Environmental Research Web: Air Pollution Comes Under Scrutiny

Friday, July 9, 2010

By Kate Ravlilious
Contributing Editor
Environmental Research Web

You might not be able to see it but you will almost certainly feel it at some point in your life. Air pollution is on the rise, bringing with it a whole host of health problems and altering the world's weather and climate. For Gregory Carmichael, an atmospheric chemist at the University of Iowa, US, understanding the impacts of air pollution has been the basis of his life's work.

Right now Carmichael is working on three major projects, each one disentangling the complex reactions that occur when pollutants are dumped into the air. One such pollutant of major concern is "black carbon" – essentially soot. Produced during incomplete burning of fossil fuels, black carbon has a warming effect on the planet by absorbing heat and by decreasing reflectivity when it is deposited on snow and ice. "Our calculations suggest that black carbon produces the second greatest warming effect after carbon dioxide, when considering anthropogenic sources," Carmichael told environmentalresearchweb (Nature Geosciences).

Unlike carbon dioxide, black carbon has a very short lifetime in the atmosphere – just one week or so. "This means that the impact would be instant if black carbon was removed," said Carmichael. But unfortunately black carbon also tends to be accompanied by other pollution products, such as sulphur dioxide, which have a cooling effect. Ironically reducing the amount of black carbon going into the atmosphere could potentially increase global warming because of the accompanying reduction in cooling aerosols. "We need to find a strategy where we can reduce black carbon faster than sulphur dioxide, for example," he explains.

And that strategy is likely to vary from region to region, depending on the most predominant source of black carbon. In South Asia most black carbon comes from burning cow dung and wood as a biofuel for cooking. Meanwhile, in Europe the major source is diesel-powered vehicles. By modelling atmospheric chemistry and taking into account regional differences, Carmichael is able to explore the likely impact of different reduction strategies and work out the optimal course of action.

Another preoccupation of Carmichael's is chemical weather – in other words predicting air quality in different regions. Pollutants like nitrogen dioxides, for example, can react to create ground-level ozone, a pollutant with severe implications for people's health. Predicting where and when ozone levels are going to be high is of great importance for those people with respiratory health problems.

Right now most air quality models rely on standard meteorological data but, as Carmichael explains, this data has limitations. "Meteorological forecasts tend to focus on predicting severe weather, such as storms, but poor air quality tends to be associated with stagnant and boring weather events, such as high-pressure systems [which aren't usually flagged up]. In addition pollution tends to occur on a higher resolution than the forecasts provide."

Carmichael and his colleagues are trying to overcome these limitations, building models that are tailored towards predicting air quality. To test their models they have carried out a number of pilot projects, including one at the Olympics in Beijing, China, and a forthcoming one in Delhi, India at the Commonwealth games in October.

Last but not least, Carmichael is interested in the long-range transport of pollutants, over entire continents and oceans. To control air quality it is essential for air-quality managers to know the relative proportions of local, regional, national and international pollutants. Carmichael and his team are trying to build this capability into their air-quality forecast models. "The nature of these faraway sources will become more important as societies mature and work toward reducing the risk of air pollution by putting more stringent air-quality controls in place," says Carmichael.