Trace elemental analysis of airborne particulate matter using dynamic reaction cell inductively coupled plasma-mass spectrometry: application to monitoring episodic industrial emission events

Abstract

The elemental composition of airborne particles is being increasingly monitored since several metals have been implicated in adverse human health outcomes and environmental deterioration while simultaneously providing clues to the identity and strength of their emission sources. However, quantification of several elements and transition metals in ambient aerosols, which are typically present only at trace levels, is fraught with interferences using quadrupole inductively coupled plasma-mass spectrometry (q-ICP-MS). We report improved measurements of key aerosol elements including Al, V, Cr, Fe, Ni, Cu, and Zn in airborne coarse particulate matter (PM(10)) by exploiting ion-molecule reactions in a dynamic reaction cell (DRC) with NH(3) as the cell gas. Numerous other elements (Na, Mg, Si, K, Ca, Sc, Ti, Mn, Co, Ga, As, Se, Rb, Sr, Zr, Mo, Cd, Sn, Sb, Cs, Ba, Pb, Th, and U) and lanthanoids (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), which are important trace components used for source apportionment studies, were also measured. Inter-laboratory comparison using sector field ICP-MS demonstrated the accuracy and precision of DRC-q-ICP-MS. This technique was used to determine the elemental composition of over 150 PM(10) samples collected from an industrialized region in Houston, TX. Samples were first digested using a combination of HF, HNO(3), and H(3)BO(3) in two stages in a microwave oven each with set points of 200°C, 1.55 MPa (225 psig), and 20 min dwell time. Trace metals were used to identify an episodic release of particles from a local source and subsequently track the atmospheric transport of the released particles. This establishes the inherent value of such measurements to developing air quality management strategies since emission events can significantly worsen air quality over a large area. Based on our findings, we recommend continuous independent monitoring of emissions to augment existing industry self-reporting regulatory requirements. Such environmental measurements will assist in establishing industrial regulatory compliance while simultaneously providing data necessary to develop scientifically defensible air quality management strategies.