Unexpected long-range transport of glyoxal and formaldehyde observed from the Copernicus Sentinel-5 Precursor satellite during the 2018 Canadian wildfires
<p>Glyoxal (CHOCHO) and formaldehyde (HCHO) are intermediate products in the tropospheric oxidation of the majority of volatile organic compounds (VOCs). CHOCHO is also a precursor of secondary organic aerosol (SOA) in the atmosphere. CHOCHO and HCHO are released from biogenic, anthropogenic,...
Main Authors: | , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2020-02-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/20/2057/2020/acp-20-2057-2020.pdf |
Summary: | <p>Glyoxal (CHOCHO) and formaldehyde (HCHO) are
intermediate products in the tropospheric oxidation of the majority of
volatile organic compounds (VOCs). CHOCHO is also a precursor of secondary
organic aerosol (SOA) in the atmosphere. CHOCHO and HCHO are released from
biogenic, anthropogenic, and pyrogenic sources. CHOCHO and HCHO
tropospheric lifetimes are typically considered to be short during the
daytime at mid-latitudes (e.g. several hours), as they are rapidly removed
from the atmosphere by their photolysis, oxidation by OH, and uptake on
particles or deposition. At night and at high latitudes, tropospheric
lifetimes increase to many hours or even days. Previous studies demonstrated
that CHOCHO and HCHO vertical column densities (VCDs) are well retrieved
from space-borne observations using differential optical absorption
spectroscopy (DOAS). In this study, we present CHOCHO and HCHO VCDs
retrieved from measurements by TROPOMI (TROPOspheric Monitoring Instrument), launched on the
Sentinel-5 Precursor (S5P) platform in October 2017. We observe strongly
elevated amounts of CHOCHO and HCHO during the 2018 fire season in British
Columbia, Canada, where a large number of fires occurred in August. CHOCHO
and HCHO plumes from individual fire hot spots are observed in air masses
travelling over distances of up to 1500 <span class="inline-formula">km</span>, i.e. much longer than expected
for the relatively short tropospheric lifetime expected for CHOCHO and
HCHO. Comparison with simulations by the particle dispersion model FLEXPART
(FLEXible PARTicle dispersion model)
indicates that effective lifetimes of 20 <span class="inline-formula">h</span> and more are needed to
explain the observations of CHOCHO and HCHO if they decay in an effective
first-order process. FLEXPART used in the study calculates accurately the
transport. In addition an exponential decay, in our case assumed to be
photochemical, of a species along the trajectory is added. We have used this
simple approach to test our assumption that CHOCHO and HCHO are created
in the fires and then decay at a constant rate in the plume as it is
transported. This is clearly not the case and we infer that CHOCHO and HCHO
are either efficiently recycled during transport or continuously formed
from the oxidation of longer-lived precursors present in the plume, or
possibly a mixture of both. We consider the best explanation of the observed
CHOCHO and HCHO VCD in the plumes of the fire is that they are produced by
oxidation of longer-lived precursors, which were also released by the fire and present
in the plume.</p> |
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ISSN: | 1680-7316 1680-7324 |