Atmospheric particulate source apportionment using stable enriched rare earth isotopic tracers.

摘要

A new intentional tracer technique, suitable for tracing particulate matter emitted from high temperature combustion sources, was developed in this study. The technique uses stable enriched rare earth isotopes as intentional tracers of particulate matter and was applied to emissions from a coal-fired power plant, diesel vehicles, and residential oil furnaces in source apportionment studies. Complete experimental procedures, including emission tagging methods, aerosol sampling, sample preparation, isotopic composition measurement, data reduction, and variance analysis, were developed. Feasibility of the technique was demonstrated by tagging particles emitted from a 400 MW (e) coal-fired power plant at a release rate of 61 mg/h enriched {dollar}sp{lcub}148{rcub}{dollar}Nd. Excess {dollar}sp{lcub}148{rcub}{dollar}Nd in fine-particles (aerodynamic diameter {dollar}<{dollar}0.65 {dollar}mu{dollar}m) 20 km from the plant was detected at a signal-to-noise ratio {dollar}>{dollar}4500, a level sufficient to trace particles over distances ranging from 80 to {dollar}>{dollar}1000 km under favorable meteorological conditions.; In the diesel vehicle and residential oil furnace emissions study, two sources were tagged simultaneously, 1.6 g of enriched {dollar}sp{lcub}149{rcub}{dollar}Sm were used to tag 264 m{dollar}sp3{dollar} of diesel fuel burned by bus and truck fleets, and 0.4 g of enriched {dollar}sp{lcub}150{rcub}{dollar}Sm were used to tag 106 m{dollar}sp3{dollar} of residential heating oil. Picogram amounts of {dollar}sp{lcub}149{rcub}{dollar}Sm and {dollar}sp{lcub}150{rcub}{dollar}Sm associated with emitted particles were determined by thermal ionization mass spectrometry and the contributions of atmospheric soot from two tagged sources were decoupled. Excellent agreement between measured and predicted tracer concentrations demonstrates the uniqueness and power of the technique in exploring source-receptor relationships. The accuracy and precision of the technique can be controlled within 10%. Because there are no natural sources of enriched rare earth isotopes, the technique is believed to be a definitive tool for verification of source apportionment models, improvement of modeling parameters, and the study of atmospheric pollutant deposition.