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) + HNO 3, H 2 SO 4 → HCl (g) (dechlorination, acidification) –Cl + VOC (CH4, C 2 H 6, etc.) → HCl –Estimates of [Cl] range from 10 3 – 10 5 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 + CH 4 → HCl –Levels ~ 1 ppbv 2007 INTEX Data Meeting

Vertical Profile of HCl over Remote North Pacific UTLS(8-12km) Mid-Trop (boundary layer – 8 km) Marine Boundary Layer - UTLS shows highest HCl from stratospheric influence and Marine Boundary layer shows enhanced HCl (~ 30 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 HCl profile over Remote Ocean Median

2007 INTEX Data Meeting HCl in Marine Boundary Layer -The strong correlation with HNO 3 in the remote ocean boundary layer is consistent with HCl production by dechlorination. HCl at low HNO 3 may be due to Cl atoms HCl NaCl (aq)VOC Deposition (Z = 0 – 1 km) HNO 3 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 O 3 -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

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

2007 INTEX Data Meeting HCl in Remote Mid -Troposphere (4-8 km) 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. Spiral 2 is enhanced in pollutants and dust Where does Enhanced HCl come from in spiral 2 Stratosphere? No high O 3,High CO, High H 2 O(g) - Negative Marine Boundary Layer? Low CH 3 I, CH 3 NO 3 - 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 ~10 3 molec. cm 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 Anchorage Houston Honolulu Flying from Boundary layer upto lower stratosphere(0 - 12km) HCl was measured during Anchorage deployment over remote ocean