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With the increase economic growth and high energy consumption in Shenzhen, pollutant emission increases gradually which leads to air pollution and affect public health. In order to undertake effective measures for preventing and controlling air pollution, it is essential to understand the transmission characteristics of PM2.5 and identify the cause of air pollution in Shenzhen. Based on LIDAR data of Shenzhen, China, the transmission characteristics of PM2.5 across Shenzhen's borders in the winter of 2017 (from December 1, 2017 to February 28, 2018) were analyzed using a four-dimensional flux method. In addition, the sources of PM2.5 in Shenzhen from December 8 to 10, 2017 were analyzed. The results revealed that the East Asian winter monsoon was primarily responsible for the transmission of PM2.5 in Shenzhen, from north to south, and its surrounding areas, and high PM2.5 flux was primarily located at the altitude range of 500–1,500 m. During the monsoon transition period, the surface wind directions changed frequently, which resulted in varying transmission directions of PM2.5 fluxes across Shenzhen. During the period from December 8 to10, PM2.5 was continuously transported to the urban areas of Shenzhen via its northern border due to the influence of strong northerly wind. The PM2.5 fluxes were positive over Songgang station (in the northwestern corner of Shenzhen) and Xiapi station (in the northeastern corner of Shenzhen) from December 8 to 9. The analysis revealed that, the PM2.5 source contribution from regional transmission (representing other land areas within the model domain) reached approximately 50%, whereas the local source contribution was only approximately 10% in Shenzhen.

IP Multimedia Subsystem (IMS) is widely considered as the main solution for the next generation multimedia rich communication. In order to provide multi-level security service in IMS to mobile users for multimedia applications, it is insufficient to take the security benefits into consideration, but adequately analyzing the impact of security policies in IMS on the performance cost quantitatively is also necessary and significant. In this paper, we first propose a novel study of IMS performance by a QPN model to much more precisely describe SIP signaling in IMS, and made performance evaluation. Then we defined totally seven levels of IMS security policies according to IMS specifications in 3GPP and proposed QoP partition model which quantitatively reflects strength of protection of SIP signaling and users' security needs. Further more, we did our original contributions to use the QPN model to evaluate the impacts of security mechanism on system performance cost quantitatively. With the multi-view security partition introduced, different security policies could be adjusted according to the application and users' security requirements, so that multi-level security service can be provided to diverse users and applications for a better tradeoff between security requirements and system performance in IMS.