MAX-DOAS IO and BrO measurements in the western pacific boundary layer

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MAX-DOAS IO and BrO measurementsin the western pacific

boundary layer

Enno Peters1, Katja Grossmann2, Folkard Wittrock1, Udo Frieß2, Anja Schönhardt1,Andreas Richter1, John P. Burrows1, Kirstin Krüger3, Birgit Quack3

EGU Vienna, 05.04.2011

1 Institut für Umweltphysik, Universität Bremen2 Institut für Umweltphysik, Universität Heidelberg3 IFM GEOMAR, Kiel

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I. Introduction

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Introduction

Importance:

Ozone depletion due to catalytic IO reactions

Sources of IO:

1. Organic sources emitting precursors and photolysis

• Seaweed

• Phytoplankton, algae (under ice spring bloom of ice algae producing organohalogens)

2. Other/Inorganic sources (directly from sea salt? / direct emission of I2

from ocean surface?)

http://seaweed.ucg.ie

http://en.wikipedia.org

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Introduction

Where has IO already been measured?

• Measurements mostly in polar regions (e.g. Spitsbergen, Antarctica) and • coastal regions, (e.g. Mace Head (Ireland), Tenerife, Tasmania).

Adapted from Anja SchönhardtUniversity of Bremen, 2009

Selected references:Wittrock et al., GRL, 2000Friess et al., GRL, 2001McFiggans et al., ACP, 2004Peters et al., ACP, 2005Saiz-Lopez et al., ACP, 2006Saiz-Lopez et al., Science, 2007Carpenter et al., Mar.Chem., 2007Read et al., Nature, 2008

1 ppt

2 ppt

2,8 ppt

6 ppt

10 ppt

2,2 ppt

2,2 ppt10 ppt

Publishedmaximum VMR

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Introduction

0 ?

IO from satellite instruments see poster session (Anja Schönhardt)

• Satellites provide global image of trace gases

• But: Problems over oceans due to low albedo and spectral structures from water

• MAX-DOAS more sensitive to tropospheric absorbers

• Opportunity to go there and check for the background (how much IO over open ocean)

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MAX-DOAS measurements

• Measuring spectra of scattered sunlight• Deriving trace gas columns and profiles from absorption features• High sensitivity for stratospheric absorbers during twilight ( am and pm values)

Light

Y-shaped optical fibre

Telescope unitSpectrometers

Scheme of a MAX-DOAS instrument

Multi Axis - Differential Optical Absorption Spectroscopy

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MAX-DOAS measurements

Multi Axis - Differential Optical Absorption Spectroscopy

• Measuring spectra of scattered sunlight• Deriving trace gas columns and profiles from absorption features• High sensitivity for stratospheric absorbers during twilight ( am and pm values)• High sensitivity for tropospheric absorbers using off-axis measurements• Converting slant columns into vertical columns/profiles

using radiative transfer models

Light

Y-shaped optical fibre

Telescope unitSpectrometers

Scheme of a MAX-DOAS instrument

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Y-shaped optical fiber bundle in

• UV-spectrometer: 315 – 384 nm (0,033 nm/pixel, resolution ~ 0,4 nm)

• Vis-spectrometer: 400 – 573 nm (0,13 nm/pixel, resolution ~ 0,8 nm)

The Bremen MAX-DOAS campaign instrument

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II. Measurements & results

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• Fitting window: 417.5 – 438.2 nm Three IO absorption bands

• Considered cross sections: Ozone, NO2, IO, H2O, VRS, Ring, Offset (straylight)

• Other fit parameters: Quadratic polynomial, fixed daily reference spectrum at 45° SZA (to avoid direct sunlight and saturation effects)

DOAS IO fit

Fit example from 14.10.2009, 3° elevation

Slant column ~ 2.6*1013 molec/cm2

Fit error 13.7 %

0.1 s exposure time30 s integration time

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BremenHeidelberg

DOAS IO fit

5° ElevationError < 30%

IO Slant columns 13-14.10.2009 fromHeidelberg and Bremen instruments

Data plotted with error < 30%, 5° Elevation

(Local time)

• More frequent Heidelberg data, because Bremen performed much more angles

• Heidelberg tends to be a bit higher than Bremen

For Heidelberg data & analysis see poster session (Katja Grossmann)

Correlation3° elevation: 72%5° elevation: 67%

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IO slant columns

IO slant colums in 1°, 6°, 15°

Error < 30%

• Slant columns separated under clear weather conditions (due to different light path) contain information about profile

• Using the profile retrieval BREAM (OEM)

(Local time)

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IO volume mixing ratios

Example day: 14.10.2009(Day with good weather conditions/sight)

14.10.2009

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IO volume mixing ratios

Mixing Layer Height, 14.10.2009(from radiosondes measurements)

Time of MAX-DOAS measurements ~ 500 – 800 m

Vertical averages during the day:Lowest 800 m: 0.4 – 0.8 pptLowest 500 m: 0.4 – 0.9 pptLowest 200 m: up to 1.1 ppt

(Local time)

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IO volume mixing ratios

Lowest 800 m

Mean VMR in MBL (assumed to be):• 0-800 m : Range between 0.4 – 0.9 ppt

(Local time)

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Complementary data

Map kindly provided by Tilman Dinter, IUP Bremen

Highest IO values over open oceanat low chlorophyll content

No biogenic release source

(Local time)

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BrO results

• BrO only detected three times (Oct 20, 21, 22), most reliable at Oct 21 afternoon

Slant Colums in 1°, 4°, 8°Errors < 30 %

(Local time)

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BrO results

• BrO only detected three times (Oct 20, 21, 22), most reliable at Oct 21 afternoon• Viewing angles not well separated• Profiling with RTM not useful

Slant Colums in 1°, 4°, 8°Errors < 30 %

(Local time)

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BrO results

(Local time)

• Simple geometric approach:

• Assuming BrO in 1000 m box profile:

212 molec/cm 103VC

ppt 1V MR

Slant Colums in 1°, 4°, 8°Errors < 30 %

Map provided by Tilman Dinter, IUP Bremen

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III. Summary

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Summary

Remote sensing IO and BrO measurements have been performed over the western pacific ocean during the TransBrom campaign.

In contrast to expectations, IO shows highest concentrations over open ocean (0.4 to 1.1 ppt) at low chlorophyll content, no reliable observation in coastal regions.

No tropospheric BrO found, only three “events” in the coral sea at late afternoon/evening local time.

As profiling is not possible, a rough estimation gives about 1 ppt BrO assuming a1000 m thick box profile.

For further interest see at poster session:

• “Shipborne MAX-DOAS Measurements of Reactive Halogen Species over the Western Pacific and the Eastern North Atlantic” (Katja Grossmann)

• “Analysing satellite data for IO vertical columns in polar and tropical regions” (Anja Schönhardt)

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Thank you!