Stratospheric influence on the concentration and seasonal cycle of lower tropospheric ozone: Observation at Mount Hehuan, Taiwan
Journal
Journal of Geophysical Research Atmospheres
Journal Volume
119
Journal Issue
6
Pages
3527-3536
Date Issued
2014
Author(s)
Abstract
Continuous measurements of ozone (O3), carbon monoxide (CO), beryllium-7 (7Be), and lead-210 (210Pb) 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 O3 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 7Be, f(7Be, 210Pb) 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 O3 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.
SDGs
Type
journal article