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

• Published in: Journal of geophysical research. Atmospheres 2017-10, Vol.122 (20), p.11,201-11,226
• Main Authors: 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., Hall, Samuel R., Hornbrook, Rebecca S., Gregory Huey, L., Josse, Beatrice, Jöckel, Patrick, Kinnison, Douglas E., Koenig, Theodore K., Le Breton, Michael, Marécal, Virginie, Morgenstern, Olaf, Oman, Luke D., Pan, Laura L., Percival, Carl, Plummer, David, Revell, Laura E., Rozanov, Eugene, Saiz‐Lopez, Alfonso, Stenke, Andrea, Sudo, Kengo, Tilmes, Simone, Ullmann, Kirk, Volkamer, Rainer, Weinheimer, Andrew J., Zeng, Guang
• Format: Article
• Language: English
• Subjects: Acetaldehyde; atmospheric chemistry; Atmospheric models; Capacity; CCMI; Chemical Sciences; Chemical transport; Chemistry; Climate; Climate models; CONTRAST; Convective transport; earth system model; Emission inventories; Emissions; Errors; Formaldehyde; Geophysics; ground-based ftir; in-situ; Kemi; Lower troposphere; marine boundary-layer; Marine environment; max-doas; mcm v3 part; Measurement; Meteorologi och atmosfärforskning; Meteorology; Meteorology & Atmospheric Sciences; Meteorology and Atmospheric Sciences; Methyl hydroperoxide in atmosphere; Mixing ratio; Nitrogen compounds; Nitrogen oxides; Nitrogen oxides emissions; NOx; observations; oxidative capacity; Representations; Satellites; Sinkholes; Transport; Tropical climate; Tropical environments; Troposphere; upper; Upper troposphere; volatile organic-compounds
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2016JD026121

Formaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HOx. In remote marine environments, such as the tropical western Pacific (TWP), it is particularly important to 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, to evaluate 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 convective transport 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%. This underestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NOx 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 to additional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere. Key Points Global chemistry climate models (CCMs) underestimate observed HCHO in the tropical western Pacific troposphere during CONTRAST by between 4 and 50% Errors in NOx chemistry and emissions are significant drivers of the measurement versus model discrepancy for HCHO in the CCMs Lack of oceanic emissions and missing in situ production of acetaldehyde leads to additional global chemistry model underestimates of HCHO