Abstract
A sampler using inertial fibrous filters (INF) has been recently developed for ultrafine particle collection by impaction and filtration. This new sampler has a low pressure drop (20–30 kPa) and can separate particles smaller than 0.1 µm with a high sampling flow rate (40 L/min). In this study, sampling performance of the INF sampler was evaluated in comparison with a reference sampler in the field as well as in the laboratory and the possible sulfate ion loss when using aluminum substrates for ion extraction in ultrasonic bath was discovered and investigated. When sampling ultrafine particles (Dp ≤ 0.1 µm) such as carbonaceous and ionic species both in the field and in the laboratory, the performance of the INF sampler was similar to that of a reference sampler despite differences of sampling mechanism, cut-point diameter, and substrate proving that the INF sampler can be an alternative for ultrafine particle collection. Underestimation of sulfate concentration appeared to be unavoidable in ultrasonic extractions from aluminum substrates regardless of whether the extraction time was 30 or 90 min. The average sulfate loss during aluminum filter extraction was 45% (± 12%; min: 12%; max: 94%). Therefore, ultrasonic extraction from aluminum filters should be avoided to obtain unbiased measurements of sulfate concentration in ambient air or other ion extraction methods should be considered to minimize sulfate loss (dissolution of aluminum ions) from aluminum filters with sufficient extraction efficiency of ionic species. The results of this study indicate that the performance of the INF sampler is almost similar to that of the nano-MOUDI sampler for ultrafine particle collection, while advantageous in terms of convenience, and analysis. Furthermore, the INF sampler can collect amounts of ultrafine particles that are sufficient for chemical analysis in a relatively short time, and the particles can be uniformly collected with a quartz fiber filter.
Highlights
Ultrafine and nanoparticles present in the air due to natural sources and processes, as well as those resulting from anthropogenic activities have attracted an increasing level of interest in the last decade (Morawska et al, 2008)
The measured particle collection values obtained from inertial fibrous filters (INF) sampler are shown in Fig. 4, particles with diameters in the range of 0.02–0.04 μm showed a loss of 5–10% within the sampling system
The 50% cut point of INF sampler was approximately 0.07 μm which well corresponds with the data obtained by Furuuchi et al (2010a) whereas that of the nano-MOUDI sampler is between 0.10–0.18 μm for the upper stage of ultrafine particles (UFPs)
Summary
Ultrafine and nanoparticles present in the air due to natural sources and processes, as well as those resulting from anthropogenic activities have attracted an increasing level of interest in the last decade (Morawska et al, 2008). Analysis of aerosols containing carbonaceous particulates requires optical corrections to minimize charring; non-uniform deposition of impactor samples causes the optical charring correction scheme to be uncertain or ineffective (Chow et al, 2004; Huang and Yu, 2008). Because the principal function of the optical (laser reflectance and transmittance) component of the analyzer is to correct for pyrolysis charring of organic carbon compounds into elemental carbon by continuously monitoring the filter reflectance and/or transmittance (via a helium-neon laser and a photodetector) throughout an analysis cycle (DRI standard operating procedure, 2005) if a non-uniform particle deposits on the filter is used for the thermal/optical carbon analysis, there would be potential sample biases making the irregular filter reflectance and/or transmittance during the analysis cycle
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