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

This study analyzes the impact of circulation types (CTs) on ozone (O) 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 O anomaly of +17.28 µg/m, 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 O increase (+8.02 µg/m) was less than that in the SWW type. Good diffusion/wet deposition and weak formation ability contributed to O decrease in AN (-12.54 µg/m) and northerly high-pressure (ESN) CTs (-12.26 µg/m). The intra-area transport of O was significant in polluted circulations (SWW- and C-CTs). In addition, higher temperature, radiation and less rainfall also contributed to higher O 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 O distribution. Under the northeasterly low-pressure CT, better formation conditions and higher precursor amount combined with the intra-area southerly transport to cause higher O values in the south than in the north. The higher O in the northwestern area under the northeasterly high-pressure type was influenced by weaker titration loss and high O concentration in previous day. Annual variation in the CTs contributed up to 86.1% of the annual variation in O. About 78%-83% of the diurnal variation in O resulted from local meteorological factors.