High resolution measurements of sulfate during the ACE-2 campaign (June--July 1997) permit detailed evaluation of the performance of a chemical transport models driven by analyzed meteorological data. At Tenerife, Canary Islands, (minimal proximate sources) the median ratio characteristic spread between model and observations, Sm/o ~1.3, was comparable to the spread of three sets of collocated observations and to the spread of observations at stations separated by ~13 km within a single model grid cell (1¿ ¿ 1¿). Somewhat greater Sm/o, ~1.6, at Sagres, Portugal is attributed to nonrepresentativeness of a single measurement site influenced by proximate sources. At Tenerife contributions from European, North American, and biogenic sources to sulfate mixing ratios are comparable, with North American sources dominating (up to ~85%) under conditions of a strong Azores high; thus substantial contributions of sulfate, and by implication other aerosols, can result from long-range midlatitude transport across the Atlantic Ocean.