Air pollution
Information on how to use the daily air quality index including additional advice for susceptible individuals.
The air pollution figure shows the 'Daily Air Quality Index', which is dependent on pollutant concentrations averaged over specified periods. These averaging periods were specifically selected by the 'Committee on the Medical Effects of Air Pollutants' (COMEAP) on the basis of epidemiology studies concerning the short-term impacts of air pollution. With these specifications the air quality index is inherently a 'daily' index and it is not possible to display values representing shorter time periods (for example 3 hourly) without distorting the intended meaning of the index.
The Met Office air pollution forecast is generated from a regional model working on a 12km grid resolution, our forecast does not represent the very localised increases in pollution that you might find close to roads or in urban centres. The forecast represents the background and regional air quality away from these strong sources of pollution. Keep checking the latest forecasts on the Defra UK Air website for up to date information.
The daily air quality index comes in three parts and includes additional advice for susceptible individuals, alongside advice for the general population:
- Instructions on how the index should be used
- The short-term health effects of air pollution and action that can be taken to reduce impacts
- Health advice linked to each band to accompany the air quality index
These are detailed below:
How to use the Daily Air Quality Index
Step 1: Determine whether you (or your children) are likely to be at-risk from air pollution. Information on groups who may be affected can be found in the Additional information on the effects of air pollution section. Your doctor may also be able to give you advice.
Step 2: If you may be at-risk, and are planning strenuous activity outdoors, check the air pollution forecast.
Step 3: Use the health messages corresponding to the highest forecast level of pollution as a guide.
Additional information on the short-term effects of air pollution
The daily air quality index (DAQI) has been developed to provide advice on expected levels of air pollution. In addition, information on the short-term effects on health that might be expected to occur at the different bands of the index (Low, Moderate, High, Very High) is provided. It is possible that very sensitive individuals may experience health effects even on Low air pollution days. This advice applies to anyone experiencing symptoms.
Short-term effects of air pollution on health
Air pollution has a range of effects on health. However, air pollution in the UK does not rise to levels at which people need to make major changes to their habits to avoid exposure; nobody need fear going outdoors.
Adults or children with lung or heart conditions: It is known that, when levels of air pollutants rise, adults suffering from heart conditions, and adults and children with lung conditions, are at increased risk of becoming ill and needing treatment. Only a minority of those who suffer from these conditions are likely to be affected and it is not possible to predict in advance who will be affected. Some people are aware that air pollution affects their health: adults and children with asthma may notice that they need to increase their use of inhaled reliever medication on days when levels of air pollution are higher than average.
Older people are more likely to suffer from heart and lung conditions than young people and so it makes good sense for them to be aware of current air pollution conditions.
The general population: At very high levels of air pollution, some people may experience a sore or dry throat, sore eyes or, in some cases, a tickly cough even in healthy individuals.
Children need not be kept from school or prevented from taking part in games. Children with asthma may notice that they need to increase their use of reliever medications on days when levels of air pollution are higher than average.
Action that can be taken
When levels of air pollution increase it would be sensible for those who have noticed that they are affected to limit their exposure to air pollutants. This does not mean staying indoors, but reducing levels of exercise outdoors would be reasonable.
Older people and those with heart and lung conditions might avoid exertion on High pollution days.
Adults and children with asthma should check that they are taking their medication as advised by their health practitioner and may notice that they need to increase their use of inhaled reliever medication.
Adults with heart and circulatory conditions should not modify their treatment schedules on the basis of advice provided by the air quality index: such modification should only be made on a health practitioner's advice.
Some athletes, even if they are not asthmatic, may notice that they find their performance less good than expected when levels of a certain air pollutant (ground level ozone) are High, and they may notice that they find deep breathing causes some discomfort in the chest: This might be expected in summer on days when ground level ozone levels are raised. This does not mean that they are in danger but it would be sensible for them to limit their activities on such days.
Health advice to accompany the Daily Air Quality Index
| Air pollution banding | Value | Accompanying health messages for at-risk groups and the general population | |
|---|---|---|---|
| At-risk individuals* | General population | ||
| Low | 1-3 | Enjoy your usual outdoor activities. | Enjoy your usual outdoor activities. |
| Moderate | 4-6 | Adults and children with lung problems, and adults with heart problems, who experience symptoms, should consider reducing strenuous physical activity, particularly outdoors. | Enjoy your usual outdoor activities. |
| High | 7-9 | Adults and children with lung problems, and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms. People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion. | Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors. |
| Very High | 10 | Adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity. People with asthma may find they need to use their reliever inhaler more often. | Reduce physical exertion, particularly outdoors, especially if you experience symptoms such as cough or sore throat. |
* Adults and children with heart or lung problems are at greater risk of symptoms. Follow your doctor's usual advice about exercising and managing your condition. It is possible that very sensitive individuals may experience health effects even on Low air pollution days. Anyone experiencing symptoms should follow the guidance provided in the Additional information on the effects of air pollution section.
Daily Air Quality Index
The bandings for the Daily Air Quality Index are detailed in the table below:
| Band | Index | Ozone | Nitrogen Dioxide | Sulphur Dioxide | PM2.5 Particles | PM10 Particles |
|---|---|---|---|---|---|---|
| Running 8 hourly mean | Hourly mean | 15 minute mean | 24 hour mean | 24 hour mean | ||
| µg m−3 | µg m−3 | µg m−3 | µg m−3 | µg m−3 | ||
| Low | 1 | 0-33 | 0-67 | 0-88 | 0-11 | 0-16 |
| 2 | 34-66 | 68-134 | 89-177 | 12-23 | 17-33 | |
| 3 | 67-100 | 135-200 | 178-266 | 24-35 | 34-50 | |
| Moderate | 4 | 101-120 | 201-267 | 267-354 | 36-41 | 51-58 |
| 5 | 121-140 | 268-334 | 355-443 | 42-47 | 59-66 | |
| 6 | 141-160 | 335-400 | 444-532 | 48-53 | 67-75 | |
| High | 7 | 161-187 | 401-467 | 533-710 | 54-58 | 76-83 |
| 8 | 188-213 | 468-534 | 711-887 | 59-64 | 84-91 | |
| 9 | 214-240 | 535-600 | 888-1064 | 65-70 | 92-100 | |
| Very High | 10 | 241 or more | 601 or more | 1065 or more | 71 or more | 101 or more |
What do we mean by air quality?
The air we breathe contains small amounts of trace gases and particles which can be harmful to our health. Pollutants such as sulphur dioxide, nitrogen oxides and particulate matter are routinely released into the atmosphere as a result of the combustion of fossil fuels and industrial processes. Chemical interactions amongst these primary pollutants, under the influence of heat and sunshine, can give rise to additional secondary pollutants, such as ozone. Individually or together, these common pollutants degrade the quality of the air we breathe and an index has been devised to quantify the air quality and its impact on human health. The Air pollution (DAQI) is the standard index defined by Defra for characterising air quality. Air quality can also be degraded by the release of other, less common pollutants, for example during an accidental release of a harmful chemical. This unexpected type of air pollution is not covered by the routine air quality forecast described here.
How do we forecast air quality?
The build-up of all of these pollutants in the atmosphere is determined by the following factors:
- Emissions of pollutants
- Transport and dispersion of pollutants by winds
- Chemical reactions amongst reactive gases and aerosols
- Removal processes, such as rain and deposition on surfaces.
The Met Office weather forecast and climate prediction model has been developed, as part of the UKCA project, to include these processes. The model uses UK and European maps of annual average pollutant emissions to simulate the release of chemical species into the atmosphere. These are then allowed to chemically react according to prescribed reaction rates which depend on factors including the concentration of the species, the temperature and the amount of sunlight. Species are then transported and dispersed within the model according to the winds and the concentrations are re-evaluated. Using the concentrations calculated in this way throughout the forecast period, the Daily Air Quality Index is calculated as an average over prescribed time periods. We have found that our air pollution forecasts can be improved by using recent observations of air quality from across the UK, together with our forecast model to give an adjusted forecast. We therefore use observations from the Automatic Urban and Rural Network (AURN) as part of our forecast system.
How do we check the accuracy of our forecasts?
Defra maintains the AURN network of air quality observation sites which provide measurements of pollutant concentration on an hourly basis across the UK. At the Met Office we use these observations to compare our forecasts against. In this way we are able to continuously monitor our forecast performance and to investigate reasons behind poor forecasts. This might occur, for example, if a new source of air pollution appears which is not accounted for in the annual average emission maps we use. In view of the fact that our model uses average emission maps and has grid boxes which are large compared to the road widths, our forecast does not represent the very localised increases in pollution that one might find close to roads in the urban environment. The forecast represents the background and regional air quality away from these strong sources of pollution.
