Using Sulfur as a Tracer of Outdoor Fine Particulate Matter

 Corresponding author e-mail:  jsarnat@hsph.harvard.edu.

 Department of Environmental Health, Harvard School of Public Health.

 Gradient Corporation.

 Department of Biostatistics, Harvard School of Public Health.

Six homes in the metropolitan Boston area were sampled between 6 and 12 consecutive days for indoor and outdoor particle volume and mass concentrations, particle elemental concentrations, and air exchange rates (AERs). Indoor/outdoor (I/O) ratios of nighttime (i.e., particle nonindoor source periods) sulfur, PM_2.5 and the specific particle size intervals were used to provide estimates of the effective penetration efficiency. Mixed models and graphical displays were used to assess the ability of the I/O ratios for sulfur to estimate corresponding I/O ratios for PM_2.5 and the various particle sizes. Results from this analysis showed that particulate sulfur compounds were primarily of outdoor origin and behaved in a manner that was representative of total PM_2.5 in Boston, MA. These findings support the conclusion that sulfur can be used as a suitable tracer of outdoor PM_2.5 for the homes sampled in this study. Sulfur was more representative of particles of similar size (0.06−0.5 μm), providing evidence that the size composition of total PM_2.5 is an important characteristic affecting the robustness of sulfur-based estimation methods.