Aerosol particle properties at a remote tropical rainforest in Borneo

Abstract

This paper aims to investigate aerosol particle properties and their seasonal variabilities at a remote tropical forest site. It also attempts to study the relationship between aerosol particles and dynamic atmospheric processes that modulate aerosol variability. Mass concentrations for particles smaller than 10 μm aerodynamic diameter (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. 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 strong intra-seasonal cycles (12–20 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 showed seasonal and annual variability bands, generally associated with the dry and wet seasons over the region.