Assessment of Air Pollution in Bangkok Metropolitan Region, Thailand

Abstract. Analysis of gaseous criteria pollutants in Bangkok Metropolitan Region (BMR), Thailand, during 2010–2014 reveals that the hourly concentrations of CO, SO 2 and NO 2 were mostly below the National Ambient Air Quality Standards (NAAQs) of Thailand. However, the hourly concentrations of O 3 exceeded the Thailand NAAQs. The maximum concentrations of O 3 ranged from 120–190 ppb. On average, the number of hourly O 3 exceedances ranged from 1–60 hours a year depending on monitoring station locations. The exceedances occurred during the summer and winter, dry seasons. Interconversion between O 3 , NO and NO 2 indicates crossover points between species occur when the concentration of NO x ([NO x ] = [NO]+[NO 2 ]) is ~ 60 ppb. However, when [NO x ] 60 ppb, O 3 is the dominant species; conversely, NO dominates when [NO x ] > 60 ppb. The calculated photochemical reaction rate (the reaction between NO 2 with sunlight), during photostationary state ranges from 0.12 to 1.22 min −1 . Linear regression analysis between the concentrations of O x ([O x ] = [O 3 ]+[NO 2 ]) and NO x provides the role of local and regional contributions to O x . Both the local and regional O x contributions enhance the concentration of O x . Values of the local and regional O x contributions during non-episode were ~ 44–54 ppb and ~ 0.13[NO x ] to 0.33[NO x ], respectively. Those values were about double during O 3 episodes ([O 3 ] > 100 ppb). Ratio analysis suggests that the major contributors of primary pollutants over BMR are mobile sources (CO/NO x = 19.8). The Air Quality Index (AQI) for BMR was predominantly between good to moderate. Unhealthy O 3 categories were observed during episode conditions in the region.