Effect of BrO Mixing Height to Ozone

Depletion Events

Sunny Choi

Ozone Depletion Events (ODEs) Low O3 events in polar boundary layer during early

springtime [Oltmans et al., 1981] O3 is destroyed by reactive Br radicals [Barrie et al.,

1988] BrO is dominant species among reactive Br species

during ODEs [Hausmann and Platt, 1994] ODEs change oxidative pathways and removal

process of atmospheric trace species, and may have impacts on local and global environment

Chemistry of ODEs

Condensed phase(liquid brine or ice surface)

HOBr BrCl Br2

Br2BrBrO

HOBr BrCl

BrO

O3

HBr

Gas phase

hv

hvhv

AldehydesAlkenes

HO2

H+, Cl- Br-

H+, Br-

Importance of BrO Mixing Height in ODEs O3 loss rate is proportional to the second order of

BrO concentration Br + O3 BrO + O2 BrO + BrO 2Br + O2 (slow, Rate Determining Step)

d[O3]/dt = -k1[BrO]2

Shallow boundary layer height is prerequisite for ODEs

Different BrO mixing heights can result in significant difference even with the same amounts of tropospheric BrO

Boundary Layer Heights for ODEs in Previous Studies Box models considering NOx and CH2O flux from

snowpack 400m (Michalowski et al., 2000) 200m (Evans et al., 2003)

1-D model considering bromine chemistry 300m (Piot and Glasow, 2008) 200m (Saiz-Lopez et al., 2008)

3-D model considering BrO mixing layer 400m (Zeng et al., 2003)

Model Study

3-D Regional chEmical trAnsport Model (REAM) Tropospheric BrO column derived from GOME-2

satellite total BrO column observation Tropospheric BrO is uniformly distributed in a mixing

layer of a fixed mixing height Set 4 different BrO mixing heights

200m, 400m, 600m and 800m Compare the results to ground-based observation

(at Barrow and Alert) and in-situ measurements during ARCTAS

Tropospheric BrO column and monthly mean surface ozone assuming mixing height is 600m

Low ozone areas coincide with high BrO regions

ODEs are intenser in April because of longer daytime

BrO Tropospheric Column and ODEs

Mar 2008

Apr 2008

Surface O3 Level at Barrow and Alert

Surface O3 depletion depends on the BrO mixing height significantly

Mixing height of 400m shows the best correlation in the simulation using GOME-2 tropospheric BrO column

Surface ozone measurements by S. Oltmans (Barrow) and K. Anlauf (Alert)

Comparison to Ozonesonde Observation at Barrow

Model could not reproduce the vertical extent of ODEs

A shallow mixing height (200m) causes overestimation ODEs on the surface, but a deep mixing height underestimates.

Ozonesonde measurements by S. Oltmans

Comparison of O3 Simulation to ARCTAS in-situ Observation

Correlation between all available measurements below 1km and corresponding simulations

Model reproduce the general trend, but not yet able to catch the detail

ODEs cannot happen with a deep mixing layer (800m)

O3 in-situ measurements by A. Weinheimer

Comparison of O3 simulation to O3 Lidar Measurements

Ozone DIAL measurements by J. Hair

Summary Bromine-driven ODEs are simulated using a 3-D model. The rate of O3 loss is proportional to [BrO]^2 With fixed amount of tropospheric BrO column, variation

of mixing height results in significant differences in O3 levels.

Shallow mixing heights (~200m) overestimates O3 depletions at the surface

Mixing heights of 400~600m can reproduce general features of ODEs

ODEs cannot happen with too high mixing heights (~800m)

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