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Abstract. This paper aims to explore the impact of meteorological factors on PM2.5 concentrations in Hong Kong. The PM2.5 and meteorology data including temperature, pressure, rainfall, relative humidity (RH), wind speed and wind direction from January to December of 2013 were collected. The correlation analysis between PM2.5 and meteorological factors were conducted for each month and season. The meteorology data were classified into several intervals and the mean PM2.5 concentrations for each interval were calculated to see the tendency. According to the correlation analysis results, the PM2.5 concentrations have a positive relationship with pressure with correlation coefficients 0.507 while have negative relationships with temperature, RH, rainfall, wind speed with correlation coefficients -0.512, -0.237, -0.524, -0.284, respectively. In addition, the wind direction influence PM2.5 concentrations through affecting the spreading direction of PM2.5. The north wind in winter increased the PM2.5 in Hong Kong while the south wind in summer decrease the PM2.5. Therefore, the meteorological factors affect the aggregation, diffusion, spread of PM2.5. They have a leading impact on PM2.5 concentrations when the domestic emission stays stable. IntroductionThe rapid development of urban construction and accelerated urbanization have caused serious pressure on atmosphere environment. As one result of the process, air pollution has increased concerns about people's health, especially for the fine particular matter (PM2.5). PM2.5 is the particular matter with an aerodynamic diameter less than 2.5 μm, which not only attenuates atmospheric visibility, but also has an adverse impact on human health [1]. Some epidemiology studies reveal that a certain relationship exists between particular matter of pollution and the mortality rate, cardiovascular and respiratory diseases [2], [3]. The PM2.5 concentrations were mainly influenced by local pollution emission, external pollution propagation and meteorological conditions including pressure, temperature, humidity, cloud coverage, precipitation and wind, etc. The meteorological factors cause spatio-temporal variation of particulate matter concentrations through influencing the conglomeration and diffusion of pollutants. Tai [4] indicate that the daily variation of meteorological parameters can cause up to 50% of the change of PM2.5 concentrations. Wang and Ogawa [5] investigated the correlation between PM2.5 and meteorological conditions in Nagasaki, Japan. The results shown that temperature had a negative, and precipitation had a positive, correlation with PM2.5. Elminir [6] found that temperature, humidity, wind speed and wind direction contribute to the air pollutants concentration. Wind direction was found to have influence on both pollutant concentrations and the correlation between pollutants. Hong Kong is located in southern China with sea on three sides and is one of the most densely populated areas. In the last decades, the economic cooperation between Hong Kong and Pearl R...

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Land subsidence, as one of the engineering geological problems in the world, is generally caused by compression of unconsolidated strata due to natural or anthropogenic activities. We employed interferometric point target analysis (IPTA) as a multi-temporal interferometric synthetic aperture radar (MT-InSAR) technique on ascending and descending Sentinel-1A the terrain observation with progressive scans SAR (TOPSAR) images acquired between January 2015 and December 2018 to analyze the spatio-temporal distribution and cause of subsidence in Abbottabad City of Pakistan. The line of sight (LOS) average deformation velocities along ascending and descending orbits were decomposed into vertical velocity fields and compared with geological data, ground water pumping schemes, and precipitation data. The decomposed and averaged vertical velocity results showed significant subsidence in most of the urban areas in the city. The most severe subsidence was observed close to old Karakorum highway, where the subsidence rate varied up to −6.5 cm/year. The subsidence bowl profiles along W–E and S–N transects showed a relationship with the locations of some water pumping stations. The monitored LOS time series histories along an ascending orbit showed a close correlation with the rainfall during the investigation period. Comparative analysis of this uneven prominent subsidence with geological and precipitation data reflected that the subsidence in the Abbottabad city was mainly related to anthropogenic activities, overexploitation of water, and consolidation of soil layer. The study represents the first ever evidence of land subsidence and its causes in the region that will support the local government as well as decision and policy makers for better planning to overcome problems of overflowing drains, sewage system, littered roads/streets, and sinking land in the city.

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