Oxidation capacity of the city air of Santiago, Chile Y. F. Elshorbany1,2, R. Kurtenbach1, P. Wiesen1, E. Lissi3, M. Rubio3, G. Villena3, E. Gramsch4, A. R. Rickard5, M. J. Pilling6, and J. Kleffmann1 1Physikalische Chemie, FB C, Bergische Universität Wuppertal, Gaußstraße 20, 42119 Wuppertal, Germany 2Environmental Sciences Division, National Research Center, Dokki, Giza, Egypt 3Faculty of Chemistry and Biology, University of Santiago de Chile, USACH, Alameda L. Bernardo O'Higgins 3363, Santiago, Chile 4Physics Department, Faculty of Science, University of Santiago de Chile, Alameda L. Bernardo O'Higgins 3363, Santiago, Chile 5National Centre for Atmospheric Science, University of Leeds, Leeds, UK 6School of Chemistry, University of Leeds, Leeds, UK
Abstract. The oxidation capacity of the highly polluted urban area of Santiago, Chile
has been evaluated during a summer measurement campaign carried out from
8–20 March 2005. The hydroxyl (OH) radical budget was evaluated
employing a simple quasi-photostationary-state model (PSS) constrained with
simultaneous measurements of HONO, HCHO, O3, NO, NO2,
j(O1D), j(NO2), 13 alkenes and meteorological parameters. In
addition, a zero dimensional photochemical box model based on the Master
Chemical Mechanism (MCMv3.1) has been used to estimate production rates and
total free radical budgets, including OH, HO2 and RO2. Besides the
above parameters, the MCM model has been constrained by the measured CO and
volatile organic compounds (VOCs) including alkanes and aromatics. Both
models simulate the same OH concentration during daytime indicating that the
primary OH sources and sinks included in the simple PSS model predominate.
Mixing ratios of the main OH radical precursors were found to be in the
range 0.8–7 ppbv (HONO), 0.9–11 ppbv (HCHO) and 0–125 ppbv (O3). The
alkenes average mixing ratio was ~58 ppbC accounting for ~12%
of the total identified non-methane hydrocarbons (NMHCs). During the daytime
(08:00 h–19:00 h), HONO photolysis was shown to be the most important primary OH
radical source comprising alone ~55% of the total initial
production rate, followed by alkene ozonolysis (~24%) and
photolysis of HCHO (~16%) and O3 (~5%). The
calculated average and maximum daytime OH production rates from HONO
photolysis was 1.7 ppbv h−1 and 3.1 ppbv h−1, respectively.
Based on the experimental results a strong photochemical daytime source of
HONO is proposed. A detailed analysis of the sources of OH radical
precursors has also been carried out.
Citation: Elshorbany, Y. F., Kurtenbach, R., Wiesen, P., Lissi, E., Rubio, M., Villena, G., Gramsch, E., Rickard, A. R., Pilling, M. J., and Kleffmann, J.: Oxidation capacity of the city air of Santiago, Chile, Atmos. Chem. Phys., 9, 2257-2273, doi:10.5194/acp-9-2257-2009, 2009.