PM2.5中类腐殖质表面活性测定方法与实例分析

建立了大气细粒子中类腐殖质（HULIS）表面活性的动态表征方法，并以华北平原乡村站点冬季大气PM_2.5样品为例，对PM_2.5中HULIS的表面活性进行表征.HULIS碳质组分（HULIS-C）浓度为2.0~4.6μg C/m³，占水溶性有机碳和总有机碳的比例分别为31%~40%和20%~26%.浓度为88~200mg C/L的HULIS水溶液，其表面张力相对于纯水降低了18%~22%.HULIS-C浓度在低于70mg C/L时表面张力降低显著，在88~320mg C/L之间降低相对缓慢.动态表面张力随着时间变化逐渐降低，在液滴形成后200s以内表面张力下降迅速，之后趋于平缓，说明表面活性分子在液滴中扩散趋于稳定需要一定的时间，该特征时间可能影响表面活性物质在云凝结核活化时的作用.证实了在污染地区的大气PM_2.5中含有一定量的表面活性物质，这些物质可能对颗粒物活化为云滴、雾滴过程产生显著影响；表面活性物质的存在可能在外界湿度变化过程中导致颗粒物发生液-液相分离现象，在颗粒物表面形成有机膜，影响活性分子摄取以及半挥发性物质的气-粒分配过程，从而影响大气非均相反应过程.

The surface activity of humic-like substances: methodology and case study

A dynamic methodology was developed to characterize the surface activity of water soluble humic-like substances (HULIS) in PM_2.5. As a case study, HULIS in PM_2.5 samples collected from a rural site during wintertime in North China Plain region were investigated. The HULIS carbon content varied from 2.0~4.6μg C/m³, accounting for 31%~40% of water-soluble organic carbon and 20%~26% of organic carbon, respectively. While the carbon content of HULIS aqueous solution ranged from 88~200mg C/L, correspondingly, the surface tension reduced by 18%~22% compared with that of pure water. The surface tension decreased significantly when the concentration was lower than 70mg C/L, while it decreased slowly between 88~320mg C/L. The dynamic measurements showed that surface tension gradually decreased with time consuming. Surface tension decreased rapidly within 200 seconds after droplet formation and then tended to be stable, indicating that the distribution of surface-active organic molecules onto the droplet surface was not instantaneous. Such process may affect droplet activation. There were substantial surface-active substances in atmospheric particulate matters in the polluted atmosphere. These surfactants may have significant impacts on the activation of aerosol particles into cloud or fog droplets. In addition, the HULIS may lead to liquid-liquid phase separation and form the core-shell structure of particles when ambient relative humidly fluctuates. Such structure could influence the uptake of reactive molecules and the gas-particle partitioning, therefore, affecting heterogeneous chemistry.