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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. 2007 INTEX Data Meeting. Introduction. HCl in Troposphere

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2007 INTEX Data Meeting

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  1. The Vertical Distribution of HCl over the Pacific during INTEX-B Saewung Kim, Bob Stickel, Greg Huey, Melody Avery, Jack Dibb, Brad Pierce 2007 INTEX Data Meeting

  2. 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

  3. 200 400 200 400 HCl (pptv) HCl (pptv) Vertical Profile of HCl over Remote North Pacific - UTLS shows highest HCl from stratospheric influence and Marine Boundary layer shows enhanced HCl (~ 30 pptv) Median UTLS(8-12km) ~ 5-10 times higher than what we measured Mid-Trop (boundary layer – 8 km) Keene et al. 1999. HCl profile over Remote Ocean - 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. Marine Boundary Layer 2007 INTEX Data Meeting

  4. 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 NaCl (aq) VOC HNO3 Cl HCl Precipitation Aerosol Deposition (Z = 0 – 1 km) HCl lifetime ~ 5 hours [Cl] ~ 3,000 molec. cm-3 2007 INTEX Data Meeting

  5. 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

  6. 2006/05/07 RAQMS vs Huey HCL RAQMS vs Avery O3

  7. HCl in Remote Mid -Troposphere (4-8 km) Spiral 2 is enhanced in pollutants and dust Stratosphere? No high O3 ,High CO, High H2O(g) - Negative Where does Enhanced HCl come from in spiral 2 Spiral 1 – typical HCl behavior Spiral 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. Marine Boundary Layer? Low CH3I, CH3NO3 - Negative 2007 INTEX Data Meeting

  8. 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. 2007 INTEX Data Meeting

  9. INTEX (Intercontinental Chemical Transport Experiment) –B, Spring 2006 Anchorage Houston Honolulu HCl was measured during Anchorage deployment over remote ocean Flying from Boundary layer upto lower stratosphere(0 - 12km) 2006 Graduate Student Symposium

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