Evaluation of particle resuspension in young children's breathing zone using stationary and robotic (PIPER) aerosol samplers

Abstract

Development of asthma in young children may be associated with high exposure to particulate matter (PM). However, typical stationary samplers may not represent the personal exposure of children ages 3 and younger since they may not detect particles resuspended from the floor as children play, thus reducing our ability to correlate exposure and disease etiology. To address this, an autonomous robot, the Pretoddler Inhalable Particulate Environmental Robotic (PIPER) sampler, was developed to simulate the movements of children as they play on the floor. PIPER and a stationary sampler took simultaneous measurements of particle number concentration in six size channels using an optical particle counter and inhalable PM on filters in 65 homes in New Jersey, USA. To study particle resuspension, for each sampler we calculated the ratio of particle concentration measured while PIPER was moving to the average concentration of particles measured during a reference period when PIPER remained still. For all investigated particle sizes, higher particle resuspension was observed by PIPER compared to the stationary sampler. In 71% of carpeted homes a more significant (at the α = 0.05 level) resuspension of particles larger than 2.5 μm was observed by PIPER compared to the stationary sampler. Typically, particles larger than 2.5 μm were resuspended more efficiently than smaller particles, over both carpeted and bare floors. Additionally, in carpeted homes estimations of PM₁₀ mass from the particle number concentrations measured on PIPER while it was moving were on average a factor of 1.54 higher compared to reference period when PIPER was not moving. For comparison, the stationary sampler measured an increase of PM_2.5 mass by a factor of only 1.08 when PIPER was moving compared to a reference period. This demonstrates that PIPER is able to resuspend particles through movement, and provide a better characterization of the resuspended particles than stationary samplers. Accurate measurement of resuspended PM will improve estimates of children's total PM exposure.

Keywords: PM size fractions; Pretoddler Inhalable Particulate Environmental Robotic sampler; children's exposures to PM; floor type; resuspension; robotic sampling platform.

Figure 1

Pretoddler Inhalable Particulate Environmental Robotic (PIPER) sampler.

Figure 2

Description of measurement setup. The sampling period started with 26 one-minute samples in which both OPCs were running, but PIPER was not moving. During the next 26 samples, PIPER moved about the room. The data shown are from the OPC sampler on PIPER, size channel 2.5 to 5.0 mm, at house number 36.

Figure 3

RP_STAT and RP_PIPER for each of the OPC's size channels. RP is the ratio of particle mass concentration while PIPER was moving to number concentration during the reference period (Equations 1 and 2). There were 43 homes with carpet and 22 homes with bare floor in the room that was sampled.

Figure 4

Comparison of the fraction of homes for which the average RP value was significantly different (p < 0.05) between the two samplers. RP is the ratio of particle mass concentration while PIPER was moving to number concentration during the reference period (Equations 1 and 2).

Figure 5

RM2.5 and RM10 measured by each sampler on bare floor and carpet. RM is the ratio of estimated mass while PIPER was moving to estimated mass during reference period (Equations 3 and 4). Out of 65 homes sampled, 43 had carpet and 22 had bare floor.

Figure 6

Comparison of the fraction of homes for which the average RM value was significantly different (p < 0.05) between the two samplers. RM is the ratio of estimated mass while PIPER was moving to estimated mass during reference period (Equations 3 and 4).