Air pollution is one of the serious problems facing urban environments worldwide, and pollution prevention and control under the background of site scale is facing tremendous pressure. Some studies believe that urban green space is essential in improving air quality. However, some studies have questioned that, and they think green space vegetation exacerbates air pollution because of the inconsistency of the conclusions. An urban green space with closed and semi-open structures and the adjacent urban square in Xi’an, China, was selected as the research sample plots. With high temporal resolution, the particle matter concentrations and meteorological factors at different horizontal distances from the road between the spaces were continuously monitored for one week. When relative humidity and the wind speed increased above certain thresholds, the particle concentration began to decrease gradually, except in the urban square where PM10 concentration increased when wind speed exceeded its threshold. The diurnal variation in particulate matter concentration was double peaks and double valleys. From 6:00 to 8:00 and 19:00 to 24:00, the concentration of particulate matter was highest, the concentration of particulate matter increased with increasing distance from the road, the concentration of particulate matter in the green space was lower than that in the square, while the concentration of particulate matter was lower from 10:00 to 18:00, the concentration of particulate matter decreased with increasing distance, the concentration of particulate matter in the green space was higher than in the square. Compared with closed green space, semi-open green space, and square, green space can effectively weaken the peak concentration of particulate matter and PM10 concentration. The results show that green space can effectively block and remove particles, especially coarse particles, by regulating the diffusion and settlement of particles mainly by affecting meteorological factors such as wind speed and humidity. This information could be used for better air pollution mitigation strategies, especially when incorporating green spaces in future urban design.