Formaldehyde over the Eastern Mediterranean during MINOS:
Comparison of Airborne In-situ Measurements with 3D-Model Results
Horst Fischer1, Robert Kormann1, Marian de Reus1,
Mark Lawrence1, Christoph Brühl1, Rolf von Kuhlmann1,
Carsten Warneke2, Joost de Gouw2, Rupert Holzinger1,
Jonathan Williams1 and Jos Lelieveld1
1Max-Planck-Institut für Chemie, J.J. Becher-Weg 22, 55128 Mainz, Germany
2NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO, USA
Formaldehyde is an important intermediate product in the photochemical oxidation
of methane and non-methane volatile organic compounds. In August 2001, airborne
formaldehyde measurements based on the Hantzsch reaction technique were performed
during the Mediterranean INtensive Oxidants Study, MINOS. In the marine boundary
layer over the eastern Mediterranean sea average HCHO concentrations were of the
order of 1.3 ppbv in reasonable agreement with results from a 3-dimensional global
model of the lower atmosphere including NMVOC chemistry (MATCH). At higher altitudes
(above 6 km) HCHO levels decreased to 0.34 ppbv, much higher values than predicted
by the model (~ 0.05 ppbv). Significant positive correlations of HCHO with CO, PAN,
acetone and methanol indicate that the formaldehyde precursors were predominately
associated with anthropogenic sources. At least part of the large discrepancy
between the model results and the measurements of HCHO in the free troposphere
are due to a strong underestimation of the upper tropospheric acetone concentration
by up to a factor of about 10 by MATCH. Therefore, sensitivity studies including
box modelling with more detailed NMVOC chemistry are used to study the free tropospheric
HCHO budget during MINOS.