Assessing PM2.5 pollution and the role of transboundary pollution emissions across Greater Kuala Lumpur, Malaysia from 2018 to 2023

Abstract

Transboundary haze events in Southeast Asia have been associated with elevated PM2.5 levels in Greater Kuala Lumpur (GKL), Malaysia. PM2.5 refers to fine particulate matter with an aerodynamic diameter of 2.5 microns or less, capable of penetrating deep into the respiratory system and posing significant health risks. GKL experiences severe transboundary haze events, primarily driven by regional biomass burning activities. These biomass burnings lead to hazardous PM2.5 pollution levels, posing significant health risks, economic losses, and environmental damage. This thesis investigates the severity of PM2.5 pollution in GKL, specifically assessing the magnitude of transboundary PM2.5 emissions from Sumatera provinces' during biomass burning events using a novel method combining backward air pathway and biomass emission data. This study includes four key approaches: i) analysing PM2.5 concentration levels across GKL, namely, Bangi (BG), Batu Muda (BM), Cheras (CS), Klang (KG), Kuala Selangor (KS), Putrajaya (PA), Petaling Jaya (PJ), and Shah Alam (SA) using observation datasets from 2018 to 2023; ii) estimating PM2.5 emissions due to biomass burning in Sumatera using three biomass emission inventories, Global Fire Assimilation System (GFASv1.2), Fire INventory from National Center for Atmospheric Research (FINNv2.5), and FINN plus Visible Infrared Imaging Radiometer Suite ( FINNv2.5VIIRS); iii) determining the pathway of air masses across GKL using Numerical Atmospheric-dispersion Modelling Environment (NAME), and iv) predicting PM2.5 levels in GKL using NAME-GFAS model during transboundary haze. Over the six years, three primary PM2.5 pollution features were observed: i. a significant peak in 2019, ii. a marked improvement of air quality between 2020 to 2022, and iii. a gradual increase in PM2.5 levels in 2023. From 2018 to 2023, 50% to 75% of the days in GKL generally experienced medium pollution days (daily concentration averages between 15 µgm-3 to 35 µgm-3 ), and the Southwest Monsoon (SWM) season showed significantly the highest seasonal averages. September 2019 marked the highest period of PM2.5 pollution levels across the eight locations, with 80% to 100% of the days exceeding the daily Malaysia Air Quality Standard (MAQS) and World Health Organisation (WHO) guidelines, resulting in extreme PM2.5 pollution levels in 2019. About 1.66 Tg (GFASv1.2), 1.18 Tg (FINNv2.5), and 1.39 Tg (FINNv2.5VIIRS) of PM2.5 mass were emitted from biomass burning within the research domain in 2019. GFASv1.2, FINNv2.5 and FINNv2.5VIIRS showed that 1.42 Tg, 1.04 Tg and 1.22 Tg originated from Sumatera. GFASv1.2 reported approximately 54% of PM2.5 emissions occurred in September, while FINNv2.5 and FINNv.25VIIRS reported 40% in September, respectively. A strong and statistically significant correlation (ρ = 0.6 to 0.8, p < 0.05) was observed in September 2019 between PM2.5 mass emissions from fires in Sumatera and elevated ambient PM2.5 concentrations in GKL in September 2019. Over 95% of September PM2.5 emissions from biomass burning in Sumatera, originated from the provinces of Riau, Jambi, South Sumatra, and Lampung. NAME indicated that air masses travelled over the Riau, Jambi, South Sumatera and Lampung provinces in September towards GKL. The model, which integrates NAME and GFAS, predicts that fires from Riau and Jambi provinces collectively account for approximately 97% of the PM2.5 levels across GKL during transboundary haze. In September 2019, a month affected by haze, Riau was identified as the primary contributor to PM2.5 concentrations in KG (59%), KS (53%), and BG (59%). During the same period, Jambi was the dominant contributor to PM2.5 levels in BM (58%), PJ (52%), CS (56%), and PA (55%). The combined utilisation of observational data, biomass burning inventories, and NAME backward run effectively provided insights into the pathways and contribution of PM2.5 from Sumatera. These findings stress the urgency of understanding the effect of biomass burning in Sumatera provinces to better address high PM2.5 levels during transboundary haze events in GKL.