AAH Conducts Evaluation of Particulate Matter Samplers

Article contribution by Air Alliance Houston Board Member Thomas H. Stock, PhD, MPH.

Air Alliance Houston (AAH) conducted a year-long study of particulate matter (PM2.5) pollution in Galena Park, Texas during 2012/2013. The final report (Air Pollution and Public Health in Galena Park, Texas, July 2014) is available here. In this study, measurements of PM2.5 mass and some of its major constituents were obtained from 24-hour filter sampling using MiniVol air samplers at several locations in Galena Park (GP). An analysis of these measurements indicated that the EPA annual primary standard (NAAQS) is likely exceeded at all the GP monitoring sites. Moreover, estimates of diesel PM obtained from concentrations of elemental carbon measured in samples suggested that the ambient air in GP poses an increased inhalation cancer risk of approximately 1 in 10,000. Although these results raise legitimate concern about the influence of emissions from the constant heavy diesel vehicle traffic on Clinton Drive, it is important to quantitatively establish the validity of these measurements. Although a comparison of the MiniVol results in this study with simultaneous measurements by TCEQ monitors at the Clinton Drive monitoring site (1-1.5 mi. from the AAH samplers) indicated good correlation and no significant differences in concentrations, it was decided that a more definitive study, employing a more rigorous and direct comparison of methods, needed to be conducted.

On nine days during the period July – November 2014, two MiniVol samplers were collocated with several TCEQ PM2.5 samplers (24-hr. filter samplers and a continuous sampler yielding 1-hr. average concentrations) and an AAH-owned continuous monitor, at the Clinton Drive air monitoring site. Filter masses from the MiniVol samplers were determined by the same lab that performed analyses for the GP study. Validated TCEQ sampler results were downloaded from the Texas Air Monitoring Information System (TAMIS). Unfortunately, due to logistic constraints and invalidated samples (both TCEQ and AAH), there were only four sampling days when results from both the TCEQ filter samplers and the MiniVols were available for comparison. Although there are insufficient data to perform a statistical analysis, from inspection there appears to be a rough equivalence of the results. Moreover, the TCEQ continuous sampler results appear to be similar to the two filter methods. A direct comparison of hourly measurements from the TCEQ (TEOM) and AAH (DustTrak II) continuous PM2.5 monitors yielded a calibration for the DustTrak instrument that will allow more accurate measurements of PM concentrations in areas dominated by diesel emissions, e.g., a current project monitoring emissions from idling buses in Hermann Park.

Additional collocation sampling is being conducted at the Clinton Drive site in order to obtain a sufficient number of comparison samples to perform a reliable statistical analysis. This is important, both to validate the GP monitoring results, and to provide a necessary test of reliability for the upcoming monitoring campaign in Pasadena.

Acknowledgements – This evaluation would not have been possible without significant contributions of time, effort and expertise from both Bel and Brian.