Hygroscopic Growth Factors of Sub-micrometer Atmospheric Aerosols at Four Selected Sites in Thailand

Hygroscopic growth factor (Gf) of aerosols is related to water loading on particles in sub-saturated conditions. It is an essential parameter for assessing the role of atmospheric particles in the radiative transfer and cloud formation process. Therefore, the temporal variation in Gf of size-selected atmospheric particles from the Aitken mode (Dp <= 100 nm) and accumulation mode (Dp > 100 nm) was measured using a humidified tandem differential mobility analyser (H-TDMA) and the relationship between particle size and Gf for various locations and meteorological conditions was determined. The origin of ambient particles primarily defines their properties and governs their participation in atmospheric processes. Thus, the measurements were performed in locations with different land-use types: urban, rural, coastal-industrial, and landlocked industrial areas. The data showed site-dependent patterns of temporal and spatial changes in Gf. The results indicated that the number-weighted Gf averaged over the investigated particle size range (30-250 nm) was highest in rural areas (Gf = 1.27), followed by coastal-industrial (Gf = 1.19), urban (Gf = 1.11), and landlocked industrial areas (Gf = 1.06). Particles in the urban and landlocked industrial areas had relatively low Gf values, suggesting that they originated mainly from fossil fuel combustion, in contrast to particles at other sites which can be attributed to coastal proximity.