title: A large atomic chlorine source inferred from mid-continental reactive nitrogen chemistry.
abstract: Halogen atoms and oxides are highly reactive and can profoundly affect atmospheric composition. Chlorine atoms can decrease the lifetimes of gaseous elemental mercury and hydrocarbons such as the greenhouse gas methane. Chlorine atoms also influence cycles that catalytically destroy or produce tropospheric ozone, a greenhouse gas potentially toxic to plant and animal life. Conversion of inorganic chloride into gaseous chlorine atom precursors within the troposphere is generally considered a coastal or marine air phenomenon. Here we report mid-continental observations of the chlorine atom precursor nitryl chloride at a distance of 1,400 km from the nearest coastline. We observe persistent and significant nitryl chloride production relative to the consumption of its nitrogen oxide precursors. Comparison of these findings to model predictions based on aerosol and precipitation composition data from long-term monitoring networks suggests nitryl chloride production in the contiguous USA alone is at a level similar to previous global estimates for coastal and marine regions. We also suggest that a significant fraction of tropospheric chlorine atoms may arise directly from anthropogenic pollutants.
authors.affiliation: Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, USA. thornton@atmos.washington.edu
authors.forename: Joel A
authors.initials: JA
authors.lastname: Thornton
authors.forename: James P
authors.initials: JP
authors.lastname: Kercher
authors.forename: Theran P
authors.initials: TP
authors.lastname: Riedel
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Wagner
authors.forename: Julie
authors.initials: J
authors.lastname: Cozic
authors.forename: John S
authors.initials: JS
authors.lastname: Holloway
authors.forename: William P
authors.initials: WP
authors.lastname: Dubé
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Wolfe
authors.forename: Patricia K
authors.initials: PK
authors.lastname: Quinn
authors.forename: Ann M
authors.initials: AM
authors.lastname: Middlebrook
authors.forename: Becky
authors.initials: B
authors.lastname: Alexander
authors.forename: Steven S
authors.initials: SS
authors.lastname: Brown
mesh_terms: D000336:Aerosols / Q000737:chemistry; D000388:Air / Q000032:analysis; D001272:Atmosphere / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D003120:Colorado; D008956:Models, Chemical; D009573:Nitrites / Q000032:analysis / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry; D013997:Time Factors
chemical_list: D000336:Aerosols; D009573:Nitrites; D009589:Nitrogen Oxides; D002713:Chlorine; D009584:Nitrogen; C445660:nitryl chloride