NDACC harmonized formaldehyde time series from 21 FTIR stations covering a wide range of column abundances
- 1Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
- 2Instituto Federal de Educaçao (IFRO), Ciência e Tecnologia de Rondônia, Porto Velho, Brazil
- 3Stichting Atmospherische en Hydrologische Ontwikkeling (SAHO), Paramaribo, Suriname
- 4Karlsruhe Institute of Technology (KIT), IMK-ASF, Karlsruhe, Germany
- 5Izaña Atmospheric Research Centre (IARC), Agencia Estatal de Meteorología (AEMET), Santa Cruz de Tenerife, Spain
- 6Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México (UNAM), 04510 Mexico City, México
- 7Atmospheric Chemistry, Observations & Modeling, National Center for Atmospheric Research (NCAR), Boulder, CO, USA
- 8Centre for Atmospheric Chemistry, University of Wollongong, Wollongong, Australia
- 9Finnish Meteorological Institute (FMI), Sodankylä, Finland
- 10LERMA-IPSL, Sorbonne Université, CNRS, PSL Research University, Observatoire de Paris, 75005 Paris, France
- 11Department of Physics, University of Toronto, Toronto, Canada
- 12Saint Petersburg State University, Atmospheric Physics Department, St Petersburg, Russia
- 13Observatoire des Sciences de l'Univers Réunion (OSU-R), UMS 3365, Université de la Réunion, Saint-Denis, France
- 14Institute of Environmental Physics, University of Bremen, Bremen, Germany
- 15Karlsruhe Institute of Technology (KIT), IMK-IFU, Garmisch-Partenkirchen, Germany
- 16National Institute of Water and Atmospheric Research Ltd (NIWA), Lauder, New Zealand
- 17Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Abstract. Among the more than 20 ground-based FTIR (Fourier transform infrared) stations currently operating around the globe, only a few have provided formaldehyde (HCHO) total column time series until now. Although several independent studies have shown that the FTIR measurements can provide formaldehyde total columns with good precision, the spatial coverage has not been optimal for providing good diagnostics for satellite or model validation. Furthermore, these past studies used different retrieval settings, and biases as large as 50 % can be observed in the HCHO total columns depending on these retrieval choices, which is also a weakness for validation studies combining data from different ground-based stations.
For the present work, the HCHO retrieval settings have been optimized based on experience gained from past studies and have been applied consistently at the 21 participating stations. Most of them are either part of the Network for the Detection of Atmospheric Composition Change (NDACC) or under consideration for membership. We provide the harmonized settings and a characterization of the HCHO FTIR products. Depending on the station, the total systematic and random uncertainties of an individual HCHO total column measurement lie between 12 % and 27 % and between 1 and 11×1014 molec cm−2, respectively. The median values among all stations are 13 % and 2.9×1014 molec cm−2 for the total systematic and random uncertainties.
This unprecedented harmonized formaldehyde data set from 21 ground-based FTIR stations is presented and its comparison with a global chemistry transport model shows consistency in absolute values as well as in seasonal cycles. The network covers very different concentration levels of formaldehyde, from very clean levels at the limit of detection (few 1013 molec cm−2) to highly polluted levels (7×1016 molec cm−2). Because the measurements can be made at any time during daylight, the diurnal cycle can be observed and is found to be significant at many stations. These HCHO time series, some of them starting in the 1990s, are crucial for past and present satellite validation and will be extended in the coming years for the next generation of satellite missions.