What are the causes of air pollution in inner cities – and how bad is it?

• We still have a long way to go to. Air quality in the UK is currently measured against the legal limits set by the EU. For PM2.5 and PM10 in particular, these legal limits are substantially higher than the guidance from the World Health Organisation.
• NO₂ levels are predicted to improve substantially with the introduction of and subsequent expansion of the Ultra Low Emissions Zone (ULEZ). Particulate matter is not predicted to improve as substantially.
• While vehicles are the single largest source of both NO₂ and particulate matter, there are a number of other major sources including construction, commercial cooking, wood burning and boilers and generators.
• People’s total exposure is determined by both outdoor and indoor pollution and the time they spend in each of these environments.

The pollutants responsible for air quality

There are three main pollutants associated with poor health in inner cities:

NO₂ (Nitrogen Dioxide), typically in areas of high vehicle traffic. Exposure to NO₂has been associated with a range of health effects including organ and neurodevelopment during pregnancy, new onset asthma in children and lung function decline in older adults.

PM2.5 or particulate matter, such as soot, smoke, dust and liquid droplets measuring less than 2.5 micrometres in diameter. These tiny particles are of particular concern to our health because they can enter the bloodstream and lodge deep in our organs.

PM10 are larger particles than PM2.5 and come from similar sources. PM of all sizes has been linked to chronic inflammation and is associated with similar health risks including lung development during pregnancy and early childhood, as well as lung function decline in older adults.

The sources of air pollution are intrinsically linked to how we live in cities. While many people see cars and transport as the most obvious causes of air pollution, nearly 70% of particulate matter is related to the built environment such as heating of buildings, construction and traffic related to it.

Only 16% is related to how residents get around the city. This system map shows the different sources of inner-city air pollution, based on data from the London boroughs of Lambeth and Southwark.

Transboundary and other sources have been given a variable source apportionment. This is because air moves around and pollutants from these sources can vary significantly depending on irregular factors such as weather conditions. Original system mapping by Keith Cotton, CrispAir.

Sources of PM10 and PM2.5

In Lambeth and Southwark, heating our buildings, construction and traffic related to it, are a much larger source of particulate matter (PM) air pollution than how people travel and get around the city.

Annual averages for PM2.5, PM10, and NO₂ show that people in Lambeth and Southwark are exposed to more air pollution in the north of the boroughs and along the main roads.

While the boroughs are within the EU legal limits for particulate matter, NO₂ currently exceeds these limits.

Pollution from particulate matter across the whole of the boroughs is above the World Health Organisation (WHO) guidance, with the north of the boroughs and main roads also exceeding WHO guidance for NO₂.

Each dot represents a small area (LSOA) in Lambeth and Southwark. Orange dots are above the WHO guidelines, grey dots are below them.

Predictive analysis shows that while NO₂ levels are expected to improve over time due to ULEZ and other emissions regulations, PM levels are not.

As part of the groundwork for our programme, we researched air pollution awareness among people living in our inner-city area. Together with partners including Global Action Plan, Opinium and BMG Research we did:

• On-street interviews with 401 local residents
• Focus groups, including one consisting of older people
• A public perception survey of 1,033 local residents

This insight will help us develop more effective projects to address poor air quality and improve the health of local residents – particularly the vulnerable groups who are the focus of our programme.

What we found:

• Talking to residents has given us new insights into the causes of local air pollution. For example, our research suggests wood burning in homes is more common than we expected.
• People have a fairly good understanding of the causes of air pollution locally. More than two-thirds of local people think transport and traffic is behind poor air quality.
• Residents feel it’s not only private cars causing the problem but delivery lorries, buses, coaches and an increase in construction traffic.
• Construction itself is seen as an issue affecting air quality.
• Some people are not aware of the main causes of air pollution.