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Online measurement of the effective density of both spherical aggregated and ordered porous particles was systematically investigated using differential mobility analyzer-aerosol particle mass analyzer (DMA-APM). Effective density was determined based on the relationship between electric mobility and mass; mobility and mass were measured using DMA and APM, respectively. The particles were prepared using a spray-drying method; a colloidal suspension of silica nanoparticles was used as the precursor, and both nanoparticles and polystyrene latex (PSL) particles were used to generate the aggregated and ordered porous particles. The effective density of aggregated particles decreased from 1916.0 to 1565.2 kg/m³ when the primary particle size was increased from 6 to 100 nm. The effects of pore size and fraction, which were controlled by PSL particle concentration and size, on the effective density of …