Toward a High Degree of Freedom Retrieval of BrO

from Mountaintops Theodore K. Koenig1,2, Barbara Dix1, François Hendrick3,

Nicolas Theys3, Michel Van Roozendael3, Jérôme Brioude4,5, Jean-Pierre Cammas5, Rainer Volkamer1,2

1Dep. of Chemistry & Biochemistry, University of Colorado, Boulder, CO;

2CIRES, University of Colorado, Boulder, CO;

3UV-VIS , BIRA-IASB, Uccle, Belgium;

4University of La Réunion, St. Denis, France;

5LACy, OSU-Réunion, St. Denis, France

MAX-DOAS on mountaintops on tropical ocean islands

• Mountaintop Observatories at Mauna Loa on Hawai’i and Maïdo on La Réunion • Aircraft campaigns (TORERO in blue; CONTRAST in green) used for BrO a priori profiles

• CONTRAST included research flight near MLO during prior 2014 deployment, useful as a case study to test retrievals

• Both mountaintops operating since February 2017 with some interruption • Intensive Operating Period currently underway at Maïdo

Generation 1 retrieval approach

dSCD = VCDtropAMFtrop(θ,φ,α)+VCDstratAMFstrat(θ,φ) - SCDRef

Daily stratospheric

O3 VCD

Daily stratospheric

NO2 VCD

BrO/ Bry

BrO/ Bry

Daily noontime stratospheric BrO a priori profile

SLIMCAT

DISORT Chemically corrected

diurnal variation

Langley Plots

Theys et al., A

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Aircraft measured tropospheric

BrO a priori profile

Wang et al., PNAS, 2015, doi: 10.1073/pnas.1505142112. Dix et al., AMT, 2016, doi: 10.5194/amt-9-5655-2016. Koenig et al., ACP, 2017, doi: 10.5194/acp-17-15245-2017.

Rayleigh Atmosphere

McArtim

Theys et al., ACP, 2007, doi: 10.5194/acp-7-4733-2007.

Stratospheric NO2 and O3 VCDs to build stratospheric BrO a priori

New spectrometer will include O3

Comparison of a priori profiles

• Maximum stratospheric a priori correspond to O3 and NO2 maxima, late spring to early summer

• Wang a priori reflects average of optimal estimation case studies from TORERO

• Dix a priori reflects TORERO campaign average using parameterization

• Koenig a priori reflects CONTRAST optimal estimation case studies • Near surface concentrations reflect

averaging over wide variability

• Connecting tropospheric and stratospheric profiles presents a challenge. • Limited information from

measurements and few studies quantify BrO both below and above the tropopause

CONTRAST RF01 case study

• Measurement site was cloud bound at time of flights precluding direct comparison

• Profiles are numbered sequentially for each ascent or descent including interior level legs

CONTRAST RF01: January 11, 2014

RF01-06

RF01-07

RF01-08

Chemical and dynamic context for case study

• Rossby wave breaking event leads to stratospheric intrusion • evident from increased

O3 and potential temperature

• Broadly the three profiles are similar, but • RF01-06 has a lofted

layers around 3 -4 km

• Layering of O3 is different at high altitude

Comparison of case study with campaign averages • Using data from all

three profiles and flat concentration a priori run first optimal estimation

• Then use retrieved profile as a priori for optimal estimation of individual profiles

• RF01-06 has significant BrO at surface as well as enhanced BrO aloft

• Difference in Ozone layering appears smoothed over

• For mountaintop pooled profile is roughly same as Dix et al.

Langley plot determination of SCDRef for January 2014 data

• Using different subsets of data SCDRef is between 5.8×1013 and 6.3×1013 molecules cm-2

• With SCDRef and a priori profiles to get Air Mass Factors have components needed for Theys et al. 2007 equation BrO dSCDs from MLO for January 2014

Application of Theys et al. 2007 method

Tropospheric a priori

SCDref

(molec cm-2) Trop VCD (<15km)

(molec cm-2)

Strat VCD (>15km)

(molec cm-2)

Total VCD (molec cm-2)

Wang et al. 5.8x1013 0.98±0.04x1013 1.48±0.04x1013 2.46±0.08x1013

Dix et al. 5.8x1013 0.77±0.03x1013 1.77±0.04x1013 2.54±0.07x1013

Koenig et al. 5.8x1013 0.71±0.04x1013 2.07±0.03x1013 2.78±0.07x1013

Wang et al. 6.3x1013 1.10±0.04x1013 1.45±0.05x1013 2.55±0.09x1013

Dix et al. 6.3x1013 0.87±0.04x1013 1.77±0.04x1013 2.64±0.08x1013

Koenig et al. 6.3x1013 0.81±0.04x1013 2.11±0.04x1013 2.92±0.08x1013

dSCD = VCDtropAMFtrop(θ,φ,α)+VCDstratAMFstrat(θ,φ) - SCDRef

• Tropospheric a priori profiles with more BrO aloft fit a larger tropospheric VCD, a smaller stratospheric VCD, and a larger total BrO VCD

• Stratospheric VCD increases out of proportion to decrease in tropospheric VCD

Examination of fitted VCDs to measured dSCDs at different elevation angles

• Zenith data indicate that lower SCDRef is more likely to be accurate

• Wang et al. fits to low angles most closely, underestimates high angles least

• Fits suggest that even Wang et al. overestimates low altitude BrO, and underestimates BrO aloft

Dashed lines: SCDRef = 5.8 × 1013 molec. cm-2 Solid lines: SCDRef = 6.3 × 1013 molec. cm-2

Generation 2 retrieval approach

dSCD = VCDtropAMFtrop(θ,φ,α)+VCDstratAMFstrat(θ,φ) - SCDRef

Daily stratospheric

O3 VCD

Daily stratospheric

NO2 VCD

BrO/ Bry

BrO/ Bry

Daily noontime stratospheric BrO a priori profile

SLIMCAT

DISORT

Langley Plots

Theys et al., A

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Aircraft measured tropospheric

BrO a priori profile

Wang et al., PNAS, 2015, doi: 10.1073/pnas.1505142112. Dix et al., AMT, 2016, doi: 10.5194/amt-9-5655-2016. Koenig et al., ACP, 2017, doi: 10.5194/acp-17-15245-2017.

Rayleigh Atmosphere

McArtim

Theys et al., ACP, 2007, doi: 10.5194/acp-7-4733-2007.

VLIDORT

Optimal Estimation

Aerosol

Optimal Estimation

Average tropospheric BrO profile

Optimal Estimation

Average stratospheric BrO profile

Chemically corrected

diurnal variation

Self consistency determination of SCDRef to increase Degrees of Freedom aloft

• Scale BrO profile iteratively until a priori and a posteriori SCDRef match

• NB: altitude grid resolution is not constant

• Additional information is located 2-20 km above instrument altitude

Coburn et al., ACP, 2016, doi: 10.5194/acp-16-3743-2016.

Generation 3 retrieval approach

Daily stratospheric

O3 VCD

Daily stratospheric

NO2 VCD

BrO/ Bry

BrO/ Bry

Daily noontime stratospheric BrO a priori profile

SLIMCAT

DISORT

Langley Plots

Theys et al., A

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Aircraft measured tropospheric

BrO a priori profile

Rayleigh Atmosphere

McArtim VLIDORT

Optimal Estimation

Aerosol

Optimal Estimation

Average tropospheric BrO profile

Optimal Estimation

Specific stratospheric BrO profile

SCDRef

Box Model

Optimal Estimation

Specific tropospheric BrO profile

VLIDORT

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Specific full BrO profile

Chemically corrected

diurnal variation

Outlook

• Need to efficiently capture radiative transfer • Examining VLIDORT as an option

• mountaintops are near Rayleigh, explicit O2-O2 based optimal estimation may be practical

• LUT approach also being examined

• Possible parameterization approach?

• Need to define data set with which to test approaches • Have roughly one year of data

from Maïdo and MLO • Generating cloud flag leveraging

O2-O2 and color ratios