多环芳烃是具有致突变、 致癌和致畸作用的一类持久性有机污染物, 广泛分布在大气、 水、 土壤等不同环境介质中。 多环芳烃一旦进入土壤便会长期存留于其中, 土壤成为环境中多环芳烃的重要储藏库和最终归宿。 土壤中的多环芳烃可以通过多种途径进入人体, 对人类健康造成威胁。 因此, 对土壤中多环芳烃的监测十分必要。 当前, 传统的土壤多环芳烃检测方法过程繁琐、 费时, 不利于污染场地多环芳烃的大范围快速检测, 而基于激光诱导荧光光谱技术的土壤多环芳烃检测法能够快速识别、 检测土壤中的有机污染物。 多环芳烃类物质具有易挥发, 可被紫外光降解等特性, 实验中紫外激光能量的选择至关重要, 本文利用实验室搭建的266 nm激光诱导荧光系统, 以蒽、 芘、 菲为研究对象, 探究不同激光能量下多环芳烃分解和荧光光谱的变化特性。 结果表明, 当激光的能量密度变化时, 荧光中心峰位置未发生偏移, 但蒽、 芘、 菲三种多环芳烃荧光峰处最大强度的相对标准偏差随激光能量密度的下降呈现出先下降后上升的趋势: 当能量密度为8.54 mJ·cm-2时, 三种物质在10次光谱测量结果的相对标准偏差均为最大, 蒽、 芘、 菲三种物质的荧光峰强度相对标准偏差分别在1.72, 1.00和1.47 mJ·cm-2的能量密度下达到最小值；蒽、 芘、 菲在100 s时, 分解率分别达到59.3%, 69.8%和63.6%, 在较高的能量下, 蒽、 芘、 菲三种物质发生了较快的分解, 芘相比于其他两种多环芳烃类物质更易发生光降解和热分解等作用, 荧光峰强度相对标准偏差也高于蒽与菲；蒽在激光能量密度为1.72 mJ·cm-2时, 10 s时的分解率已经接近于0, 100 s时分解率仅为12.8%, 荧光峰强度相对标准偏差达到最低, 当激光能量密度降至0.88 mJ·cm-2时, 蒽在100 s内的分解几乎可以忽略不计；对于芘而言, 当激光能量密度降至1.00 mJ·cm-2以下时, 分解作用基本趋于一致, 100 s时分解率在47.3%~47.4%；而对于菲而言, 当激光的能量密度低于1.47 mJ·cm-2后, 分解率不再随激光能量密度的降低而明显下降, 在100 s时的分解率在36.8%~38.6%；在低能量密度土壤中芘与菲下仍发生分解作用。

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants (POPs) which are mutagenic, carcinogenic and teratogenic. They are widely distributed in air, water and soil. Once PAHs enter the soil, they remain in the soil for a long time. PAHs are concentrated in the soil. They can enter the human body in many ways and pose a threat to human health. Therefore, it is necessary to monitor PAHs in soil. Now, traditional detection methods are cumbersome and time-consuming, which is not conducive to the widely rapid detection of PAHs in the contaminated sites. The method based on laser-induced fluorescence spectroscopy can quickly identify and detect organic pollutants in the soil. However, PAHs are volatile and can be degraded by ultraviolet light, so the selection of UV laser energy is very important. In this work,a 266nm laser-induced fluorescence system is established in the laboratory. Anthracene, pyrene, and phenanthrene are used to investigate the decomposition and fluorescence spectra of PAHs under different laser energies. The results showed that when the energy density of the laser changed, the peak positions of the fluorescence center did not shift, but the relative standard deviations of the maximum intensity at the fluorescence peaks of three PAHs decreased firstly and increased then. When the energy density was 8.54 mJ·cm-2, the relative standard deviations of the three PAHs in 10 spectral measurements were the largest, and the relative standard deviations of the fluorescence peak intensities of anthracene, pyrene and phenanthrene reach the minimum value at 1.72, 1.00 and 1.47 mJ·cm-2. The decomposition rates were 59.3%, 69.8% and 63.6% for anthracene, pyrene and phenanthrene at 100 s, respectively. At higher energies, three PAHs decompose rapidly. Compared with the other two PAHs, pyrene was more prone to photodegradation and thermal decomposition, and the relative standard deviation of fluorescence peak intensity was also higher than that of anthracene and phenanthrene. For anthracene, when the laser energy density was 1.72 mJ·cm-2, the decomposition rate was close to 0 at 10 s and 12.8% at 100 s, and the relative standard deviation of the fluorescence peak intensity was the lowest. When the laser energy density was reduced to 0.88 mJ·cm-2, the decomposition of anthracene in 100s was almost negligible. For pyrene, when the laser energy density dropped below 1.00 mJ·cm-2, the decomposition tended to be consistent, and the decomposition rate was 47.3%～47.4% at 100 s. For phenanthrene, when the energy density of the laser was lower than 1.47 mJ·cm-2, the decomposition rates no longer decreased, and the decomposition rates were 36.8%～38.6%. Pyrene and phenanthrene still decompose in low energy density.