Abstract: The pollution characteristics and sources of size-resolved particles were studied in a typical tropical coastal city, Haikou, China. PM_2.5 and PM₁₀ were collected at four air quality monitoring sites in spring and winter 2012. In order to estimate the source contributions, source samples were collected and chemical species were analyzed simultaneously. The chemical mass balance (CMB) receptor model was applied to apportion source contributions to ambient PM₁₀ and PM_2.5 using actual source profiles and ambient receptor measurements. The results showed that the seasonal variations of source contributions were distinctive, and spatial variations were perceptible. The major sources of PM₁₀ and PM_2.5 in winter were soil dust, vehicle exhaust, sulfates, and coal combustion, and the contribution ratios in PM₁₀ and PM_2.5 were 23.6%, 16.7%; 17.5%, 29.8%; 13.3%, 15.7%; and 13.0%, 15.3% respectively. While in spring, the dominant sources were vehicle exhaust, soil dust, cement dust, and sulfates, and the contribution ratios in PM₁₀ and PM_2.5 were 27.5%, 35.0%; 20.2%, 14.9%; 12.8%, 6.0%; and 9.5%, 10.5% respectively. In winter, most of the particulate matter was originated from the southern inland areas. The influence of regional transport for coal combustion and sulfates was more remarkable than for other source categories.