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| Titel |
Seasonal in situ observations of glyoxal and methylglyoxal over the temperate oceans of the Southern Hemisphere |
| VerfasserIn |
S. J. Lawson, P. W. Selleck, I. E. Galbally, M. D. Keywood, M. J. Harvey, C. Lerot, D. Helmig, Z. Ristovski |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 1 ; Nr. 15, no. 1 (2015-01-12), S.223-240 |
| Datensatznummer |
250119294
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| Publikation (Nr.) |
 copernicus.org/acp-15-223-2015.pdf |
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| Zusammenfassung |
| The dicarbonyls glyoxal and methylglyoxal have been measured with
2,4-dinitrophenylhydrazine (2,4-DNPH) cartridges and high-performance liquid
chromatography (HPLC), optimised for dicarbonyl detection, in clean marine
air over the temperate Southern Hemisphere (SH) oceans. Measurements of a
range of dicarbonyl precursors (volatile organic compounds, VOCs) were made
in parallel. These are the first in situ measurements of glyoxal and
methylglyoxal over the remote temperate oceans. Six 24 h samples were
collected in summer (February–March) over the Chatham Rise in the south-west
Pacific Ocean during the Surface Ocean Aerosol Production (SOAP) voyage in
2012, while 34 24 h samples were collected at Cape Grim Baseline Air
Pollution Station in the late winter (August–September) of 2011. Average glyoxal mixing
ratios in clean marine air were 7 ppt at Cape Grim and 23 ppt over Chatham
Rise. Average methylglyoxal mixing ratios in clean marine air were 28 ppt at
Cape Grim and 10 ppt over Chatham Rise. The mixing ratios of glyoxal at Cape
Grim are the lowest observed over the remote oceans, while mixing ratios
over Chatham Rise are in good agreement with other temperate and tropical
observations, including concurrent Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations. Methylglyoxal
mixing ratios at both sites are comparable to the only other marine
methylglyoxal observations available over the tropical Northern Hemisphere
(NH) ocean. Ratios of glyoxal : methylglyoxal > 1 over Chatham
Rise but < 1 at Cape Grim suggest that a different formation and/or loss
processes or rates dominate at each site. Dicarbonyl precursor VOCs,
including isoprene and monoterpenes, are used to calculate an upper-estimate
yield of glyoxal and methylglyoxal in the remote marine boundary layer and
explain at most 1–3 ppt of dicarbonyls observed, corresponding to 10% and
17% of the observed glyoxal and 29 and 10% of the methylglyoxal at
Chatham Rise and Cape Grim, respectively, highlighting a significant but as
yet unknown production mechanism. Surface-level glyoxal observations from
both sites were converted to vertical columns and compared to average
vertical column densities (VCDs) from GOME-2 satellite retrievals. Both
satellite columns and in situ observations are higher in summer than winter;
however, satellite vertical column densities exceeded the surface
observations by more than 1.5 × 1014 molecules cm−2 at both sites.
This discrepancy may be due to the incorrect assumption that all glyoxal
observed by satellite is within the boundary layer, or it may be due to
challenges retrieving low VCDs of glyoxal over the oceans due to
interferences by liquid water absorption or the use of an inappropriate
normalisation reference value in the retrieval algorithm. This study
provides much-needed data to verify the presence of these short-lived gases
over the remote ocean and provide further evidence of an as yet unidentified
source of both glyoxal and also methylglyoxal over the remote oceans. |
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