Characterization of ambient ozone and its precursors around a coking plant.

The local-scale relationship between ambient ozone (O3) and its precursors was examined around a coking plant in northern China. The upwind, plant boundary, and downwind locations were selected for investigation during the summer and autumn seasons in 2012. It was found that propene, toluene, and benzene were the top three non-methane hydrocarbon (NMHC) species for O3 formation at plant boundary, while propene, toluene, and m/p-xylene were the top three NMHC species at downwind location. Isoprene was the dominant species for O3 formation at upwind location. It was also found that an O3 depressing process occurred at plant boundary as a result of high NO emissions. Both local photochemistry and transport led to O3 accumulation at the downwind locations. The variation of NMHC concentration during O3 polluted and non-polluted episodes was investigated, and it indicated that NMHC concentration was higher during non-polluted episodes than polluted episodes. The impacts of precursors on O3 formation under different meteorological conditions were also examined.