1 MAX-DOAS IO and BrO measurements in the western pacific boundary layer Enno Peters 1, Katja Grossmann 2, Folkard Wittrock 1, Udo Frieß 2, Anja Schönhardt 1, Andreas Richter 1, John P. Burrows 1, Kirstin Krüger 3, Birgit Quack 3 EGU Vienna, Institut für Umweltphysik, Universität Bremen 2 Institut für Umweltphysik, Universität Heidelberg 3 IFM GEOMAR, Kiel

2 I.Introduction

3 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 I 2 from ocean surface?)

4 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 Schönhardt University of Bremen, 2009 Selected references: Wittrock et al., GRL, 2000 Friess et al., GRL, 2001 McFiggans et al., ACP, 2004 Peters et al., ACP, 2005 Saiz-Lopez et al., ACP, 2006 Saiz-Lopez et al., Science, 2007 Carpenter et al., Mar.Chem., 2007 Read et al., Nature, ppt 2 ppt 2,8 ppt 6 ppt 10 ppt 2,2 ppt 10 ppt Published maximum VMR

5 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)

6 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 unit Spectrometers Scheme of a MAX-DOAS instrument Multi Axis - Differential Optical Absorption Spectroscopy

7 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 unit Spectrometers Scheme of a MAX-DOAS instrument

8 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

9 II.Measurements & results

10 Fitting window: – nm  Three IO absorption bands Considered cross sections: Ozone, NO 2, IO, H 2 O, 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 , 3° elevation Slant column ~ 2.6*10 13 molec/cm 2 Fit error 13.7 % 0.1 s exposure time 30 s integration time

11 Bremen Heidelberg DOAS IO fit 5° Elevation Error < 30% IO Slant columns from Heidelberg 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) Correlation 3° elevation: 72% 5° elevation: 67%

12 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)

13 IO volume mixing ratios Example day: (Day with good weather conditions/sight)

14 IO volume mixing ratios Mixing Layer Height, (from radiosondes measurements) Time of MAX-DOAS measurements  ~ 500 – 800 m Vertical averages during the day: Lowest 800 m: 0.4 – 0.8 ppt Lowest 500 m: 0.4 – 0.9 ppt Lowest 200 m: up to 1.1 ppt (Local time)

15 IO volume mixing ratios Lowest 800 m Mean VMR in MBL (assumed to be): m : Range between 0.4 – 0.9 ppt (Local time)

16 Complementary data Map kindly provided by Tilman Dinter, IUP Bremen Highest IO values over open ocean at low chlorophyll content  No biogenic release source (Local time)

17 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)

18 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)

19 BrO results (Local time) Simple geometric approach: Assuming BrO in 1000 m box profile: Slant Colums in 1°, 4°, 8° Errors < 30 % Map provided by Tilman Dinter, IUP Bremen

20 III.Summary

21 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 a 1000 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)

22 Thank you!