4. Evaluation of air quality monitoring

A comparison between measurement data from 2021 and the former and new WHO AQG is carried for each of the Nordic countries where the maximum value of any measurement station within the country is compared with the WHO guidelines. This provides an overview of exceedances of the new WHO guidelines in the Nordic countries. Furthermore, it also describes how the exceedances have changed between the former and new WHO guidelines.

Additionally, an analysis is carried out based on available measurements in 2021 from rural background, suburban/urban background and traffic stations in the selected cities and the results are compared with the new WHO guidelines and the proposed EU Air Quality Directive. This analysis gives an indication of the concentration contribution of the cities (the difference between urban background and rural concentrations) and further the contributions of hotspots (the difference between traffic concentrations and urban background concentrations). The latter complements the modelling activities that only include rural and urban background concentrations.

Further, the proposed new European air quality directive is described and the overall implications for the Nordic countries are outlined.

4.1 WHO AQ guidelines and the EU Air Quality Directive

The current EU Directive (EU, 2008) and the 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)), will in the future be merged into one directive, following the adoption of the newly proposed EU Directive on ambient air quality (EU, 2022).

A comparison of the levels in the 2005 and 2021 WHO AQG (WHO, 2006; WHO 2021) with the corresponding limit and target values of the current and the proposed EU Directive on ambient air quality and cleaner air for Europe (AQD) of October 2022 is shown in Table 4.1. The pollutants presented here is limited to particulate matter (PM_2.5 and PM₁₀), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂) and carbon monoxide (CO), which are the pollutants treated by WHO (2021). It should therefore be noticed that pollutants included in the EU Directive 2004/107/EC of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air (EU, 2004), often mentioned as the so-called Fourth Daughter Directive, are not described here. It should also be remarked that limits and targets in relation to protection of vegetation and natural ecosystems are not included either as the focus is solely on air pollutants with the potential of affecting human health.

Table 4.1. Overview of the different concentration levels mentioned in the 2005 and 2021 WHO AQG compared with the corresponding limit and target values of the current directive (2008) and in the October 2022 proposed EU Directive (P2022) on ambient air quality and cleaner air for Europe (AQD). Numbers not marked are simple mean values of the averaging times given. Numbers that are marked with a superscript are explained in the notes below the table.

Pollutant	Averaging time	Unit	WHO AQG	WHO AQG	EU AQD^c1	EU AQD^c2
			2005	2021	2008	P2022
PM_2.5	Annual	µg/m³	10	5	25	10
	24-hour	µg/m³	25^a	15^a	n.a.	25^d
PM₁₀	Annual	µg/m³	20	15	40	20
	24-hour	µg/m³	50^a	45^a	50^e	45^f
O₃	Peak season	µg/m³	n.a.	60^b	n.a.	n.a.
	8-hour	µg/m³	120^a	100^a	120^g	120^h
NO₂	Annual	µg/m³	20	10	40	20
	24-hour	µg/m³	n.a.	25^a	n.a.	50
	1-hour	µg/m³	200	200	200ⁱ	200^j
SO₂	Annual	µg/m³	n.a.	n.a.	n.a.	20
	24-hour	µg/m³	20	40^a	125^k	50^L
	1-hour	µg/m³	n.a.	n.a.	350^m	350ⁿ
	10-minutes	µg/m³	500	500	n.a.	n.a.
CO	24-hour	mg/m³	n.a.	4^a	n.a.	4^o
	8-hour	mg/m³	10	10	10^p	10^p
	1-hour	mg/m³	35	35	n.a.	n.a.
	15-min	mg/m³	100	100	n.a.	n.a.

Notes to the recommended levels in the WHO AQG

^a 99th percentile (i.e. 3–4 exceedance days per year)

^b Average of daily maximum 8-hour mean O₃ concentrations in the six consecutive months with the highest six-month running-average O₃ concentration.

Notes to the limit and target values in the EU Directives on ambient air quality and cleaner air for Europe (AQD) in relation to human health

NB. Except for ozone which are Target values, all other numbers are Limit values.

^c1 EU Directive 2008/50/EC on ambient air quality and cleaner air for Europe (AQD)

^c2 Proposal for a revision of the EU Directives on ambient air quality, 26 October 2022

^d Limit value. 25 μg/m³ not to be exceeded more than 18 times a calendar year

^e Limit value. 50 μg/m³ not to be exceeded more than 35 times a calendar year

^f Limit value. 45 μg/m³ not to be exceeded more than 18 times a calendar year

^g Target value. 120 μg/m³ not to be exceeded on more than 25 days per calendar year averaged over three years

^h Target value. 120 μg/m³ not to be exceeded on more than 18 days per calendar year averaged over three years

ⁱ Limit value. 200 μg/m³ not to be exceeded more than 18 times a calendar year

^j Limit value. 200 μg/m³ not to be exceeded more than 1 time a calendar year

^k Limit value. 125 μg/m³ not to be exceeded more than 3 times a calendar year

^L Limit value. 50 μg/m³ not to be exceeded more than 18 times a calendar year

^m Limit value. 350 μg/m³ not to be exceeded more than 24 times a calendar year

ⁿ Limit value. 350 μg/m³ not to be exceeded more than 1 time a calendar year

^o Limit value. 4 mg/m³ not to be exceeded more than 18 times a calendar year

^p Limit value. Maximum daily eight hour mean

General comments to the WHO AQG

The 2005 WHO AQG mentions 12 parameters in total and the 2021 AQG mentions 15 parameters. The recommended concentration levels in the WHO AQG as can be seen in Table 4.1 have generally been reduced considerably from the WHO 2005 to the WHO 2021. The perhaps most pronounced differences are PM_2.5 annual average and NO₂ annual average where the recommended levels have been decreased to 50% of the former levels.

Of the in total 15 parameters, 6 have had their concentration levels reduced without changing the statistical calculation of the parameter, that is PM₁₀ and PM_2.5 annual, PM₁₀ and PM_2.5 24-hours, ozone 8-hours, and NO₂ annual.

Only 1 out of the 15 parameters have had the statistical calculation of the parameter changed, that is SO₂ 24-hour where the calculation has changed from a simple average to the 99^th percentile.

Out of the 15 parameters, 5 remain unchanged that is NO₂1-hour, SO₂10-min., CO 8-hour, CO 1-hour and CO 15-min.

Out of the 15 parameters in the WHO 2021 AQG, 3 new parameters have been introduced, that is ozone peak season, NO₂24-hour, and CO24-hour.

When comparing the WHO AQG levels and the EU AQD values it should be noted that there is not one to one correspondence from the WHO AQG to the EU AQ Directive values and the statistical calculation of the concentration levels / values are different in most cases.

General comments to the proposed EU Air Quality Directive

In the proposal for the new Air Quality Directive (EU, 2022) a tightening of the current requirements for the exposure concentration (also known as AEI – Average Exposure Indicator) of PM_2.5 is suggested and similar requirements for the exposure concentration of NO₂ are introduced. The new proposal to reduce the exposure concentration for PM_2.5 states that the exposure concentration should decrease by 25% over a ten-year period. The reduction requirement will apply from 2030 and every year thereafter. For example, this means that the exposure concentration in 2030 (average of the three years 2028–2030) should be 25% lower than measured in 2020 (average of 2018–2020). The reduction requirement applies until the average exposure concentration is in line with the proposed exposure concentration target set at 5 μg/m³ for PM_2.5, i.e. similar to the air quality guideline established by WHO (WHO, 2021). If for example the mean exposure concentration for PM_2.5 was 10 μg/m³ in 2020, it should thus be reduced to 7.5 μg/m³ by 2030, and thereafter until the target of 5 μg/m³ is achieved. For NO₂, completely new requirements related to exposure concentration have been suggested in the proposal for a revised Air Quality Directive. As for PM_2.5, it is proposed that the exposure concentration for NO₂ should decrease by 25% over a ten-year period. The reduction requirement will apply from 2030 until the proposed exposure concentration target is reached. For NO₂, a target of 10 μg/m³ has been proposed, i.e. similar to the air quality guideline established by WHO (WHO, 2021).

4.2 Present air quality in Nordic countries and WHO guidelines

In this section, measurements from 2021 in the Nordic countries are compared with the former 2005 WHO AQG WHO (2006) and the new WHO AQG for 2021 (WHO, 2021).

Index values representing the percentage of annual concentration measured levels for 2021 with respect to the 2005 WHO AQG (WHO, 2006) are compared with corresponding index values with respect to the 2021 WHO AQG (WHO, 2021). A set of two figures is shown per country so the differences between the two sets of WHO guidelines are displayed for each of the five Nordic countries.

General comments to the measurement data

The source of the data is the database at EEA - European Air Quality Portal where annual statistics of air quality values originating both from AirBase and AQ e-Reporting can be extracted. The European Air Quality Portal contains only quality-approved data reported to the EU. Only datasets with a data coverage of more than 85% has been extracted following the general recommendations for reporting air quality data in the EU.

The year 2021 is the latest year with full data reporting and it has therefore been chosen as the year for comparing the two different WHO AQG sets described respectively in WHO (2006) and WHO (2021). The year 2021 can be regarded as a measuring year where the societies after the Covid-19 lock-down have returned to more normal conditions compared with the preceding year 2020 which could be believed to have been affected much more by the Covid-19 lock-down. The first one to two months of 2021 were still, however, affected e.g. by reduced traffic. For the year 2022 the deadline for the EU data reporting is in the autumn 2023 which means that 2022 is not a possibility to use either. This leaves the year 2021 perhaps as the best compromise compared with going back to before the Covid-19 lock-down e.g. to 2019 where air pollution levels would be less relevant than 2021.

For each of the pollutants listed in Table 4.1 under the WHO columns the highest values fulfilling the data coverage criteria of 85% has been selected for each country. As an example, the highest value for PM_2.5 annual average is simply the highest average value measured at all the stations in the country in question in 2021 regardless of station type and can e.g. also include the site category Industrial. These stations can also be outside the selected cities. Another example is the highest value for PM_2.5 24-hour average, which is defined as the highest 99th percentile (i.e. 3–4 exceedance days are allowed per year) measured at all the stations in the country in question in 2021 regardless of station type. The index values presented in the following figures are thus displaying the highest values for the year 2021 for the parameters according to the WHO AQG statistics but for the short-term exposure, it is not necessarily the same as an exceedance of the WHO AQG levels. The 99th percentile short-term exposures are representing index values in relation to the highest calculated 99th percentile value alone, but strictly speaking there is only an exceedance of the WHO AQG levels, when there are more than 3–4 exceedance days of the 99th percentile per year.

In the 10 figures for the five Nordic countries, all the axes are kept at the same scale for the sake of comparison although index values vary a lot. The first figure for each country is indexing the 2021 measurements according to the WHO 2005 guideline levels and the second figure is indexing the 2021 measurements according to the WHO 2021 guideline levels. Index values of very short averaging times for SO₂ (10 min.) and CO (15 min.) the WHO AQG concentrations levels have been omitted due to lack of reporting these measurements. The statistical definitions of the WHO AQG concentration levels when these differ from simple average values will appear from the notes following Table 4.1. WHO guideline values for O₃ 8-hour max peak season, NO₂ 24-hour max, and CO 24-hour max were defined in the 2021 WHO AQG but not in the 2005 version. This is the reason why these data are not presented in the WHO 2005 figures but are presented in the WHO 2021 figures.

Figures 4.1.-4.5 present the results for the Nordic countries.

Sweden

In Figure 4.1 is the index values in relation to the 2005 and 2021 WHO AQG for measurements of 2021 in Sweden.

Figure 4.1. Index values in relation to 2005 and 2021 WHO AQG) for concentration levels for 2021 measurements in Sweden. The index value for each parameter has been calculated from the highest measured concentration with a data coverage > 85%. It should be pointed out that the 99th percentile short-term exposures are representing index values in relation to the highest calculated 99th percentile value alone, but strictly speaking there is only an exceedance of the WHO AQG levels, when there are more than for 3–4 exceedance days of the 99th percentile per year.

The relatively high levels of SO₂ were due to emissions from sulphite pulp production at an industrial plant. This was discontinued at the end of 2021 and concentrations during 2022 have been much lower.

Norway

In Figure 4.2 is the index values in relation to the 2005 and 2021 WHO AQG for measurements of 2021 in Norway.

Figure 4.2. Index values in relation to 2005 (top panel) and 2021 (bottom panel) WHO AQG for concentration levels for 2021 measurements in Norway. The index value for each parameter has been calculated from the highest measured concentration with a data coverage > 85%. It should be pointed out that the 99th percentile short-term exposures are representing index values in relation to the highest calculated 99th percentile value alone, but strictly speaking there is only an exceedance of the WHO AQG levels, when there are more than for 3–4 exceedance days of the 99th percentile per year.

Iceland

In Figure 4.3 is the index values in relation to the 2005 and 2021 WHO AQG for measurements of 2021 in Iceland.

Data for ozone and carbon monoxide have according to the EEA - European Air Quality Portal seemingly not been reported for Iceland for 2021 which is the reason why these two parameters cannot be found in the figures for Ice-land. The high values for SO₂ especially for 2005 are due to volcanic eruptions that is a natural source of SO₂ therefore fluctuating from year to year.

Figure 4.3. Index values in relation to 2005 (top panel) and 2021 (bottom panel) WHO AQGAQG (AQG) for concentration levels for 2021 measurements in Iceland. The index value for each parameter has been calculated from the highest measured concentration with a data coverage > 85%. Ozone and carbon monoxide is not reported for Iceland 2021. It should be pointed out that the 99th percentile short-term exposures are representing index values in relation to the highest calculated 99th percentile value alone, but strictly speaking there is only an exceedance of the WHO AQG levels, when there are more than for 3–4 exceedance days of the 99th percentile per year.

Finland

In Figure 4.4 is the index values in relation to the 2005 and 2021 WHO AQG for measurements of 2021 in Finland. The urban CO measurements have been ceased due to concentration levels well below the lower assessment threshold of European legislation (Directive 2008/50/EC). In 2021, Finland used indicative reporting for CO based on satellite measurements. Based on this the CO concentrations are well below both 2005 and 2021 WHO guideline levels (pers.com, K. Kyllönen, FMI).

Figure 4.4. Index values in relation to 2005 (top panel) and 2021 (bottom panel) WHO AQG for concentration levels for 2021 measurements in Finland. The index value for each parameter has been calculated from the highest measured concentration with a data coverage > 85%. Carbon monoxide is not reported for Finland 2021. It should be pointed out that the 99th percentile short-term exposures are representing index values in relation to the highest calculated 99th percentile value alone, but strictly speaking there is only an exceedance of the WHO AQG levels, when there are more than for 3–4 exceedance days of the 99th percentile per year.

Denmark

In Figure 4.5 is the index values in relation to the 2005 and 2021 WHO AQG for measurements of 2021 in Denmark.

Figure 4.5. Index values in relation to 2005 (top panel) and 2021 (bottom panel) WHO AQG) for concentration levels for 2021 measurements in Denmark. The index value for each parameter has been calculated from the highest measured concentration with a data coverage > 85%. It should be pointed out that the 99th percentile short-term exposures are representing index values in relation to the highest calculated 99th percentile value alone, but strictly speaking there is only an exceedance of the WHO AQG levels, when there are more than for 3–4 exceedance days of the 99th percentile per year.

All Nordic countries

The health impacts of air pollution are by far the largest for long-term exposure to PM_2.5 then followed by NO₂, both as annual means, and then exposure to elevated levels of ozone. All five Nordic countries exceed the 2021 WHO AQG for annual means of PM_2.5 and NO₂, and ozone (8h peak season) (except Iceland with no data) based on highest measured values in 2021.

4.3 NO₂ and PM_2.5 in the selected Nordic cities in 2021

Measurements of annual average concentrations of NO₂ and PM_2.5 for 2021 for the selected cities in the five Nordic countries in relation to the 2022 proposed EU Air Quality Directive (EU, 2022) and the 2021 WHO Guidelines (WHO, 2021), are presented in the following. It should be noted that for each of the selected cities only the one station with the highest concentration measured, is representing that particular city. The three selected cities for each of the five Nordic countries have been mentioned in chapter 2 but for the sake of completeness they are given here as well. For Iceland, only one city has been selected.

Sweden: Stockholm, Göteborg and Malmö;
Denmark: København, Aarhus and Odense;
Finland: Helsinki, Tampere and Oulu;
Norway: Oslo, Bergen and Trondheim;
Iceland: Greater Reykjavík.

For each of the selected Nordic cities, the highest measured concentration levels of NO₂ and PM_2.5 have been found for each of the three site categories: A) Traffic, B) Urban-/suburban background, and C) rural background and are presented in Figure 4.6 and 4.7.

Traffic: Urban traffic stations or street stations (shortened in the figure to ‘traffic’). Urban/suburban background: Urban background and suburban stations. No distinction has in this connection been made between these two categories (shortened in the figure to ‘sub/urb’). Rural and rural background: Rural and rural background stations. No distinction in this connection have been made between these two categories (shortened in the figure to ‘rural’). It should be noted that no industrial sites are included in this section because the focus is to complement the modeling data in the other chapters of the above mentioned three site categories with actual measurements.

The source of the data is as in the above, the EEA database, European Air Quality Portal, where annual statistics of air quality values originating both from AirBase and AQ e-Reporting can be extracted. The European Air Quality Portal contains only quality-approved data reported to the EU. Only datasets with a data coverage of more than 85% have been extracted following the general recommendations for reporting air quality data in the EU.

Figure 4.6. Highest measured annual average NO₂ concentrations for 2021 fulfilling the data coverage criteria of 85% for each of the selected cities for each category of measuring station in relation to the WHO AQG) concentration levels for 2021 (10 µg/m³) and in relation to the suggested limit value (20 µg/m³) in the newly proposed EU Directive (EU, 2022). For the numbers used and comments to these, see Appendix 3. It should also be noticed that rural background stations are not necessarily located within the immediate vicinity of the city it is supposed to represent, see text and Appendix 3.

Figure 4.7. Highest measured annual average PM_2.5 concentrations for 2021 fulfilling the data coverage criteria of 85% for each of the selected cities for each category of measuring station in relation to the WHO AQG concentration levels for 2021 (5 µg/m³) and in relation to the suggested limit value (10 µg/m³) in the newly proposed EU Directive (EU, 2022). Dashed red line: Proposed EU AQD limit value; Dashed black line: 2021 WHO AQG concentration level. For the numbers used and comments to these, see Appendix 3. It should also be noticed that rural background stations are not necessarily located within the immediate vicinity of city it is supposed to represent, see text and Appendix 3.

Some reservations, however, should be taken when linking rural background measurements of NO₂ and PM_2.5to 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 PM_2.5. 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 PM_2.5 representing rural or rural background only is measured at one station (Risø about 30 km W of København). The PM_2.5 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 PM_2.5 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 PM_2.5 (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 PM_2.5, respectively, 9 out of 13 traffic stations are exceeding the proposed annual limit value for NO₂ and only one for PM_2.5. None of the urban or suburban background nor the rural or rural background stations, are exceeding the annual limit values of NO₂ and PM_2.5 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 PM_2.5 (except for Reykjavík). For the urban or suburban background stations, 5 out of 12 are exceeding the NO₂ guideline levels. For PM_2.5, 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 PM_2.5 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 PM_2.5 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 PM_2.5 at the urban background station shows higher values than the measurement at the traffic station. And in Göteborg where the PM_2.5 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.

In cases where concentrations are above the assessment threshold, there is still the possibility of reducing the number of fixed measurements that should be carried out by the reference methods or by equivalent methods to the half, if the fixed measurements are supplemented by other methods. The new proposal for the air quality directive sets out four conditions to be met, of which one tightening is of particular importance: “The number of indicative measurements shall be the same as the number of fixed measurements, which they replace, and the indicative measurements shall have a duration of at least two months per calendar year" (EU, 2022, Article 9(3)). This is a significant tightening in relation to the current air quality directive (EU, 2008), which does not require one-to-one replacement of fixed measurements with indicative measurements, and this is of great importance for the cost of the measurement program in question.

Requirements for the establishment of monitoring supersites

The new proposal for the Air Quality Directive requires the establishment of supersites in all EU Member States with the aim of increasing knowledge about particle pollution at EU level. For Denmark as an example, this means that a supersite needs to be established at an urban background site and at a rural background site. Supersites require the measurement of a large number of new particle components, of which the requirement to measure the oxidative potential of PM is something completely new in the context of air quality monitoring. The background for the requirement to measure PM's oxidative potential is that the latest research indicates that PM's oxidative potential can be a better measure of the harmful effect of particle pollution than the particle mass (Gao et al., 2020). There are many different types of measurement methods for measuring the oxidative potential of PM and the proposed new Air Quality Directive does not specify how it should be measured. Another new feature is that measurements of total deposition of arsenic, cadmium, mercury, nickel, benzo(a)pyrene and selected polycyclic aromatic hydrocarbons (PAHs) shall in the example of Denmark be carried out at an urban background measuring station as well. In the Danish example, this type of measurement so far has only been done at a rural background station. In connection with the deposition measurements, the wording around the deposition measurements has been tightened, as "bulk deposition" has been sharpened to "total deposition" (EU, 2022). This may have implications for how the measurements of these components are carried out in each country.

Requirements for public information on actual air quality

The proposal for a new air quality directive imposes significantly stricter requirements on information on current air quality including obligatory hourly updates. However, the proposal is not entirely precise in all respects. The text of the directive itself states that informing the public about current air quality should be provided for all regulated air pollution components in outdoor air (EU, 2022; paragraph 35). This could e.g. include information of the public on air quality of benzo(a)pyrene or cadmium, which would not be possible to carry out on an hourly basis. In the revised Annex IX to the Directive it is required only that information (on an hourly up-date) should be provided on current air quality levels for PM_2.5, PM₁₀, nitrogen dioxide, ozone, sulphur dioxide, and carbon monoxide. On the other hand, there is a requirement that there must be hourly up-date information on air quality at least for the minimum number of required measuring points indicated in Annex III (EU, 2022).

Requirements for the establishment of Air Quality Index

In the proposed directive it is stated that: Member States shall establish an air quality index covering sulphur dioxide, nitrogen dioxide, particulate matter (PM₁₀ and PM_2.5) and ozone, and make it available through a public source providing an hourly update. The air quality index shall consider the recommendations by the WHO and build on the air quality indices at European scale provided by the European Environmental Agency.

Monitoring of ultrafine particles

The proposal for a new Air Quality Directive requires measurements of ultrafine particles (UFP) and on the size distribution of ultrafine particles, but there are not defined limit values, target values or similar other regulation included in the proposal (EU, 2022). In the previous directive, there were no requirements for measuring ultrafine particles (EU, 2008). In the new proposal for the Air Quality Directive there are requirements in connection with supersites and there is a requirement for measurements in areas where high concentrations of ultrafine particles can be expected. The purpose of the latter is to obtain more information on the concentrations of ultrafine particles in areas which may be affected by emissions from for example airports, ports, road traffic, industrial sites or domestic heating (EU, 2022). The new air quality directive proposal requires at least one fixed location measurements of ultrafine particles (EU, 2022). The proposal for a new Air Quality Directive calls for cooperation with ACTRIS in relation to the implementation of the measurements (EU, 2022). ACTRIS has requirements on measuring size range that the instruments should be able to measure e.g. particles with diameters up to 800 nm, which might be different from the measuring range of the instruments already in use in the networks.

Requirement for air quality modelling

The new proposal for the Air Quality Directive includes model calculations as an obligatory element where concentrations of pollutants exceed limit values, or target values. There are also a large number of requirements in relation to the modelling calculations (EU, 2022, Annex IV, Section F): "

(a) that the designated reference institutions participate in the European network of air quality modelling set up by the Commission's Joint Research Centre;
that best practices in air quality modelling identified by the network through scientific consensus are adopted in relevant applications of air quality modelling for the purposes of fulfilling legal requirements pursuant to Union legislation, without prejudice to model adaptations necessitated by singular circumstances;
that the quality of relevant applications of air quality modelling is periodically checked and improved through intercomparison exercises organised by the Commission’s Joint Research Centre;
that the European network of air quality modelling be responsible for the periodic review, at least every 5 years, of the ratio of modelling uncertainties listed in the final columns of Tables 1 and 2 of this Annex and subsequent proposal of any necessary changes to the Commission.”

In addition to this, there is also a requirement to implement model calculations in cases where the limit values are exceeded in a zone. Also, it is proposed that, in connection with the notification of the public where there are episodes of high concentrations of ozone, nitrogen dioxide, PM_2.5 and PM₁₀, short-term air quality forecasts shall be carried out. If the prognosis indicates a risk of exceeding the information threshold, the population should be notified of this. This is supposedly already being done in the Nordic countries, but this will need to be extended to include the proposed information thresholds for PM_2.5 and PM₁₀.

New requirements for average exposure concentrations, AEI

In the proposal for the new Air Quality Directive a strengthening of the requirements for reducing the average exposure indicator concentration for PM_2.5 (AEI) is introduced together with similar requirements for NO₂ (EU, 2022). The new air quality directive appears to impose the same requirements on the number of urban background measuring stations where the average exposure concentration is to be measured.

Increased requirements for documentation of spatial representativeness

The wording regarding documentation of the monitoring carried out has generally been tightened. An example of this is that there are comprehensive requirements for the documentation of the geographical representativeness of the measurements at the measuring stations, where, among other things, there are requirements for the use of model calculations.

Increased requirements for documentation of monitoring network

There are extensive requirements for documentation of the design of the measurement program and the network of measuring stations. Annex IV, Section D (EU, 2022) sets out following: “

D. Site selection, its review and documentation

The competent authorities responsible for air quality assessment shall for all zones fully document the site-selection procedures and record information to support the network design and choice of location for all monitoring sites. The design of the monitoring network shall be supported at least by either modelling or indicative measurements.
The documentation shall include the location of the sampling points through spatial coordinates, detailed maps and shall include information on the spatial representativeness of all sampling points. “

The above quotation indicates the first two requirements out of 10 listed in Annex IV, section D. They illustrate the tightening of the documentation requirements set out in the proposal for the new air quality directive.