@article{LuRohrerHollandetal.2012, author = {Lu, K. D. and Rohrer, F. and Holland, F. and Fuchs, H. and Bohn, Birger and Brauers, Theo and Chang, C. C. and H{\"a}seler, R. and Hu, M. and Kita, K. and Kondo, Y. and Li, X. and Lou, S. R. and Nehr, Sascha and Shao, M. and Zeng, L. M. and Wahner, A. and Zhang, Y. H. and Hofzumahaus, A.}, title = {Observation and modelling of OH and HO2 concentrations in the Pearl River Delta 2006: a missing OH source in a VOC rich atmosphere}, series = {Atmospheric Chemistry and Physics}, volume = {12}, journal = {Atmospheric Chemistry and Physics}, number = {3}, publisher = {Copernicus}, issn = {1680-7324}, doi = {10.5194/acp-12-1541-2012}, pages = {1541 -- 1569}, year = {2012}, abstract = {Abstract. Ambient OH and HO2 concentrations were measured by laser induced fluorescence (LIF) during the PRIDE-PRD2006 (Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta, 2006) campaign at a rural site downwind of the megacity of Guangzhou in Southern China. The observed OH concentrations reached daily peak values of (15-26) × 106 cm-3 which are among the highest values so far reported for urban and suburban areas. The observed OH shows a consistent high correlation with j(O1D) over a broad range of NOx conditions. The correlation cannot be reproduced by model simulations, indicating that OH stabilizing processes are missing in current models. The observed OH exhibited a weak dependence on NOx in contrast to model predictions. While modelled and measured OH agree well at NO mixing ratios above 1 ppb, a continuously increasing underprediction of the observed OH is found towards lower NO concentrations, reaching a factor of 8 at 0.02 ppb NO. A dependence of the modelled-to-measured OH ratio on isoprene cannot be concluded from the PRD data. However, the magnitude of the ratio fits into the isoprene dependent trend that was reported from other campaigns in forested regions. Hofzumahaus et al. (2009) proposed an unknown OH recycling process without NO, in order to explain the high OH levels at PRD in the presence of high VOC reactivity and low NO. Taking a recently discovered interference in the LIF measurement of HO2 into account, the need for an additional HO2 → OH recycling process persists, but the required source strength may be up to 20\% larger than previously determined. Recently postulated isoprene mechanisms by Lelieveld et al. (2008) and Peeters and M{\"u}ller (2010) lead to significant enhancements of OH expected for PRD, but an underprediction of the observed OH by a factor of two remains at low NO (0.1-0.2 ppb). If the photolysis of hydroperoxy aldehydes from isoprene is as efficient as proposed by Peeters and M{\"u}ller (2010), the corresponding OH formation at PRD would be more important than the primary OH production from ozone and HONO. While the new isoprene mechanisms need to be confirmed by laboratory experiments, there is probably need for other, so far unidentified chemical processes to explain entirely the high OH levels observed in Southern China.}, language = {en} } @article{EmanuelssonHallquistKristensenetal.2013, author = {Emanuelsson, E. U. and Hallquist, M. and Kristensen, K. and Glasius, M. and Bohn, Birger and Fuchs, H. and Kammer, B. and Kiendler-Scharr, A. and Nehr, Sascha and Rubach, F. and Tillmann, R. and Wahner, A. and Wu, H.-C. and Mentel, Th. F.}, title = {Formation of anthropogenic secondary organic aerosol (SOA) and its influence on biogenic SOA properties}, series = {Atmospheric Chemistry and Physics}, volume = {13}, journal = {Atmospheric Chemistry and Physics}, number = {5}, publisher = {Copernicus}, issn = {1680-7324}, doi = {10.5194/acp-13-2837-2013}, pages = {2837 -- 2855}, year = {2013}, abstract = {Abstract. Secondary organic aerosol (SOA) formation from mixed anthropogenic and biogenic precursors has been studied exposing reaction mixtures to natural sunlight in the SAPHIR chamber in J{\"u}lich, Germany. In this study aromatic compounds served as examples of anthropogenic volatile organic compound (VOC) and a mixture of α-pinene and limonene as an example for biogenic VOC. Several experiments with exclusively aromatic precursors were performed to establish a relationship between yield and organic aerosol mass loading for the atmospheric relevant range of aerosol loads of 0.01 to 10 μg m-3. The yields (0.5 to 9\%) were comparable to previous data and further used for the detailed evaluation of the mixed biogenic and anthropogenic experiments. For the mixed experiments a number of different oxidation schemes were addressed. The reactivity, the sequence of addition, and the amount of the precursors influenced the SOA properties. Monoterpene oxidation products, including carboxylic acids and dimer esters were identified in the aged aerosol at levels comparable to ambient air. OH radicals were measured by Laser Induced Fluorescence, which allowed for establishing relations of aerosol properties and composition to the experimental OH dose. Furthermore, the OH measurements in combination with the derived yields for aromatic SOA enabled application of a simplified model to calculate the chemical turnover of the aromatic precursor and corresponding anthropogenic contribution to the mixed aerosol. The estimated anthropogenic contributions were ranging from small (\≈8\%) up to significant fraction (50\%) providing a suitable range to study the effect of aerosol composition on the aerosol volatility (volume fraction remaining (VFR) at 343 K: 0.86-0.94). The aromatic aerosol had higher oxygen to carbon ratio O/C and was less volatile than the biogenic fraction. However, in order to produce significant amount of aromatic SOA the reaction mixtures needed a higher OH dose that also increased O/C and provided a less volatile aerosol. The SOA yields, O/C, and f44 (the mass fraction of CO2+ ions in the mass spectra which can be considered as a measure of carboxylic groups) in the mixed photo-chemical experiments could be described as linear combinations of the corresponding properties of the pure systems. For VFR there was in addition an enhancement effect, making the mixed aerosol significantly less volatile than what could be predicted from the pure systems. A strong positive correlation was found between changes in volatility and O/C with the exception during dark hours where the SOA volatility decreased while O/C did not change significantly. Thus, this change in volatility under dark conditions as well as the anthropogenic enhancement is due to chemical or morphological changes not affecting O/C.}, language = {en} } @article{GrotkampCibisBrueggemannetal.2020, author = {Grotkamp, Sabine and Cibis, Wolfgang and Br{\"u}ggemann, Silke and Coenen, M. Michaela and Gm{\"u}nder, Hans-Peter and Keller, Klaus and N{\"u}chtern, Elisabeth and Schwegler, Urban and Seger, Wolfgang and Staubli, Stefan and von Raison, B. Bia and Weißmann, R. and Bahemann, A. and Fuchs, H. and Rink, M. and Schian, Marcus and Schmitt, Klaus}, title = {Personal Factors of the Bio-Psycho-Social Model (WHO): A Revised Classification by the German Society for Social Medicine and Prevention (DGSMP)}, series = {Gesundheitswesen}, volume = {82}, journal = {Gesundheitswesen}, number = {1}, publisher = {Thieme}, doi = {10.1055/a-1011-3161}, pages = {107 -- 116}, year = {2020}, language = {de} } @article{FuchsAcirBohnetal.2014, author = {Fuchs, H. and Acir, Ismail-Hakki and Bohn, Birger and Brauers, Theo and Dorn, Hans-Peter and H{\"a}seler, R. and Hofzumahaus, A. and Holland, F. and Kaminski, M. and Li, X. and Lu, K. and Lutz, A. and Nehr, Sascha and Rohrer, F. and Tillmann, R. and Wegener, R. and Wahner, A.}, title = {OH regeneration from methacrolein oxidation investigated in the atmosphere simulation chamber SAPHIR}, series = {Atmospheric Chemistry and Physics}, volume = {14}, journal = {Atmospheric Chemistry and Physics}, number = {15}, publisher = {Copernicus}, issn = {1680-7324}, doi = {10.5194/acp-14-7895-2014}, pages = {7895 -- 7908}, year = {2014}, abstract = {Abstract. Hydroxyl radicals (OH) are the most important reagent for the oxidation of trace gases in the atmosphere. OH concentrations measured during recent field campaigns in isoprene-rich environments were unexpectedly large. A number of studies showed that unimolecular reactions of organic peroxy radicals (RO2) formed in the initial reaction step of isoprene with OH play an important role for the OH budget in the atmosphere at low mixing ratios of nitrogen monoxide (NO) of less than 100 pptv. It has also been suggested that similar reactions potentially play an important role for RO2 from other compounds. Here, we investigate the oxidation of methacrolein (MACR), one major oxidation product of isoprene, by OH in experiments in the simulation chamber SAPHIR under controlled atmospheric conditions. The experiments show that measured OH concentrations are approximately 50\% larger than calculated by the Master Chemical Mechanism (MCM) for conditions of the experiments (NO mixing ratio of 90 pptv). The analysis of the OH budget reveals an OH source that is not accounted for in MCM, which is correlated with the production rate of RO2 radicals from MACR. In order to balance the measured OH destruction rate, 0.77 OH radicals (1σ error: ± 0.31) need to be additionally reformed from each reaction of OH with MACR. The strong correlation of the missing OH source with the production of RO2 radicals is consistent with the concept of OH formation from unimolecular isomerization and decomposition reactions of RO2. The comparison of observations with model calculations gives a lower limit of 0.03 s-1 for the reaction rate constant if the OH source is attributed to an isomerization reaction of MACR-1-OH-2-OO and MACR-2-OH-2-OO formed in the MACR + OH reaction as suggested in the literature (Crounse et al., 2012). This fast isomerization reaction would be a competitor to the reaction of this RO2 species with a minimum of 150 pptv NO. The isomerization reaction would be the dominant reaction pathway for this specific RO2 radical in forested regions, where NO mixing ratios are typically much smaller.}, language = {en} } @article{NehrBohnDornetal.2014, author = {Nehr, Sascha and Bohn, Birger and Dorn, Hans-Peter and Fuchs, H. and H{\"a}seler, R. and Hofzumahaus, A. and Li, X. and Rohrer, F. and Tillmann, R. and Wahner, A.}, title = {Atmospheric photochemistry of aromatic hydrocarbons: OH budgets during SAPHIR chamber experiments}, series = {Atmospheric Chemistry and Physics}, volume = {14}, journal = {Atmospheric Chemistry and Physics}, number = {13}, publisher = {Copernicus}, issn = {1680-7324}, doi = {10.5194/acp-14-6941-2014}, pages = {6941 -- 6952}, year = {2014}, abstract = {Abstract. Current photochemical models developed to simulate the atmospheric degradation of aromatic hydrocarbons tend to underestimate OH radical concentrations. In order to analyse OH budgets, we performed experiments with benzene, toluene, p-xylene and 1,3,5-trimethylbenzene in the atmosphere simulation chamber SAPHIR. Experiments were conducted under low-NO conditions (typically 0.1-0.2 ppb) and high-NO conditions (typically 7-8 ppb), and starting concentrations of 6-250 ppb of aromatics, dependent on OH rate constants. For the OH budget analysis a steady-state approach was applied in which OH production and destruction rates (POH and DOH) have to be equal. The POH were determined from measurements of HO2, NO, HONO, and O3 concentrations, considering OH formation by photolysis and recycling from HO2. The DOH were calculated from measurements of the OH concentrations and total OH reactivities. The OH budgets were determined from DOH/POH ratios. The accuracy and reproducibility of the approach were assessed in several experiments using CO as a reference compound where an average ratio DOH/POH = 1.13 ± 0.19 was obtained. In experiments with aromatics, these ratios ranged within 1.1-1.6 under low-NO conditions and 0.9-1.2 under high-NO conditions. The results indicate that OH budgets during photo-oxidation experiments with aromatics are balanced within experimental accuracies. Inclusion of a further, recently proposed OH production via HO2 + RO2 reactions led to improvements under low-NO conditions but the differences were small and insignificant within the experimental errors.}, language = {en} } @article{FuchsHofzumahausRohreretal.2013, author = {Fuchs, H. and Hofzumahaus, A. and Rohrer, F. and Bohn, Birger and Brauers, Theo and Dorn, Hans-Peter and H{\"a}seler, R. and Holland, F. and Kaminski, M. and Li, X. and Lu, K. and Nehr, Sascha and Tillmann, R. and Wegener, R. and Wahner, A.}, title = {Experimental evidence for efficient hydroxyl radical regeneration in isoprene oxidation}, series = {Nature Geoscience}, volume = {6}, journal = {Nature Geoscience}, number = {12}, publisher = {Springer Nature}, issn = {1752-0894}, doi = {10.1038/NGEO1964}, pages = {1023 -- 1026}, year = {2013}, language = {en} } @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} }