(NH_(4))_(2)SO_(4),NH_(4)NO_(3)和(NH_(4))_(2)SO_(4)/NH_(4)NO_(3)混合气溶胶吸湿质量增长因子的快速测量方法

Measurement on Mass Growth Factors of (NH_(4))_(2)SO_(4),NH_(4)NO_(3) and Mixed (NH_(4))_(2)SO_(4)/NH_(4)NO_(3) Aerosols Under Linear RH Changing Mode

气溶胶颗粒的吸湿性决定了其尺寸、浓度、化学组成以及相态,从而显著影响着全球气候、大气异相化学以及人类健康。运用在线、原位、连续扫描衰减全反射傅里叶变换红外光谱(ATR-FTIR)技术,结合线性湿度(RH)控制系统,实现了RH连续变化条件下气溶胶FTIR-ATR光谱的快速测量。根据水弯曲振动谱带(~1 640 cm^(-1))峰面积随RH的变化,得到了(NH_(4))_(2)SO_(4),NH_(4)NO_(3)和(NH_(4))_(2)SO_(4)/NH_(4)NO_(3)混合气溶胶的质量增长因子(MGFs)、潮解点(DRH)和风化点(ERH)。与气溶胶的E-AIM模型预测值相比较,实验结果表现出良好的一致性,证实该方法是一种测量大气气溶胶MGFs, ERH和DRH的快速测量方法。

The hygroscopicity of aerosol particles determines their size, concentration, chemical compositions and phase states, and thus affects the global climate, heterogeneous atmospheric chemistry and human health. In this study, an on-line and in-situ rapid scan attenuated total reflection Fourier transform infrared(ATR-FTIR) technique coupled with a linear relative humidity(RH) controlling system was utilized to obtain the IR spectra of aerosols under different RH. The mass growth factors(MGFs), deliquescence relative humidity(DRH) and efflorescence relative humidity(ERH) of(NH_(4))_(2)SO_(4),NH_(4)NO_(3) and mixed(NH_(4))_(2)SO_(4)/NH_(4)NO_(3) aerosols were determined rapidly by measuring the peak areas of the bending vibration band of liquid water(~1 640 cm-1). Comparisons between the measurements and the predictions from the E-AIM model showed good consistency, which verifies the rapid scan ATR-FTIR as a powerful tool for investigating hygroscopic behaviors and phase transitions of atmospheric aerosols. Furthermore, pure(NH4)2SO4 and NH4NO3 particles were found to effloresce at 49% and 25% RH, respectively, while mixed(NH_(4))_(2)SO_(4)/NH_(4)NO_(3) aerosols with a mole ratio of 1∶1 and 1∶2 exhibited one-stage efflorescence transition beginning at 44% and 38% RH, respectively, upon dehydration. These results indicate that the presence of NH4NO3 can inhibit the crystallization of(NH4)2SO4, and formed(NH4)2SO4 seeds will act as heterogeneous nuclei to promote the efflorescence of NH4NO3 at higher RH. In addition, the double salt(NH_(4))_(2)SO_(4)·2 NH_(4)NO_(3) was formed upon efflorescence of mixed particles. These findings are critical for understanding complex phase transitions of mixed inorganic aerosols and interpretation for RH dependency of heterogeneous reaction rates of atmospheric reactive species.