The budget of reactive nitrogen species at ground based station on Crete during the MINOS
2001 campaign
Lutz Lange1, Jonathan Williams1, Mark Lawrence1,
Rolf von Kuhlmann1, Mihalis Vrekoussis2, Constantina Economou2,
Nikos Mihalopoulos2 and Jos Lelieveld1
1 Max Planck Institute for Chemistry, Mainz, Germany
2 Department of Chemistry - University of Crete, Iraklion, Crete
During the MINOS 2001 campaign we performed measurements of reactive nitrogen species
at a ground based station in Finokalia, Crete. Continuous measurements of NO, NO2, PAN,
NO3, HNO3 and NOy are were made for three weeks in August 2001. During this time
predominantly Eastern European air was advected to the measurement site by strong
northwesterly trade winds. PAN concentrations ranged between a few pptv and 50 pptv
during the "clean air events" and 100-300 pptv during more polluted conditions. HNO3
varied between 200 pptv and 1.2 ppbv. NO concentrations were usually below the detection
limit of the instrument (25 pptv) while NOy ranged from 0.5 pptv to 1.5 pptv. The
relative proportions of the various NOy components are presented.
The budget of PAN is relatively complex in this region. Cloudless conditions and
strong sunlight allow PAN to be rapidly formed during the photochemical decomposition
of advected European hydrocarbons in the presence of NOx. However under the conditions
prevalent in the Mediterrean boundary layer it can rapidly thermally decompose and be
deposited to surfaces. Comparison of measured PAN with results from the MATCH model show
that while some of the variations in PAN are succesfully reproduced in the model,
additional variations of similar size are apparant in the data. No evidence for a sea
breeze effect was observed at the Finokalia site during the campaign. The possible causes
for the variations not seen in the modelled data are investigated by comparison of PAN
data with O3, HNO3, CO, radon and back trajectory information.