Comparisons of box model calculations and measurements of formaldehyde from the 1997 North Atlantic Regional Experiment

Abstract

Formaldehyde (CH 2 O) measurements from two independent instruments are compared with photochemical box model calculations. The measurements were made on the National Oceanic and Atmospheric Administration P-3 aircraft as part of the 1997 North Atlantic Regional Experiment (NARE 97). The data set considered here consists of air masses sampled between 0 and 8 km over the North Atlantic Ocean which do not show recent influence from emissions or transport. These air masses therefore should be in photochemical steady state with respect to CH 2 O when constrained by the other P-3 measurements, and methane oxidation was expected to be the predominant source of CH 2 O in these air masses. For this data set both instruments measured identical CH 2 O concentrations to within 40 parts per trillion by volume (pptv) on average over the 0-800 pptv range, although differences larger than the combined 2a total uncertainty estimates were observed between the two instruments in 11% of the data. Both instruments produced higher CH 2 O concentrations than the model in more than 90% of this data set, with a median measured-modeled [CH 2 O] difference of 0.13 or 0.18 ppbv (depending on the instrument), or about a factor of 2. Such large differences cannot be accounted for by varying model input parameters within their respective uncertainty ranges. After examining the possible reasons for the model-measurement discrepancy, we conclude that there are probably one or more additional unknown sources of CH 2 O in the North Atlantic troposphere. Copyright 2002 by the American Geophysical Union.