Vertical and horizontal profiles of airborne particulate matter near major roads in Macao, China

Vertical profiles, horizontal profiles and size distribution of airborne particulate matter were measured near major roads in Macao using DustTrak and TEOM monitors. A significant decrease in the concentrations of PM10, PM2.5 and PM1, as the height above the ground increases from 2 to 79 m, was found. At the height of 79 m, the concentrations of PM10, PM2.5 and PM1, decrease to about 60%, 62% and 80% of the maximum occurring at 2 m above the ground, respectively. However, the horizontal profiles near another major road revealed there was no significant trend of decrease in concentrations of particulate matter as the distance from the road increases. Over the total measured distance (0–228 m), the maximum decreases of PM10, PM2.5 and PM1 are only 7%, 9% and 10%, of the maximum occurring at 2 m from the road, respectively. The daytime averaged PM2.5 and PM1 contribute 66–67% and 51–60%, respectively, of the total PM10 mass after the particle readings by DustTrak were recalibrated by TEOM. It showed that fine particles and submicrometer particles contributed a major part of PM10 at the roadside in Macao, which is most likely attributed to the combinations of local sources including exhausted particulate matter from vehicles and resuspended fine dust, and secondary particles (sulfate, nitrate and ammonium) of regional scales.