Mumbai 3rd most polluted among 10 int’l cities during lockdown: Study
Coinciding with the 50th anniversary of Earth Day, the report released by Swiss-based air quality research group IQAir collated real-time PM2.5 concentrations from monitoring stations over the three-week lockdown period.Updated: Apr 23, 2020, 11:17 IST
The city was the third most polluted among 10 international cities during the first three weeks of the lockdown imposed owing to the Covid-19 pandemic, according to a report published on Wednesday.
Coinciding with the 50th anniversary of Earth Day, the report released by Swiss-based air quality research group IQAir collated real-time PM2.5 concentrations from monitoring stations over the three-week lockdown period.
While the timeframe for seven of 10 cities was March 23-April 13, the period was different for Rome (March 9-30), and Wuhan and Seoul (February 26 to March 18).
Even though Mumbai witnessed a 42% reduction in average PM2.5 levels recorded between March 23 and April 13, compared to average PM2.5 levels (during the same period) over the past four years, and a 34% reduction compared to the same period in 2019, the city ranked third most polluted with PM2.5 concentration at 28.8 micrograms per cubic metre (μg/m³) during the lockdown period.
Wuhan, China was the most polluted at 35.1 μg/m³ followed by Delhi, second most polluted at 32.8 μg/m³. New York had the lowest PM2.5 levels at 4.4 μg/m³, which had the cleanest air across 10 cities, followed by Los Angeles USA at 5.5 μg/m³, and Madrid, Spain at 6.4 μg/m³. Sao Paulo, Brazil recorded 10.1 μg/m³, London UK 16.2 μg/m³, Rome, Italy 16.7 μg/m³, and Seoul, South Korea 24.1 μg/m³. Nine of 10 key global cities experienced PM2.5 reductions of 25-60% from the same period in 2019, the study said.
PM (particulate matter) is a mix of organic and chemical particles suspended in the air and can aggravate respiratory illnesses. PM2.5 is breathable particulate matter (solid and liquid particles) which is 2.5 microns in size or smaller, which can cause health ailments. The annual mean safe limit for PM2.5 is 10 μg/m³, according to the World Health Organisation. A recent US-based study suggests that even an increase of just 1 μg/m³ of PM2.5 in breathable air is associated with a 15% increase in the Covid-19 death rate.
“Although Asian cities had higher average PM levels, we observed that cities with historically higher average PM2.5 levels such as Delhi, Mumbai, Seoul, and Wuhan, experienced more drastic reductions in particulate pollution,” said Kelsey Duska, air quality outreach specialist at IQAir through an email response to HT.
“It is likely that cities in India are still observing higher PM2.5, relative to cities in Europe or the US, because people are still using energy. This energy may be sourced from dirtier sources, such as coal-based power plants. Similarly, biomass burning or fossil fuels used for domestic heating or cooking can further contribute to this effect,” said Duska.
During March, Mumbai experienced average PM2.5 levels of 34.5 µg/m³ – making it the cleanest March on record, despite lockdown measures only being implemented in the later part of the month, the study said, adding, “There is high possibility that April too would be the cleanest April on record if measures are to continue throughout the month.”
Significant reductions in particle pollution were primarily the result of restrictions on movement (greatly reducing traffic congestion) and industry, the study said.
Duska pointed out that overall air quality improvement for Mumbai was still unprecedented. The study examined the amount of hours spent in different AQI categories (as classified by the US), from March 23 to April 13. AQI levels are categorised as 0-50 as good, 51-100 as moderate, 101-150 as unhealthy for sensitive groups, 151-200 as unhealthy, 201-300 as very unhealthy, and 301-500 as hazardous.
“It was observed that Mumbai’s ‘unhealthy’ and worse rated air quality hours fell from 22.5% in 2019 to 0.4% during this lockdown period. This means that of all the hours between Mar 23 and April 13 (528 hours), only two were classified with ‘unhealthy’ air quality,” said Duska. As compared, Delhi’s ‘unhealthy’ and worse rated hours plummeted from 68% in 2019 to 17% during the lockdown period.
The study also presented a chart visualising the distribution of air quality hours during the lockdown period, which were classified into AQI categories. For Mumbai’s lockdown period, the chart showed that 66.2% of hours were classified as ‘moderate,’ while 33.4% of hours were ‘unhealthy for sensitive groups’ and only 0.4% were ‘unhealthy.’ In 2019, the distribution for ‘moderate’, ‘unhealthy for sensitive groups’, and ‘unhealthy’ was 51%, 23.3% and 22.5% - showing significantly more hours in the worse rated AQI levels.