Atmos. Chem. Phys. Discuss., 10, 1719-1754, 2010
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Ozone reservoir layers in a coastal environment – a case study in Southern Taiwan
C.-H. Lin1, Y.-L. Wu2, and C.-H. Lai1
1Department of Environmental Engineering and Science, Fooyin University, Kaohsiung, Taiwan
2Department of Environmental Engineering, National Cheng-Kung University, Tainan, Taiwan

Abstract. The air layer between the nocturnal boundary layer and the top of the daily mixing layer in an ozone-polluted area is known to serve as an ozone reservoir since the ozone that is produced in the previous daytime mixing layer can be well preserved throughout the night in the air layer. Ozone reservoir layers are capable of enhancing surface ozone accumulation on the following day. However, our knowledge of the characteristics of ozone reservoir layers and their effects on the daily ozone accumulations is limited. In this work, ozone reservoir layers were experimentally investigated at a coastal, near-mountain site in Southern Taiwan, 30 km away from the coastlines. Tethered ozone soundings were performed to obtain vertical profiles of ozone and meteorological variables during a four-day ozone episode in November 2006. Observation-based methods are adopted to evaluate the influences of the ozone reservoir layers on the surface ozone accumulation during the four-day ozone episode. Ozone reservoir layers were found to develop every evening with a depth of 1200–1400 m. Ozone concentrations within the reservoir layers reached over 140 parts per billion (ppb). From each evening to midnight, the size of the ozone reservoir layer and the ozone concentration inside dramatically changed. As a result, a concentrated, elevated ozone reservoir layer formed with a depth of 400 m at 800–1200 m every midnight. For the rest of each night, the elevated ozone reservoir layer gradually descended until it reached 500–900 m in the next morning. Local circulations and nocturnal subsidence are responsible for the observed evolution. The ozone concentration at the study site was maximal at 15:00–17:00 LT daily because of the addition of the daily produced ozone on the preceding day. Hourly downward mixing ozone concentrations due to the ozone reservoir layers can be as high as 35–45 ppb/h in the late morning. The contribution of the ozone carried over from the preceding day can be 75–85 ppb, which contributes over 50% to the daily ozone pollution as compared with ozone produced on the study day.

Citation: Lin, C.-H., Wu, Y.-L., and Lai, C.-H.: Ozone reservoir layers in a coastal environment – a case study in Southern Taiwan, Atmos. Chem. Phys. Discuss., 10, 1719-1754, doi:10.5194/acpd-10-1719-2010, 2010.
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