2007 INTEX Data Meeting

The Vertical Distribution of HCl over the Pacific during INTEX-B

Saewung Kim, Bob Stickel, Greg Huey, Melody Avery, Jack Dibb, Brad Pierce

Introduction• HCl in Troposphere

– Marine Boundary Layer – NaCl(aq) + HNO3, H2SO4 → HCl (g) (dechlorination, acidification)

– Cl + VOC (CH4, C2H6, etc.) → HCl– Estimates of [Cl] range from 103 – 105 molec. cm-3

– HCl observations range from – tens to hundreds of pptv up to altitudes of 6 km.

– Upper Trop. - Marcy et al. [2004] report low background levels of HCl (< 5 pptv) but observe significant levels correlated w/ stratospheric ozone. Inconsistent w/ earlier studies.

• HCl in Stratosphere – Primary source CFCs → Cl + CH4 → HCl– Levels ~ 1 ppbv

2007 INTEX Data Meeting

2007 INTEX Data Meeting

Vertical Profile of HCl over Remote North Pacific

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806040200HCl (pptv)

Mean HCl Average HCl

UTLS(8-12km)

Mid-Trop(boundary layer – 8 km)

Marine BoundaryLayer

- UTLS shows highest HCl from stratospheric influence and Marine Boundary layer shows enhanced HCl (~ 30 pptv)

200 400 200 400HCl (pptv) HCl (pptv)

- Keene et al., 1999 calculated HCl budget of global troposphere with above profiles of HCl over remote ocean environment. They reported large deficit in source of HCl.

~ 5-10 times higher than what we measured

Keene et al. 1999. HCl profile over Remote Ocean

Median

2007 INTEX Data Meeting

HCl in Marine Boundary Layer

-The strong correlation with HNO3 in the remote ocean boundary layer is consistent with HCl production by dechlorination.HCl at low HNO3 may be due to Cl atoms

HCl

NaCl (aq) VOC

Deposition(Z = 0 – 1 km)

HNO3 Cl

Precipitation

Aerosol

HCl lifetime ~ 5 hours[Cl] ~ 3,000 molec. cm-3

HCl in Upper Trop. and Lower Strat.

-HCl has very strong correlation with O3

-Observations are consistent with Marcy et al. but slope ~ a factor of 2 lower.

- For Anchorage deployment 41% of air masses above 8 km contain observable HCl i.e. recent stratospheric input.

(Z = 8 – 12 km)

2007 INTEX Data Meeting

2006/05/07RAQMS vs Huey HCLRAQMS vs Avery O3

2007 INTEX Data Meeting

HCl in Remote Mid -Troposphere (4-8 km)

Spiral 1 – typical HCl behaviorSpiral 2 - HCl was observed in the mid-troposphere but doesn’t appear to be from MBL or stratosphere. May be due to acidification of mineral dust.

Spiral 2 is enhanced inpollutants and dust

Wheredoes Enhanced HClcome from in spiral 2

Stratosphere?No high O3 ,High CO, High H2O(g) - Negative

Marine BoundaryLayer?Low CH3I, CH3NO3 - Negative

2007 INTEX Data Meeting

Summary

1. HCl in marine boundary layer is primarily due to acidification of sea salt and extends to less than 4 km.

2. Observed levels of HCl in MBL are consistent with lower estimates of Cl atom levels of ~103 molec. cm-3.

3. Background levels of HCl in mid and upper troposphere are almost always below detection limit (< 2 pptv).

4. HCl is an excellent tracer for stratospheric influence above 8 km. However, acidification of mineral dust or other mechanisms may produce HCl in the free troposphere.

5. Observed levels of HCl in the troposphere are considerably lower than previous observations.

2006 Graduate Student Symposium

INTEX (Intercontinental Chemical Transport Experiment) –B, Spring 2006

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9:00 PM5/9/2006

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Anchorage

HoustonHonolulu

Flying from Boundary layer uptolower stratosphere(0 - 12km)

HCl was measured during Anchoragedeployment over remote ocean