NDACC harmonized formaldehyde time series from 21 FTIR stations covering a wide range of column abundances
<p>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 fo...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/11/5049/2018/amt-11-5049-2018.pdf |
| Summary: | <p>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.</p><p>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 11×10<sup>14</sup> molec cm<sup>−2</sup>, respectively. The median values among all
stations are 13 % and 2.9×10<sup>14</sup> molec cm<sup>−2</sup> for the total
systematic and random uncertainties.</p><p>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 10<sup>13</sup> molec cm<sup>−2</sup>) to highly polluted levels (7×10<sup>16</sup> molec cm<sup>−2</sup>).
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.</p> |
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| ISSN: | 1867-1381 1867-8548 |