Depth profile analysis in secondary ion mass spectrometry (SIMS) is applied for fly ash particles collected from three electrostatic precipitators in coal combustion type Thermoelectric Power Plant in Warsaw, Poland. Prior to analysis, particles of the collected material were size separated in nine stage cascade impactor with rotating substrate plates. Bulk analysis of the chosen size fractions was performed by atomic absorption spectroscopy. For SIMS depth profile analysis, particles were deposited on indium foils of high purity. Sputtering with 5 keV Ar+, 100 µm diameter ion beam was performed over 1.2 × 1.8 mm area of the indium foil in SIMS system (SAJW-05 model) equipped with Physical Electronics ion gun and QMA-410 Balzers quadrupole analyzer. SIMS data are quantified based on bulk concentration values of: carbon, sodium, aluminium, silicon, calcium, chromium, manganese, iron and nickel. Core–shell structure, and also cenosphere structure, is found. Depth profile analysis shows that shell layers of particles are enriched in carbon, calcium, chromium and nickel. Inner parts of particles or their cores are enriched in sodium and aluminium. Copyright © 2012 John Wiley & Sons, Ltd.