HOCl and Cl observations in marine air

TY - JOUR

T1 - HOCl and Cl observations in marine air

AU - Lawler, M.J.

AU - Sander, R.

AU - Carpenter, L.J.

AU - Lee, J.D.

AU - Von Glasow, R.

AU - Sommariva, R.

AU - Saltzman, E.S.

PY - 2011/1/1

Y1 - 2011/1/1

N2 - Cl atoms in the marine atmosphere may significantly impact the lifetimes of methane and other hydrocarbons. However, the existing estimates of Cl atom levels in marine air are based on indirect evidence. Here we present measurements of the Cl precursors HOCl and Cl in the marine boundary layer during June of 2009 at the Cape Verde Atmospheric Observatory in the eastern tropical Atlantic. These are the first measurements of tropospheric HOCl. HOCl and Cl levels were low in air with open ocean back trajectories, with maximum levels always below 60 and 10 ppt (pmol/mol), respectively. In air with trajectories originating over Europe, HOCl and Cl levels were higher, with HOCl maxima exceeding 100 ppt each day and Cl reaching up to 35 ppt. The increased Cl cycling associated with long distance pollutant transport over the oceans likely impacts a wide geographic area and represents a mechanism by which human activities have increased the reactivity of the marine atmosphere. Data-constrained model simulations indicate that Cl atoms account for approximately 15 % of methane destruction on days when aged polluted air arrives at the site. A photochemical model does not adequately simulate the observed abundances of HOCl and Cl , raising the possibility of an unknown HOCl source.

AB - Cl atoms in the marine atmosphere may significantly impact the lifetimes of methane and other hydrocarbons. However, the existing estimates of Cl atom levels in marine air are based on indirect evidence. Here we present measurements of the Cl precursors HOCl and Cl in the marine boundary layer during June of 2009 at the Cape Verde Atmospheric Observatory in the eastern tropical Atlantic. These are the first measurements of tropospheric HOCl. HOCl and Cl levels were low in air with open ocean back trajectories, with maximum levels always below 60 and 10 ppt (pmol/mol), respectively. In air with trajectories originating over Europe, HOCl and Cl levels were higher, with HOCl maxima exceeding 100 ppt each day and Cl reaching up to 35 ppt. The increased Cl cycling associated with long distance pollutant transport over the oceans likely impacts a wide geographic area and represents a mechanism by which human activities have increased the reactivity of the marine atmosphere. Data-constrained model simulations indicate that Cl atoms account for approximately 15 % of methane destruction on days when aged polluted air arrives at the site. A photochemical model does not adequately simulate the observed abundances of HOCl and Cl , raising the possibility of an unknown HOCl source.

UR - http://www.scopus.com/inward/record.url?scp=79961017274&partnerID=8YFLogxK

U2 - 10.5194/acp-11-7617-2011

DO - 10.5194/acp-11-7617-2011

M3 - Article

AN - SCOPUS:79961017274

SN - 1680-7316

VL - 11

SP - 7617

EP - 7628

JO - Atmospheric Chemistry and Physics

JF - Atmospheric Chemistry and Physics

IS - 15

ER -