Rainfall pattern and its chemical characteristics in Singapore

• Main Author: Tan, Li Jun.
• Other Authors: Chang Wei-Chung
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Civil engineering::Water resources
• Online Access: http://hdl.handle.net/10356/15885
• Institution: Nanyang Technological University

The World Wildlife Fund (WWF) estimates that if the current consumption patterns continue, at least 3.5 billion people – nearly half the world’s projected population – will live in water water-stressed basins by 2025 [1]. As such, the need to improve on the quality of potable water is a pressing issue. There are two parts to this project, namely the practical and the theoretical aspects of the effects of wet and dry deposition. For the practical aspect of this project, I will monitor the amount of particulate matter (PM) and nutrients washed down from the sky as a result of a rain event. The nutrients to be monitored are: nitrogen, phosphorus, sulphur among many others. I would also keep tab on the amount of particulate matter (to be determined by a particulate matter counter) present in the air before, during and after a rain event. The theoretical aspect would be carried out by data mining the 2007/2008 data obtained from National Environment Agency (NEA) as well as Public Utilities Board (PUB). The data are those collected from the Bishan air monitoring station. These data would allow me to plot the rainfall intensity graphs as well as graphs of the various types of nutrients measured in the air during a rain event. The rainfall intensity graphs show that Singapore’s rain follows a general pattern: heavy initially and tapering off at the end. There might be peaks in between but the heaviest intensity is normally seen at the beginning. This is supported by the rain sample collected on 4th February 2009. From NEA’s data, we can observe that PM10 behaves differently from other elements such as PM2.5 and SO4 2-. This might be due to the fact that the amount of PM10 in the air is determined by the number of vehicles on the street and the time of measurement (and these are extremely significant factors because the Bishan air monitoring station is situated near the road). PM2.5 and SO4 2- behave almost identically during the course of the rain event – both increases when the rainfall intensity decreases and vice versa. However, it has been noted that PM2.5 decrease and not increase at the start of the rain event. This might be due to the size of PM2.5. Its small size makes it very susceptible to changes in the wind speed and direction. Dry deposition is also determined using data from NEA. Similar to results obtained during a rain event, PM10 shows a different behaviour from both PM2.5 and SO4 2-. It fluctuates more frequently than the other two elements. Such phenomenon may once again be linked to the number of vehicles present and the time of measurement. SO4 2-, on the other hand, is relatively constant during periods where there is no rain. This might be due to the fact that SO4 2- is usually removed from the air by wet rather than dry deposition. The experimental data showed a general decrease for most elements such as SO4 2-, NO3 - etc. However, Cl-, Na+ etc. showed slightly different behaviours. These might be explained by solubility of the element, changes in wind direction as well as sources of production (for instance is determined by the frequency and availability of sea spray). However, despite the individual characteristic of each element, we can see that wet and dry deposition do take place. Thus, there is a need for us to reduce emissions of elements into the air s as to prevent euthrophication from occurring.