Elemental Analysis of Atmospheric Fine Particles at Trace and Ultra-Trace Levels using Microwave Acid Digestion and Inductively Coupled Plasma - mass Spectrometry

摘要

The toxicity of trace metals that only constitute a small fraction of total particulate mass (PM) and their use as markers in source - receptor modeling studies have resulted in a need to accurately determine the elemental composition of airborne PM. Data on metals composition of PM are also useful in determining the anthropogenic and non-anthropogenic sources of PM to develop effective air quality management strategies. High temperature - high pressure microwave assisted acid digestion followed by inductively coupled plasma - mass spectrometry (ICP-MS) is capable of accurately quantitating a wide variety of elements in airborne PM. To date, the vast majority of studies have focused on determining only the main groups and main transition series elements. These studies have not quantified rare earth elements (REEs) that can be unique tracers to track PM emissions from petroleum refining operations. The loss of REE enriched zeolite catalysts from refineries' fluidized bed catalytic cracking (FCC) is the major source of REEs in atmospheric fine particles (PM{sub}2.5). Therefore, it is crucial to analyze REEs in ambient PM{sub}2.5 and FCC catalysts. A major challenge in quantifying FCC emissions is that they are present in trace to ultra-trace levels in ambient PM{sub}2.5 and the lack of an analytical method (using ICP-MS) due to absence of certified reference material for FCC catalysts. The principal goal of this presentation will be to document some of our recent research on developing innovative microwave digestion methods and on the impacts of petroleum refining operations on REEs in Houston area fine particles. Specific objectives are to: (1) develop a PM dissolution method using microwave assisted acid digestion followed by ICP-MS analysis to accurately quantify wide range of elements in the atmospheric PM at trace levels (2) evaluate feasibility of generating HF in-situ in closed Teflon lined vessels during digestion to avoid direct handling of hazardous HF, and (3) optimize the digestion method for accurate and precise quantification of REEs in FCC catalysts, which can also be used to determine REE concentrations in ambient PM{sub}2.5.