In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 22, No. 16 ( 2022-08-17), p. 10467-10488
Abstract:
Abstract. We present a novel approach to derive indirect global
information on the hydroxyl radical (OH), one of the most important
atmospheric oxidants, using state-of-the-art satellite trace gas observations
(key sinks and sources of OH) and a steady-state approximation (SSA). This
is a timely study as OH observations are predominantly from spatially sparse
field and infrequent aircraft campaigns, so there is a requirement for
further approaches to infer spatial and temporal information on OH and its
interactions with important climate (e.g. methane, CH4) and air quality
(e.g. nitrogen dioxide, NO2) trace gases. Due to the short lifetime of
OH (∼1 s), SSAs of varying complexities can be used to model
its concentration and offer a tool to examine the OH budget in different
regions of the atmosphere. Here, we use the well-evaluated TOMCAT
three-dimensional chemistry transport model to identify atmospheric regions
where different complexities of the SSAs are representative of OH. In the
case of a simplified SSA (S-SSA), where we have observations of ozone
(O3), carbon monoxide (CO), CH4 and water vapour (H2O) from
the Infrared Atmospheric Sounding Interferometer (IASI) on board ESA's
MetOp-A satellite, it is most representative of OH between 600 and 700 hPa
(though suitable between 400–800 hPa) within ∼20 %–30 % of
TOMCAT modelled OH. The same S-SSA is applied to aircraft measurements from
the Atmospheric Tomography Mission (ATom) and compares well with the
observed OH concentrations within ∼26 %, yielding a
correlation of 0.78. We apply the S-SSA to IASI data spanning 2008–2017 to
explore the global long-term inter-annual variability of OH. Relative to the
10-year mean, we find that global annual mean OH anomalies ranged from −3.1 % to +4.7 %, with the largest spread in the tropics between −6.9 % and +7.7 %. Investigation of the individual terms in the S-SSA
over this time period suggests that O3 and CO were the key drivers of
variability in the production and loss of OH. For example, large enhancement
in the OH sink during the positive 2015/2016 El Niño–Southern Oscillation (ENSO) event was due to large-scale CO emissions from drought-induced wildfires in South East Asia. The
methodology described here could be further developed as a constraint on the
tropospheric OH distribution as additional satellite data become available
in the future.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-22-10467-2022
DOI:
10.5194/acp-22-10467-2022-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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