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| Titel |
Aircraft measurements of BrO, IO, glyoxal, NO2, H2O, O2–O2 and aerosol extinction profiles in the tropics: comparison with aircraft-/ship-based in situ and lidar measurements |
| VerfasserIn |
R. Volkamer, S. Baidar, T. L. Campos, S. Coburn, J. P. DiGangi, B. Dix, E. W. Eloranta, T. K. Koenig, B. Morley, I. Ortega, B. R. Pierce, M. Reeves, R. Sinreich, S. Wang, M. A. Zondlo, P. A. Romashkin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 5 ; Nr. 8, no. 5 (2015-05-20), S.2121-2148 |
| Datensatznummer |
250116364
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| Publikation (Nr.) |
 copernicus.org/amt-8-2121-2015.pdf |
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| Zusammenfassung |
| Tropospheric chemistry of halogens and organic carbon over tropical oceans
modifies ozone and atmospheric aerosols, yet atmospheric models remain
largely untested for lack of vertically resolved measurements of bromine
monoxide (BrO), iodine monoxide (IO) and small oxygenated hydrocarbons like
glyoxal (CHOCHO) in the tropical troposphere. BrO, IO, glyoxal, nitrogen
dioxide (NO2), water vapor (H2O) and O2–O2 collision
complexes (O4) were measured by the University of Colorado Airborne Multi-AXis Differential
Optical Absorption Spectroscopy (CU AMAX-DOAS) instrument, aerosol
extinction by high spectral resolution lidar (HSRL), in situ aerosol size
distributions by an ultra high sensitivity aerosol spectrometer (UHSAS) and
in situ H2O by vertical-cavity surface-emitting laser (VCSEL) hygrometer. Data are presented from two research flights (RF12, RF17) aboard
the National Science Foundation/National Center for Atmospheric
Research Gulfstream V aircraft over the tropical Eastern Pacific Ocean (tEPO) as
part of the "Tropical Ocean tRoposphere Exchange of Reactive halogens and
Oxygenated hydrocarbons" (TORERO) project (January/February 2012). We assess the
accuracy of O4 slant column density (SCD) measurements in the presence
and absence of aerosols. Our O4-inferred aerosol extinction
profiles at 477 nm agree within 6% with HSRL in the boundary layer and
closely resemble the renormalized profile shape of Mie calculations
constrained by UHSAS at low (sub-Rayleigh) aerosol extinction in the free
troposphere. CU AMAX-DOAS provides a flexible choice of geometry, which we
exploit to minimize the SCD in the reference spectrum (SCDREF, maximize
signal-to-noise ratio) and to test the robustness of BrO, IO and glyoxal
differential SCDs. The RF12 case study was conducted in pristine marine and
free tropospheric air. The RF17 case study was conducted above the NOAA RV Ka'imimoana (TORERO cruise, KA-12-01) and provides independent validation
data from ship-based in situ cavity-enhanced DOAS and MAX-DOAS. Inside the
marine boundary layer (MBL) no BrO was detected (smaller than 0.5 pptv), and
0.2–0.55 pptv IO and 32–36 pptv glyoxal were observed. The near-surface
concentrations agree within 30% (IO) and 10% (glyoxal) between ship
and aircraft. The BrO concentration strongly increased with altitude to 3.0 pptv at 14.5 km (RF12, 9.1 to 8.6° N; 101.2 to 97.4° W).
At 14.5 km, 5–10 pptv NO2 agree with model predictions and demonstrate
good control over separating tropospheric from stratospheric absorbers
(NO2 and BrO). Our profile retrievals have 12–20 degrees of freedom
(DoF) and up to 500 m vertical resolution. The tropospheric BrO vertical column density (VCD) was 1.5 × 1013 molec cm−2 (RF12)
and at least 0.5 × 1013 molec cm−2 (RF17, 0–10 km, lower limit). Tropospheric IO VCDs correspond to
2.1 × 1012 molec cm−2 (RF12) and 2.5 × 1012 molec cm−2
(RF17) and glyoxal VCDs of 2.6 × 1014 molec cm−2 (RF12) and 2.7 × 1014 molec cm−2 (RF17).
Surprisingly, essentially all BrO as well as
the dominant IO and glyoxal VCD fraction was located above 2 km (IO:
58 ± 5%, 0.1–0.2 pptv; glyoxal: 52 ± 5%, 3–20 pptv). To our
knowledge there are no previous vertically resolved measurements of BrO and
glyoxal from aircraft in the tropical free troposphere. The atmospheric
implications are briefly discussed. Future studies are necessary to better
understand the sources and impacts of free tropospheric halogens and
oxygenated hydrocarbons on tropospheric ozone, aerosols, mercury oxidation
and the oxidation capacity of the atmosphere. |
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