Effect of protesting by burning barricades on PM_2.5: chemical composition and oxidative potential evaluation

Protests have become a global phenomenon, with road blockades among the most common methods used to express objection. In many countries, these blockades involve the open burning of materials such as tires, wood, and waste. In this study, PM_2.5 was collected during an active burning protest episode as well as over the subsequent days. PM_2.5 was characterized for the carbonaceous fraction, water-soluble ions, elements, and organic compounds (alkanes, polycyclic aromatic hydrocarbons (PAHs), phthalates, fatty acids, hopanes, levoglucosan, dioxins, furans, and dioxin-like polychlorobiphenyls (PCDD/Fs and DL-PCBs). The major contributors to PM_2.5 during the burning episode were elemental carbon, organic carbon, and zinc, which collectively accounted for 42% of total PM_2.5. The chemical profile also revealed a marked increase in combustion-related compounds such as alkanes, PAHs, PCDD/Fs, and DL-PCBs, highlighting the strong influence of open burning emissions on air quality. Oxidative potential (OP) assays showed a clear increase during the burning day, with peak values of 6.6 nmol/min/m³ for OP-DTT and 5.8 nmol/min/m³ for OP-AA. While these OP levels were nearly double those of non-burning days, the increase was notably less pronounced compared to the sharp fluctuations observed in chemical tracers and toxic equivalents. The temporal trends also indicated differing sensitivities between the assays, with OP-DTT more closely following OC levels, while OP-AA was more influenced by EC and elemental content. These findings highlight the complex chemical nature of emissions from protest-related burning and underscore the need for non-toxic alternatives to such practices.