On inferring isoprene emission surface flux from atmospheric boundary layer concentration measurements 1Meteorology and Air Quality Section, Wageningen University, The Netherlands
2Applied Physics Department, Technical University of Catalonia and Institute for Space Studies of Catalonia, Spain
Received: 14 Nov 2008 – Published in Atmos. Chem. Phys. Discuss.: 09 Feb 2009 – Published: 04 Jun 2009Abstract. We examine the dependence of the inferred isoprene surface emission flux from atmospheric concentration on the diurnal
variability of the convective boundary layer (CBL). A series of systematic numerical experiments
carried out using the mixed-layer technique enabled us to study the sensitivity of
isoprene fluxes to the entrainment process, the partition of surface fluxes, the horizontal
advection of warm/cold air masses and subsidence. Our findings demonstrate the key role played by the evolution of boundary layer height
in modulating the retrieved isoprene flux. More specifically, inaccurate values
of the potential temperature lapse rate lead to changes in the dilution capacity of the CBL
and as a result the isoprene flux may be overestimated or underestimated by as much as 20%. The inferred
emission flux estimated in the early morning hours is highly dependent on the
accurate estimation of the discontinuity of the thermodynamic values between the residual layer
and the rapidly forming CBL.
Uncertainties associated with the partition of the sensible and latent heat flux
also yield large deviations in the calculation of the isoprene surface flux. Similar results
are obtained if we neglect the influence of warm or cold advection in the development of the CBL.
We show that all the above-mentioned processes are non-linear, for which reason
the dynamic and chemical evolutions of the CBL must be solved simultaneously. Based on the discussion of our results, we suggest the
measurements needed to correctly apply the mixed-layer technique in order to minimize the
uncertainties associated with the diurnal variability of the convective boundary layer.
Citation: Vilà-Guerau de Arellano, J., van den Dries, K., and Pino, D.: On inferring isoprene emission surface flux from atmospheric boundary layer concentration measurements, Atmos. Chem. Phys., 9, 3629-3640, doi:10.5194/acp-9-3629-2009, 2009.