Insights on the biological role of ultrafine particles of size PM<0.25: A prospective study from New Delhi

When the total ambient PM2.5 levels are several-fold higher than the recommended limit, it may be important to study the distributions of different sizes of particulate matter (PM). Here, we assess the distributions of various sizes of total PM2.5 for 12 months (on a monthly basis) in New Delhi, India. Importantly, we found that ultrafine particles (i.e., particles <0.5 mu m) contribute significantly to total PM2.5. PM<0.25 were the most cytotoxic particles to human lung epithelial cells in all the 12 months. In addition, PM<0.25 were associated with significantly higher cytotoxicity per unit mass compared to other size fractions constituting PM2.5. For any given size of PM, the amount of reactive oxygen species (ROS) generated per unit mass is higher for the month of March as compared to that for the rest of the months in the year. The higher ROS generations for all sizes of PM collected in the month of March was not explained by differences in their metal content values. Our data suggests the lack of correlation between total PM2.5 levels and the highly cytotoxic PM<0.25. In summary, this work establishes the need for policy changes to routinely monitor PM<0.25 and the necessity to establish exposure limits for PM<0.25, especially when the total PM2.5 levels are breached. (C) 2020 Published by Elsevier Ltd.

Automated summary

The study evaluates the distributions of total PM2.5 of different sizes in New Delhi, India over 12 months and finds that ultrafine particles significantly contribute to total PM2.5 and are most cytotoxic to human lung epithelial cells. In March, higher amounts of reactive oxygen species are generated per unit mass for all sizes of PM, without correlation to metal content values.