Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM-Chem and the CCMI Models

ANDERSON, DANIEL C.; NICELY, JULIE M.; WOLFE, GLENN M.; HANISCO, THOMAS F.; SALAWITCH, ROSS J.; CANTY, TIMOTHY P.; DICKERSON, RUSSELL R.; APEL, ERIC C.; BAIDAR, SUNIL; BANNAN, THOMAS J.; BLAKE, NICOLA J.; CHEN, DEXIAN; DIX, BARBARA; FERNANDEZ, RAFAEL P.; KINNISON, DOUGLAS E.; KOENIG, THEODORE K.; PAN, LAURA L.; SAIZ-LOPEZ, ALFONSO; VOLKAMER, RAINER

Journal of Geophysical Research: Atmospheres

American Geophysical Union

Año: 2017 vol. 122 p. 11201 - 11226

Formaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HO x . In remote marine environments, such as the tropical western Pacific (TWP), it is particularly importantto understand the processes controlling the abundance of HCHO because model output from these regions is used to correct satellite retrievals of HCHO. Here we have used observations from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, conducted during January and February 2014, toevaluate our understanding of the processes controlling the distribution of HCHO in the TWP as well as its representation in chemical transport/climate models. Observed HCHO mixing ratios varied from ~500 parts per trillion by volume (pptv) near the surface to ~75 pptv in the upper troposphere. Recent convectivetransport of near surface HCHO and its precursors, acetaldehyde and possibly methyl hydroperoxide, increased upper tropospheric HCHO mixing ratios by ~33% (22 pptv); this air contained roughly 60% less NO than more aged air. Output from the CAM-Chem chemistry transport model (2014 meteorology) as well as nine chemistry climate models from the Chemistry-Climate Model Initiative (free-running meteorology) are found to uniformly underestimate HCHO columns derived from in situ observations by between 4 and 50%. Thisunderestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NO x emissions inventories and/or in the model chemical mechanisms. Likewise, the lack of oceanic acetaldehyde emissions and potential errors in the model acetaldehyde chemistry lead toadditional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere.