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Stratospheric influence on the concentration and seasonal cycle of lower tropospheric ozone: Observation at Mount Hehuan, Taiwan
Author(s) -
Lin YuChi,
Huh ChihAn,
Hsu ShihChieh,
Lin ChuanYao,
Liang MaoChang,
Lin PoHsiung
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2013jd020736
Subject(s) - troposphere , environmental science , atmospheric sciences , mount , tropospheric ozone , ozone , climatology , ozone depletion , ozone layer , stratosphere , meteorology , geography , geology , computer science , operating system
Continuous measurements of ozone (O 3 ), carbon monoxide (CO), beryllium‐7 ( 7 Be), and lead‐210 ( 210 Pb) in aerosols along with relative humidity (RH) were carried out at the Mount Hehuan site (24.05°N, 121.10°E, 3380 m above sea level (asl)) from September 2011 to September 2012 in order to investigate the seasonality of stratospheric influence (SI) and its effect on surface ozone concentration in the subtropical free troposphere over central Taiwan. During the 13 month period, the measured O 3 concentration fluctuated around a mean of 41 ppb and showed a broad springtime maximum and summertime minimum that can be attributed to regional circulation over subtropical Asia. Beryllium‐7, CO, RH, and the normalized fraction of 7 Be, f( 7 Be, 210 Pb) were used to identify SI days based on several criteria. Of the total analyzed days, 14 SI days (approximately 4.6%) were found, indicating that SI phenomenon in the subtropical region is much less frequent than at northern midlatitudes. About two thirds of the SI days occurred in the winter, whereas none were found in the summer. The seasonality of SI occurrence could be related to the position of the subtropical jet stream. The proportion of surface O 3 derived from the stratosphere was estimated to be only 1.3% on a yearly basis, increasing to ~3.2% in the winter and 27% during the SI days, demonstrating the importance of downward transport of stratospheric air in affecting the level of surface ozone.