Assessment of gaseous criteria pollutants in the Bangkok Metropolitan Region, Thailand

Abstract

Abstract. The analysis of gaseous criteria pollutants in the Bangkok Metropolitan Region (BMR), Thailand, from 2010 to 2014 reveals that while the hourly concentrations of CO, SO2 and NO2 were mostly within the National Ambient Air Quality Standards (NAAQs) of Thailand, the hourly concentrations of O3 frequently exceeded the standard. The results reveal that the problem of high O3 concentration continuously persisted in this area. The O3 photolytic rate constant (j1) for BMR calculated based on assuming a photostationary state ranged from 0.008 to 0.013 s−1, which is similar to the calculated j1 using the NCAR TUV model (0.021±0.0024 s−1). Interconversion between O3, NO and NO2 indicates that crossover points between the species occur when the concentration of NOx (= NO + NO2) is ∼60 ppb. Under a low-NOx regime ([NOx] < 60 ppb), O3 is the dominant species, while, under a high-NOx regime ([NOx] > 60 ppb), NO dominates. Linear regression analysis between the concentrations of Ox (= O3 + NO2) and NOx provides the role of local and regional contributions to Ox. During O3 episodes ([O3]hourly > 100 ppb), the values of the local and regional contributions were nearly double of those during non-episodes. Ratio analysis suggests that the major contributors of primary pollutants over BMR are mobile sources. The air quality index (AQI) for BMR was predominantly good to moderate; however, unhealthy O3 categories were observed during episode conditions in the region.

Investigating the background and local contribution of the oxidants in London and Bangkok

“…Daily activity cycles, and speciation of NMVOC emissions (see Supplementary Information, Table S1), have been imposed (see details in Chen et al 43 and Lowe). 44 The 25 study are caused by the fact that the Bangkok data set is a much longer data set, and the initial years of the study (2005)(2006)(2007)(2008)(2009) resulted in much higher local pollution levels as emissions control technologies or vehicle fleet composition were not implemented during this time period. Fig.…”

“…This might be explained by the mobile sources (e.g. vehicles) in Bangkok Metropolitan Region, 25 which is highly dependent on traffic density and traffic flow. The NO x emissions from vehicles are dependent on fuel type and speed of the vehicles, 50 which can be responsible for the variation of the [OX] L for different roadside sites in Bangkok.…”

“…24 A recent study showed that NO x levels in Bangkok are mostly below the National Ambient Air Quality Standards (NAAQS), but, O 3 levels in Bangkok frequently exceed the NAAQS. 25 Uttamang et al 25 analysed the Bangkok Metropolitan Region pollutant data for 2010-2014 and found that both local and background OX contributions are responsible for increasing the concentration of O 3 . We update the work of Uttamang et al 25 using more calendar year-coverage data (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), highlighting roadside and kerbside locations in Bangkok and compare the results with those of the Marylebone Road site in London to investigate any systematic differences in the magnitudes and time dependences of the oxidant components for the two different scenarios (midaltitude vs tropics).…”

Investigation on the Impacts of COVID-19 Lockdown and Influence Factors on Air Quality in Greater Bangkok, Thailand

“…In additional, many studies report that O3 concentrations had increasing trends [28][29][30], while in this study we found decreasing O3 concentrations over Greater Bangkok. NO2 is an oxidation product from Nitrogen oxides (NOx) and O3, which is emitted from combustion sources such as vehicle exhausts, industries, power plants and residential heating [14]. Thus, this decrease in O3 could be due to greater increases in NO2 concentrations.…”

“…Recently, Bangkok has experienced winter pollution events with more frequency. Previous studies have mentioned that the common sources of PM2.5 emissions in Bangkok are from biomass burning, traffic and industrial activities with varying concentration caused by seasonal factors [12][13][14]. Moreover, Watcharavitoon, et al [15] presented spatial and temporal variation trends of gaseous air pollutant concentrations for O3, NOx, CO, and SO2 from 1996 to 2009 in Bangkok between residential and roadside areas.…”