Wintertime gas-particle partitioning and speciation of inorganic chlorine in the lower troposphere over the northeast United States and coastal ocean

However, limited measurements of gas and particle composition necessary to constrain this chemistry exist. We present measurements from the Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign that show inorganic tropospheric chlorine compounds (Cl-y) measured in the lower troposphere are dominated by HCl and PM4 particulate chloride (pCl(-)), with contributions from trace chlorine species like nitryl chloride (ClNO2), hypochlorous acid (HOCl), and molecular chlorine (Cl-2).

We observed elevated Cly mixing ratios over the ocean (540-625 pptv) compared to over land (178-225 pptv). Observations show 0-20% (0-0.2 mu g/m(3)) of measured chlorine partitions into particles with a diameter less than 1 mu m under typical WINTER conditions. The thermodynamic model, ISORROPIA II, overpredicts submicron pCl(-) by a factor of 2 but is brought into agreement, assuming a small fraction of unmeasured, refractory sea salt <0.1 mu g/m(3) exists.