Measurements from monitoring stations are only able to report air quality at that particular location, and cannot predict future condentrations. The annual map uses a detailed model to show a prediction of what air quality is like across the whole of Greater London. This model was created for the GLA using a set of assumptions about future pollution emissions and policies.

The three pollutants chosen are ones which are known to have an effect on health within London and are able to be predicted with this model. Ozone (O₃) has not been mapped because this is a very regional pollutant, and it is harder to influence it with local policy changes. Levels of carbon monoxide (CO) are now well below EU Limit Values and have not been mapped. Concentrations of sulphur dioxide (SO₂) are too unpredictable to create a map using this method. Each pollutant has different sources and behaviour, so try selecting each pollutant in turn to get a full picture of air quality at your chosen location.

Annual means give a good indication of the average level of a pollutant and long-term exposure. Increasingly evidence is pointing to long-term exposure to air pollution as being more important than exposure to short-term peaks. The map scale is shown such that areas above the EU Limit Value are shown as yellow through orange to red. Greatest concentrations of traffic pollutants are often predicted in the middle of road junctions or in the centre of busy roads where the public do not normally have access. These are not generally areas of relevant exposure for the assessment of EU Limit Values and UK air quality objectives.

This study was based on 2013 data, and then looked far enough ahead for policy and technology changes to have an impact. These maps were based on projected policies in 2013, which have since been changed. These maps also used outdated emissions factors, and used old methods for estimating emisions from construction and other sources. We expect to update these maps when we can.

Pollution levels are forecast to fall mostly as a consequence of improving engine standards and restrictions on engine types within London. New vehicles are meant to create less pollution, and as vehicles are replaced overall pollution should decrease. Other policies on things like construction emissions and wood burning are also expected to change pollution levels.

Real world conditions can vary dramatically from standard tests, and recent technology changes like direct NO2 production and the VW emissions scandal show that forecasts can be wrong. Policies can also change over time, and the 2013 model has some out of date emissions factors and sources.