Temporal dynamics between COVID-19 cases and particulate matter in Bangkok: Impact of lockdown policies on air quality and disease transmission

This study investigates the relationship between COVID-19 transmission and ambient air pollution in Bangkok, Thailand, during multiple pandemic waves from January 2020 to January 2022. The objectives were to quantify correlations between COVID-19 cases and criteria air pollutants (PM2.5, PM10, CO, NO2, O3) across pandemic phases, analyze relationship variations during different waves and control periods, delineate temporal and seasonal trends, and evaluate lockdown effects on disease transmission and air quality. We employed comprehensive time-series analysis using data from six air quality monitoring stations and daily COVID-19 case records. Air quality parameters were measured using reference-grade instrumentation including Beta-attenuation monitors for particulate matter, non-dispersive infrared spectroscopy for CO, chemiluminescence for NO2, and ultraviolet photometry for O3. Statistical analyses included Pearson correlation with Bonferroni correction, multiple linear regression with assumption verification, and Seasonal Autoregressive Integrated Moving Average (SARIMA) forecasting, stratified by seasonal variations, lockdown periods, and viral variant periods. During the first lockdown (March-June 2020), moderate positive correlations existed between COVID-19 cases and particulate matter (PM2.5: r = 0.159; PM10: r = 0.093), with both infection rates and pollution levels decreasing significantly (PM2.5 declined 18.7%). During Delta variant prevalence (July-August 2021), correlations shifted negative (PM2.5: r = −0.073; PM10: r = −0.125), indicating variant dynamics superseded environmental influences. Multiple regression revealed nitrogen dioxide from vehicular sources as the primary PM2.5 predictor (β = 0.682, p < 0.001), explaining 72.4% of variation. Seasonal analysis showed particulate pollution peaked during winter months, with average PM2.5 levels (36.54 ± 18.73 μg/m3) exceeding WHO guidelines. This research demonstrates that Bangkok's air quality improvements during COVID-19 restrictions resulted primarily from reduced vehicular emissions rather than industrial changes, suggesting targeted traffic emission reduction strategies could substantially improve air quality while highlighting complex environmental-disease transmission relationships during pandemics.