© Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics Observations of heterogeneous reactions between Asian pollution

Abstract. In-situ airborne measurements of trace gases, aerosol size distributions, chemistry and optical properties were conducted over Mexico and the Eastern North Pacific during MILAGRO and INTEX-B. Heterogeneous reactions between secondary aerosol precursor gases and mineral dust lead to sequestration of sulfur, nitrogen and chlorine in the supermicrometer particulate size range. Simultaneous measurements of aerosol size distributions and weak-acid soluble calcium result in an estimate of 11 wt % of CaCO3 for Asian dust. During transport across the North Pacific, ∼5–30 % of the CaCO3 is converted to CaSO4 or Ca(NO3)2 with an additional ∼4 % consumed through re-actions with HCl. The 1996 to 2008 record from the Mauna Loa Observatory confirm these findings, indicating that, on average, 19 % of the CaCO3 has reacted to form CaSO4 an