Origins of aerosol chlorine during winter over north central Colorado, USA

Academic Article


  • AbstractThe Nitrogen, Aerosol Composition, and Halogens on a Tall Tower campaign (February–March 2011) near Boulder, Colorado, investigated nighttime ClNO2 production and processing. Virtually all particulate Cl was in the form of ionic Cl. The size distributions of Cl and Na+ were similar, with most of the mass in the supermicrometer size fraction, suggesting primary sources for both. Median Cl concentrations were about half those of Na+ and Ca2+ for particle diameters centered at 1.4 and 2.5 µm. To investigate potential sources of Na+ and Cl, four cases were studied that featured the prevalence of Na+ and Cl and different transport pathways based on FLEXible PARTicle dispersion model (FLEXPART) retroplumes. Estimates of supermicrometer Na+ particle lifetime against deposition indicate that long‐range transport of marine aerosols could account for the observed Na+. However, measured molar ratios of Ca2+ to Na+ (0.143–0.588) compared to seawater (0.022) indicate significant contributions from crustal sources to the supermicrometer aerosol composition during these four case studies. Further, low molar ratios of Mg2+ to Na+ (0.007–0.098) relative to seawater (0.114) suggest that some of the Na+, and presumably associated Cl, originated from non‐sea‐salt sources. The heterogeneous chemical composition of saline soils throughout the western U.S., along with the nonlinearity of wind‐driven soil deflation as a function of various surface soil properties, precludes a quantitative apportionment of soil, marine, and anthropogenic sources to the observed coarse‐fraction aerosol. Nonetheless, results suggest that deflation of saline soils was a potentially important source of particulate Cl that sustained atmospheric ClNO2 production and associated impacts on oxidation processes over northern Colorado.
  • Authors

  • Jordan, CE
  • Pszenny, Alexander
  • Keene, WC
  • Cooper, OR
  • Deegan, B
  • Maben, J
  • Routhier, M
  • Sander, R
  • Young, AH
  • Status

    Publication Date

  • January 27, 2015
  • Digital Object Identifier (doi)

    Start Page

  • 678
  • End Page

  • 694
  • Volume

  • 120
  • Issue

  • 2