基于新型中红外光源的HONO快速准确检测技术研究

Nitrous acid (HONO) is an important source of OH radical，and plays a critical role in the formation of photochemical smog. The contribution rate of nitrous acid on OH radical can be as high as 50% in the daytime. But there is not a uniform view on the sources of HONO until now. .Current study on HONO sources is still inadequate, and domestic systematic research is also not enough.In view of these facts, rapid and precise detection of gaseous nitrous acid is carried out with the mid-infrared laser absorption spectroscopy technology based on the principle of tunable diode laser absorption spectroscopy (TDLAS) in the present project. Two sets of HONO measurement devices based on an 8 μm quantum cascade laser and another 2.8 μm distributed feedback laser are optimized and completed respectively. Taking advantage of the characteristics of quick scan and no interference of other gases in the measurement region, combining with wavelength modulation and Allan variance to obtain high sensitivity, the resulting one-second detection limit is 200 ppt, and carrying out field measurements in two places. By comparing the field experiment results, we can seclect the wave band with higher detection efficiency. The absorption line parameters of nitrous acid are studied for the first time by using the 2.8 μm DFB laser, to enrich nitrous acid spectrum database in this wavelength range. In the meantime, the possible sources of HONO in the atmosphere are analyzed based on the results of field measurements.

亚硝酸(HONO)是OH自由基的主要来源，对光化学烟雾形成有重要作用。日间高值HONO对OH的贡献率可高达50%以上。但是大气中HONO的来源国内外至今没有统一的解释。.本项目针对目前HONO源研究不足和国内系统研究缺乏的现状，基于可调谐半导体激光吸收光谱(TDLAS)原理开展中红外激光吸收光谱技术对HONO的快速准确探测研究。优化集成并完善一套基于8 μm量子级联激光器和另一套2.8μm分布反馈式（DFB）激光器的HONO气体测量装置。利用激光器的快速扫描特性和在所测量波段无其它气体干扰等优点，结合波长调制和Allan方差获得高的灵敏度，1s探测限为200ppt，进行两处HONO外场测量实验。通过实验比较得出HONO检测效率较高的波段。用2.8μm DFB激光器开展HONO在该波段的吸收线参数测量，丰富HONO在该波段的光谱数据库，并根据外场测量结果解析大气中可能的HONO来源。

亚硝酸(HONO)是OH自由基的主要来源，对光化学烟雾形成有重要作用。日间高值HONO对OH的贡献率可高达50%以上。但是大气中HONO的来源国内外至今没有统一的解释。.本项目针对目前HONO源研究不足和国内系统研究缺乏的现状，基于可调谐半导体激光吸收光谱(TDLAS)原理开展中红外激光吸收光谱技术对HONO的快速准确探测研究。优化集成并完善了一套基于8 µm量子级联激光器(QCL)的HONO气体测量装置。利用激光器的快速扫描特性和在所测量波段无其它气体干扰等优点，结合波长调制和Allan方差获得高的灵敏度，1 s探测限为400 ppt。用2.8 µm差频产生(DFG)激光器开展了HONO在该波段的吸收线参数测量，丰富HONO在该波段的光谱数据库。其中波数为3598.49 cm-1的HONO吸收线线强为1.06 *10-20 cm-1/mole.cm-2，适合于探测大气中的HONO。目前能够查阅到的HONO的吸收线参数在8 μm波段仅有9条，所以也实验总结分析了HONO在1251.8-1257.2 cm-1范围的52条吸收线参数，这个波段最强吸收线的频率和线强分别为1252.2109 cm-1和2.1*10-20 cm-1/molec.cm-2，而且不受CO2, H2O等其他气体吸收的干扰，与2.8 μm波段的最强吸收线线强相比，更适合于探测大气中的HONO。HONO的光解和光化学过程在两个典型的时间被观测到：无雪天和下雪天。下雪天，在太阳辐射下，因为光化学反应使HONO浓度升高。在无雪天，白天因为光解使HONO浓度降低，在早上HONO浓度升高是因为夜间NO2在潮湿的表面发生的非均相反应。