Analysis of observed surface ozone in the dry season over Eastern Thailand during 1997-2012

This study analyzed observed surface ozone (O-3) in the dry season over a long-term period of 1997-2012 for the eastern region of Thailand and incorporated several technical tools or methods in investigating different aspects of O-3. The focus was the urbanized and industrialized coastal areas recently recognized as most O-3-polluted areas. It was found that O-3 is intensified most in the dry-season months when meteorological conditions are favorable to O-3 development. The diurnal variations of O-3 and its precursors show the general patterns of urban background. From observational O-3 isopleth diagrams and morning ratios of non-methane volatile organic compounds (NMVOC) and nitrogen oxides (NOx), the chemical regime of O-3 formation was identified as VOC-sensitive, and the degree of VOC sensitivity tends to increase over the years, suggesting emission control on VOC to be suitable for O-3 management. Both total oxidant analysis and back-trajectory modeling (together with K-means clustering) indicate the potential role of regional transport or influence in enhancing surface 03 level over the study areas. A meteorological adjustment with generalized linear modeling was performed to statistically exclude meteorological effects on the variability of O-3. Local air-mass recirculation factor was included in the modeling to support the coastal application. The derived trends in O-3 based on the meteorological adjustment were found to be significantly positive using a Mann-Kendall test with block bootstrapping. (C) 2016 Elsevier B.V. All rights reserved.