Paper Title
Seasonal Pattern of Air Pollution in Metropolitan Area in The Central of Thailand, During 1995 to 2018

Abstract
The severe air pollution in the metropolitan area is an important issue; especially it has a negative effect on human health, the environment, and causes economic loss. This study aimed to investigate the seasonal pattern of weekly average air pollutions in metropolitan area in the central region of Thailand. The hourly air pollution data during 1995 to 2018 was obtained from the Pollution Control Department of the Ministry of Natural Resources and Environment, Thailand. The data consists of carbon monoxide (CO), Ozone (O3), Nitrogen dioxide (NO2), Sulfur dioxide (SO2), Nitrogen oxides (NOX) and Particulate matter (PM10 and PM2.5). The quantile-quantile (Q-Q) plot and boxplot were used to present the distribution of the data. Cubic spline functions were fitted to show seasonal patterns of weekly average air pollution. The results show that, the seasonal patterns of weekly average air pollutants concentrations were high at the begining of summer andslightly decrease at the end of the season. The decreasing pattern is stable in rainy season and increase again in winter. The highest overall seasonal pattern for each air pollutants were found in the stations such as PAO.27 (CO and SO2 ), Rehabilitation.08 (NO2,NOX,PM10 and PM2.5) and Mueang mai.19 (O3).The results of this study will provide usefull information for policy maker to reduce air pollution in the area. Keywords - Seasonal Pattern of Air pollution, Cubic Spline, Metropolitan Area in the Central of Thailand.