In the present study, the spatial and temporal variation of fine particulate pollution in a small but complex coastal city, Macau, was investigated by using the Mobile Air Quality Monitoring Platform (MAP). Real-time street level measurements of aerosol size distribution were carried out three times per day by using the on-board Wide-range Particle Spectrometer (WPS) along the main route of Macau from Feb. 18 to 24, 2009. The measured aerosol size distributions were further transformed into PM2.5 mass concentrations for assessment based on the empirical relationship estimated from the co-located measurements between the WPS and the Tapered Element Oscillating Microbalance (TEOM). This study is the first of its kind that could assess PM2.5 mass concentrations of the entire city within a short period of time (~1 to 2 hours) for systematic comparison. By comparing the spatial statistics of the estimated PM2.5 concentrations within these seven consecutive days with the target value adopted from the 24-hour primary National Ambient Air Quality Standards (NAAQS) of the United States, a significant probability of exceedance (~1/3) was observed; hence concluding the severity of fine particulate pollution in Macau. Within the monitoring sessions showing exceedance, 66.7% occurred in the morning. It is suspected that this might be caused by the morning traffic during the rush hour (08:00AM-09:30AM). In addition, obvious spatial variation of the estimated PM2.5 mass concentrations was observed among different districts and the majority of the hotspots (~85.7% of all monitoring sessions) were belonged to the districts of the Macau peninsula, which has significantly higher traffic volume, and less favourable dispersion conditions. Therefore, it is clear that local traffic pattern plays an important role on the PM2.5 spatial distribution in Macau. In addition to the local contribution, regional transport of fine particulates from the northern part of the Pearl River Delta region could influence the distribution of PM2.5 in Macau in a larger scale. This was observed based on the whole area assessment of the instantaneous PM2.5 mass concentrations of the main route on Feb. 19 and 20, which had distinct wind conditions. It was found that the passage of the cold front on Feb. 20 could lead to the rapid rise in the background concentrations over the entire area due to the accumulation of the particle enriched air masses transported from the northern part of the Pearl River Delta region and this signified the the regional land source influence that could shadow the local one.