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Centre for Atmospheric Science

CityFlux Project

Air Pollution from cities - some of the issues

Central Manchester viewed from the Cessna aircraft during a flight for the Cityflux project.
Central Manchester viewed from the Cessna aircraft during a flight for the Cityflux project.

Most air pollution in European cities comes from traffic. Emissions include greenhouse gases, like CO2, which affect the climate globally. Other emissions have negative impacts (like acid rain) on the surrounding countryside. But other emissions are harmful to human health and directly impact those of us who live and work in cities. These toxic emissions include gases, like nitrogen dioxide (NO2), but also microscopic particles. These particles include things like fine oily mists from vehicle exhausts, but also flecks of dust from tyre, brake and road wear. Numerous studies have shown that particles have the greatest effect on our health. The effect of particles on our climate, both locally and globally, is poorly understood compared to the effect of greenhouse gases.

Two key issues about which we need to know more are.

1. What levels of particles, and what kind, are we exposed to in the city, and what do the levels depend on?

2. At what rate are particles exported from the city on the wind, and what does this rate depend upon?

The essence of CityFlux is to investigate both of these issues simultaneously by measuring the rate at which turbulent gusts of wind remove particles from the network of street 'canyons' in a city centre where we live and breathe, into the air above, from where they can blow away on the wind.

What exactly is being done in this study?
This project is all about making measurements. We measure the number, size and chemical composition of particles in the air on busy streets, on nearby rooftops and on the top of tall buildings. To understand how the air is moving particles around we also measure the wind speed very rapidly using ultrasonic anemometers. This allows us to measure every gust as well as the average wind. We use state-of-the-art instrumentation that gives us huge amounts of information about the particles, which helps us understand any chemical and physical reactions that happen in the atmosphere, affecting the particles' toxicity and the way they influence climate.

When and Where?
These kind of experiments make very intensive use of instruments and personnel. As a result we conduct them as campaigns - usually around a month long. So far there have been measurement campaigns in Gothenburg (2005), Manchester (June-July 2005) and Edinburgh (Dec 2005). The largest campaign will be in May 2006 in Manchester, with a further campaign in London late in 2006.