北京春季大气气溶胶光学特性研究

为了解北京春季气溶胶光学特性,利用AERONET Level 2.0数据资料研究了2010～2014年北京市春季大气气溶胶光学参数,以晴空作为背景,比较分析了春季及沙尘期间大气气溶胶光学性质的差异.研究发现,北京春季与沙尘期间粗粒子消光占总消光的28%和59%,沙尘期间粒子吸收仅占消光的11.4%,说明沙尘天气发生时以粗粒子消光为主且吸收作用弱.沙尘天气溶胶光学厚度呈现出高值,其值为春季平均值的1.7倍.Angstrom波长指数在沙尘期间远小于非沙尘期间,且有85%小于0.6.北京春季体积尺度谱以粗模态峰为主,其中沙尘天粗模态的体积浓度为0.81μm³/μm²明显大于春季的值(0.25μm³/μm²).沙尘期间单次散射反照率随波长增加递增,在波长440~1020nm间的平均值大于春季均值.复折射指数实部在沙尘过程的平均值达到1.51(440nm),春季均值为1.48(440nm),表明沙尘气溶胶的散射能力更强;复折射指数虚部随波长增大呈减小趋势,且春季平均值大于沙尘期间的值.沙尘期间辐射强迫大于春季值,并远高于春季晴空条件下均值.

Aerosol optical properties in spring over urban Beijing

The purpose of this study is to investigate the optical properties of aerosols during spring in Beijing. A comparison of aerosol optical properties was performed between spring and dusty days from Aerosol Robotic Network (AERONET) measurements during 2010~2014. The extinction of coarse particles (r > 0.6μm) accounted for 28% and 59% of that of total particle in spring and dusty days respectively. Average absorption percent out of extinction for total particles were 11.4% during dusty days. This result indicated that aerosol extinction was dominated by coarse particles. The aerosol optical depth showed high values in dusty days with the average value was 1.7 times higher than that of spring. Angstrom exponents during dusty days were higher than those of spring, and about 85% of them less than 0.6 during dusty days. The aerosol volume size distributions presented abimodal structure (fine and coarse modes), and the coarse mode was dominant in spring. The volume concentrations of coarse mode in spring were evidently lower than those of dusty days. The single scattering albedo showed an increasing trend with wavelengths during dusty days in Beijing. The averaged single scattering albedos were about 0.92 for dusty days and 0.89 for spring during 440~1020nm. The real parts of the refractive index at 440nm were 1.48 during spring and 1.51 during dusty days, suggested the aerosol particles from dust source regions were involved in a stronger scattering. The imaginary parts of refractive index showed a decreasing trend with wavelength sand the average value in dusty days were higher than that of spring. The averaged aerosol radiative forcing in dusty days was higher than that of in spring and in clean days in Beijing.