Some reservations, however, should be taken when linking rural background measurements of NO2 and PM2.5 to specific cities as in Figure 4.6 and 4.7. Although rural or rural background stations are supposed to spaciously represent larger geographical areas, the distance between a rural station and a city can be so large, that the representativeness of this station for the immediate rural or rural background level for that particular city can be questionable because of eventual regional concentration gradients. The most pronounced examples are e.g. for the city Oulu (Finland), where the distance between the rural station representing the background for Oulu and the city itself is 230 km for the station measuring NO2 and 330 km for the station measuring PM2.5. For Bergen (Norway), the distance to the nearest rural or rural background station is about 280 km SE of Bergen (Birkenes observatoriet, 30 km NE of Kristiansand), to the second nearest it is about 310 km E of Bergen (Hurdal25, 50 km NE of Oslo), and to the third nearest it is about 320 km NE of Bergen (Kårvatn), but none of these were found suitable to represent the rural or rural background for the oceanic climate influenced location of Bergen, which is why Bergen was left without representative rural or rural background measurements in Figure 4.6 and 4.7. A third example is Denmark, where PM2.5 representing rural or rural background only is measured at one station (Risø about 30 km W of København). The PM2.5 measurements at Risø are thus representing all the three selected stations in Denmark i.e. it is the same value for København, Aarhus and Odense rural that is presented in Figure 4.7. Modelling estimates of the regional background PM2.5 concentration levels for Denmark indicate a weak southern to northern gradient with the highest levels in the South. The three selected cities in Denmark are located in the central-south part of the country within a rather limited band not extending more than about 80 km north-south, supporting the assumption that Risø to a reasonable extent, can represent the rural background level of the three selected Danish cities.
In all the selected cities in the five Nordic countries annual NO2 and PM2.5 (see Figure 4.6 and 4.7) are well below the annual limit values (40 μg/m3 and 25 μg/m3, respectively) of the present Air Quality Directive (EU, 2008) in 2021. In relation to the annual limit values in the newly proposed EU Air Quality Directive (EU, 2022) of 20 μg/m3 and 10 μg/m3 for NO2 and PM2.5, respectively, 9 out of 13 traffic stations are exceeding the proposed annual limit value for NO2 and only one for PM2.5. None of the urban or suburban background nor the rural or rural background stations, are exceeding the annual limit values of NO2 and PM2.5 of the newly proposed directive. It should be emphasised here that for each of the selected cities only the one station with the highest concentration measured, is representing that particular city, and especially for traffic sites there often exists more than one station in the same city.
When it comes to the new 2021 WHO guidelines (WHO, 2021) for NO2 all the traffic stations shown with valid measurements have concentrations higher than the guideline levels. The same applies to PM2.5 (except for Reykjavík). For the urban or suburban background stations, 5 out of 12 are exceeding the NO2 guideline levels. For PM2.5, 8 out of the 10 are exceeding the guideline levels. For NO2 on the rural or rural background stations all the stations with measurements are well below the guideline levels. For PM2.5 however on the rural or rural background stations 4 out of 11 with measurements are exceeding the guideline levels. Again, it should be emphasised that for each of the selected cities only the one station with the highest concentration measured, is representing that particular city, and especially for traffic sites there often exists more than one station in the same city.
In general the measurements of NO2 and PM2.5 in 2021 are following the expected concentration levels and the expected pattern with the highest values for the traffic stations and the lowest at rural background with sub-/urban in-between and there is only two exceptions from this: In Trondheim (Norway) where the measurement of PM2.5 at the urban background station shows higher values than the measurement at the traffic station. And in Göteborg where the PM2.5 concentration measured at the rural background station (Råö) is higher than the concentration measured at the traffic station. For both of these cases it is indicated (by the commenting of the text by the representatives of the two countries) that the automatic PM measurement methods used, might play a role.
4.4 General implications of proposed AQ Directive
On October 26, 2022, the European Commission published its proposal for a revised Air Quality Directive (EU, 2022). The proposal for the new directive brings together the current EU Directive, Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe (EU, 2008) and the so-called Fourth Daughter Directive, EU Directive 2004/107/EC of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air (EU, 2004). This section will try to give an overview of the essential changes of the newly proposed Air Quality Directive and its implication for the air quality programs and measuring networks in the Nordic countries in general. To analyze in detail all the implications including e.g. the economic consequences for each of the Nordic countries, will include analysis of e.g. the zone or agglomeration classifications and assessment thresholds for the different pollutants, however, this will be beyond the scope of this analysis. Therefore, only the most essential and general implications that are found to be of common interest for the Nordic countries have been analyzed. Because it is an overview of only the essential changes for the Nordic countries in general, the actual conditions for the air quality program in the single country might deviate due to e.g. the concentration levels of the pollutants, assessment thresholds and number of zones.
Implications for requirements on measurements
General improvements in the air quality in the Nordic countries over the past 10 years have influenced the commitments in relation to the EU air quality directives regarding the fixed measurements of regulated air pollution components that have been significantly reduced. To estimate the level of monitoring in the EU Member States, the measure of the assessment thresholds is used to determine the level of monitoring in the Member States. If the concentration of a pollutant is above the upper assessment threshold, fixed measurements of high quality shall be applied, while at concentrations below the lower assessment threshold it is possible only to use indicative methods (EU, 2004, 2008). With the general improvements in the air quality in the Nordic countries in relation to the present EU air quality directive (EU, 2008) for some pollutants it would in principle be possible only to estimate concentration levels using indicative methods.
In relation to the present EU Air Quality Directive and the general improvements in the air quality in the Nordic countries over the past 10 years, a comprehensive reorganization would be expected to take place of the air monitoring programmes with cheaper methods and fewer measuring points. However, the new proposal for the EU Air Quality Directive radically changes this possibility, since the tightening of the limit values is accompanied by more stringent assessment thresholds used to determine the number of measuring points and the requirements for the measurement methods. At the same time, the system is simplified so that the two previous assessment thresholds (upper and lower assessment thresholds) are replaced by a single assessment threshold.
In addition to the above major changes in the requirements of the new proposal for the air quality directive, there are also several minor adjustments to the main text of the directive and to the many appendices. An example is e.g. when an exceedance of a limit value is calculated by modelling, then one year of fixed high quality measurements shall be carried out (if the area covered by the modelling is not already represented by fixed measurements).
The assessment thresholds establish the minimum level of the extent of measurements of the various air pollution components and the quality of the measurements. If the concentrations are above the assessment threshold, then the AQ Directive specifies the number of measurements to be carried out in the individual zones based on the number of inhabitants living in the zone. If the assessment threshold is exceeded, then fixed measurements with the reference methods specified in the AQ Directive or by equivalent methods need to be carried out. If the concentrations are below the assessment threshold requirements for the measurements are not as strong. In these cases, only indicative measurements or objective estimations are needed.