NEW DELHI: This March recorded the lowest particulate matter (PM2.5) levels-fine, respirable pollutants-in the past four years. While this could seem like a relief at the moment, scientists at the Indian Institute of Tropical Meteorology (IITM) say pollution levels are becoming increasingly unpredictable because of erratic meteorological conditions. The average monthly PM2.5 level dropped to 72 microgram per cubic metre this year from 112 (approximately) in March 2012.

Scientists who analysed the data said the extreme pollution event in 2012 could be linked to the dust storm in the Gulf that time. "The 2012 event was like the Saharan dust cloud that has covered England. This year, winds are blowing from cleaner places at a relatively high speed and have swept away the pollutants. Such events can either take air pollution to dangerous levels, or bring it down. So while the local emissions are increasing, we need to factor in climate change," says Gufran Beig, chief project scientist at System of Air Quality Weather Forecasting and Research. The PM2.5 levels in 2008, 2009 and 2010 were around 100 microgram per cubic metre, he said.

IITM, under the ministry of earth sciences, is preparing a report on the link between air quality and climate change. "The higher temperature raises boundary layer and a relatively high wind speed swept away the local pollutants. This brought down the PM2.5 levels in March 2014. The trend will change soon," added Beig.

While the monthly average for March 2012 may not seem too high, there were instances of PM2.5 levels crossing 250 microgram per cubic metre against a standard of 60. "Between October 7 and October 9 in 2012, peak levels touched 500 microgram per cubic metre. The winds that usually come from the northeast and are usually clean changed direction and came from northern India. Burning of the agricultural residue in Punjab and Haryana meant the winds were laden with particles that added to the pollution. Instances of extreme weather have affected pollution levels," said Beig.

"It's obvious that the unusual rain in February and March this time has swept away all pollutants. But I am not sure if the 2012 pollution levels were linked to dust from the Gulf. We will have to go through IITM's study to see the link with climate change," said Anumita Roychowdhury of Centre for Science and Environment.