On the budget of hydroxyl radicals at Schauinsland: role of biogenic volatile organic compounds

The concentration of hydroxyl radicals is estimated from the degradation of NO_x and selected Volatile Organic Compounds (VOCs) during the transport of polluted air masses from the city of Freiburg to the Schauinsland mountain through a steep valley called 'Grosses Tal'. The approach is based upon chemical and meteorological measurements made during the SLOPE (Schauinsland Ozone Precursor Experiment) campaign at two ground based sites and aboard a small aircraft. Separation of chemistry and transport is achieved through the degradation of chemical compounds with significantly different reactivity towards OH. The transport time of the air between the two measurements (100#+-#200 min) and the influence of mixing with background air on the calculated OH concentration is quantified with the help of the results from a dispersion experiment with SF_6 and from airborne chemical measurements made during SLOPE. By combining all ground based VOC measurements (C_2-C_1_5), it was found that the total VOC concentration is dominated by anthropogenic hydrocarbons (alkanes and aromatics) at the site. The contribution of biogenic VOCs to the total VOC reactivity (#SIGMA#[VOC_i] x k_O_H_i) in the air masses is about 30% at the entrance of the valley and about 70% at Schauinsland. OH concentrations of 1#+-#0.2 x 10"7 cm"-"3 are estimated from the degradation of VOCs and NO_x between the two measuring sites. (orig.)Available from TIB Hannover: RA 831(3647) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman