Research on Optical Absorption Characteristics of Atmospheric Aerosols at 1064 nm Wavelength

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 with the development of optoelectronic engineering. Based on photoacoustic spectroscopy (PAS), a set of optical absorption coefficient (OAC) measurement device for aerosol at 1064nm 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 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, number concentration of aerosol was varied slightly (less than 4%), but OAC increased from 6Mm-1 to 17Mm-1 with the growth of aerosol particles size from ~ 120nm to ~ 175nm. With the results of 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 strong correlation with 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 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.