IIT Delhi’s Study on Ultrafine Particles | 12 Oct 2020

Why in News

A study titled ‘Insights on the biological role of ultrafine particles of size PM<0.25: a prospective study from New Delhi’ suggested higher cytotoxicity in human lung cells because of fractions of Particulate Matter (PM) 2.5 when compared to larger particulate matters.

Key Points

• Methodology: Data for the study was collected six times every month between January and December 2017, through a cascade impactor measurement device- for measuring fine particle size distribution- installed at IIT Delhi.
  
  • Airborne particles in five sizes — 2.5, 1, 0.5, 0.25 and below 0.25 micrometers (µm) — were collected through the filters.
• Findings:
  
  • Proportion of Ultrafine Particles:
    
    • Particulate matter of below 0.25 micrometers constituted the highest share in the composition of PM2.5 around the year as compared to particles of other sizes.
      
      • The PM<0.25 particles constituted over 40% of PM2.5 levels during the post-monsoon season and over 30% during winters and pre-monsoon periods between March and May.
    • A decrease in total PM 2.5 levels may not be associated with a decrease in PM<0.25 levels.
      
      • This suggests that total PM2.5 levels are not good indicators of PM<0.25 levels.
    • Exposure to ultrafine particles of below 0.25 micrometers was also associated with over two-fold higher cytotoxicity (effect of being toxic to cells), as compared to exposure to other sizes.
  • Mass Concentration: For PM particles of size up to 2.5 µm, 1.0 µm, 0.5 µm, and <0.25µm, the cumulative average mass concentration values were found to be highest for the post-monsoon season (October-December), followed by winter (January-February).
    
    • High levels of PM2.5 are recorded in Delhi every year during post-monsoon and winter months, which in the past have led authorities to declare a public health emergency on some days and close schools.
  • Reasons: The observed high levels of PM in the post-monsoon and winter months partially due to:
    
    • Celebration of Diwali.
    • Agricultural residue burning in neighbouring states of Punjab and Haryana.
    • Secondary formation of particles due to favourable meteorological conditions.
      
      • The low temperature and high humidity during winter nights enhance the fog-smog-fog cycle and result in 2-3-fold increase in PM concentration compared to pre-monsoon and South-West monsoon season.
• Health Impacts: The adverse impact on health from chronic exposure to PM2.5 is well established — including stroke, lung cancer, and other heart and lung related problems.
  
  • Health impact of different size fractions within PM2.5 is not well studied yet.
• The National Ambient Air Quality Standard (NAAQS) has fixed a threshold for PM2.5 at 60 µg/m3 for 24 hours and 40 µg/m3 annually, but it does not have specific policies for ultrafine particles.
  
  • NAAQS was notified by CPCB in 2009.
  • Pollutants covered under NAAQS are Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), Particulate Matter (PM 10, PM 2.5), Ozone (O3), Lead (Pb), Carbon Monoxide (CO), Ammonia (NH3), Benzene (C6H6), Benzo(a)Pyrene (BaP), Arsenic(As), Nickel (Ni).

Way Forward

• Findings demonstrate a potentially important link between PM<0.25 levels and human health.
• Work provides novel insights for policy changes in monitoring PM, especially the need to routinely monitor PM<0.25
• The necessity to start working towards establishing exposure limits for PM<0.25 when the total PM2.5 levels are breached.

Source: IE