Over the last three decades, Thailand's rapid industrialization and urbanization have led to an impact on urban air quality. A majority of the country's
development has occurred within and around Bangkok (BKK), the capital city of Thailand, and the Bangkok Metropolitan Region (BMR). Since 1995, the BMR
has experienced air quality degradation, in particular, enhanced ozone (O-3) due to a combination of the local increase in emissions from accelerated
growth in automotive and industrial activities, local meteorology including strong solar radiation, high temperature and high humidity, and potential longrange
effects of regional transport from China. To investigate the O-3 formation in the BMR due to the effects of long-range transport and local meteorology
feedbacks, we perform a multi-scale simulation with the Weather Research and Forecasting model with Chemistry (WRF-Chem) during the O-3 season
(January to March), 2010; since O-3 mixing ratio exceedances in the BMR occur primarily during this period The results in this study indicate the significance
of China's emission reductions on the regional-scale and the local-scale pollution, as far as the BMR region and southern Thailand. Applying China's oxide of
nitrogen (NOx)-only emission controls, generally, enhance the domain-wide monthly-average peroxyacetyl nitrate (PAN) and O-3 in the regional scale, in the
order of similar to 1-7% and similar to 1-5%, respectively, while those in the local scale are similar to 0.2-6% and similar to 0.1-5% compared with the
baseline simulation. However, the increases in PAN and O-3 are mitigated by 40% China's Volatile Organic Compound (VOC) reduction along with 40% NO R
reduction. The results, supported by an indicator analysis, suggest that northern and eastern China, northern and central Thailand and the BMR, are likely
VOC-limited during the O-3 season. Since the BMR is VOC-limited regime, controlling anthropogenic VOC emissions will show more benefit to control O-3
than controlling NO R -only emissions. Other factors that influence on O-3 levels in the BMR are biogenic VOC emissions from the Tenasserim range and
land- and sea-breeze circulations that recirculate and disperse pollutants along the coastal areas