Buoyancy-Corrected Gravimetric Analysis of Lightly Loaded Filters

Abstract

Numerous sources of uncertainty are associated with the gravimetric analysis of lightly loaded air filter samples (Ͻ100 g). The purpose of the study presented here is to investigate the effectiveness and limitations of air buoyancy corrections over experimentally adjusted conditions of temperature (21-25°C) and relative humidity (RH) (16 -60% RH). Conditioning (24 hr) and weighing were performed inside the Archimedes M3 environmentally controlled chamber. The measurements were performed using 20 size-fractionated samples of resuspended house dust loaded onto Teflo (PTFE) filters using a Micro-Orifice Uniform Deposit Impactor representing a wide range of mass loading (7.2-3130 g) and cut sizes (0.056 -9.9 m). By maintaining tight controls on humidity (within 0.5% RH of control setting) throughout pre-and postweighing at each stepwise increase in RH, it was possible to quantify error due to water absorption: 45% of the total mass change due to water absorption occurred between 16 and 50% RH, and 55% occurred between 50 and 60% RH. The buoyancy corrections ranged from Ϫ3.5 to ϩ5.8 g in magnitude and improved relative standard deviation (RSD) from 21.3% (uncorrected) to 5.6% (corrected) for a 7.2 g sample. It is recommended that protocols for weighing low-mass particle samples (e.g., nanoparticle samples) should include buoyancy corrections and tight temperature/humidity controls. In some cases, conditioning times longer than 24 hr may be warranted.

Development of temporally refined land-use regression models predicting daily household-level air pollution in a panel study of lung function among asthmatic children

“…The Archimedes M3TM chamber was designed to simultaneously monitor air pressure, temperature, dew point temperature and RH and record these parameters automatically. Gravimetric measurements made with a Mettler UMX2 microbalance (readability of 0.1 mg) were subsequently corrected for changes in air buoyancy determined at 1 min intervals as described by Rasmussen et al 30 Calculation of the laboratory detection limit (LDL) was based on three times the SD of 13-14 measurements of each of two reference filters per day.…”

Windsor, Ontario Exposure Assessment Study: Design and Methods Validation of Personal, Indoor, and Outdoor Air Pollution Monitoring

“…33 Average daily SD of blank reference filter measurements was typically Ϯ0.5-0.6 g (n ϭ 10 -14), resulting in daily laboratory detection limits (LDLs) of 1.5-1.6 g on the basis of 3 times the standard deviation (SD). 34 Method detection limits for the study presented here are based on variability introduced throughout all preweighing and postweighing steps, including storage for the entire time elapsed from removal of the filter from its packaging to the final postweighing (typically 1-2 months). PM 2.5 and PM 10 measurements were collected in all three locations (indoor, outdoor, and personal) during the 2005 monitoring.…”

Filter Processing and Gravimetric Analysis for Suspended Particulate Matter Samples

“…The Earth's gravitational attraction varies with position (Hirt et al 2013), Aerosol Sci Eng (2017) 1:93-105 101 but the effect is negligible for practical situations. Normal fluctuations in air density (caused by pressure, temperature, and water vapor variations) do not require buoyancy corrections (Hanninen et al 2002;Koistinen et al 1999;Rasmussen et al 2010), but such corrections are necessary when there is a substantial change with balance elevation ([500 m) between the pre-and postsample weighing. It is best to avoid changes in weighing elevations.…”