Abstract

Fine mode particulate matter (PM) is known to be a major risk for human health as it can cause respiratory and cardiovascular diseases. Whether produced from anthropogenic or natural processes, fine mode PM is often electrically charged with positive, negative and/or bipolar charges. These preexisting charges can, in some cases, significantly affect measurements from sensors which involve a charging stage prior to measurement by, e.g., electrometry. In this work, we demonstrate quantitatively the impact of preexisting charges ($q=0,\pm 1,\pm 2$) on three different unipolar diffusion charging (DC) configurations using both simulations and experiments. The DC configurations include traditional steady state (SS) DC and pulsed modes of DC, where in all configurations a positive corona charger is used. We show that the impact of preexisting charges on SS and modulated precipitation (MP) DC is comparable. Positively pre-charged particles cause a larger deviation for SS and MP DC, in contrast to modulated diffusion charging (MDC), where negatively pre-charged particles have a greater impact. In addition, we show that the ion concentration in the charging region can be increased to significantly reduce the resulting error caused by the pre-charges for both SS DC and MP DC, in contrast to MDC. These results show that the influence of unipolarly pre-charged particles is very differently pronounced for the different modes of DC. The impact strongly depends on the polarity of the pre-charges, characteristics of the charger and the DC configuration itself. These insights are particularly interesting for the design and the application of DC based sensors.

摘要

众所周知，精细模式颗粒物（PM）是人类健康的主要风险，因为它会引起呼吸系统疾病和心血管疾病。无论是从人为过程还是自然过程中产生，精细模式的PM经常带有正，负和/或双极性电荷。在某些情况下，这些预先存在的电荷可能会严重影响来自传感器的测量结果，这些传感器在进行测量之前（例如通过静电测定法）涉及一个充电阶段。在这项工作中，我们从数量上证明了预先收费的影响（$q=0，\pm \mathrm{1个}，\pm \mathrm{2个}$）在三种不同的单极扩散充电（DC）配置上使用仿真和实验方法。DC配置包括传统的稳态（SS）DC和DC的脉冲模式，在所有配置中均使用正电晕充电器。我们表明，预先存在的电荷对SS和调制降水（MP）DC的影响是可比的。与调制扩散充电（MDC）相比，带正电的粒子会对SS和MP DC造成更大的偏差，而带负电的粒子具有更大的影响。此外，我们发现，与MDC相比，可以增加充电区域中的离子浓度，从而显着降低SS DC和MP DC的预充电所导致的结果误差。这些结果表明，对于不同的DC模式，单极性预充电粒子的影响差异很大。影响很大程度上取决于预充电的极性，充电器的特性以及直流配置本身。这些见解对于基于DC的传感器的设计和应用特别有趣。