Inhoud
Legend
Explanation of the legend
The measurements which are recorded every hour and shown on the internet are divided into bands according to quality. The air quality in the Netherlands is never so bad that it constitutes an acute health threat. Were that ever to be the case, the public would be informed. Legislation contains limits for various substances above which steps must be taken. Even if there is no acute threat, the air pollution can still be too high in the long term. In order to assess this, the annual mean measurement is observed. The annual mean value is the most important in assessing air quality. It is published annually in the Air in Figures report
The measurements vary from hour to hour. The variation is rather greater for some substances than for others. The 1-hour mean depends, among other things, on the time of year (usually lower in the summer than in the winter) and the time of day. In the morning and during the rush hour the concentrations are often higher than in the middle of the day. Based on measurements over many years, DCMR knows approximately what the 1-hour mean measurements, under average circumstances, will be at any given moment. Based on this data and the requirements which legislation imposes on the annual mean concentrations, the 1-hour values are given a colour.
4 colours may appear on the graphs, i.e.:
| Very high | |
| High | |
| Moderate | |
| Low |
Very high
Generally speaking, 1-hour measurements in the "very poor"; band do not occur. Very rarely, such as when a major incident occurs or there are prolonged exceptional weather conditions, now and again there may be a very poor hour.
High
A 1-hour mean may now and again be "high"; without this being alarming as long as the measurements quickly fall again. High concentrations which persist for hours at a stretch indicate severe air pollution. This may occur during a major incident or extreme weather conditions.
Moderate
The 1-hour mean measurements will frequently be "moderate";. At the sampling points in the Rijnmond region this is often the case: after all, the sampling points are not located in the least polluted areas. If the measurements are permanently "moderate"; the standards for the annual mean will be exceeded. Although the air quality during a "moderate"; hour is not alarming in the short term, in the long term this would represent an excessive level of air pollution
Good
The measurement during this hour is better than expected. If concentrations mainly fluctuate in the "low"; zone this means that it will also be possible to meet the standards for the annual mean.