Observations of annual cycles of meteorological phenomena and atmospheric aerosols at Maldives

Climate change impacts, such as floods and droughts, are a great threat to people living in South-Asia. Rainfall related to monsoon circulation is essential for people in this region, because it is the main source of fresh water. One of the major questions is how the monsoon circulation would be impacted by climate change. The interaction between atmospheric aerosols and the monsoon circulation has been studied with models, but the connections between aerosol properties and meteorological parameters in the tropics haven't been widely studied with in-situ measurements. In this study the aim is to use in-situ measurements to analyse the correlations between the properties of aerosols and meteorological parameters in Maldives. The measurements of this study were done at the Maldives Climate Observatory of Hanimaadhoo. The island is located near the west side of the southern tip of India. The location is unique and representative for as a backround site for measuring the pollution coming from the Indian subcontinent. The instruments used for the aerosol measurements were Aerodynamic Particle Sizer (APS), Differential Mobility Particle Sizer (DMPS), Scanning Mobility Particle Sizer (SMPS) and Sun photometer. The monsoon and Madden-Julian oscillation indices were used to analyse the aerosol properties during these phenomena. Both the wind direction and precipitation amount change between seasons. From the size distributions of aerosols could be identified that during the dry season anthropogenic fine particles were transported from over the Indian subcontinent to Maldives. During the monsoon season there could be seen the Hoppel minimum in the size distribution which indicates that marine air, consisting of natural aerosols, was passing over the Maldives. There was a small negative correlation between the number concentration of fine particles and wind speed, but not so clear correlation between the mass concentration of large particles or AOD. The effects of monsoon and Madden-Julian oscillation on aerosols and meteorological parameters were also studied. It could be observed that when both phenomena were ongoing, there were less aerosol particles in the atmosphere, but the size of aerosol particles was much larger.