National Atmospheric Research Laboratory (NARL), Gadanki, India.
National Atmospheric Research Laboratory (NARL), Gadanki, India.
Sci Total Environ. 2022 Jan 1;802:149758. doi: 10.1016/j.scitotenv.2021.149758. Epub 2021 Aug 19.
It is well known that the atmospheric boundary layer (ABL) plays a significant role in controlling the variability of atmospheric constituents such as aerosols and trace-gases. Hence, significant diurnal and seasonal variation in these will be observed as the ABL altitude does. However, on several occasions, high aerosol concentration in the lidar measurements is observed even above the ABL altitude. This raised a question that up to what extent ABL altitude acts as a capping layer for these pollutants? From the detailed analysis carried out using long-term (2010-2018) lidar observations and simultaneous radiosonde profiles obtained from Gadanki, India, we show that 'there exist thermal inversions (TI), which are stronger than the ABL inversions, that fully control the vertical extent'. The detailed characteristics of TI (inversion strength (IS) and inversion depth (ID)) are also obtained. The results revealed that aerosol concentrations below the TI altitude increases with IS (ID) up to 3-4 K (300-400 m) during winter whereas in pre-monsoon it increases up to 2-3 K (100-200 m). Thus, IS of up to 2-4 K is required to fully trap the aerosol concentrations and this TI coincide with the ABL inversions for 51.7% only, particularly during the winter and pre-monsoon seasons. This analysis is further extended to different geographical locations of India using the aerosol profiles obtained from CALIPSO and a network of 23 radiosonde stations. The observed results provided further evidence that the vertical distribution of aerosols is restricted to the maximum extent by the TI but not the ABL altitude. These observations lead us to propose a hypothesis that 'trapping of aerosols fully occurs up to particular IS and ID only and the ABL altitude is not the deciding factor most of the time for capping the aerosol vertical distribution'. These findings will greatly help in modeling the diffusion and transport of air pollutants in the lower troposphere.
众所周知，大气边界层（ABL）在控制大气成分（如气溶胶和痕量气体）的变异性方面起着重要作用。因此，随着 ABL 高度的变化，这些成分会出现明显的日变化和季节变化。然而，在某些情况下，即使在 ABL 高度以上，激光雷达测量中也会观察到高气溶胶浓度。这就提出了一个问题，即在多大程度上 ABL 高度可以作为这些污染物的覆盖层？通过使用长期（2010-2018 年）激光雷达观测和来自印度 Gadanki 的同时获得的无线电探空仪剖面进行的详细分析，我们表明“存在比 ABL 逆温更强的热逆温（TI），完全控制着垂直范围”。还获得了 TI（逆温强度（IS）和逆温深度（ID））的详细特征。结果表明，冬季 TI 高度以下的气溶胶浓度随 IS（ID）增加，最高可达 3-4 K（300-400 m），而前季风季最高可达 2-3 K（100-200 m）。因此，需要达到 2-4 K 的 IS 才能完全捕获气溶胶浓度，而这种 TI 仅在 51.7%的情况下与 ABL 逆温同时出现，特别是在冬季和前季风季。使用从 CALIPSO 和 23 个无线电探空站网络获得的气溶胶廓线，将这种分析扩展到印度的不同地理位置。观察结果进一步证明，气溶胶的垂直分布仅受到 TI 的最大限制，而不受 ABL 高度的限制。这些观测结果使我们提出了一个假设，即“气溶胶的完全捕获仅在特定的 IS 和 ID 下发生，而 ABL 高度并非大多数情况下限制气溶胶垂直分布的决定因素”。这些发现将极大地有助于在低对流层中模拟空气污染物的扩散和传输。
