Measurements of vertical and horizontal distributions of ozone over Beijing from 2007 to 2010

• The vertical and horizontal distributions of O3 over Beijing region was analyzed.
• A peak O3 concentration occurring at ∼1 km over Beijing is observed.
• O3 concentration in the downwind of the city plumes was enhanced.
• A transition of O3 formation from VOC-limited to NOx-limited at ∼1 km is found.

The vertical distributions of ozone (O3) over a mega city (Beijing, China), and the horizontal O3 distributions in the lower troposphere (2–3.6 km) over Beijing and its surrounding areas located in the North China Plain (NCP), were analyzed based on the aircraft measurements from 159 flights during 2007–2010. The results are highlighted as follows: (1) There was a peak of O3 concentration occurring at ∼1 km over Beijing, and the peak values ranged between 60 and 120 ppbv. (2) There was an O3 minimum at the surface. The minimum was largely caused by the chemical reaction of NO + O3. This process produced about 30 ppbv of the O3 reduction below 0.5 km in the morning (9:00–10:00). (3) There was a transition altitude (∼1 km), below which the ozone formation was in a VOC-limited condition, and above which the ozone formation was in a NOx-limited condition. (4) The analysis of the horizontal distribution shows that O3 concentrations were enhanced in the downwind of the city plumes. This result suggests that there was an important regional O3 chemical production in the NCP region.