____________________________Near Tropopause Halogen

Heterogeneous Chemistry Indicators using Occultation Observations and

CESM1 (WACCM) Simulations________________________________

Doug Kinnison, (NCAR, USA)Susan Solomon and Catherine Wilka (MIT, USA)

Special Thanks to Lynn Harvey (LASP, USA)

Whole Atmosphere Working Group , 19 June 2018

Hypothesis: Occultation NO2 observations (e.g., SAGEII, SAGEIII-Meteor, and

SAGEIII-ISS) can be used as an indicator of near tropopause heterogeneous halogen activation.

Heterogeneous Chemistry: Heterogeneous halogen reactions on sulfate converts NO2 to reservoir

species, e.g.,NO2 + ClO + M => ClONO2 +M, ClONO2 + hv => ClO + NO2 (fast recycling)

ClONO2 + HCl (het) => HNO3 + Cl2 ClONO2 + H2O (het) => HNO3 + HOCl

Approach: Compare profile output from SAGE instruments to two SD-WACCM

(MERRA) simulations: 1) with sulfate halogen chemistry; 2) without sulfate halogen chemistry. Water-Ice Het chemistry is turned off.

The N2O5 + H2O => 2HNO3 heterogeneous reaction is included in all simulations, i.e., only looking at the halogen impact.

With and Without Heterogeneous Halogen Chemistry

Monsoon Region• Lat: 0-30N, • Lon: 0-180E• Period: July• SAGEII• Solomon et al.,

JGR, 2017.

Subpolar Region1• Lat: 45S-60S• Lon: 0-360.• Period: Sept.-Oct. • SAGEIII-Meteor

Subpolar Region2• Lat: 50S-67S• Lon: 0-360• Period: Oct-Nov• SAGEIII-ISS

SD-WACCM/MERRA 24-hour average results shown above.

Three illustrious regions are shown.

SAGEII

SAGEIII-Meteor SAGEIII-ISS

Northern Hemisphere, Summer, Monsoon Region

Solomon, S., D. E. Kinnison, R. R. Garcia, J. Bandoro1, M. Mills, C. Wilka, R. R. Neely III, A. Schmidt, J. Barnes, J-P Vernier, M. Hopfner, Monsoon circulations and tropical heterogeneous chlorine chemistry in the stratosphere, Geophys. Res. Lett., doi:10.1002/2016GL071778, 2016.

July, 2011

Transport processes associated with the summer monsoon can create a”perfect storm” in which abundances of HCl can be brought into contactwith liquid sulfate aerosols near the cold tropical tropopause leading toheterogeneous chemical activation. Solomon et al., 2016.

HCl => ClO

Why SAGEII

Tick Marks are the 15th of the given month.

July *** Lat: 0-30N *** Lon: 0-180E *** 1984-2005Observations

Total Profiles = 1049

Temperatures are <200K in the Lower Stratosphere (red line).

July *** Lat: 0-30N *** Lon: 0-180E *** 1984-2005Model

Model species profiles are in good agreement in absolute magnitude with SAGEII.

SAGEII limit

July *** Lat: 0-30N *** Lon: 0-180E *** 1984-2005Model

Red dashed lines show region where halogen heterogeneous activation occurs.

July *** Lat: 0-30N *** Lon: 0-180E *** 1984-2005Model NoHet

Without halogen heterogeneous chemistry NO2 depletion is reduced.

July *** Lat: 0-30N *** Lon: 0-180E *** lev: 118-68hPa

PDFs were created for region between the previous slide red dashed lines.

total points = 2702 25 pptv bin width

July *** Lat: 0-30N *** Lon: 0-180E *** lev: 118-68hPa

OBS and WACCM have a higher frequency of low NO2

OBS and WACCM have a lower frequency of high NO2 relative to NoHet

total points = 2702 25 pptv bin width

Tick Marks are the 15th of the given month.

SAGE III - Meteor

SAGEIII-Meteor has better Vertical Resolution, Extent, and Accuracy than SAGEII

Southern Hemisphere, Spring, Subpolar Region 1

1 Sept – 15 Oct ** Lat 56-48S ** Lon 0-360 ** 2003-2005Observations

Temperatures are <200K in the Lower Stratosphere (red line).

Total Profiles = 2045

1 Sept – 15 Oct ** Lat 56-48S ** Lon 0-360 ** 2003-2005Model

Model species profiles are in good agreement in absolute magnitude with SAGEIII-M.

1 Sept – 15 Oct ** Lat 56-48S ** Lon 0-360 ** 2003-2005Model

Red dashed lines show region where NO2 PDFs will be derived.

Log Scale

Sept – Oct ** Lat: 56-48S ** Lon: 0-360 ** 2003-2005Model NoHet

Without halogen heterogeneous chemistry NO2 depletion is reduced.

Sept-Oct ** Lat: 56-48S ** Lon; 0-360 ** lev; 170-72hPa

total points = 8064

OBS have a higher frequency of low NO2 relative to WACCM?

25 pptv bin width

Lat: 56-48S *** Lon: 0-360 *** lev: 170-72hPa

OBS and WACCM have a higher frequency of low NO2

OBS and WACCM have a lower frequency of high NO2 relative to NoHet

total points = 8064 25 pptv bin width

Tick Marks are the 15th of the given month.

SAGE III - ISS

SAGEIII-ISS has better global coverage than SAGEIII-Meteor.

Southern Hemisphere, Spring, Subpolar Region 2

15 Oct - 15 Nov *** Lat 67-50S *** Lon 0-360 *** 2017

This comparison is later in the year and higher in latitude than the SAGEIII-Meteor.

H2O Vapor not available.

Observations

Total Profiles = 238

15 Oct - 15 Nov *** Lat 67-50S *** Lon 0-360 *** 2017Model

Model NO2 profiles are in good agreement in absolute magnitude with SAGEIII-ISS.

15 Oct - 15 Nov *** Lat 67-50S *** Lon 0-360 *** 2017Model

Less Chlorine activation shown in the years 2003-2005 (SAGEIII-Meteor comparison).

15 Oct - 15 Nov *** Lat 67-50S *** Lon: 0-360 *** 2017Model NoHet

Oct-Nov ** Lat: 67-50S ** Lon: 0-360 ** lev; 180-72hPa

Excellent Model / SAGEIII – ISS agreement.

total points = 1179 25 pptv bin width

Oct-Nov ** Lat: 67-50S ** Lon; 0-360 ** lev; 180-72hPa

OBS and WACCM have a higher frequency of low NO2 versus the NoHet simulation.

total points = 1179 25 pptv bin width

Summary

• We have shown that NO2 occultation observations (SAGEII, SAGEIII-Meteor, and SAGEIII-ISS) in conjunction with 3-D chemistry climate model results can identify regions where sulfate heterogeneous chemistry is operating in the near tropopause region. This work examined the subtropical and subpolar regions.

• This approach may also be useful in identifying the aerosol / PSC type (e.g., sulfate vs water-ice) based on temperature and H2O vapor considerations.

• This approach can also be applied to ozone and HCl.

Sulfate Aerosol Reaction Probability as function of H2O vapor