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Photochemical processes in ambient air were studied using the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich, Germany. Ambient air was continuously drawn into the chamber through a 50 m high inlet line and passed through the chamber for 1 month in each season throughout 2019. The residence time of the air inside the chamber was about 1 h. As the research center is surrounded by a mixed deciduous forest and is located close to the city Jülich, the sampled air was influenced by both anthropogenic and biogenic emissions. Measurements of hydroxyl (OH), hydroperoxyl (HO 2), and organic peroxy (RO 2) radicals were achieved by a laser-induced fluorescence instrument. The radical measurements together with measurements of OH reactivity (kOH , the inverse of the OH lifetime) and a comprehensive set of trace gas concentrations and aerosol properties allowed for the investigation of the seasonal and diurnal variation of radical production and destruction pathways. In spring and summer periods, median OH concentrations reached 6 × 10 6 cm -3 at noon, and median concentrations of both HO 2 and RO 2 radicals were 3 × 10 8 cm -3. The measured OH reactivity was between 4 and 18 s -1 in both seasons. The total reaction rate of peroxy radicals with NO was found to be consistent with production rates of odd oxygen (O x= NO 2+ O 3) determined from NO 2 and O 3 concentration measurements. The chemical budgets of radicals were analyzed for the spring and summer seasons, when peroxy radical concentrations were above the detection limit. For most conditions, the concentrations of radicals were mainly sustained by the regeneration of OH via reactions of HO 2 and RO 2 radicals with nitric oxide (NO). The median diurnal profiles of the total radical production and destruction rates showed maxima between 3 and 6 ppbv h -1 for OH, HO 2 , and RO 2. Total RO X (OH, HO 2 , and RO 2) initiation and termination rates were below 3 ppbv h -1. The highest OH radical turnover rate of 13 ppbv h -1 was observed during a high-temperature (max. 40 ∘ C) period in August. In this period, the highest HO 2 , RO 2 , and RO X turnover rates were around 11, 10, and 4 ppbv h -1 , respectively. When NO mixing ratios were between 1 and 3 ppbv, OH and HO 2 production and destruction rates were balanced, but unexplained RO 2 and RO X production reactions with median rates of 2 and 0.4 ppbv h -1 , respectively, were required to balance their destruction. For NO mixing ratios above 3 ppbv, the peroxy radical reaction rates with NO were highly uncertain due to the low peroxy radical concentrations close to the limit of NO interferences in the HO 2 and RO 2 measurements. For NO mixing ratios below 1 ppbv, a missing source for OH and a missing sink for HO 2 were found with maximum rates of 3.0 and 2.0 ppbv h -1 , respectively. The missing OH source likely consisted of a combination of a missing inter-radical HO 2 to OH conversion reaction (up to 2 ppbv h -1) and a missing primary radical source (0.5–1.4 ppbv h -1). The dataset collected in this campaign allowed analyzing the potential impact of OH regeneration from RO 2 isomerization reactions from isoprene, HO 2 uptake on aerosol, and RO 2 production from chlorine chemistry on radical production and destruction rates. These processes were negligible for the chemical conditions encountered in this study. [ABSTRACT FROM AUTHOR]

GANDALF (Gas Analyzer for Nitrogen Dioxide Applying Laser-induced Fluorescence), a new instrument for the detection of nitrogen dioxide based on the laser-induced fluorescence (LIF) technique, is presented in this paper. GANDALF is designed for ground-based and airborne deployment with a robust calibration system. In the current set-up, it uses a multi-mode diode laser (447–450 nm) and performs in situ, continuous, and autonomous measurements with a laser pulse repetition rate of 5 MHz. The performance of GANDALF was tested during the summer of year 2011 (15 August–10 September) in a field experiment at Kleiner Feldberg, Germany. The location is within a forested region with an urban influence, where NOx levels were between 0.12 and 22 parts per billion by volume (ppb). Based on the field results, the limit of detection is estimated at 5–10 parts per trillion by volume (ppt) in 60 s at a signal-to-noise ratio (SNR) of 2. The overall accuracy and precision of the instrument are better than 5 % (1 σ) and 0.5%+3 ppt (1 σ min-1), respectively. A comparison of nitrogen dioxide measurements based on several techniques during the field campaign PARADE 2011 is presented to explore methodic differences. [ABSTRACT FROM AUTHOR]

Atmospheric measurements of hydroxyl radicals (OH) are challenging due to a high reactivity and consequently low concentration. The importance of OH as an atmospheric oxidant has motivated a sustained effort leading to the development of a number of highly sensitive analytical techniques. Recent work has indicated that the laser-induced fluorescence of the OH molecules method based on the fluorescence assay by gas expansion technique (LIF-FAGE) for the measurement of atmospheric OH in some environments may be influenced by artificial OH generated within the instrument, and a chemical method to remove this interference was implemented in a LIF-FAGE system by Mao et al. (2012). While it is not clear whether other LIF-FAGE instruments suffer from the same interference, we have applied this method to our LIF-FAGE HORUS (Hydroxyl Radical Measurement Unit based on fluorescence Spectroscopy) system, and developed and deployed an inlet pre-injector (IPI) to determine the chemical zero level in the instrument via scavenging the ambient OH radical. We describe and characterise this technique in addition to its application at field sites in forested locations in Finland, Spain and Germany. Ambient measurements show that OH generated within the HORUS instrument is a non-negligible fraction of the total OH signal, which can comprise 30 to 80% during daytime and 60 to 100% during the night. The contribution of the background OH varied greatly between measurement sites and was likely related to the type and concentration of volatile organic compounds (VOCs) present at each particular location. Two inter-comparisons in contrasting environments between the HORUS instrument and two different chemical ionisation mass spectrometers (CIMS) are described to demonstrate the efficacy of IPI and the necessity of the chemical zeroing method for our LIF-FAGE instrument in such environments. [ABSTRACT FROM AUTHOR]

Cryogenic time-resolved laser-induced fluorescence spectroscopy was successfully used to identify uranium binding forms in selected German mineral waters of extremely low uranium concentrations (<2.0 μg/L). The measurements were performed at a low temperature of 153 K. The spectroscopic data showed a prevalence of aquatic species Ca 2UO 2(CO 3) 3 in all investigated waters, while other uranyl–carbonate complexes, viz, UO 2CO 3(aq) and UO 2(CO 3) 22−, only existed as minor species. The pH value, alkalinity (CO 32−), and the main water inorganic constituents, specifically the Ca 2+ concentration, showed a clear influence on uranium speciation. Speciation modeling was performed using the most recent thermodynamic data for aqueous complexes of uranium. The modeling results for the main uranium binding form in the investigated waters indicated a good agreement with the spectroscopy measurements. [ABSTRACT FROM AUTHOR]

Membrane treatment can be used to selectively remove chemical species, such as uranium complexes from mine effluent. However, uranium speciation depends on different chemical factors such as inorganic and organic reaction partners, temperature, and pH, complicating a deeper understanding of the underlying mechanisms. Currently, membrane separation is not employed in the treatment of uranium-bearing effluent from the former uranium mines in Germany. In this study the potential of membrane separation for selective uranium removal was assessed for two real water samples. Speciation for such complex chemical conditions was determined with two independent methods in parallel: predictive modeling using the speciation codes "PhreeqC" and "EQ3/6", and direct measurement using cryo-TRLFS (time-resolved laser-induced fluorescence spectroscopy). Different nanofiltration membranes and reverse osmosis membranes were characterized in a first step, for their potential rejection, and pure water flux. The best performing membrane was then employed in cross-flow experiments and reached retentions over 99% and U/Na-selectivities of 200. Uranium retentions showed a low dependency on feed uranium speciation. Continuing research is necessary for an exact determination of separation mechanisms for each membrane. [ABSTRACT FROM AUTHOR]