Abstract
Free to read on publisher website Airborne particles have been shown to be associated with a wide range of adverse health effects, which has led to a recent increase in medical research to gain better insight into their health effects. However, accurate evaluation of the exposure-dose-response relationship is highly dependent on the ability to track actual exposure levels of people to airborne particles. This is quite a complex task, particularly in relation to submicrometer and ultrafine particles, which can vary quite significantly in terms of particle surface area and number concentrations. Therefore, suitable monitors that can be worn for measuring personal exposure to these particles are needed. This paper presents an evaluation of the metrological performance of six diffusion charger sensors, NanoTracer (Philips Aerasense) monitors, when measuring particle number and surface area concentrations, as well as particle number distribution mean when compared to reference instruments. Tests in the laboratory (by generating monodisperse and polydisperse aerosols) and in the field (using natural ambient particles) were designed to evaluate the response of these devices under both steady-state and dynamics conditions. Results showed that the NanoTracers performed well when measuring steady state aerosols, however they strongly underestimated actual concentrations during dynamic response testing. The field experiments also showed that, when the majority of the particles were smaller than 20 nm, which occurs during particle formation events in the atmosphere, the NanoTracer underestimated number concentration quite significantly. Even though the NanoTracer can be used for personal monitoring of exposure to ultrafine particles, it also has limitations which need to be considered in order to provide meaningful results.
Highlights
In recent years, a number of studies have focused on aerosol monitoring in order to estimate human exposure to particle concentrations
The daily PM10 concentration is determined at a fixed sampling point (FSP) that is characteristic of the examined area, and it is used to evaluate the exposure of the entire population living nearby
The most important results are calibration correction factors, defined as the ratio between the value measured by the NanoTracer and the reference instrument (CPC, Scanning Mobility Particle Sizer (SMPS), Nanoparticle Surface Area Monitors (NSAMs) or Fast Mobility Particle Sizer (FMPS)), as well as supplementary data as particle number size distribution, stability, etc
Summary
A number of studies have focused on aerosol monitoring in order to estimate human exposure to particle concentrations This increase in technical and scientific attention was motivated by medical studies relating high particle concentration exposure to adverse health effects (Kreyling et al, 2006; Pope and Dockery, 2006; Schmid et al, 2009). With regard to urban air quality (city and outdoor scales), regulatory authorities (Directive 2008/50/EC) have only standardized threshold limits for PM10 (mass of particulate matter with an aerodynamic diameter less than 10 μm), these are still stated in terms of average values obtained by time integrated measurements (particles collected over a 24 h period) and do not take into account daily variations in particle concentration, which could be related to atmospheric dynamics, as well as source emission characteristics (Buonanno et al, 2011a). The measurements from a FSP cannot be accurately used to characterize real exposure in outdoor or indoor microenvironments
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