Design of a Cost-Effective Weighing Facility for PM_2.5 Quality Assurance

Abstract

The U.S. Environmental Protection Agency (EPA) Quality Assurance (QA) Guidance Document 2.12: Monitoring PM_2.5 in Ambient Air Using Designated Reference or Class I Equivalent Methods¹ (Document 2.12) requires conditioning of PM_2.5 filters at 20-23 °C and 30-40% relative humidity (RH) for 24 hr prior to gravimetric analysis. Variability of temperature and humidity may not exceed ±2 °C and ±5% RH during the conditioning period. The quality assurance team at EPA Region 2’s regional laboratory designed a PM_2.5 weighing facility that operates well within these strict performance requirements.

The traditional approach to meeting the performance requirements of Document 2.12 for PM_2.5 filter analysis is to build a walk-in room, with costs typically exceeding $100,000. The initial one-time capital cost for the laboratory at EPA’s Edison, NJ, facility was approximately $24,000. Annual costs [e.g., National Institute of Standards and Technology (NIST) recertifications and nitrogen replacement cylinders used for humidity control] are approximately $500. The average 24-hr variabilities in temperature and RH in the Region 2 weighing chamber are small, ±0.2 °C and ±0.8% RH, respectively. The mass detection limit for the PM_2.5 weighing system of 47-mm stretched Teflon (lab blank) filters is 6.3 μg. This facility demonstrates an effective and economical example for states and other organizations planning PM_2.5 weighing facilities.