under a Creative Commons License. Atmospheric Chemistry and Physics Direct observations of the atmospheric processing of Asian

Abstract. The accumulation of secondary acids and am-monium on individual mineral dust particles during ACE-Asia has been measured with an online single-particle mass spectrometer, the ATOFMS. Changes in the amounts of sul-phate, nitrate, and chloride mixed with dust particles cor-relate with air masses from different source regions. The uptake of secondary acids depended on the individual dust particle mineralogy; high amounts of nitrate accumulated on calcium-rich dust while high amounts of sulphate accumu-lated on aluminosilicate-rich dust. Oxidation of S(IV) to S(VI) by iron in the aluminosilicate dust is a possible expla-nation for this enrichment of sulphate, which has important consequences for the fertilization of remote oceans by solu-ble iron. This study shows the segregation of sulphate from nitrate and chloride in individual aged dust particles for th