研究半挥发性气溶胶物质的气粒分配对于更准确地描述大气气溶胶的组成和尺寸分布是至关重要的。 硝酸铵是亚微米颗粒物的主要组成部分, 特别是在高污染事件中。 为了更深入的了解硝酸铵气溶胶的气粒分配问题, 利用激光悬浮技术捕获、 悬浮半挥发性无机物硝酸铵液滴单颗粒（2～10 μm）, 控制相对湿度条件、 温度条件, 并采集氢-氧振动带的受激拉曼峰位信息, 利用非弹性米氏散射理论计算实时液滴半径尺寸、 折射率和浓度, 利用稳态传质模型Maxwell公式推算出了不同湿度下的蒸汽压。 实验数据计算出的硝酸铵的饱和蒸汽压值的数量级与文献报道一致。 当RH分别恒定在80%, 73%, 68%, 57.3%, 55.4%, 44.8%时, 饱和蒸汽压值为(1.67±0.24)×10-3, (1.82±0.19)×10-3, (2.91±0.13)×10-3, (3.5±0.28)×10-3, (4.59±0.22)×10-3和(6.64±0.3)×10-3 Pa, 显然, 随着相对湿度的降低, 饱和蒸汽压值增大, 即湿度降低促进硝酸铵的挥发。 此外, 还推算了不同湿度下硝酸铵气溶胶液滴的挥发通量, 挥发通量值在(4.01±0.79)×10-7～(3.32±0.77)×10-8 mol·(s·m2)-1之间。 这对更好的了解气溶胶在挥发过程中的微观过程有重要意义。

Measurements of the particle-to-gas partitioning of semi-volatile atmospheric aerosols are crucial for providing more accurate descriptions of the compositional and size distributions of atmospheric aerosol. As a major component of semi-volatile aerosol species, ammonium nitrate (NH4NO3) is ubiquitous in the sub-micron particulate matter, particularly in high pollution episodes. In order to further understand gas-particle partitioning of NH4NO3, determination of the saturated vapor pressure of NH4NO3 is needed. Here, we investigate the volatility of NH4NO3 at different relative humidities (RHs) using aerosol optical tweezers coupled with Raman spectroscopy as an instrument for sampling and detecting. According to the Maxwell equation, the vapor pressures at different RHs are calculated, and the values are (1.67±0.24)×10-3, (1.82±0.19)×10-3, (2.91±0.13)×10-3, (3.5±0.28)×10-3, (4.59±0.22)×10-3 and (6.64±0.3)×10-3 Pa, when the RH is 80%, 73%, 68%, 57.3%, 55.4%, 44.8% respectively. Obviously, the vapor pressures of NH4NO3 increase with RH decreasing, i.e. low RH promotes the evaporation of ammonium nitrate. Additionally, we also calculate the volatilizing flux of NH4NO3 at different RHs, and the values are in the range of (4.01±0.79)×10-7~(3.32±0.77)×10-8 mol·(s·m2)-1. The results obtained herein are of important significance in understanding the partitioning processes of semi-volatile aerosols.