Contribution of different sources and sinks to the acetone,
methanol, CO and PAN budget over the Mediterranean sea
Rupert Holzinger1, Jonathan Williams1, Thomas Klüpfel1,
Horst Fischer1, Marian de Reus1, Bert Scheeren2,
Carsten Warnecke3, Joost de Gouw3, Mark Lawrence1,
Rolf von Kuhlmann1, Michael Traub1 and Jos Lelieveld1
1Max-Planck-Institut für Chemie, J.J. Becher-Weg 22, 55128 Mainz, Germany
2Institute for Marine and Atmospheric Research Utrecht (IMAU),
Utrecht University, the Netherlands
3NOAA Aeronomy Laboratory, 325 Broadway, Boulder, CO, USA
Airborne measurements of acetone, methanol, PAN (by Proton Transfer Reaction
Mass Spectrometry, PTRMS) and CO (by Tunable Diode Laser, TDL) have been
performed during the Mediterranean INtensive Oxidants Study (MINOS).
Typical volume mixing ratios in the lower troposphere (0-4 km), mid troposphere
(4-8 km) and upper troposphere (8-13 km), respectively, in units of nmol/mol are
as follows: 1.8-2.8, 1.5, 1 for acetone; 1.5-3.5, 1.2, 0.7 for methanol; 0.4-0.8,
0.4, 0.2 for PAN; and 100-170, 80, 70 for CO. The oxidation of acetone and methanol
is an important source of HO in the upper troposphere. In remote areas CO, together
with CH4, controls the oxidation power of the atmosphere. Reactive nitrogen can be
sequestered in PAN and transported to regions far from pollution sources, thereby
impacting atmospheric chemistry on a global scale. The understanding of the sources
of acetone, methanol and PAN and/or their precursors is not yet satisfactory.
The agreement between the MINOS measurements and results from a 3-dimensional
global model of the lower atmosphere, which includes VOC chemistry (MATCH), is
generally poor. Using volatile organic compounds as tracers the contributions of
different sources and sinks have been assessed; a clear influence from biomass
burning was observed. By analysing relative enhancements to acetonitrile in biomass
burning plumes it was possible to estimate contributions around 10 % (acetone, PAN and CO)
and 15 % (methanol) to the atmospheric burden encountered in the course of the campaign.
A 5-day back-trajectory analysis indicated that air masses from east and western Europe
were encountered in the lower troposphere (0-4 km); air masses from Northern Atlantic
were measured in the mid troposphere (4-8 km); from August 3 to 8 2001 air coming from
South Asia was observed at altitudes between 8-14 km. Characteristic ratios of acetone,
methanol and PAN to CO are presented.