Observation-based estimation of aerosol-induced reduction of planetary boundary layer height

Radiative aerosols are known to influence the surface energy budget and hence the evolution of the planetary boundary layer. In this study, we develop a method to estimate the aerosol-induced reduction in the planetary boundary layer height (PBLH) based on two years of ground-based measurements at a site, the Station for Observing Regional Processes of the Earth System (SORPES), at Nanjing University, China, and radiosonde data from the meteorological station of Nanjing. The observations show that increased aerosol loads lead to a mean decrease of 67.1 W m−2 for downward shortwave radiation (DSR) and a mean increase of 19.2 W m−2 for downward longwave radiation (DLR), as well as a mean decrease of 9.6 Wm−2 for the surface sensible heat flux (SHF) in the daytime. The relative variations of DSR, DLR and SHF are shown as a function of the increment of column mass concentration of particulate matter (PM2.5). High aerosol loading can significantly increase the atmospheric stability in the planetary boundary layer during both daytime and nighttime. Based on the statistical relationship between SHF and PM2.5 column mass concentrations, the SHF under clean atmospheric conditions (same as the background days) is derived. In this case, the derived SHF, together with observed SHF, are then used to estimate changes in the PBLH related to aerosols. Our results suggest that the PBLH decreases more rapidly with increasing aerosol loading at high aerosol loading. When the daytime mean column mass concentration of PM2.5 reaches 200 mg m−2, the decrease in the PBLH at 1600 LST (local standard time) is about 450 m.摘要大气气溶胶通过吸收和散射太阳辐射影响地表能量平衡, 从而影响行星边界层的发展. 本文利用南京大学 SORPES (the Station for Observing Regional Processes of the Earth System) 超级站的两年地面观测数据以及南京探空站的遥感观测数据, 估算大气气溶胶含量对行星边界层高度的影响. 地面观测结果表明: 白天大气气溶胶的存在导致向下短波辐射的年平均值下降 67.1 W m−2; 向下长波辐射的年平均值上升 19.2 W m−2; 地面感热通量的年平均值下降 9.6 W m−2. 并且大气辐射量的变化与 PM2.5 柱浓度的增加有很强的相关性. 利用地面感热通量与 PM2.5 柱浓度之间的统计学关系, 本文估算出气溶胶含量极低 (背景天) 时地面感热通量的大小. 并利用估算出的地面感热通量以及其观测结果, 计算出因气溶胶含量增加而导致的边界层高度的降低量. 本文的结果认为随着大气中气溶胶含量的增加, 边界层高度加速降低. 当白天气溶胶平均柱浓度达到 200 mg m−2时, 16 时 (当地时间) 时边界层高度下降约 450 m.

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