Panel 1
Giorgio Cattani, Mariacarmela Cusano, Alessandro Di Menno di Bucchianico, Raffaela Gaddi, Alessandra Gaeta, Giuseppe Gandolfo, Gianluca Leone
The indicator is based on the ozone concentration data in the atmosphere measured during 2024, in monitoring stations distributed across the national territory, collected and archived in ISPRA in the InfoAria database, in accordance with the provisions of Directive 2008/50/EC (and the legislative decree transposing Legislative Decree 155/2010) and Decision 2011/850/EU. The monitoring stations that measured and for which O. Data were transmitted 3 there are 348., of which those with sufficient time coverage for the verification of the threshold values and the long-term objective for the protection of human health are 331. The suburban, rural and rural background stations that respect the minimum percentage required for the calculation of the long-term objective for the protection of vegetation (AOT40v) are 158. The long-term objective for the protection of human health (OLT) was exceeded in almost all the stations: 83.4%. The percentage of stations where the OLT was exceeded for more than 25 days was 43.5%. The information threshold for health protection was exceeded in 17.5% of the stations while the alarm threshold was exceeded in only 1 station. The WHO reference value, equal to 100 µg/m³ as the 99th percentile, is exceeded in 310 stations (equal to 94% of the stations with sufficient temporal coverage). The long-term objective for vegetation protection (AOT40v) was exceeded in almost all stations (92.4%).
Tropospheric ozone is a secondary pollutant that forms through photochemical processes in the presence of primary pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). It is the main representative of the complex mixture of substances called "photochemical smog" which forms in the lower layers of the atmosphere as a result of the aforementioned processes. Photochemical pollution, as well as being local, is a transboundary phenomenon that occurs on large spatial scales; consequently the levels found in a certain area are not always exclusively attributable to emission sources located near the area itself, but the most important contribution can come from the surrounding areas. The highest ozone concentrations are recorded in the hottest months of the year and in the hours of maximum solar radiation. In urban areas, ozone is formed and transformed very quickly and with a very complex behavior that is different from that observed for other pollutants. The main sources of emission of ozone precursor compounds are: road transport, civil heating and energy production.
The indicator was developed on the basis of the ozone concentration data in the atmosphere, measured in monitoring stations distributed throughout the national territory, collected and archived in ISPRA, in the InfoAria database in accordance with the provisions of Decision 2011/850/EU. In addition to the parameters for a comparison with the information and alarm threshold values, with the long-term objective values for the protection of human health and vegetation established by the reference legislation (Legislative Decree 155/2010) and with the reference values established by the WHO for the protection of human health (WHO-AQG, 2021), average, 5°, 25°, 50°, 75°, 95° and 99.8th percentile and maximum of the hourly average values.
Provide information on the state of air quality through the statistical parameters calculated from the ozone concentration data in ambient air, the verification of compliance with the limit values established by the legislation and the comparison with the reference values established by the WHO.
- 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.
- Legislative Decree 155/2010 - Legislative Decree 13 August 2010, n. 155 Implementation of Directive 2008/50/EC relating to ambient air quality and cleaner air in Europe (Official Gazette, no. 216 of 09/15/2010 – ord. Suppl. No. 217 – in force from 09/30/2010)
Decision 2011/850/EU: Commission Implementing Decision of 12 December 2011 laying down provisions for the implementation of Directives 2004/107/EC and 2008/50/EC of the European Parliament and of the Council as regards the mutual exchange and communication of information on ambient air quality. The objective of Directive 2008/50/EC is to allow the assessment of ambient air quality on a common basis, to obtain information on the state of air quality in order to combat air pollution, to ensure the public availability of information and to promote cooperation between Member States.
Legislative Decree 155/2010, which implements the aforementioned directive at a national level, also has the objective of allowing autonomous regions and provinces to evaluate and manage ambient air quality. The limit values of Legislative Decree 155/2010 represent the ambient air quality objectives to be pursued to avoid, prevent and reduce harmful effects on human health and the environment. The WHO reference values represent a guide to follow in reducing the impact of air pollution on human health. The information and alarm threshold values, objectives and long-term target values for the protection of human health and vegetation from ozone in ambient air pursuant to Legislative Decree 155/2010 together with the WHO reference values are shown in Table A.
Panel 2
ISPRA, Environmental data yearbook, various editions
SNPA (2024), Air quality in Italy. Ed. 2023
WHO (2021) global air quality guidelines. Particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Geneva: World Health Organization.
Data quality assessment
Autonomous Provinces Regions SNPA (National System for Environmental Protection)
InfoAria Database - ISPRA
National;
Regional (20/20);
Provincial: (99/110);
Municipal (300/8,047);
2015-2024
Indicator assessment
The indicator is based on the ozone concentration data in the atmosphere, measured in monitoring stations distributed throughout the national territory, collected and archived in ISPRA, in the InfoAria database as required by Decision 2011/850/EU. Parameters were calculated for a comparison with the information and alarm threshold values, with the objectives and long-term objective values for the protection of human health and vegetation established by the reference legislation (Legislative Decree 155/2010). All parameters were calculated according to European rules and were subjected to verification by the Regions/Pa/ARPA/APPA. The number of days of exceeding is equal to the number of days in which at least one exceeding of the thresholds and objectives indicated in Table A was recorded. The exceedings expected for the protection of human health and the statistical parameters were calculated for all urban, suburban, rural stations (grouping the rural and rural typology near-city ) and rural backgrounds (grouping the remote rural and regional rural typologies) following the macro-scale location criteria set out in Annex VIII of Legislative Decree 155/2010. Verification of compliance with the long-term objective for vegetation protection (AOT40v) was carried out for all suburban, rural and rural background stations; the values used for the evaluation refer to data series with minimum coverage of 90% in the time period defined for the calculation of the AOT40v (May-July, from 8am to 8pm).
The statistical analysis of trend (2015-2024) was conducted with the seasonally corrected Mann-Kendall method. Implementing a deseasonalization method allows us to minimize the effect of interannual oscillations due to the differences found in the various years compared to the average seasonal cycle, to highlight the existence of an underlying trend, to quantify its statistical significance and to estimate the variation in average annual concentration in the observation period.
In 2024, the long-term objective for the protection of human health (OLT) was exceeded in 276 stations out of 331, equal to 83.4% of the stations with sufficient temporal coverage according to the criteria of Annex I Legislative Decree 155/2010; the OLT was exceeded for more than 25 days in 144 stations (43.5%, Figure 2). The 55 stations where no OLT exceedances were recorded are located in urban, suburban and rural sites. The objective value for health protection was exceeded in 169 stations out of 344 stations with sufficient data coverage as an average over 3 years according to the criteria of Annex I Legislative Decree 155/2010. The information and alarm thresholds were exceeded in 58 (17.5%) and 1 station out of 331 respectively (Table 1). The WHO value, referring to the long-term objective for the protection of human health of 100 µg/m³ as the 99th percentile, is almost always exceeded (317 stations out of 331, equal to 96%). The long-term objective for vegetation protection (AOT40v) was exceeded in 146 out of 158 stations (92.4%) with values much higher than the regulatory limit (6,000 µg/m³*h) (Table 2 – Figure 3).
From the statistical analysis conducted with the Mann-Kendall method corrected for seasonality, it emerges that in 47% of the stations (158 out of 333) it is not possible to identify a trend statistically significant; the underlying trend appears substantially monotonous, and the interannual fluctuations are attributable to the natural fluctuations of the seasonal component. It was therefore not possible to exclude the null hypothesis (absence of trend ) for the given confidence level (95%). Instead, we observe a trend decreasing statistically significant in 32% of cases (107 monitoring stations out of 333), with estimated average annual variation: -1.4 µg/m³y [-4.3 µg/m³y ÷ -0.4 µg/m³y]). On the portion of the sample considered for which a trend statistically significantly decreasing, an average annual reduction of 1.6% (- 4.6% ÷ - 0.5%) is observed (Table 4, Figures 4 and 5). Furthermore, a statistically significant increasing trend is observed in 20% of cases (68 monitoring stations out of 333), with an estimated average annual variation: 1.6 µg/m³y [0.3 µg/m³y ÷ 13.8µg/m³y]). On the portion of the sample considered for which a trend statistically significant increase, an average annual increase of 3.1% (0.4% ÷ 72.0%) is observed (Table 4, Figures 4 and 5).
Data
Table A: O₃ – Information threshold, alert threshold, long-term objective, and target value for the protection of human health and vegetation pursuant to Legislative Decree 155/2010, and WHO reference values
D.Lgs.155/2010; OMS, WHO global air quality guidelines 2021
Figura 1: O3- Classificazione dei punti di campionamento secondo i criteri di ubicazione su macroscala di cui all’Allegato VIII, D.Lgs.155/2010 (2024)
Elaborazione ISPRA su dati SNPA
Figure 2: O₃ – Monitoring stations and exceedances of the long-term objective for the protection of human health (2024).
Processing by ISPRA based on SNPA data
Figure 3: O₃ – Monitoring stations and exceedances of the long-term objective for the protection of vegetation (2024)
Processing by ISPRA based on SNPA data
Figure 4: O₃ – Spatial distribution of the analyzed monitoring stations and estimated mean annual percentage change in concentration. Source: ISPRA processing based on SNPA data. Notes: Results of the trend analysis (2015–2024) using the Kendall test on a sample of 333 monitoring stations.
Processing by ISPRA based on SNPA data
Results of the trend analysis (2015–2024) using the Kendall test on a sample of 333 monitoring stations.
Figure 5: O₃ – Percentage distribution of monitoring stations according to the observed trend over the period 2015–2024.
Processing by ISPRA based on SNPA data
p ≤ 0.05: the observed trend is statistically significant;
p > 0.05: the null hypothesis (no trend) cannot be rejected.
Summary of the results of the trend analysis (2015–2024) using the Kendall test adjusted for the seasonality of O₃ concentrations in Italy, based on a selection of 333 monitoring stations distributed across the national territory.
Table 1: O₃ – Monitoring stations: data and statistical parameters for air quality assessment (2024).
Processing by ISPRA based on SNPA data
¹ Area type: U = URBAN, S = SUBURBAN, R = RURAL
² Station type: T = TRAFFIC; F = BACKGROUND; I = INDUSTRIAL
³ Values shown in bold indicate data with sufficient coverage in compliance with the criteria set out in Annex I of Legislative Decree 155/2010.
⁴ “--” value not calculated due to insufficient data coverage when averaged over 3 years according to the criteria of Annex I of Legislative Decree 155/2010; at least one year of valid data within the last 3 years is required.
⁵ Flag = 1 for time series with at least 90% valid data in summer and 75% valid data in winter, excluding data losses due to periodic calibration or routine maintenance (in accordance with the criteria of Annex I of Legislative Decree 155/2010); Flag = 0 for insufficient data coverage or lack of valid data.
⁶ Flag = 1 for time series with at least 5 summer months out of 6 meeting the requirement of 27 available daily values per month (in accordance with the criteria of Annex VII of Legislative Decree 155/2010); Flag = 0 for insufficient data coverage or lack of valid data.
“–” value not calculated due to lack of valid data.
Table 2 – O₃: Monitoring stations: data for the assessment of the long-term objective and the target value for the protection of vegetation (2024).
Processing by ISPRA based on SNPA data
“1” Values shown in bold meet the criteria set out in Annex VII for the calculation of AOT40 (90% of hourly values within the time period defined for AOT40 calculation).
“2” AOT40v corrected in accordance with the provisions of Annex VII of Legislative Decree 155/2010.
Table 3 – O₃: Assessment of exceedances of the long-term objective in accordance with Legislative Decree 155/2010 (2024).
Processing by ISPRA based on SNPA data
Zone: a delimited portion of the national territory, defined pursuant to Legislative Decree 155/2010, for the purposes of ambient air quality assessment and management;
Agglomeration: a zone consisting of an urban area or a group of urban areas located no more than a few kilometres apart, or of a main urban area together with a set of smaller urban areas that depend on the main one in terms of population, services, and flows of people and goods, having:
- a population exceeding 250,000 inhabitants; or
- a population below 250,000 inhabitants and a population density greater than 3,000 inhabitants per km²;
Exceedance of the target value and the long-term objective (LTO): considered to occur when an exceedance has been determined at at least one monitoring station located within the territory of the zone;
Maximum annual mean: the highest annual mean value recorded within the zone.
Table 4 – O₃. Trend analysis by monitoring station (2015–2024).
Processing by ISPRA based on SNPA data
p ≤ 0.05: the observed trend is statistically significant;
p > 0.05: the null hypothesis (no trend) cannot be rejected;
Δy: estimated mean annual change based on the results of the Kendall test adjusted for seasonality.
In 2024, monitoring stations that measured and reported O 3 for the protection of human health there are 348 (Table 1). The data series with sufficient time coverage for verifying the threshold values and the long-term objective for the protection of human health are 95.1% (331 out of 348). The suburban, rural and rural background stations that respect the minimum percentage required for calculating the long-term objective for vegetation protection (AOT40v) are 146 out of 158 (Table 2).
The classification of O. Monitoring stations 3 according to the macro-scale location criteria envisaged by the legislation, it is represented in Figure 1, with a prevalence of urban sites.
The entire national territory is divided into zones and agglomerations for the purposes of assessing the quality of ambient air pursuant to Legislative Decree 155/2010. Contrary to what is provided for other pollutants, for ozone the areas are not classified with respect to certain thresholds. However, it is indicated whether the long-term objective has been exceeded in the previous five years, since otherwise, the number of ozone measurement stations can be reduced according to the criteria set out in Annex IX, point 4 of Legislative Decree 155/2010.
If in the year under review the long-term objective was exceeded in at least one monitoring station, the entire area is exceeded.
In 2024, the long-term objective for the protection of human health (OLT) was exceeded in 61 out of 67 areas (Table 3).