The study of aerosal variations over danum valley in Borneo tropical rainforest

Abstract

Aerosols plays an important role in earth’s solar radiation budget and water cycle balance, in human health, and in climate change dynamics. The Danum Valley rainforest, located at the centre of the tropical maritime continent in Southeast Asia is a unique site for investigating the effects of anthropogenic sources over a naturally clean environment. The aims of this study were to investigate the aerosol properties and seasonal variabilities at a remote tropical forest site. It also attempts to study the relationship between aerosols and dynamic atmospheric processes that modulate aerosol variations. Mass concentrations for particles smaller than 10 μm aerodynamic diametre (PM10) and optical aerosol particle properties were measured at Danum Valley tropical rainforest in Borneo Island. The particle mass concentrations were measured using a Tapered Element Oscillating Microbalance (TEOM). Measurements of aerosol particle optical properties, i.e., the particle light absorption and scattering coefficients, were conducted using a Multi-Angle Absorption Photometer (MAAP) and nephelometer, respectively. The single scattering albedo (SSA) and scattering Angstrom exponent (SAE) were calculated from the aerosol scattering and absorption coefficients. The results showed that the daily average of PM10 mass concentrations was 12.3 μgm-3, while the particle light absorption coefficients at wavelength 637 nm and scattering coefficients at wavelength 525 nm were reported as 2.7 Mm-1 and 21.7 Mm-1, respectively. There was variation in the diurnal cycle, and the monsoonal seasons were also shown to influence the variations of aerosol properties. Higher concentrations and coefficients were observed during the southwest and transition between monsoons due to the aerosol sources and synoptic factors. The daily average SSA and SAE recorded were 0.89 and 1.44, respectively. The SSA showed no seasonal variations while higher SAE was observed during the dry season due to the influence of biomass burning originating from the southern region of Borneo. The wavelet analysis showed periodicity characteristics in the aerosol data at this remote site. There were strong intra-seasonal cycles (12-20 days and 32-64 days) which suggest the influence of Quasi-BiWeekly (QBW) oscillation and Madden-Julian Oscillation (MJO) on the aerosol variability over the tropics. The analysis also revealed clear seasonal and annual characteristics bands, generally associated with the dry and wet seasons and the annual cycle over the region. This study has provided a new understanding on the level and aerosol variation properties in tropical rainforest over the Maritime Continent which is an important reference for other studies on the background conditions of a clean natural environment.