The first evaluation of formaldehyde column observations by improved Pandora spectrometers during the KORUS-AQ field study
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Author/Creator ORCID
Date
2018-08-31
Type of Work
Department
Program
Citation of Original Publication
Spinei, E., et al. “The first evaluation of formaldehyde column observations by improved Pandora spectrometers during the KORUS-AQ field study” Atmos. Meas. Tech. 11 (31 Aug 2018): 4943–4961. https://doi.org/10.5194/amt-11-4943-2018.
Rights
This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Subjects
Abstract
The Korea–United States Air Quality Study
(KORUS-AQ) conducted during May–June 2016 offered
the first opportunity to evaluate direct-sun observations of
formaldehyde (HCHO) total column densities with improved
Pandora spectrometer instruments. The measurements highlighted in this work were conducted both in the Seoul megacity area at the Olympic Park site (37.5232◦ N, 27.1260◦ E;
26 m a.s.l.) and at a nearby rural site downwind of the
city at the Mount Taehwa research forest site (37.3123◦ N,
127.3106◦ E; 160 m a.s.l.). Evaluation of these measurements
was made possible by concurrent ground-based in situ observations of HCHO at both sites as well as overflight by the
NASA DC-8 research aircraft. The flights provided in situ
measurements of HCHO to characterize its vertical distribution in the lower troposphere (0–5 km).
Diurnal variation in HCHO total column densities followed the same pattern at both sites, with the minimum
daily values typically observed between 6:00 and 7:00 local time, gradually increasing to a maximum between 13:00
and 17:00 before decreasing into the evening. Pandora vertical column densities were compared with those derived
from the DC-8 HCHO in situ measured profiles augmented
with in situ surface concentrations below the lowest altitude of the DC-8 in proximity to the ground sites. A comparison between 49 column densities measured by Pandora
vs. aircraft-integrated in situ data showed that Pandora values were larger by 16 % with a constant offset of 0.22 DU
(Dobson units; R
2 = 0.68). Pandora HCHO columns were
also compared with columns calculated from the surface
in situ measurements over Olympic Park by assuming a wellmixed lower atmosphere up to a ceilometer-measured mixedlayer height (MLH) and various assumptions about the small
residual HCHO amounts in the free troposphere up to the
tropopause. The best comparison (slope = 1.03±0.03; intercept = 0.29±0.02 DU; and R
2 = 0.78±0.02) was achieved
assuming equal mixing within ceilometer-measured MLH
combined with an exponential profile shape. These results
suggest that diurnal changes in HCHO surface concentrations can be reasonably estimated from the Pandora total column and information on the mixed-layer height. More work
is needed to understand the bias in the intercept and the slope
relative to columns derived from the in situ aircraft and surface measurements.