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

Nitrogen dioxide (NO 2 ) and sulfur dioxide (SO 2 ) are important air pollutants that affect air quality, human health, and climate. The concentrations of NO 2 and SO 2 were measured in Xi’an, China with passive samplers deployed at 70 sites in summer and winter. The average concentrations of NO 2 and SO 2 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 SO 2 were significant but those for NO 2 were not. The concentrations of NO 2 and SO 2 in the Beilin district were higher than other districts, while those in Baqiao were relatively low. The concentrations of NO 2 in commercial mixed areas were higher compared with other functional areas, and SO 2 in the residential/educational areas during winter was high. Spatial distributions of NO 2 and SO 2 were obtained by ordinary kriging interpolation, and the results showed high summertime NO 2 concentrations in the central urban and northwestern parts of the sampling grid and high wintertime NO 2 in the central part of the grid. Summer SO 2 concentrations were higher in the northern and lower in the southern parts of the grid, while SO 2 was in winter high in the mid-west and low in the east.