作为一种尼古丁传送的电子设备，电子烟通过电热丝加热烟油使烟油蒸发进入气相，在下游烟油蒸气冷却而形成气溶胶。电子烟在2003年进入市场后，被宣传为香烟代替品，全球使用人数和销售额快速增长，近年来吸引了很多青少年消费者的使用。目前对电子烟健康风险的认识尚不清晰，电子烟气溶胶粒径分布和有机组分的测量是评估其危害的关键。 论文研发了电子烟气溶胶粒径分布稀释系统，有效解决了现有稀释系统可能存在的混合不均匀、时间控制电磁阀造成的颗粒物损失、停留时间过长等问题。新稀释系统基于多孔混合稀释原理，气密性良好，烟气和稀释气混合均匀，结果稳定，竖放和横放条件、正压和负压条件下均可适用，同时系统内流量恒定，便于实际采样。以本稀释系统为基础，用常见的粒径分布测量仪器搭建了3套测量系统，对电子烟气溶胶粒径分布进行测量。发现数浓度粒径分布呈双峰分布，峰值粒径分别为10~50 nm和100~300 nm，另外在700~800 nm处也发现小型粒径峰，质量浓度粒径分布呈单峰分布，峰值粒径为150~700 nm。各组分均匀分布在颗粒物中，电子烟气溶胶数浓度粒径双峰分布可能主要与加热丝升温速率和气道内颗粒物浓度有关。而利用ICRP模型模拟，电子烟气溶胶主要沉积于上呼吸道和肺泡中，占比分别为2.7%~18.8%和6.8%~9.6%。 不同测量条件得到的粒径分布结果存在较大差异，测量仪器和器具也会影响粒径分布结果。一般来说，停留时间越长，或稀释比越小，粒径越大。稀释前停留时间影响更大，从0.28 s增加至14.14 s时，颗粒物质量浓度峰值粒径从0.6 μm增加至0.91 μm。稀释比从261增加至2011时，数浓度粒径分布由原来的峰值位置在约400 nm的单峰分布变为峰值位置在约40 nm和200 nm的双峰分布。在电子烟气溶胶粒径分布测量中，要注意降低高浓度颗粒物的停留时间，并尽量避免气溶胶经过阀门等复杂组件而导致颗粒物损失；若需稀释，需要评价所使用的稀释方法是否实现均匀稀释。另外由于电子烟气溶胶的非稳定性质和测量仪器的测量原理差异可能会使不同测量仪器的测量结果有差异。烟油中丙二醇和植物甘油的比例对粒径分布有较显著的影响，植物甘油含量高的烟油产生的气溶胶粒径更大。而陶瓷和棉芯发热体、4.5~8.0 W范围内功率的变化、0~50 mg/mL范围内的尼古丁含量变化以及口味则对粒径分布影响不大。

Electronic cigarette is a kind of electronic nicotine delivery systems. The heating unit with e-liquid is heated by the heating wire. The e-liquid thus evaporates and the vapor condenses to form aerosols. Electronic cigarettes have gained an increasing number of users and sales since 2003, promoted as cigarette substitutes. Electronic cigarettes have attracted many young people to get access to. However, there is still no clear and accurate understanding of the health risks of electronic cigarettes. The measurement of particle size distribution and organic components is the key to the hazard assessment of electronic cigarette aerosols. In this paper, the electronic cigarette aerosols dilution system for particle size distribution was developed, which effectively solved the problems of some existing dilution systems, such as uneven mixing, particle loss caused by the time control solenoid valve, and long residence time. The new dilution system was based on air distribution plate dilution, with a good gas-tight performance. The flue gas and diluent gas could mix evenly and results kept stable under both vertical and horizontal conditions or positive and negative pressure conditions. The flow rate in the system was constant, which was convenient for sampling. Three sets of measurement systems based on the dilution system and three common measuring instruments were built to measure the particle size distribution of the electronic cigarette aerosols. The count distribution showed a bimodal distribution with peak particle sizes of 10~50 nm and 100~300 nm, respectively. In addition, a small peak was also found at 700~800 nm. While the peak particle size of the mass distribution was 150~700 nm. The components were evenly distributed in the aerosols, and the bimodal count distribution of electronic cigarette aerosols might be mainly related to the heating rate of heating wire and the concentration of particles in the airway. Based on ICRP simulation, electronic cigarette aerosols were mainly deposited in the head airways region and alveolar region, accounting for 2.7%~18.8% and 6.8%~9.6% respectively. It was found that the particle size distribution results under different measurement conditions were different, and measuring instruments as well as electronic cigarette’s conditions could also affect the results. In general, the longer residence time or the smaller dilution ratio was, the larger the particle size was. The effect of residence time before dilution was greater; when it increased from 0.28 s to 14.14 s, the peak size of the particle mass distribution increased from 0.6 μm to 0.91 μm. When the dilution ratio increased from 261 to 2011, the count distribution changed from a single-peak distribution with a peak size at about 400 nm to a bimodal distribution with peak positions at about 40 nm and 200 nm. In the measurement of particle size distribution of electronic cigarette aerosols, it should be emphasized to shorten the residence time of high-concentration particles, and avoid the particle loss caused by valves or other complex devices. Evaluation of dilution performance is necessary when dilution is applied. In addition, the volatility of the electronic cigarette aerosols and difference in measurement principle of the instruments might also differ the measurement results of different measurement instruments. The ratio of propylene glycol to vegetable glycerin in the e-liquid had a relatively significant effect on the particle size distribution, as the larger particle size with higher vegetable glycerin content. While ceramic and cotton heating unit, power level in the range of 4.5 to 8.0 W, nicotine content in the range of 0 to 50 mg/mL, as well as flavor could hardly affect the particle size.