Pv. Doskey et Wg. Gao, Vertical mixing and chemistry of isoprene in the atmospheric boundary layer: Aircraft-based measurements and numerical modeling, J GEO RES-A, 104(D17), 1999, pp. 21263-21274
Vertical profiles of isoprene, methanol, and ozone (O-3) concentrations wer
e measured between the middle and upper atmospheric boundary layer (ABL) fr
om a research aircraft and were numerically simulated for the ABL and a dec
iduous forest canopy with a one-dimensional model coupling turbulence diffu
sion and atmospheric chemistry. Isoprene emissions from the deciduous fores
t canopy were estimated by coupling an existing biogenic emission algorithm
with estimates of canopy leaf density inferred from satellite remote sensi
ng observations. Numerical simulations predicted low isoprene concentration
s in the middle and upper ABL; however, the agreement between the simulatio
ns and the measured values was poor for two of the three profiles, indicati
ng that a three-dimensional transport model might be necessary in future si
mulations. Chemical oxidation of isoprene by O-3 and hydroxyl radical (OH),
particularly in the middle and upper ABL, tends to reduce the isoprene con
centrations and influences the vertical fluxes in that layer; however, chem
ical reactions have little effect on fluxes of isoprene near the emission s
ource, where turbulent mixing is much faster than chemical reactions and wh
ere the emission process controls the vertical flux. The isoprene flux decr
eases rapidly with increasing height, with little isoprene escaping from th
e ABL. Vertical profiles of methanol concentrations were simulated with the
biogenic emission algorithm used for isoprene; these vertical profiles wer
e similar to the measured values for the well-mixed ABL but were much lower
than the measured concentrations in the lower layers of the growing ABL be
cause of weaker calculated mixing in the upper ABL during the morning. The
results of this investigation indicate that chemical oxidation of isoprene
is rapid enough to allow O-3 and other oxidants to accumulate in the ABL on
a regional scale if sufficient levels of nitrogen oxides are present; howe
ver, methanol is much more stable, and biogenic emissions of this compound
have the potential to form O-3 and other oxidants in areas distant from the
emission source.