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Welcome to the latest edition of air quality update -the insiders’ guide to air pollution in the borough. This month we run through the basic facts on nitrogen dioxide and give you the latest readings of recorded pollutant levels.

Focus on nitrogen dioxide

What it is and how it affects the environment

Nitrogen dioxide is a gas, with the chemical formula NO2. A related gas, nitric oxide, has a chemical formula NO. Both are released into the air when fuels are burned - for example, petrol or diesel in a car engine, or natural gas in a domestic central-heating boiler.

NO2 can damage our health and high levels can inflame our lungs and, over time, affect how well our lungs work. People with asthma are particularly affected. NO2 can also damage plants.

Where does NO2 come from?

Road transport is the largest source of these emissions in the UK.

However, emissions from road transport are falling due to improvements in engine design and fitting catalysts to petrol cars. By contrast, it is expected that emissions from heating systems will increase.

NO2 is also formed in the atmosphere in a chemical reaction between NO and ozone (O3).

How is NO2 measured?

Nitrogen dioxide is measured using an instrument called a chemiluminescence analyser. There are over 200 monitoring sites using these analysers throughout the UK.

What about places without monitoring sites?

We use computer models to assess concentrations in places without monitoring sites and to predict future concentrations of NO2.

What conditions lead to very high concentrations of NO2?

'Pollution episodes' are short periods of very high levels of pollution. There are two types of episode: in winter, when the ground is cold and there is little wind, emissions are trapped near to the ground; summer episodes take place when the weather is hot and sunny with little wind. Ozone is created by chemical reactions and which in turn convert more NO into NO2.

Monitoring air quality in Islington

Air quality is monitored at two sites. The site in Upper Street shows air quality experienced by the majority of Islington residents. The Holloway Road site shows the worst conditions in Islington.

Airborne particulates objectives

· Annual average concentration of 40µg/m³ by the end of 2004

· Daily average concentration with up to 35 exceedences a year of 50µg/m³ by the end of 2004