Spatial and temporal variation of fine particulate pollution in a complex small coastal city, Macau, was investigated by using a mobile air quality monitoring platform. Real-time street level measurements of aerosol size distribution were carried out three times per day by using an on-board wide-range particle spectrometer along a designed route covering the main area of the city for one week. The measured distributions were then transformed into PM mass concentrations for assessment based on an empirical relation estimated from a clocated measurement calibration process. Within this week, the averaged PM mass concentrations of the morning, afternoon, and evening sessions are 51.76 μg m-, 28.87 μg m- and 30.77 μg m-, respectively. By comparing the spatial statistics of the estimated PM concentrations with the US 24-hour primary NAAQS as a reference, a significant probability of exceedance (> 86%) was observed in 1/3 of the monitoring sessions, particularly in the morning of high traffic volume. Meanwhile, majority of the hotspots were found in the districts of the Macau peninsula. In addition, by performing analysis of the backward trajectories, daily MODIS images, and comparison of the PM patterns of the entire route of three selected measuring sessions during weekdays and weekend, it was observed that long range transport of fine particulates may affect Macau in a larger scale. Therefore, regional land source influence could shadow the local one when the ambient conditions are met.