted atmospheric conditions the main driving force of sesquiterpene emissions is the temperature, but when ambient ozone mixing ratios exceed a critical threshold of (36.6±3.9) ppb v, the emissions become primarily correlated with ozone. Considering the complete dataset, cross correlation analysis resulted in highest correlation with ambient ozone mixing ratios (CCO3 =0.63±0.01; CC T = 0.47±0.02 at t =0 h for temperature) with a time shift 2-4 h prior to the emissions. An only temperature dependent algorithm was found to substantially underestimate the induced emissions (20% of the measured; R 2 =0.31). However, the addition of an ozone dependent term improved substantially the fitting between measured and modelled emissions (81% of the modelled emissions could be explained by the measurements; R2 =0.63), providing confidence about the reliability of the suggested parameterisation for the spruce forest site investigated. © Author(s) 2012. Source

Homuth B.,Goethe University Frankfurt | Rumpker G.,Goethe University Frankfurt | Deckert H.,Bingen University of Applied Sciences | Kracht M.,Hessian Agency for the Environment and Geology

We present new results for the microseismic activity in the northern Upper Rhine Graben by analyzing seismogram recordings from two temporary networks of up to 13 broad-band stations in combination with data from permanent stations. Previous studies have mainly focused on the southern and intermediate sections of the Upper Rhine Graben, where the station coverage by regional networks is more dense. Between October 2010 and September 2013 we recorded 56 earthquakes that occurred within the immediate vicinity of the northern Upper Rhine Graben with local magnitudes ranging from 0.5 to 3.2. The majority of the hypocenters are located beneath the eastern graben shoulder and in the graben itself, while activity observed along the western graben shoulder is lower. A further active region is located along the southern rim of the Taunus Mountains to the northwest of the study area. The seismicity extends to a depth of 25. km; the hypocentral depth distribution exhibits a pronounced peak of seismic energy release in the depth range between 12 and 18. km. Fault plane solutions for a total of 58 earthquakes (including data from previous recordings) were derived from P-polarities and SV/P amplitude ratios. This new data set more than quadruples the number of available data for regional stress field analysis. The majority of the focal mechanisms show predominantly strike-slip movements; only a few events are of reverse or normal-faulting type. T-axis trends are oriented NE-SW. The calculated focal mechanisms presented in this study confirm that the area is in transtension, however, in contrast to previous studies, a stronger strike-slip component is identified. We also derived the azimuths of the principal stress axes by inverting the fault plane solutions and calculated the direction of the maximum horizontal stress, which is mainly oriented N135°E. © 2014 Elsevier B.V. Source

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