ec7fa8a17afb4ed09668ca3cba134dcd IAQ- Air Quality Index

 IQA - Air quality index



What is IQA


Air pollution is an important risk factor for human health. In order to communicate to the population in a simple and immediate way the quality level of the air they breathe, ARPAE Emilia-Romagna has decided to define an air quality index (IQA) that summarizes the overall state of atmospheric pollution

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The choice of pollutants


The pollutants usually included in the definition of air quality indices are those that have short-term effects, such as carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), particulate matter (PTS, PM10 or PM2.5 depending on the size). This choice, albeit questionable, arises from the fact that the indices are formulated with a view to giving daily indications to the population to avoid precisely these types of effects (generally of a cardiovascular or respiratory type).

In the calculation of the index for Emilia-Romagna it was decided to include only PM10, NO2 and O3 which among the pollutants with short-term effects are those that present the greatest problems in our region. On the other hand, CO and SO2 have been excluded, which have experienced a drastic decrease in their concentrations in recent decades, so much so that they are now firmly and well below the legal limits.

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How it is calculated


Once the pollutants have been defined, the main steps in building an air quality index:

1. Construction of a dimensionless scale (sub-index) for each pollutant.

2. Construction of a single synthetic index, starting from the sub-indices defined for each pollutant.

The sub-index for each pollutant is defined by dividing the measured or expected concentration of the pollutant considered by the limit set by the legislation for the defense of health (in the case of several limits, the lowest is chosen) and multiplying by 100. The table below shows the limits that were used for the calculation of the three sub-indices.

The next step in the construction of the index is the definition of the methods of aggregation of the various sub-indexes. In line with the approach adopted by most of the indices used internationally, it was decided to define the value of the synthetic index as the value of the worst sub-index.

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The classes


The values ​​of the index have been grouped into five classes with a uniform interval width equal to 50. The adoption of a small number of classes is linked to the accuracy achievable by the forecasting models.

The following table shows the classes identified with the corresponding ranges of numerical values ​​and chromatisms.

Therefore, an orange, red or purple color (corresponding to an index value greater than 100) indicates that at least one of the pollutants exceeds the legal limit.
IQA - Air quality index What is IQA Air pollution is an important risk factor for human health. In order to communicate to the population in a simple and immediate way the quality level of the air they breathe, ARPAE Emilia-Romagna has decided to define an air quality index (IQA) that summarizes the overall state of atmospheric pollution _____________________________________________________________________________ The choice of pollutants The pollutants usually included in the definition of air quality indices are those that have short-term effects, such as carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), particulate matter (PTS, PM10 or PM2.5 depending on the size). This choice, albeit questionable, arises from the fact that the indices are formulated with a view to giving daily indications to the population to avoid precisely these types of effects (generally of a cardiovascular or respiratory type). In the calculation of the index for Emilia-Romagna it was decided to include only PM10, NO2 and O3 which among the pollutants with short-term effects are those that present the greatest problems in our region. On the other hand, CO and SO2 have been excluded, which have experienced a drastic decrease in their concentrations in recent decades, so much so that they are now firmly and well below the legal limits. _____________________________________________________________________________ How it is calculated Once the pollutants have been defined, the main steps in building an air quality index: 1. Construction of a dimensionless scale (sub-index) for each pollutant. 2. Construction of a single synthetic index, starting from the sub-indices defined for each pollutant. The sub-index for each pollutant is defined by dividing the measured or expected concentration of the pollutant considered by the limit set by the legislation for the defense of health (in the case of several limits, the lowest is chosen) and multiplying by 100. The table below shows the limits that were used for the calculation of the three sub-indices. The next step in the construction of the index is the definition of the methods of aggregation of the various sub-indexes. In line with the approach adopted by most of the indices used internationally, it was decided to define the value of the synthetic index as the value of the worst sub-index. _____________________________________________________________________________ The classes The values ​​of the index have been grouped into five classes with a uniform interval width equal to 50. The adoption of a small number of classes is linked to the accuracy achievable by the forecasting models. The following table shows the classes identified with the corresponding ranges of numerical values ​​and chromatisms. Therefore, an orange, red or purple color (corresponding to an index value greater than 100) indicates that at least one of the pollutants exceeds the legal limit. _____________________________________________________________________________ The value of the index is higher than 100 in about 30% of the days (remember that the value of the index is higher than 100 if at least one of the pollutants considered in the calculation exceeds the legal limit). About 60% of the overall exceedances are caused by PM10; O3 is responsible for the remaining 40%. NO2 is sometimes the pollutant with the worst sub-index, but it never is if the limits are exceeded. The contribution of the various pollutants to the calculation of the index is closely linked to the season. In summer, ozone is responsible for most of the exceedances (approximately 90%), while in winter the only responsible for exceedances is PM10. _____________________________________________________________________________ The health significance of the index To construct an air quality index on a scientific basis, it would be necessary to know the health risk associated with every possible combination of pollutant levels. The current state of knowledge in the epidemiological field is, however, quite far from this objective: statistical and toxicological difficulties in fact make it difficult to know the effect of both individual pollutants and the various combinations of different pollutants. The number and definition of the index classes are determined by communicative needs rather than by epidemiological or toxicological reasons. In fact, literature has not identified a no-effect threshold for any pollutant, nor concentration ranges within which specific health effects occur. Therefore, it was decided to communicate the state of air quality with a criticality scale that reflects a health risk proportional to the levels of pollution, without however associating specific advice with the levels themselves.




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The value of the index is higher than 100 in about 30% of the days (remember that the value of the index is higher than 100 if at least one of the pollutants considered in the calculation exceeds the legal limit).

About 60% of the overall exceedances are caused by PM10; O3 is responsible for the remaining 40%. NO2 is sometimes the pollutant with the worst sub-index, but it never is if the limits are exceeded.

The contribution of the various pollutants to the calculation of the index is closely linked to the season. In summer, ozone is responsible for most of the exceedances (approximately 90%), while in winter the only responsible for exceedances is PM10.


_____________________________________________________________________________



The health significance of the index


To construct an air quality index on a scientific basis, it would be necessary to know the health risk associated with every possible combination of pollutant levels. The current state of knowledge in the epidemiological field is, however, quite far from this objective: statistical and toxicological difficulties in fact make it difficult to know the effect of both individual pollutants and the various combinations of different pollutants.

The number and definition of the index classes are determined by communicative needs rather than by epidemiological or toxicological reasons. In fact, literature has not identified a no-effect threshold for any pollutant, nor concentration ranges within which specific health effects occur. Therefore, it was decided to communicate the state of air quality with a criticality scale that reflects a health risk proportional to the levels of pollution, without however associating specific advice with the levels themselves.
IQA - Air quality index What is IQA Air pollution is an important risk factor for human health. In order to communicate to the population in a simple and immediate way the quality level of the air they breathe, ARPAE Emilia-Romagna has decided to define an air quality index (IQA) that summarizes the overall state of atmospheric pollution _____________________________________________________________________________ The choice of pollutants The pollutants usually included in the definition of air quality indices are those that have short-term effects, such as carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), particulate matter (PTS, PM10 or PM2.5 depending on the size). This choice, albeit questionable, arises from the fact that the indices are formulated with a view to giving daily indications to the population to avoid precisely these types of effects (generally of a cardiovascular or respiratory type). In the calculation of the index for Emilia-Romagna it was decided to include only PM10, NO2 and O3 which among the pollutants with short-term effects are those that present the greatest problems in our region. On the other hand, CO and SO2 have been excluded, which have experienced a drastic decrease in their concentrations in recent decades, so much so that they are now firmly and well below the legal limits. _____________________________________________________________________________ How it is calculated Once the pollutants have been defined, the main steps in building an air quality index: 1. Construction of a dimensionless scale (sub-index) for each pollutant. 2. Construction of a single synthetic index, starting from the sub-indices defined for each pollutant. The sub-index for each pollutant is defined by dividing the measured or expected concentration of the pollutant considered by the limit set by the legislation for the defense of health (in the case of several limits, the lowest is chosen) and multiplying by 100. The table below shows the limits that were used for the calculation of the three sub-indices. The next step in the construction of the index is the definition of the methods of aggregation of the various sub-indexes. In line with the approach adopted by most of the indices used internationally, it was decided to define the value of the synthetic index as the value of the worst sub-index. _____________________________________________________________________________ The classes The values ​​of the index have been grouped into five classes with a uniform interval width equal to 50. The adoption of a small number of classes is linked to the accuracy achievable by the forecasting models. The following table shows the classes identified with the corresponding ranges of numerical values ​​and chromatisms. Therefore, an orange, red or purple color (corresponding to an index value greater than 100) indicates that at least one of the pollutants exceeds the legal limit. _____________________________________________________________________________ The value of the index is higher than 100 in about 30% of the days (remember that the value of the index is higher than 100 if at least one of the pollutants considered in the calculation exceeds the legal limit). About 60% of the overall exceedances are caused by PM10; O3 is responsible for the remaining 40%. NO2 is sometimes the pollutant with the worst sub-index, but it never is if the limits are exceeded. The contribution of the various pollutants to the calculation of the index is closely linked to the season. In summer, ozone is responsible for most of the exceedances (approximately 90%), while in winter the only responsible for exceedances is PM10. _____________________________________________________________________________ The health significance of the index To construct an air quality index on a scientific basis, it would be necessary to know the health risk associated with every possible combination of pollutant levels. The current state of knowledge in the epidemiological field is, however, quite far from this objective: statistical and toxicological difficulties in fact make it difficult to know the effect of both individual pollutants and the various combinations of different pollutants. The number and definition of the index classes are determined by communicative needs rather than by epidemiological or toxicological reasons. In fact, literature has not identified a no-effect threshold for any pollutant, nor concentration ranges within which specific health effects occur. Therefore, it was decided to communicate the state of air quality with a criticality scale that reflects a health risk proportional to the levels of pollution, without however associating specific advice with the levels themselves.
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