Tunable diode laser measurements of formaldehyde during the TOPSE 2000 study: Distributions, trends, and model comparisons

Authors

A Fried, University of Colorado Boulder
Yuhang Wang, Georgia Institute of Technology - Main Campus
C A. Cantrell, National Center for Atmospheric Research
B Wert, University of Colorado, Boulder
J Walega, NCAR
Brian Ridley, NCAR
Elliot Atlas, NCARFollow
R E. Shetter, NOAA
Barry Lefer, University of Houston - Main
Michael T. Coffey, NCAR
James W. Hannigan, NCAR
D R. Blake, University of California, Irvine
N J. Blake, University of California, IrvineFollow
Simone Meinardi, University of California, Davis
R. Talbot, University of New HampshireFollow
Jack E. Dibb, University of New HampshireFollow
Eric Scheuer, University of New Hampshire - Main CampusFollow
Oliver Wingenter, New Mexico Institute of Mining and Technology
J Snow, University of Rhode Island
B J. Heikes, University of Rhode Island
Dieter Ehhalt, Institute for Atmospheric Chemistry, Julich, Germany

Abstract

Airborne measurements of formaldehyde (CH₂O) were acquired employing tunable diode laser absorption spectroscopy (TDLAS) during the 2000 Tropospheric Ozone Production About the Spring Equinox (TOPSE) study. This study consisted of seven deployments spanning the time period from 4 February to 23 May 2000 and covered a wide latitudinal band from 40°N to 85°N. The median measured CH₂O concentrations, with a few exceptions, did not show any clear temporal trends from February to May in each of five altitude and three latitude bins examined. Detailed measurement–model comparisons were carried out using a variety of approaches employing two different steady state models. Because recent emissions of CH₂O and/or its precursors often result in model underpredictions, background conditions were identified using a number of chemical tracers. For background conditions at temperatures warmer than −45°C, the measurement–model agreement on average ranged between −13% and +5% (measurement–model/measurement), which corresponded to mean and median (measurement–model) differences of 3 ± 69 and −6 parts per trillion by volume (pptv), respectively. At very low temperatures starting at around −45°C, significant and persistent (measurement–model) differences were observed from February to early April from southern Canada to the Arctic Ocean in the 6–8 km altitude range. In such cases, measured CH₂O was as much as 392 pptv higher than modeled, and the median difference was 132 pptv (83%). Low light conditions as well as cold temperatures may be important in this effect. A number of possible mechanisms involving the reaction of CH₃O₂ with HO₂ to produce CH₂O directly were investigated, but in each case the discrepancy was only minimally reduced. Other possibilities were also considered but in each case there was no compelling evidence to support any of the hypotheses. Whatever the cause, the elevated CH₂O concentrations significantly impact upper tropospheric HO_x levels at high latitudes (>57°N) in the February–April time frame.

Department

Earth Sciences, Earth Systems Research Center

Publication Date

2-27-2003

Journal Title

Journal of Geophysical Research

Publisher

Wiley

Digital Object Identifier (DOI)

10.1029/2002JD002208

Document Type

Article

Recommended Citation

Fried, A., et al. (2003), Tunable diode laser measurements of formaldehyde during the TOPSE 2000 study: Distributions, trends, and model comparisons, J. Geophys. Res., 108, 8365, doi:10.1029/2002JD002208, D4.

Rights

Copyright 2003 by the American Geophysical Union.