Detailed comparisons of airborne formaldehyde measurements with box models during the 2006 INTEX-B and MILAGRO campaigns: potential evidence for significant impacts of unmeasured and multi-generation volatile organic carbon compounds

Abstract

Abstract. Detailed comparisons of airborne CH 2 O measurements acquired by tunable diode laser absorption spectroscopy with steady state box model calculations were carried out using data from the 2006 INTEX-B and MILARGO campaign in order to improve our understanding of hydrocarbon oxidation processing. This study includes comparisons over Mexico (including Mexico City), the Gulf of Mexico, parts of the continental United States near the Gulf coast, as well as the more remote Pacific Ocean, and focuses on comparisons in the boundary layer. Select previous comparisons in other campaigns have highlighted some locaCorrespondence to: A. Fried (fried@ucar.edu) tions in the boundary layer where steady state box models have tended to underpredict CH 2 O, suggesting that standard steady state modeling assumptions might be unsuitable under these conditions, and pointing to a possible role for unmeasured hydrocarbons and/or additional primary emission sources of CH 2 O. Employing an improved instrument, more detailed measurement-model comparisons with better temporal overlap, up-to-date measurement and model precision estimates, up-to-date rate constants, and additional modeling tools based on both Lagrangian and Master Chemical Mechanism (MCM) runs, we have explained much of the disagreement between observed and predicted CH 2 O as resulting from non-steady-state atmospheric conditions in the vicinity of large pollution sources, and have quantified Published by Copernicus Publications on behalf of the European Geosciences Union. the disagreement as a function of plume lifetime (processing time). We show that in the near field (within ∼4 to 6 h of the source), steady-state models can either over-orunderestimate observations, depending on the predominant non-steady-state influence. In addition, we show that even far field processes (10-40 h) can be influenced by non-steadystate conditions which can be responsible for CH 2 O model underestimations by ∼20 %. At the longer processing times in the 10 to 40 h range during Mexico City outflow events, MCM model calculations, using assumptions about initial amounts of high-order NMHCs, further indicate the potential importance of CH 2 O produced from unmeasured and multigeneration hydrocarbon oxidation compounds, particularly methylglyoxal, 3-hydroxypropanal, and butan-3-one-al.

Modeling of HCHO and CHOCHO at a semi-rural site in southern China during the PRIDE-PRD2006 campaign

“…Since HCHO and CHOCHO are mainly coming from the reaction of OH with NMHCs, the above effects can be tested through the sensitivity of the The parameter τ D can be used as a scale of the generic removal of species included in the model. The shorter the τ D , the faster the removal, resulting in less reaction time t (i.e., similar to the photochemical age as used by Fried et al (2011)) and less oxidation products of primary emitted NMHCs. As described by Lou et al (2010), oxidation product of the measured NMHCs account for more than 50 % of the measured total OH reactivity (k OH ) at the BG site.…”

“…Although numerical simulations of HCHO, either by multi-dimensional models or box models, can in some cases reproduce HCHO observations (Wagner et al, 2001;Fried et al, 2003b;MacDonald et al, 2012), significant discrepancies between modeled and measured HCHO concentration have been frequently found (Choi et al, 2010;Fried et al, 2011, and references therein). The model underestimation can arise from the following: deviation from the steadystate assumption (Fried et al, 2003a), direct emissions and their transport (Fried et al, 2011), missing consideration of HCHO production from unmeasured precursors (Kormann et al, 2003;Choi et al, 2010), etc. If the steady-state assumption is disturbed, e.g., in the vicinity of fresh emissions, the model can also overpredict the measured HCHO concentration (Fried et al, 2011).…”

“…The model underestimation can arise from the following: deviation from the steadystate assumption (Fried et al, 2003a), direct emissions and their transport (Fried et al, 2011), missing consideration of HCHO production from unmeasured precursors (Kormann et al, 2003;Choi et al, 2010), etc. If the steady-state assumption is disturbed, e.g., in the vicinity of fresh emissions, the model can also overpredict the measured HCHO concentration (Fried et al, 2011).…”

The formaldehyde budget as seen by a global-scale multi-constraint and multi-species inversion system

“…Considering that OMI data integrate the atmospheric column of HCHO, comparison with aircraft observations are of particular interest. The airborne HCHO measurements made during INTEX-B (Intercontinental Chemical Transport Experiment B) (Singh et al, 2009;Fried et al, 2011) Multidisciplinary Analysis) (Reeves et al, 2010;Borbon et al, 2012) . We compute the ratio of the posterior to the prior bias between modeled and observed concentrations.…”

The First Evaluation of Formaldehyde Column Observations by Pandora Spectrometers during the KORUS-AQ Field Study

“…The degradation of HCHO can also constitute an important secondary source of HO x (HO + HO 2 ), serving to 10 amplify oxidation rates in polluted atmospheres. A more detailed discussion of HCHO chemistry can be found in Fried et al, (2011) and references therein.…”