Tracing fly ash emitted from a coal-fired power plant with enriched rare-earth isotopes: An urban scale test

Artificially enriched isotopes of neodymium (Nd) were released from a 100 MW(e) coal-fired power plant at rates ranging from 40 to 61 mg h⁻¹ in an experiment designed to test a new intentional particulate tracer technique. During each release, ambient samples of airborne particles with diameters < 2.5 μm were collected for 6 h at 13 locations along a 72° arc 20 km from the plant on 47-mm diameter Teflon filters operated at nominal flow rates of 130 l min⁻¹. Samples collected when estimates of the meteorological dispersion parameter, X/Q, ranged from 0.3 × 10⁻¹⁰ to 350 × 10⁻¹⁰ s m⁻³, were analysed for total Nd mass and excess ¹⁴⁸Nd, the tracer isotope, by thermal-ionization mass spectrometry. Measured concentrations were in good agreement with predictions of ambient tracer concentrations made with a Gaussian plume model in which lateral and vertical plume dispersion parameters were derived from the standard deviation of the horizontal wind direction. The observed tracer concentrations correspond to signal-to-noise ratios (S:N) of 150–450. The concentration of ¹⁴⁸Nd measured in particles <0.65 μm in diameter corresponds to an S:N in excess of 4500.