This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Fine particulate matter (PM2.5) is commonly associated with both health concerns and poor visibility. However, these two effects do not necessarily improve or worsen at the same time.
Professor Yu-Chieh Ting and his research team examined this relationship by comparing particle oxidative potential (OP), a laboratory measure of the ability of particles to participate in reactions related to oxidative stress, with their ability to reduce atmospheric visibility. The study is published in the Journal of Hazardous Materials. By grouping the samples according to their OP and light extinction (bext), the researchers identified four different pollution conditions.
Notably, some samples showed relatively high oxidative potential even when light extinction was low. The comparison also showed that PM2.5 mass concentration alone could not fully explain either the oxidative activity of the particles or their effects on visibility. In other words, air that appears visually cleaner does not necessarily contain particles with proportionally lower oxidative activity.
The researchers then investigated why these two properties sometimes diverged. The amount of water contained in atmospheric aerosols played an important role. When aerosol water content (ALWC) was high, water uptake and particle growth enhanced light scattering and therefore increased visibility impairment.
Under drier conditions, oxidative activity became relatively more important compared with light extinction. Particle acidity was also related to this balance, but its influence was weaker than that of ALWC. These results suggest that changes in atmospheric conditions can alter how the same particle pollution is expressed in terms of oxidative and optical effects.
The source analysis further shows that different types of pollution do not affect oxidative potential and visibility equally. Secondary sulfate and organic aerosols, traffic-related emissions and fossil fuel combustion contributed to both properties. In contrast, secondary nitrate strongly affected light extinction but contributed very little to oxidative potential.
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