Influence of circulation types on temporal and spatial variations of ozone in Beijing

This study analyzes the impact of circulation types (CTs) on ozone (O₃) pollution in Beijing. The easterly high-pressure (SWW) circulation occurred most frequently (30%; 276 day), followed by northwesterly high-pressure (AN) circulation (24.3%; 224 day). The SWW type had the highest O₃ anomaly of +17.28 µg/m³, which was caused by excellent photochemical reactions, poor diffusion ability and regional transport. Due to the higher humidity and precipitation in the low-pressure type (C), the O₃ increase (+8.02 µg/m³) was less than that in the SWW type. Good diffusion/wet deposition and weak formation ability contributed to O₃ decrease in AN (-12.54 µg/m³) and northerly high-pressure (ESN) CTs (-12.26 µg/m³). The intra-area transport of O₃ was significant in polluted circulations (SWW- and C-CTs). In addition, higher temperature, radiation and less rainfall also contributed to higher O₃ in northern Beijing under the SWW type. For the clean CTs (AN and ESN CTs), precursor amount and intra-area transport played a dominant role in O₃ distribution. Under the northeasterly low-pressure CT, better formation conditions and higher precursor amount combined with the intra-area southerly transport to cause higher O₃ values in the south than in the north. The higher O₃ in the northwestern area under the northeasterly high-pressure type was influenced by weaker titration loss and high O₃ concentration in previous day. Annual variation in the CTs contributed up to 86.1% of the annual variation in O₃. About 78%-83% of the diurnal variation in O₃ resulted from local meteorological factors.