Field evaluation of particulate matter measurements using tapered element oscillating microbalance in a layer house

Abstract

The tapered element oscillating microbalance (TEOM) is one type of continuous ambient particulate matter (PM) monitor. Adsorption and desorption of moisture and semivolatile species may cause positive or negative artifacts in TEOM PM mass measurement. The objective of this field study was to investigate possible uncertainties associated with TEOM measurements in the poultry operation environment. For comparisons of TEOM with filter-based gravimetric method, four instruments (TEOM-PM₁₀, low-volume PM₁₀ sampler, TEOM-PM_2.5, and PM_2.5 speciation sampler) were collocated and tested inside a poultry house for PM_2.5 and PM₁₀ (PM with aerodynamic equivalent diameter ≤2.5 and ≤10 μm, respectively) measurements. Fifteen sets of 24-hr PM₁₀ concentrations and 13 sets of 24-hr PM_2.5 measurements were obtained. Results indicate that compared with filter-based gravimetric method, TEOM gave significantly lower values of both PM₁₀ and PM_2.5 mass concentrations. For PM₁₀, the average ratio of TEOM to the gravimetric method was 0.936. For PM_2.5, the average ratio of TEOM to the gravimetric method was 0.738. Particulate matter in the poultry houses possibly contains semivolatile compounds and moisture due to high levels of relative humidity (RH) and gas pollutants. The internal heating mechanism of the TEOM may cause losses in mass through volatilization. To investigate the effects of TEOM settings on concentration measurements, the heaters of two identical TEOMs were set at 50 °C, 30 °C, or no heating at all. They were collocated and tested for total suspended particle (TSP), PM₁₀, and PM_2.5 measurements in layer house for 6 weeks. For all TSP, PM₁₀, and PM_2.5 measurements, the internal TEOM temperature setting had a significant effect (P < 0.05). Significantly higher PM mass concentrations were measured at lower temperature settings. The effects of environmental (i.e., temperature, RH, NH₃ and CO₂ concentrations) and instrumental (i.e., filter loading and noise) parameters on PM measurements were also assessed using regression analysis.

Implications

Because of its potential health and environmental effects, particulate matter (PM) emissions from animal feeding operations (AFOs) have been a great concern to the public and to the regulatory agencies. The tapered element oscillating microbalance (TEOM) PM monitor has been was adapted for continuous PM measurements in some AFO air quality studies. This study investigated possible uncertainties associated with TEOM measurements in an egg production environment. It was discovered that there was a significant bias in TEOM measurements of PM₁₀ as compared with federal reference method. Internal temperature settings of a TEOM have significant impact on its PM measurement.

Acknowledgments

This project was supported in part by USDA NRI grant 2008–35112–18757 and NSF CAREER Award CBET-0954673.

The PM_2.5 ion analysis was conducted by Dr. Jayanty's group at RTI International, Research Triangle Park, North Carolina. The NH₃ and CO₂ concentrations were measured under the National Air Emission Monitoring Study (NAEMS)—Southeast Layer Site, which was funded by the American Egg Board. The authors would also like to thank the egg production farm for the gracious support.

Dr. John T. Walker from EPA, and Drs. Sanjay Shah, Ratna Sharma, and Wayne Robarge from North Carolina State University reviewed the manuscript and provided valuable technical advices. The authors also are grateful for the peer review comments.