Vertical transport of chemical compounds from the surface to the UT/LS:

What do we learn from SEAC4RS?

Qing Liang1

&

Thomas Hanisco2, Steve Wofsy3, Jasna Pittman3, Elliot Atlas4, Sue Schauffler5, Donald R. Blake6, Rushan Gao7, Thomas Ryerson7, Paul Wennberg8, Michael Manyin9

1 NASA Goddard Space Flight Center/ USRA GESTAR2 NASA Goddard Space Flight Center3 Harvard University4 University of Miami5 NCAR Atmospheric Chemistry Observations and Modeling Laboratory6 University of California, Irvine

7 NOAA ESRL8 California Institute of Technology9 NASA Goddard Space Flight Center/SSAI

Motivation and Goals

Surface to the UT/LS transport of trace gases can exert significant impacts on atmospheric abundances of ozone (O3) and hydroxyl radical (OH), which will have chemical and radiative impacts on the atmosphere.• Vertical transport of CO and NMHCs

• Vertical transport of very-short-lived (VSL) halogen compounds, i.e. CHBr3 and CH2Br2.

Questions of interest• What is the surface to UT/LS transport timescale?• What are transport efficiency of chemical compounds (the impact of tracer lifetime and solubility)? • What are the regional differences in convective lofting – North America (SEAC4RS & DC3) vs. the Western Pacific (ATTREX/CONTRAST)?

• V2 - GEOS-5 with standard stratospheric chemistry and detailed VSL bromocarbons • V3 - GEOS-5 with stratosphere-troposphere full chemistry• GCM simulations for the SEAC4RS period

o Horizontal resolution is 2° latitude x 2.5° longitudeo 72 vertical layers from surface to 0.01 hPa, with ~1 km/layer resolution at the UT/LS region

(will conduct a future simulation with MERRA meteorology further comparison)

NASA GEOS-5 Chemistry Climate Model (GEOSCCM)

The model simulations are sampled at the same geographical and vertical location for the corresponding time as the observations for model-observation comparison.

Two new CO2 tracers

– transport clock as well as model transport diagnostics1) Regular CO2 - with surface boundary conditions

from the NOAA observations (latitude and monthly variable)

2) Annual CO2 – same as regular CO2 but with seasonal cycle removed at all latitude grids.

Model annual-based CO2 shows a linear correlation with age of air, thus an accurate clock tracer for transport

CO2 as a transport clock tracer

CO2 as a transport clock tracer

However, the actual application as a clock tracer is complicated due to the surface seasonal variations in CO2

Model CO2 with seasonality

Evaluation of model transport with observed CO2

• GEOSCCM modeled CO2 agrees well with the SEAC4RS observations• A slight high CO2 bias at 350-370 K – vertical transport is biased slow (insufficient convective injection?)

Quantification of vertical transport timescale using model age of air

Average ascent rate ~ 6 days/K (2 months/10K)

Model transport slow-biased?

Surface to UT/LS transport of pollution tracers

CO C2H2 C2H6

Loss reactions CO + OH -> C2H2 + OH ->C2H2 + O3 ->

C2H6 + OH -> C2H5 --> CH3CHO --> PANC2H6 + Cl -> C2H5 --> CH3CHO --> PAN

400-450K ~ 2 years ~ 6 months ~ 4 months

350-400K ~ 1 year ~ 10 months ~ 10 monthsTroposphere ~ 1 month ~ 0.5 month ~ 3 months

Tracer lifetime At different layers

The increasing efficiency of C2H6 loss via the C2H6 + Cl reaction creates a large vertical as well as tropical vs. high-latitude gradients in C2H6 -> making C2H6 an excellent transport tracer for tropical convective lofting.

Convective injection above 350K?

GEOSCCM vs. Observations

Credible transportCredible OH

Lack of the critical C2H6 + Cl; Missing surface emissions

Why a stratospheric ozone bias (~ +200 ppb)? Chemical?

Not enough convective scavenging

Surface to UT/LS transport of CHBr3 and CH2Br2

-- Model vs. ObservationsCHBr3 CH2Br2

Model high bias(JPL-10 k-OH-CH2Br2 too slow for T ~200K range??)

Tropospheric low biases -> Surface emissions of CHBr3 and CH2Br2 are too small?

This contradicts the findings from the Western Pacific observations (CONTRAST) as well as those in Hossaini et al. (2013) (GEOSCCM emissions are fine, slightly high-based).

High levels of CHBr3 and CH2Br2 during SEAC4RS

SEAC4RS

~12 ppt Br in the MBL

High CHBr3/CH2Br2 ratios during SEAC4RS

Pacific campaigns

Emission ratio:1.3 ppt CHBr3/1 ppt CH2Br2

High CHBr3/CH2Br2 ratios during SEAC4RS

Pacific campaigns

Emission ratios:1.3 ppt CHBr3/1 ppt CH2Br2

3.0 ppt CHBr3/1 ppt CH2Br2

(Gulf of Mexico)

High CHBr3/CH2Br2 ratios during SEAC4RS

Pacific campaigns

Emission ratios:1.3 ppt CHBr3/1 ppt CH2Br2

3.0 ppt CHBr3/1 ppt CH2Br2

2.0 ppt CHBr3/1 ppt CH2Br2

(Gulf of Mexico)

(US East coast)

The Atlantic Ocean features much higher biogenic bromocarbon emissions, in particular CHBr3, than the Pacific Ocean

~ 6 ppt organic Br at the base of TTL + inorganic products (ppt??)

VSL bromine at the North American tropical UT

• Rapid convective ventilation below 355K topped by slow ascent from 355K to 450K at a rate of ~6 days/K

• Among all potential choices, C2H6 appears as an excellent convective transport tracer for pollution

• SEAC4RS C2H6 observations indicate sporadic convective injection above 355K

• The Golf of Mexico (and the Atlantic Ocean) features very high emissions of very-short-lived bromocarbons, in particular CHBr3 (~12 ppt organic Br available at the surface)– Need to revisit the VSLS emissions as the same emission distribution does

apply to both CHBr3 and CH2Br2

– How much of this surface VSL bromine gets to the stratosphere?

• How does the surface to UT/LS transport over continental US (DC3) and the western Pacific (CONTRAST/ATTREX) differ from SEAC4RS?

Conclusions and future work