@article {24963,
	title = {Comparison of OH reactivity measurements in the atmospheric simulation chamber SAPHIR},
	journal = {Atmospheric Measurement Techniques},
	volume = {10},
	year = {2017},
	pages = {4023-4053},
	abstract = {Hydroxyl (OH) radical reactivity (k(OH)) has been measured for 18 years with different measurement techniques. In order to compare the performances of instruments deployed in the field, two campaigns were conducted performing experiments in the atmospheric simulation chamber SAPHIR at Forschungszentrum Julich in October 2015 and April 2016. Chemical conditions were chosen either to be representative of the atmosphere or to test potential limitations of instruments. All types of instruments that are currently used for atmospheric measurements were used in one of the two campaigns. The results of these campaigns demonstrate that OH reactivity can be accurately measured for a wide range of atmospherically relevant chemical conditions (e.g. water vapour, nitrogen oxides, various organic compounds) by all instruments. The precision of the measurements (limit of detection \&lt; 1 s(-1) at a time resolution of 30 s to a few minutes) is higher for instruments directly detecting hydroxyl radicals, whereas the indirect comparative reactivity method (CRM) has a higher limit of detection of 2 s(-1) at a time resolution of 10 to 15 min. The performances of the instruments were systematically tested by stepwise increasing, for example, the concentrations of carbon monoxide (CO), water vapour or nitric oxide (NO). In further experiments, mixtures of organic reactants were injected into the chamber to simulate urban and forested environments. Overall, the results show that the instruments are capable of measuring OH reactivity in the presence of CO, alkanes, alkenes and aromatic compounds. The transmission efficiency in Teflon inlet lines could have introduced systematic errors in measurements for low-volatile organic compounds in some instruments. CRM instruments exhibited a larger scatter in the data compared to the other instruments. The largest differences to reference measurements or to calculated reactivity were observed by CRM instruments in the presence of terpenes and oxygenated organic compounds (mixing ratio of OH reactants were up to 10 ppbv). In some of these experiments, only a small fraction of the reactivity is detected. The accuracy of CRM measurements is most likely limited by the corrections that need to be applied to account for known effects of, for example, deviations from pseudo first-order conditions, nitrogen oxides or water vapour on the measurement. Methods used to derive these corrections vary among the different CRM instruments. Measurements taken with a flow-tube instrument combined with the direct detection of OH by chemical ionisation mass spectrometry (CIMS) show limitations in cases of high reactivity and high NO concentrations but were accurate for low reactivity (\&lt; 15 s(-1)) and low NO (\&lt; 5 ppbv) conditions.},
	author = {Fuchs, Hendrik and Novelli, Anna and Michael Rolletter and Hofzumahaus, Andreas and Eva. Y. Pfannerstill and Stephan Kessel and Achim Edtbauer and Jonathan Williams and Vincent Michoud and Sebastien Dusanter and Nadine Locoge and Nora Zannoni and Valerie Gros and Francois Truong and Roland Sarda-Esteve and Danny R. Cryer and Charlotte A. Brumby and Lisa K. Whalley and Daniel Stone and Paul W. Seakins and Dwayne E. Heard and Coralie Schoemaecker and Marion Blocquet and Sebastien Coudert and Sebastien Batut and Christa Fittschen and Alexander B. Thames and William H. Brune and Cheryl Ernest and Hartwig Harder and Jennifer. B. A. Muller and Thomas Elste and Dagmar Kubistin and Stefanie Andres and Bohn, Birger and Hohaus, Thorsten and Holland, Frank and Xin Li and Rohrer, Franz and Astrid Kiendler-Scharr and Ralf Tillmann and Robert Wegener and Zhujun Yu and Qi Zou and Wahner, Andreas}
}
