Formaldehyde in the Tropical Western Pacific: Evaluation of model chemistry and emissions with in situ observations

Atmospheric formaldehyde (HCHO) is an important tracer of deep convection, a decomposition product of most volatile organic compounds (VOCs), and a large contributor to HOx (HOx = OH + HO2) production in both urban and remote environments. Accurate representation of HCHO sources, chemistry, and distribution in global models [i.e., chemical transport models (CTMs) and chemistry climate models (CCMs)] is therefore vital for accurate estimation of HOx. Here, we present in situ HCHO observations from the CONTRAST field campaign, conducted in winter 2014 in the remote, tropical western Pacific. Observed HCHO is compared to output from a photochemical box model as well as the CAM-Chem CTM run using winter 2014 meteorology. Both models show consistent underestimation of observed HCHO, indicating possible oceanic HCHO emissions and/or unaccounted VOC sources. Both options are explored. The data will also be compared to output of HCHO in the POLMIP CTMs and newly formed CCMI archives. Implications for HCHO remote sensing will also be discussed.