Assessment of black carbon concentrations, emission sources and health risks in two cities of Peninsular Malaysia

Black carbon (BC) is known as a pollutant that poses serious risks to both the climate system and human health. The Southeast Asia region relies heavily on fossil fuels, and experiences frequent biomass burning that contributes significantly to BC emissions, yet research on BC measurements remains limited. To address these knowledge gaps, the present study aims to investigate the BC levels at two sites in Peninsular Malaysia, apportion the potential sources, and estimate the associated human health risks from BC exposure. The measurement campaign was conducted from August to November 2024 at Putrajaya and April to May 2025 at Johan Setia, Klang respectively. Real-time measurements of aerosol light absorption were continuously obtained using a AE33 aethalometer. The measured mean equivalent BC mass concentrations of 4.61 ± 1.75 g m^-3 and 2.53 ± 0.75 g m^-3 were observed in Johan Setia and Putrajaya, respectively. Johan Setia records higher BC concentrations due to multiple local emission sources from traffic, industries, residential, agricultural and commercial activities. BC from fossil fuel (BC_ff) dominated both sampling sites throughout the study period with several irregular localized peak episodes. Daily variations in BC concentrations reflect the critical contributions of traffic emissions during weekdays. A well-planned township like Putrajaya exhibits lower BC emissions, with consistent patterns indicating that light-duty vehicles are the primary source, reflecting its role as a government administrative and residential township. Elevated BC_ff were observed from midnight to early morning at Johan Setia, driven by emissions from nearby industrial facilities, power stations and heavy-duty vehicles operate at night because the position of the site lies along the main route connecting Klang to Port Klang, one of Malaysia’s busiest seaports. In addition, increasing trends of BC concentrations from biomass burning (BC_bb) were prevalent from late evening until night at Johan Setia, likely due to the burning of agricultural residues by the residents. The BC index at both sites shows a dominant of the satisfactory category, with BC concentrations ranging from 1 to 3 g m^-3. Health risk assessments revealed that the calculated chronic hazard quotient (HQ) for BC across the exposed groups was less than 1 (HQ < 1). Both sampling sites recorded cancer risk values exceeding the acceptable value of 1 x 10^-6. This work provides a foundation of understanding BC pollution in the tropical region of Malaysia. Recognising the implications of BC on climate and health, Malaysia should establish BC monitoring efforts and give sufficient attention to evidence-based policies to reduce black carbon emissions.