相对湿度对室内细颗粒物粒径分布影响的试验研究

Experimental research on effects of the relative humidity on the size distributions of indoor fine particles

为了研究相对湿度对室内2.5μm以下细颗粒物(PM2.5)分布的影响,设计了如下试验:在恒温房间中点燃卫生香,作为较稳定的污染源向室内释放细颗粒物,当室内颗粒物浓度达到一定值时,停止源释放,测量颗粒物粒径谱随时间的变化情况;利用蒸汽加湿器改变室内相对湿度,得到不同相对湿度下细颗粒物的粒径分布;同时,利用惯性捕捉法采集颗粒物样本,并用扫描电镜进行微观观察。结果表明,室内相对湿度达到80%左右时,可吸入颗粒物的粒径分布发生明显变化,其中1μm以下细颗粒物数密度百分率都明显减小,而1μm以上较大颗粒物数密度百分率明显增加。扫描电镜微观观测结果表明,室内颗粒物从发生源产生后即容易凝并,而相对湿度大于65%时,可采集到较多由细颗粒并聚而成的较大颗粒物,特别是相对湿度达到80%时更加显著。研究表明,室内相对湿度增加可以导致颗粒物吸湿长大且可促进细颗粒物并聚成较大颗粒物,相对湿度较大导致颗粒物粒径分布向大的方向偏移。

In order to study the influence of related humidity on size distribution of indoor fine particles less than 2.5 μm, we have de signed experiments in this work as follows： a lighted incense stick was used as a more stable kind of pollutant source in the constant temper ature room when the inhalable particles＇ concentration in the indoorcondition was let to go up to a given value, then, the pollutant source would be taken away, and, next, the particle size spectra in the in door room were recorded in two hours. By changing the indoor rela tive humidity with the steam humidifier during this process, the size distributions of fine particles in different relative degrees of humidity were tested. Meanwhile, the samples of particles were trapped under the inertial effect, and observed by the FESEM （field mission scan ning electron microscopy ）. Measuring the size distributions of the particles, we can see the effects of the relative humidity on the coag ulation and hygroscopic growth of the particles. And, moreover, by observing the microscopic morphology of individual particle in differ ent relative degrees of humidity, further studies could be done with the probability of the cohesive particulates. Results have shown that, when the indoor relative humidity was up to about 80%, the size dis tributions of the particles would change significantly, and the concen tration of fine particle sizes less than 1 ttm turns to decrease apparent ly while the concentration of coarse particle numbers with the size over 1 μm may also increase apparently. Excluding the experimental errors of particle number concentration caused by the humidifier＇ s pe riodical release steam, the declines of the concentration of particle numbers sized from 0.3 0.6μm, 0.6 μm to 1.0μm, and from 1.0 μm to 2.5 μm are likely to move slower in turn. In addition, it was observed via the FESEM that particles would be likely to coagulate after resource emission, and there would be more bigger particles co agulated by the smaller particles trapped in when the RH increased by over 65%, especially when they increased up to 80%. It can thus be concluded that, when the relative humidity increased, the mois ture the particles have absorbed would grow bigger, with the fine par ticles coalesced to the bigger ones consequently. Therefore, the high er the relative humidity becomes, the bigger the size of the particles spectra would be moving to.