Homogeneous Mixing of Sea Spray and Biomass Burning Tracer Elements Within Single Particles Observed Over Southeast Asia

Abstract

Aerosols from sea spray and biomass burning play an important role in climate due to their considerable abundance in the atmosphere. The magnitude of their atmospheric impact depends on the chemical and physical properties of individual particles. The elemental composition of aerosol particles from Thailand, Southeast Asia, was analyzed using transmission electron microscopy (TEM) equipped with an energy dispersive X-ray spectrometer, with a special focus on sodium (Na) and potassium (K) as tracer elements for sea spray and biomass burning, respectively. Our analysis revealed that nearly all particles with aerodynamic diameters between 300 and 700 nm contained either Na or K, with approximately 74% of the particles containing both elements, that is, homogeneously mixed in the form of sulfate. While both Na and K were present in the same particles and K-rich particles were generally more abundant than Na-rich particles in all samples, higher Na fractions were observed when the particles were mainly transported from the ocean. The Na and K containing aerosol particles were often mixed with soot and organic particles. These results demonstrate the significant mixing of sea spray and biomass burning aerosols during their atmospheric transport. Such mixing can affect the hygroscopicity, viscosity, and optical properties of aerosols. This study highlights the significant mixing of natural aerosols from different sources at the individual particle level and suggests the need for accurate representation of aerosol properties in climate models.