Development and evaluation of an ultrasonic personal aerosol sampler

Abstract

Assessing personal exposure to air pollution has long proven challenging due to technological limitations posed by the samplers themselves. Historically, wearable aerosol monitors have proven to be expensive, noisy, and burdensome. The objective of this work was to develop a new type of wearable monitor, an ultrasonic personal aerosol sampler (UPAS), to overcome many of the technological limitations in personal exposure assessment. The UPAS is a time-integrated monitor that features a novel micro-pump that is virtually silent during operation. A suite of on-board environmental sensors integrated with this pump measure and record mass air flow (0.5–3.0 L/min, accurate within 5%), temperature, pressure, relative humidity, light intensity, and acceleration. Rapid development of the UPAS was made possible through recent advances in low-cost electronics, open-source programming platforms, and additive manufacturing for rapid prototyping. Interchangeable cyclone inlets provided a close match to the EPA PM2.5 mass criterion (within 5%) for device flows at either 1.0 or 2.0 L/min. Battery life varied from 23–45 hrs depending on sample flow rate and selected filter media. Laboratory tests of the UPAS prototype demonstrate excellent agreement with equivalent federal reference method samplers for gravimetric analysis of PM2.5 across a broad range of concentrations.

A low-cost particulate matter (PM<sub>2.5</sub>) monitor for wildland fire smoke

“…The Outdoor Aerosol Sampler (OAS) was based upon the Ultrasonic Personal Aerosol Sampler (UPAS) described previously (Volckens et al, 2017). The original UPAS was designed as a wearable device to estimate personal exposure to PM 2.5 across a 24 h period.…”

“…The massflow sensor within the unit (Omron model DP6F) is dependent on air density, which can vary as a function of temperature, humidity, and pressure. These variables were monitored in real-time using an atmospheric condition sensor (Bosch BME280) and used to correct mass-flow readings (Volckens et al, 2017). The UPAS creates a small amount of heat during operation as a by-product of battery discharge and pump work.…”

“…In the laboratory, 10 OAS units were arrayed with three PM 2.5 impactor samplers (PEM PM 2.5 2 L min −1 , SKC Inc.) in a 0.75 m 3 aerosol chamber to verify OAS accuracy and precision relative to a commerciallyavailable PM 2.5 sampler operating at similar flow rate. Sodium chloride was used as the test aerosol following the protocol described in Volckens et al (2017). Additionally, we evaluated OAS precision through a series of outdoor deployments whereby two OAS devices were co-located outdoors to sample ambient air concentrations for 48 h in Fort Collins, CO (n = 23 paired deployments).…”

A low-cost PM<sub>2.5</sub> monitor for wildland fire smoke

“…The Outdoor Aerosol Sampler (OAS) was based upon the Ultrasonic Personal Aerosol Sampler (UPAS) described previously (Volckens et al, 2017). The original UPAS was designed as a wearable device to estimate personal exposure to PM 2.5 across a 24-hour period.…”

“…The mass-flow sensor within the unit (Omron model DP6F) is dependent on air density, which can vary as a function of temperature, humidity, and pressure. These variables were monitored in real-time and used to correct mass-flow readings (Volckens et al, 2017). The UPAS creates a small amount of heat during operation as a by-product of battery discharge and pump work.…”