Spatio-temporal variability of urban particulate matter using GIS: a lesson from COVID-19 restrictions

Abstract

BACKGROUND AND OBJECTIVES: Air pollution and its associated health impacts have become a major concern worldwide, particularly in developing countries. Anthropogenic activities were significantly reduced during the COVID-19 pandemic, allowing for the opportunity for source reduction of air pollutants. A number of studies have been conducted in Dhaka, but most of them are concentrated on a single ground-monitoring station, making it impossible to draw a comprehensive pollution scenario for the entire city. In contrast, this study evaluated the spatio-temporal changes of urban Particulate Matters (PM) in 70 locations from five different land use categories. Hence, this study investigated the influence of the COVID-19 pandemic on PM1 (aerodynamic diameter ≤1 µm), PM2.5 (aerodynamic diameter ≤2.5 µm) and PM10 (aerodynamic diameter ≤10 µm) concentration during three specific time frames: November 2019 (Pre-lockdown), April 2020 (During lockdown), and November 2020 (Post-lockdown).METHODS: The data were collected through portable air quality meter (AEROQUAL 500) during lockdown (April 2020) and post-lockdown (November 2020) period. Data set of pre-lockdowns (November 2019) was collected from Center for Atmospheric Pollution Studies (CAPS). The Tukey's Post Hoc Multiple Comparison Test was conducted using Statistical Package for the Social Sciences (SPSSv26) to address the significant changes in air quality between the periods. Additionally, the GIS (Geographical Information System) platform was used to see the spatial and temporal variations of PMs over the city.FINDINGS: The study found that average ground level PM1, PM2.5 and PM10 concentration reduced by 75.1, 75.4, 69.6% and 41.1, 32.6, 29.2% respectively during lockdown compared to pre-lockdown and post-lockdown periods. Moreover, the reduction during lockdown was significant at α=0.05 level. The highest reduction was seen in residential areas from the pre-lockdown to lockdown period, whereas in the lockdown to post-lockdown phase that was found in the industrial areas. Interestingly, the northern part of Dhaka city was less polluted than the southern part in all three studied periods. Besides, the Dhaka city dwellers enjoyed comparatively good quality air in lockdown.CONCLUSION: This study suggested that land use-based source apportionment is required to eliminate the particulate concentration from Dhaka city. Besides, 24 hours continuous data is also important to understand the interaction between particulate concentration and climatic forces. Promoting cleaner transportation options, such as electric vehicles and public transportation is recommended as a means of reducing vehicle emissions. Furthermore, governments could consider implementing emissions regulations, setting limits on emissions, or mandating the use of cleaner fuels and technologies to reduce industrial pollution.