@article{FuchsDornBachneretal.2012, author = {Fuchs, H. and Dorn, Hans-Peter and Bachner, M. and Bohn, Birger and Brauers, Theo and Gomm, S. and Hofzumahaus, A. and Holland, F. and Nehr, Sascha and Rohrer, F. and Tillmann, R. and Wahner, A.}, title = {Comparison of OH concentration measurements by DOAS and LIF during SAPHIR chamber experiments at high OH reactivity and low NO concentration}, series = {Atmospheric Measurement Techniques}, volume = {5}, journal = {Atmospheric Measurement Techniques}, number = {7}, publisher = {Copernicus}, issn = {1867-8548}, doi = {10.5194/amt-5-1611-2012}, pages = {1611 -- 1626}, year = {2012}, abstract = {Abstract. During recent field campaigns, hydroxyl radical (OH) concentrations that were measured by laser-induced fluorescence (LIF) were up to a factor of ten larger than predicted by current chemical models for conditions of high OH reactivity and low NO concentration. These discrepancies, which were observed in forests and urban-influenced rural environments, are so far not entirely understood. In summer 2011, a series of experiments was carried out in the atmosphere simulation chamber SAPHIR in J{\"u}lich, Germany, in order to investigate the photochemical degradation of isoprene, methyl-vinyl ketone (MVK), methacrolein (MACR) and aromatic compounds by OH. Conditions were similar to those experienced during the PRIDE-PRD2006 campaign in the Pearl River Delta (PRD), China, in 2006, where a large difference between OH measurements and model predictions was found. During experiments in SAPHIR, OH was simultaneously detected by two independent instruments: LIF and differential optical absorption spectroscopy (DOAS). Because DOAS is an inherently calibration-free technique, DOAS measurements are regarded as a reference standard. The comparison of the two techniques was used to investigate potential artifacts in the LIF measurements for PRD-like conditions of OH reactivities of 10 to 30 s-1 and NO mixing ratios of 0.1 to 0.3 ppbv. The analysis of twenty experiment days shows good agreement. The linear regression of the combined data set (averaged to the DOAS time resolution, 2495 data points) yields a slope of 1.02 ± 0.01 with an intercept of (0.10 ± 0.03) × 106 cm-3 and a linear correlation coefficient of R2 = 0.86. This indicates that the sensitivity of the LIF instrument is well-defined by its calibration procedure. No hints for artifacts are observed for isoprene, MACR, and different aromatic compounds. LIF measurements were approximately 30-40\% (median) larger than those by DOAS after MVK (20 ppbv) and toluene (90 ppbv) had been added. However, this discrepancy has a large uncertainty and requires further laboratory investigation. Observed differences between LIF and DOAS measurements are far too small to explain the unexpected high OH concentrations during the PRIDE-PRD2006 campaign.}, language = {en} } @article{FuchsBohnHofzumahausetal.2011, author = {Fuchs, H. and Bohn, Birger and Hofzumahaus, A. and Holland, F. and Lu, K. D. and Nehr, Sascha and Rohrer, F. and Wahner, A.}, title = {Detection of HO2 by laser-induced fluorescence: calibration and interferences from RO2 radicals}, series = {Atmospheric Measurement Techniques}, volume = {4}, journal = {Atmospheric Measurement Techniques}, number = {6}, publisher = {Copernicus}, issn = {1867-8548}, doi = {10.5194/amt-4-1209-2011}, pages = {1209 -- 1225}, year = {2011}, abstract = {Abstract. HO2 concentration measurements are widely accomplished by chemical conversion of HO2 to OH including reaction with NO and subsequent detection of OH by laser-induced fluorescence. RO2 radicals can be converted to OH via a similar radical reaction sequence including reaction with NO, so that they are potential interferences for HO2 measurements. Here, the conversion efficiency of various RO2 species to HO2 is investigated. Experiments were conducted with a radical source that produces OH and HO2 by water photolysis at 185 nm, which is frequently used for calibration of LIF instruments. The ratio of HO2 and the sum of OH and HO2 concentrations provided by the radical source was investigated and was found to be 0.50 ± 0.02. RO2 radicals are produced by the reaction of various organic compounds with OH in the radical source. Interferences via chemical conversion from RO2 radicals produced by the reaction of OH with methane and ethane (H-atom abstraction) are negligible consistent with measurements in the past. However, RO2 radicals from OH plus alkene- and aromatic-precursors including isoprene (mainly OH-addition) are detected with a relative sensitivity larger than 80 \% with respect to that for HO2 for the configuration of the instrument with which it was operated during field campaigns. Also RO2 from OH plus methyl vinyl ketone and methacrolein exhibit a relative detection sensitivity of 60 \%. Thus, previous measurements of HO2 radical concentrations with this instrument were biased in the presence of high RO2 radical concentrations from isoprene, alkenes or aromatics, but were not affected by interferences in remote clean environment with no significant emissions of biogenic VOCs, when the OH reactivity was dominated by small alkanes. By reducing the NO concentration and/or the transport time between NO addition and OH detection, interference from these RO2 species are suppressed to values below 20 \% relative to the HO2 detection sensitivity. The HO2 conversion efficiency is also smaller by a factor of four, but this is still sufficient for atmospheric HO2 concentration measurements for a wide range of conditions.}, language = {en} } @article{WannekNehrVahlenkampetal.2009, author = {Wannek, C. and Nehr, Sascha and Vahlenkamp, M. and Mergel, J. and Stolten, D.}, title = {Pseudo-half-cell measurements on symmetrical catalyst-coated membranes and their relevance for optimizing DMFC anodes}, series = {Journal of Applied Electrochemistry}, volume = {40}, journal = {Journal of Applied Electrochemistry}, number = {1}, publisher = {Springer Nature}, issn = {0021-891X}, doi = {10.1007/s10800-009-9960-9}, pages = {29 -- 38}, year = {2009}, language = {en} } @article{NehrBohnWahner2012, author = {Nehr, Sascha and Bohn, Birger and Wahner, Andreas}, title = {Prompt HO2Formation Following the Reaction of OH with Aromatic Compounds under Atmospheric Conditions}, series = {The Journal of Physical Chemistry A}, volume = {116}, journal = {The Journal of Physical Chemistry A}, number = {24}, publisher = {American Chemical Society (ACS)}, issn = {1089-5639}, doi = {10.1021/jp210946y}, pages = {6015 -- 6026}, year = {2012}, language = {en} } @article{NehrBohnFuchsetal.2011, author = {Nehr, Sascha and Bohn, Birger and Fuchs, Hendrik and Hofzumahaus, Andreas and Wahner, Andreas}, title = {HO2 formation from the OH + benzene reaction in the presence of O2}, series = {Physical Chemistry Chemical Physics}, volume = {13}, journal = {Physical Chemistry Chemical Physics}, number = {22}, publisher = {Royal Society of Chemistry (RSC)}, issn = {1463-9076}, doi = {10.1039/c1cp20334g}, year = {2011}, language = {en} } @article{UruciFlorouPaglioneetal.2025, author = {Uruci, Petro and Florou, Kalliopi and Paglione, Marco and Kaltsonoudis, Christos and Picquet-Varrault, B{\´e}n{\´e}dicte and Doussin, Jean-Fran{\c{c}}ois and Cazaunau, Mathieu and Leskinen, Ari and Hao, Liqing and Virtanen, Annele and Bell, David M. and Mutzel, Anke and Mothes, Falk and Herrmann, Hartmut and R{\´o}denas, Milagros and Mu{\~n}oz, Amalia and Fuchs, Hendrik and Bohn, Birger and Nehr, Sascha and Alfarra, M. Rami and Voliotis, Aristeidis and McFiggans, Gordon and Patroescu-Klotz, Iulia V. and Illmann, Niklas and Pandis, Spyros N.}, title = {Toluene photo-oxidation and secondary organic aerosol formation: EUROCHAMP-2020 multi-chamber experiments}, series = {Journal of Atmospheric Chemistry}, volume = {82}, journal = {Journal of Atmospheric Chemistry}, number = {2}, publisher = {Springer Nature}, issn = {0167-7764}, doi = {10.1007/s10874-025-09485-2}, year = {2025}, language = {en} } @inproceedings{NehrBausCınar2025, author = {Nehr, Sascha and Baus, Lukas and {\c{C}}{\i}nar, H.}, title = {L{\"u}ftung in Bildungseinrichtungen, 29. Oktober 2025, K{\"o}ln}, series = {2. K{\"o}lner Innenraum-Forum}, booktitle = {2. K{\"o}lner Innenraum-Forum}, publisher = {HYGIUM - Zentrum f{\"u}r Hygiene und Umweltmedizin GmbH}, year = {2025}, language = {de} } @article{NehrBausCınar2025, author = {Nehr, Sascha and Baus, Lukas and {\c{C}}{\i}nar, Hasan}, title = {Gute Luft in Schulen - Ein Balanceakt zwischen Gesundheitsschutz und Energieeffizienz}, series = {Gefahrstoffe Reinhaltung der Luft}, volume = {85}, journal = {Gefahrstoffe Reinhaltung der Luft}, number = {03-04}, publisher = {VDI-Verlag}, issn = {0949-8036}, doi = {10.37544/0949-8036-2025-03-04-77}, pages = {77 -- 80}, year = {2025}, language = {de} }