HR: 08:45h
AN: A31E-03    [Abstracts]
TI: On tracer correlations in the troposphere: The case of ethane and propane
AU: Zeng, T
EM: tzeng@eas.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Drive school of earth and atmos. sci., atlanta, ga 30332 United States
AU: * Wang, Y
EM: ywang@eas.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Drive school of earth and atmos. sci., atlanta, ga 30332 United States
AB: To investigate the reasons for and the utility of tropospheric tracer correlations, we examine the interrelationship between ethane and propane on the basis of the observations and global 3-D chemical transport model (GEOS-CHEM) simulations. Ethane and propane have reasonably well defined sources and sinks. We chose to examine the correlation between propane and ethane/propane ratio because it is more sensitive to mixing and is less dependent on temperature than that between ethane and propane. We find that the linear correlation in the log space of propane and ethane/propane ratios are better characterized away from the source regions. Observations at northern mid and high latitudes (TOPSE) and over the tropical Pacific (PEM-Tropics B) are therefore investigated. We show that the correlation generally follows the one determined by chemical (loss) kinetics and that the deviation from the kinetics slope reflects the difference in the strength of mixing relative to chemical loss between ethane and propane. The comparison of observed and simulated correlation slopes can therefore be used to evaluate the coupling of chemistry and transport simulated in the model. At northern mid and high latitudes, the model is generally in agreement with the observations in February and March but simulates a wrong seasonal change of the correlation from March to May. The model appears to overestimate the transport from lower to mid latitudes and the horizontal mixing at high latitudes in May. Over the tropical Pacific, the model reproduces well the observed two-branch structure of the correlation. The minor branch results from different transport and chemistry coupling characteristics in the southern from northern hemisphere. The discrepancy between observed and simulated correlation slope values appears to reflect an underestimate of continental convective transport at northern mid latitudes and an overestimate of latitudinal transport into the tropics. In addition, we show that the correlation can be used to define the subset of observations, for which the coupling between chemistry and transport is simulated reasonably well in the model. Using the subsets of observed and simulated data for inverse modeling would reduce (systematic) biases introduced by systematic model transport errors. We show that in the data we examined, only those for March at mid latitudes and February-April at high latitudes conform to the criterion. On the basis of those data, we find that the model underestimates the emissions of ethane and propane by 14ø+-5%.
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting