Outdoor Air Quality in Urban Areas

The air we breathe impacts our health and well being in subtle, and sometimes not so subtle ways every single day of our life. Understanding this impact is vital if we are to have the opportunity to make beneficial changes in our lifestyle, and critical to this understanding is a comprehensive oversight into the environmental conditions that we find ourselves in daily. Measurement data from fixed stations as well as portable sensors deployed as part of the CITI-SENSE project are used to assess air pollution in many of our cities in Europe in order to provide people with information about air quality and the health impact that air pollution can have on vulnerable groups.

What can I do to improve the air quality?

Example of weather data from May

How are specific air pollutants formed and what risks do they pose to you


Description and main  sources

Potential effects on health/environment

Oxides of nitrogen


All combustion processes in air produce oxides of nitrogen (NOx). Nitrogen dioxide (NO2) and nitric oxide (NO) are both oxides of nitrogen and together are referred to as NOX. Road transport is the main source, followed by the electricity supply industry and other industrial and commercial sectors.

NO2 is associated with adverse effects on human health. It can affect the liver, lung, spleen and blood. At high levels NO2 causes inflammation of the airways. Long term exposure may affect lung function and respiratory symptoms. NO2 also enhances the response to allergens in sensitive individuals. High levels of NOx can have an adverse effect on vegetation, including leaf or needle damage and reduced growth. Deposition of pollutants derived from NOx emissions contribute to acidification and/or eutrophication of sensitive habitats leading to loss of biodiversity, often at locations far removed from the original emissions. NOx also contributes to the formation of secondary particles and ground level ozone, both of which are associated with ill-health effects. Ozone also damages vegetation.

Ozone (O3)

Ground level (tropospheric) ozone is not emitted directly from any human-made source. Instead it forms in the atmosphere from a chain of photochemical reactions (with the help of sunlight) between various air pollutants, primarily NOx and Volatile Organic Compounds (VOCs), but also CO and methane. Formation can take place over several hours or days and may have arisen from emissions many hundreds, or even thousands of kilometres away.

Exposure to high concentrations may cause irritation to eyes and nose. Very high levels can damage airways leading to inflammatory reactions. Ozone reduces lung function and increases incidence of respiratory symptoms, respiratory hospital admissions and mortality. Ground level ozone can also cause damage to many plant species leading to loss of yield and quality of crops, damage to forests and impacts on biodiversity. Ozone is also a greenhouse gas contributing to warming of the atmosphere.

Carbon monoxide (CO)

Formed from incomplete combustion of carbon containing fuels. The largest source is road transport, with residential and industrial combustion making significant contributions. CO reacts with other pollutants producing ground-level ozone

Substantially reduces capacity of the blood to carry oxygen to the body’s tissues and blocks important biochemical reactions in cells, leading to heart disease and damage to the nervous system. First symptoms include headache, dizziness and fatigue. People with existing diseases which affect delivery of oxygen to the heart or brain, such as angina, are at particular risk.

The CITI-SENSE sensors in Ljubljana are currently measuring NO, NO2, CO, O3 as well as temperature, relative humidity and pressure.

This project has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no 308524.