Ground-high altitude joint detection of ozone and nitrogen oxides in urban areas of Beijing

Based on observational data of ozone (O₃) and nitrogen oxide (NOx) mixing ratios on the ground and at high altitude in urban areas of Beijing during a period of six days in November 2011, the temporal and spatial characteristics of mixing ratios were analyzed. The major findings include: urban O₃ mixing ratios are low and NO_x mixing ratios are always high near the road in November. Vertical variations of the gases are significantly different in and above the planetary boundary layer. The mixing ratio of O₃ is negatively correlated with that of NO_x and they are positively correlated with air temperature, which is the main factor directly causing vertical variation of O₃ and NO_x mixing ratios at 600-2100 m altitude. The NO_x mixing ratios elevated during the heating period, while the O₃ mixing ratios decreased: these phenomena are more significant at high altitudes compared to lower altitudes. During November, air masses in the urban areas of Beijing are brought by northwesterly winds, which transport O₃ and NO_x at low mixing ratios. Due to Beijing's natural geographical location, northwest air currents are beneficial to the dilution and dispersion of pollutants, which can result in lower O₃ and NO_x background values in the Beijing urban area.