大气气溶胶的光吸收特性是全球气候变化和区域天气的重要影响因素。 随着国家重大光电工程技术的快速发展, 近红外波段的大气气溶胶光吸收特性受到越来越多的关注。 基于光声光谱技术, 自行搭建了一套1 064 nm波长气溶胶光学吸收系数测量装置, 结合扫描电迁移率粒径谱仪对合肥近郊科学岛附近的大气气溶胶的光吸收系数和粒径谱进行了9 d的连续测量, 获取了气溶胶的光学吸收系数、 粒子数浓度及粒径谱的长时间测量数据。 基于测得的光吸收系数与粒子数浓度进行相关性分析。 结果表明, 当气溶胶粒径谱相对稳定时, 气溶胶光吸收系数与数浓度之间具有很好的相关性, 相关系数为0.62~0.99。 此外, 还观测到了夜间粒子的粒径增长过程。 在该时段内粒子数浓度相对稳定, 气溶胶粒子的平均粒径从120 nm左右增长到175 nm附近, 其吸收系数随着粒径的增长从6 Mm^-1增加到17 Mm^-1。 通过对吸收截面和粒子平均粒径之间的相关性进行理论拟合和分析可知, 该时段内的气溶胶粒子更接近于面吸收体。 最后, 结合环境质量观测站点给出的空气质量监测数据, 对测量期间出现的雾霾天、 晴天、 阴雨天等三种典型天气条件下的气溶胶粒子的光吸收系数和粒径谱的日变化测量数据进行对比分析。 分析结果表明, 三种天气条件下吸收系数和粒子数浓度的日变化趋势具有明显的气象特征: 雾霾时段, 环境中的粒子数浓度及其中的大粒子浓度逐渐增多, 光吸收系数增大; 晴天时, 附近道路上的机动车在交通繁忙时段的尾气排放使得大气中的细粒子在短时间内急剧增多, 导致光吸收系数显著增强; 雨天时, 降水对大气中的气溶胶粒子具有明显的清洗作用, 使得环境中的粒子数浓度显著减少, 导致其吸收系数变小。 实际大气气溶胶光吸收系数的观测与相关测量数据的比对和分析结果验证了所建立测量装置的可靠性, 也为近红外波段气溶胶光吸收特性的深入研究积累了经验。

Absorption of atmospheric aerosol is an important factor affecting global climate change and local weather. Characteristics of aerosol optical absorption in the near infrared wavelength have attracted more and more attention to the development of optoelectronic engineering. Based on photoacoustic spectroscopy (PAS), a set of optical absorption coefficient (OAC) measurement device for aerosol at 1 064 nm wavelength was built. OAC and particle size distribution have obtained by the photoacoustic spectrometer and scanning mobility particle sizer spectrometer (SMPS) on Science Island (near suburban of Hefei) for 9 days. Firstly, the correlation between OAC and particle number concentration was analyzed based on the measured data. The results show that the OAC had a strong correlation with number concentration and the correlation coefficient varied between 0.62 and 0.99 while the aerosol particle size distribution was relatively stable. Secondly, the particle size growth process was observed at night time. In this process, the number concentration of aerosol was varied slightly (less than 4%), but OAC increased from 6 Mm^-1 to 17 Mm^-1 with the growth of aerosol particles size from ~120 nm to ~175 nm. With the results of the theoretical fitting and analysis of the correlation between the absorption cross section and the average particle diameter, aerosol particles in this process were found to be surface absorbers approximately. Finally, combined with the air quality index (AQI) released by environmental protection administration, the diurnal variation of the OAC and particle size distribution of aerosol particles in different weather, were compared and analyzed. OAC and particle number concentration indicates a strong correlation with the weather and environmental condition, such as haze, traffic, rain. In haze day, OAC increased gradually with the increase of larger portion and the total particle number concentration in the air. In sunny days, the exhaust emission of vehicles on nearby roads during traffic busy caused sharply growth of the fine particles in the air in a short period of time, resulting in a significant increase in the OAC. In a rainy day, precipitation has a clear cleaning effect on aerosol particles, which reduces the number of particles in the air dramatically, leading to a decrease in the OAC. This observation experiment and the analysis verified the reliability of the photoacoustic spectrometer. It also accumulates experience for the future study on the aerosol optical absorption characteristics in near infrared wavelength.