Characterizing Spatial Patterns of NO2 and SO2 in Xi’an by Passive Sampling

Abstract

Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are important air pollutants that affect air quality, human health, and climate. The concentrations of NO2 and SO2 were measured in Xi’an, China with passive samplers deployed at 70 sites in summer and winter. The average concentrations of NO2 and SO2 were 19.82 μg m−3 and 2.24 μg m−3, respectively, in summer and 21.09 μg m−3 and 7.99 μg m−3 in winter. Statistical analyses showed that the seasonal differences in SO2 were significant but those for NO2 were not. The concentrations of NO2 and SO2 in the Beilin district were higher than other districts, while those in Baqiao were relatively low. The concentrations of NO2 in commercial mixed areas were higher compared with other functional areas, and SO2 in the residential/educational areas during winter was high. Spatial distributions of NO2 and SO2 were obtained by ordinary kriging interpolation, and the results showed high summertime NO2 concentrations in the central urban and northwestern parts of the sampling grid and high wintertime NO2 in the central part of the grid. Summer SO2 concentrations were higher in the northern and lower in the southern parts of the grid, while SO2 was in winter high in the mid-west and low in the east.