Airborne flux measurements of biogenic isoprene over California
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Authors
Misztal, P.K.
Karl, T.
Weber, R.
Jonsson, H.H.
Guenther, A.B.
Goldstein, A.H.
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Date of Issue
2014
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Abstract
Biogenic isoprene fluxes were measured onboard
the CIRPAS Twin Otter aircraft as part of the California Airborne
Biogenic volatile organic compound (BVOC) Emission
Research in Natural Ecosystem Transects (CABERNET)
campaign during June 2011. The airborne virtual disjunct
eddy covariance (AvDEC) approach used measurements
from a proton transfer reaction mass spectrometer
(PTR–MS) and a wind radome probe to directly determine
fluxes of isoprene over 7400 km of flight paths focusing on
areas of California predicted to have the largest emissions.
The fast Fourier transform (FFT) approach was used to calculate
fluxes of isoprene over long transects of more than
15 km, most commonly between 50 and 150 km. The continuous
wavelet transformation (CWT) approach was used
over the same transects to also calculate instantaneous isoprene
fluxes with localization of both frequency and time independent
of non-stationarities. Fluxes were generally measured
by flying consistently at 400m±50m (a.g.l.) altitude,
and extrapolated to the surface according to the determined
flux divergence determined in the racetrack-stacked profiles.
The wavelet-derived surface fluxes of isoprene averaged to
2 km spatial resolution showed good correspondence to basal
emission factor (BEF) land-cover data sets used to drive
BVOC emission models. The surface flux of isoprene was
close to zero over Central Valley crops and desert shrublands,
but was very high (up to 15 mgm−2 h−1) above oak
woodlands, with clear dependence of emissions on temperature
and oak density. Isoprene concentrations of up to 8 ppb
were observed at aircraft height on the hottest days and over
the dominant source regions.
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Article
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The article of record as published may be located at http://dx.doi.org/10.5194/acp-14-10631-2014
The Supplement related to this article is available online at doi:10.5194/acp-14-10631-2014-supplement.
The Supplement related to this article is available online at doi:10.5194/acp-14-10631-2014-supplement.
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Meteorology
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Atmospheric Chemistry and Physics, Vol. 14, pp. 10631–10647, 2014, DOI: 10.5194/acp-14-10631-2014
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.