Size distribution and chemical compositions of particulate matter during various atmospheric conditions in each month

Abstract

Persistent free radicals (PFRs) in particulate matter (PM) are highly reactive and transient species that can exist for extended periods, ranging from days to months or even years. These species are often associated with particles of varying sizes and are closely related to the chemical composition of aerosols. PFRs are an emerging hazardous substance with significant environmental impacts. The primary sources of PFRs in PM are incomplete combustion of fossil fuels and biomass burning. The chemical composition of atmospheric aerosols can vary due to factors such as environmental conditions, seasonal changes, and human activities, which can have varying effects on health. PFRs in PM, especially those produced during combustion, may pose a more significant risk to human health than other chemical constituents of aerosols. This is because PFRs are highly reactive and remain active chemically in aerosols, which increases the risk to human health. The study area was Chia Nan University of Pharmacy and Science. The samples were collected during the winter and summer of 2022. Sample collection took place during winter from 25 January to 9 February 2022, and during summer from 30 June to 11 July 2022. The water-soluble ions, saccharides, and carboxylates in PM were determined by using an ion chromatograph. PFRs in PM were measured by using an electron spin resonance (ESR) spectrometer. The concentrations of PFRs in droplet mode (0.32-2.5 µm) are 9.70±3.97×1014 spins/m3 in winter’s daytime and 8.87±2.11×1014 spins/m3 in winter’s nighttime. Besides, 4.79±1.93×1014 spins/m3 in summer’s daytime and 3.04±1.34×1014 spins/m3 in summer’s nighttime. In winter PFRs in PM have concentrations peaking at 1 µm in daytime and 1.8 µm in nighttime. While summer PFRs in PM have concentrations peaking at 1.8 µm in daytime and 1.8 µm in nighttime. The concentrations of PFRs in PM have shown a strong correlation with specific chemical compositions such as levoglucosan, nss-sulfate, nss-nitrate, formate, oxalate, and phthalate. This finding suggests that the sources of PFRs in PM extend beyond biomass burning and include secondary aerosols formed through photochemical processes and other human activities. Levoglucosan, a marker compound for biomass burning, has long been associated with the presence of PFRs. However, the high correlation between PFRs in PM and other chemical constituents, such as nss-sulfate, nss-nitrate, formate, oxalate, and phthalate, indicates that PFRs in PM are sourced from additional processes. These correlations suggest that PFRs in PM can also be formed through photochemical reactions involving precursor compounds emitted from various human activities, including industrial processes, transportation, and other combustion sources. The complexity of PFR in PM formation and its correlation with multiple chemical constituents highlights the need for a comprehensive understanding of the sources and pathways leading to their production. By identifying and quantifying these sources, policymakers and researchers can develop targeted strategies to mitigate PFR emissions and reduce their environmental and health impacts. Overall, the high correlation between the concentrations of PFRs in PM and specific chemical compositions beyond biomass burning signifies the multifaceted nature of PFR in PM sources. It underscores the importance of considering secondary aerosols generated by photochemical processes and other human activities when assessing the environmental impact of PFRs.