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 NOx 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 NOx and they are positively correlated with air temperature, which is the main factor directly causing vertical variation of O3 and NOx mixing ratios at 600–2100 m altitude. The NOx 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 NOx 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 NOx background values in the Beijing urban area.