The haze of pollution that hangs over many large cities is a threat to human health but has the perverse effect of reducing the global warming effects of the sun.
This does not mean we should allow air quality to decline as a way to counter global warming, according to Dr Colin O'Dowd, director of the Centre for Climate and Air Pollution Studies within NUI Galway's Environmental Change Institute.
"The issue now is how we move forward in the future in having clean air and also blocking global warming," Dr O'Dowd said yesterday at the start of a five-day international meeting on atmospheric science hosted by NUI Galway.
More than 250 delegates from around the world are attending the International Committee on Nucleation and Atmospheric Aerosols, a meeting held every three to four years and last held in 2004 in Kyoto, Japan.
The meeting will hear the latest scientific findings on natural and man-made particles released into the air column above us that lead to a process known as nucleation and the production of aerosols in the atmosphere.
Aerosols are liquid or solid particles suspended in the air. Understanding their formation and distribution are essential to the study of climate change and air quality, added Dr O'Dowd, who is co-chairing the meeting with Prof Paul Wagner of the University of Vienna.
Suspended particles can start as small as a millionth of a millimetre across and then grow over time in a complex process that involves both chemistry and physics, Dr O'Dowd said.
Eventually they grow large enough to block solar radiation in the form of pollutant hazes and can attract moisture to form cloud particles.
"Without these aerosols there would be no clouds, so they have an important influence on solar radiation and precipitation," Dr O'Dowd said.
The birth or nucleation of the minute particles is a complex process that was undergoing extensive study worldwide, he added, given its associations with global warming but also with air quality and climate.
The nucleation process is driven by natural sources including iodine oxides released by sea algae and churned into the atmosphere by waves, and by volatile organic compounds (VOCs) released by boreal forests around the world, he said.
Pollution is another source with volatile organic compounds such as benzene and toluene released by burning fossil fuel along with sulphur dioxide and soot particles.
Dr O'Dowd said that natural and man-made sources could drive nucleation to produce pollution haze or seed cloud cover that could block solar radiation, hence its importance in countering global warming.
The delegates heard keynote speaker Prof Veerabhadran Ramanathan of Scripps Institute of Oceanography describe his study of the brown cloud pollution above the Indian Ocean and published this month in the journal Nature.
He and colleagues found that the soot-laden clouds have boosted the solar heating effect on the lower atmosphere by up to 50 per cent. Yet the clouds reduce temperatures at the surface, thus masking the true impact of solar heating.
Finnish Academy member Prof Markku Kulmala of the University of Helsinki delivered another key address. He is a world expert on nucleation theory and the complex processes involved in nucleation.
This important international meeting returns to Ireland for the third time. The committee held its first meeting in Dublin in 1955 organised by the Dublin Institute for Advanced Studies. The ninth committee meeting took place in Galway in 1977.
The current event is the 17th in the ongoing series, Dr O'Dowd said. "We do have a good history of aerosol research in Ireland," he added. NUI Galway's Mace Head research station on the western seaboard was central to the international effort to understand atmospheric processes.