Measurement of spatial and temporal variation in volatile hazardous air pollutants in Tacoma, Washington, using a mobile membrane introduction mass spectrometry (MIMS) system

Abstract

The objective of this study was to use membrane introduction mass spectrometry (MIMS), implemented on a mobile platform, in order to provide real-time, fine–scale, temporally and spatially resolved measurements of several hazardous air pollutants. This work is important because there is now substantial evidence that fine-scale spatial and temporal variations of air pollutant concentrations are important determinants of exposure to air pollution and adverse health outcomes. The study took place in Tacoma, WA during periods of impaired air quality in the winter and summer of 2008 and 2009. Levels of fine particles were higher in winter compared to summer, and were spatially uniform across the study area. Concentrations of vapor phase pollutants measured by membrane introduction mass spectrometry (MIMS), notably benzene and toluene, had relatively uniform spatial distributions at night, but exhibited substantial spatial variation during the day—daytime levels were up to 3-fold higher at traffic-impacted locations compared to a reference site. Although no direct side-by-side comparison was made between the MIMS system and traditional fixed site monitors, the MIMS system typically reported higher concentrations of specific VOCs, particularly benzene, ethylbenzene and naphthalene, compared to annual average concentrations obtained from SUMA canisters and gas chromatographic analysis at the fixed sites.

Keywords:

• Air toxics
• exposure assessment
• woodsmoke
• diesel exhaust
• MIMS
• membrane introduction mass spectrometry
• membrane inlet mass spectrometry
• field portable tandem mass spectrometry
• MS/MS

Acknowledgments

The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the US EPA. We also would like to acknowledge the assistance provided by numerous staff and students at the University of Washington and the PSCAA who assisted with the field-work. The authors also thank Vancouver Island University and the University of Victoria for their ongoing support of both faculty and graduate students.

Funding

This work was supported in part by the US EPA under Grant Agreement XA96069801.