Research on the temporal and spatial distribution of PM_2.5 at the township scales: a case study in Shijiazhuang City

The spatial and temporal distribution characteristics of PM_2.5 were analyzed at the township scales with the monitoring data from 261 automatic air quality monitoring stations of Shijiazhuang City in 2018, using the spatial analysis method of geographic information systems (GIS). The correlation characteristics between PM_2.5 and its precursors (SO₂, NO₂) were also discussed. The results showed that the annual concentration of PM_2.5 in 261 townships was 41-112 μg/m³ in 2018, which exceeded the secondary standard limit of Ambient Air Quality Standards (GB 3095-2012). The concentration of PM_2.5 was generally lower in the mountainous area with higher terrain in the northwest than that in the plain area in the southeast, and it was lower in the main urban area than that in the surrounding counties (cities and districts). In respect of seasonal variation, the average concentrations of PM_2.5 in Shijiazhuang City was the highest in winter and lowest in summer. Monthly average concentrations of PM_2.5 showed that it was from January to March and from November to December that the data of PM_2.5 were higher than those of the rest months of the year, August was the month that with the lowest monthly average concentration. The concentration of PM_2.5 was significantly positively correlated with the concentration of both SO₂ and NO₂ in the observation period. The degree of the correlation was the weakest in summer and the strongest in winter, and the more serious the pollution was, the more significant the degree of regional correlation was.