Assessment of 24-h moving average PM(2.5) concentrations in Bangkok, Thailand against WHO guidelines

Particulate matter less than 2.5 μm in diameter (PM(2.5)) pollution has gained more concern, as can be seen from the World Health Organization (WHO) revised air quality guideline (AQG) value. To compare with the 24-h AQG value, the 24-h mean (daily average) of hourly monitoring data has been widely used, but the nature of data in hourly variation has been lost. The 24-h moving average can be an alternative approach to preserving hourly data behavior, while various positions of the hour (leftmost, center, or rightmost hour) can be used to store the moving average. In this study, similarity testing by cross-correlation and Euclidean distance was performed to present a suitable 24-h moving average time series for hourly data, and then presented proportions of PM(2.5) concentrations within each interim target and AQG ranges. The PM(2.5) time series of the leftmost and rightmost 24-h moving average revealed lags of − 13 to − 10 h and 10 to 13 h for the observed hourly data, respectively. The lags of the center 24-h moving average time series were of − 2 to 1 h, which showed more similar events to the hourly PM(2.5) fluctuation than the leftmost and rightmost time series. The center 24-h moving average concentrations measured in Bangkok were categorized into interim target and AQG ranges. The results revealed that the proportion of concentrations lower than AQG during nighttime and daytime was approximately 40 and 28%, respectively. However, the results given from the leftmost and rightmost time series showed time shifts and differences in diurnal variation caused by the position used to store the average value. To keep hourly PM(2.5) variation that can be compared with the 24-h WHO guidelines, this should be performed with careful and precautionary consideration of misinterpretation over a time scale, especially for implementing countermeasures and policies. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s42834-023-00165-y.