Abstract

The Alphasense optical particle counter (OPC) provides a low-cost and lightweight solution for measurements of the size and number concentration of airborne particulate matter (PM). The micro fan with which it is originally equipped cannot, however, achieve a high enough pressure differential for maintaining an adequate flow rate when connected to sampling/pretreatment aerosol lines, limiting its use for air quality monitoring. Here, we propose a simple modification on the sample flow system that enables the connection of the Alphasense OPC with sampling/pretreatment lines (e.g., dryers) commonly employed on ground observational sites, as well as its use onboard Unmanned Aerial Systems (UASs). Tests of the modified OPC using monodisperse polystyrene spherical (PS) particles having sizes between 0.8 and 2.5 μm show that both the sizing and counting performance of the modified instrument is in agreement with that of a calibrated reference OPC at concentrations from ca. 50 to 800 #/ml, which are typically encountered in the atmosphere in that size range. For particle number concentrations below or above this range, we observed a concentration-dependent counting efficiency, which can be corrected using a polynomial function derived from our measurements. Tests conducted under reduced pressure and temperature conditions demonstrate the capability of the modified OPC for accurately (i.e., within 13% deviation from the reference measurements) determining the size and number concentration of the sampled particles. The tests reported in this work show that the proposed modification can qualify the Alphasense OPC for use in both ground and aerial observations without affecting its performance, and at the same time maintaining its strongly desired characteristics (i.e., cost effectiveness and high portability).

Copyright © 2020 American Association for Aerosol Research

摘要

Alphasense光学粒子计数器（OPC）提供了一种低成本，轻巧的解决方案，用于测量空气中颗粒物（PM）的大小和数量浓度。但是，最初配备的微型风扇在连接到采样/预处理气雾剂管线时，无法获得足够高的压差来维持足够的流量，从而限制了其在空气质量监测中的用途。在这里，我们建议对样品流系统进行简单的修改，以使Alphasense OPC与通常在地面观测站点上使用的采样/预处理管线（例如，干燥机）相连接，以及在机载无人机系统（UAS）上的使用。使用尺寸在0.8到2之间的单分散聚苯乙烯球形（PS）颗粒对改性OPC进行测试 5μm表明，经修改的仪器的定尺寸和计数性能均与浓度大约为5％的标准参比OPC一致。50至800＃/ ml，通常在该尺寸范围的大气中会遇到。对于低于或高于此范围的颗粒数浓度，我们观察到了浓度依赖性的计数效率，可以使用从我们的测量中得出的多项式函数进行校正。在减压和高温条件下进行的测试表明，改进的OPC能够准确（即，与参考测量值相差13％以内）确定所采样颗粒的大小和数量浓度。

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