MUMBAI: Small particles of air pollution and dust may play a role in enhancing a good monsoon while aggravating a poor one.That is one implication of a new IIT-Bombay study that found a link between the amount of aerosols in the atmosphere and cloud formation during the monsoon. Aerosols refer to small particles of dust and pollutants like soot.For the study, scientists analysed observational data on aerosols and clouds over central and north India between 20002009 monsoons. They were surprised by what they found: high levels of aerosols were correlated with modifications in cloud formation -but in diametrically opposite ways in good and bad monsoon years.In deficient monsoon years, scientists found, dust and pollutant particles built up in the atmosphere during frequent breaks in rainfall. This accumulation of aerosols coincided with the formation of smaller cloud droplets and shallower clouds. When clouds are shallow, they drain out quickly.The opposite trend was seen in good monsoon years. During these years, high levels of aerosols coincided with bigger cloud droplets. Clouds also grew much taller resulting in greater ice formation. “Taller clouds and greater ice formation are linked respectively to more intense rainfall and cold rain,“ said IIT professor and study co-author Chandra Ven kataraman.The findings imply that aerosols could further inhibit cloud development during a deficient monsoon while invigorating cloud formation during a good monsoon, she added.The mechanisms underlying these processes need to be studied further, scientists said.And while this paper only looked at links to changes in cloud properties, the investigation of actual rainfall changes is also underway, said Venkataraman There has been relatively little research looking at the effect of local factors like land use or air pollution on monsoon cloud formation. Monsoon studies have traditionally focused on the impact of large-scale factors like El Nino or La Nina. Some studies have looked at the effect of aerosols on the overall monsoon through temperature changes since aerosols can both cool and warm the atmosphere. Those studies have linked aerosols to short-term increases in rainfall as well as longer-term drying out of some regions.“We have to understand local processes along with largerscale monsoon dynamics,“ said Venkataraman.The study, by PhD students Nitin Patil and Prashant Dave and Venkataraman, was published in the journal Scientific Reports this month.