Panel 1
Massimiliano BULTRINI, Simona BUSCEMI, Giorgio CATTANI, Alessandra GAETA, Federica NOBILE (Dipartimento di Epidemiologia del Servizio Sanitario Regionale-Regione Lazio ASL Roma 1), Maria Antonietta REATINI, Massimo STAFOGGIA (Dipartimento di Epidemiologia del Servizio Sanitario Regionale-Regione Lazio ASL Roma 1)
Estimates of the population-weighted annual average exposure (Population Weighted Exposure, PWE) to nitrogen dioxide (NO₂) have been developed at the municipal level through an integrated use of measurements and statistical models. The data, covering the period 2016–2022, enable comparison of PWE across all municipalities and provide a comprehensive overview of average exposure at the national scale.
In 2022, 82% of the population was exposed to NO₂ levels exceeding the WHO guideline value of 10 µg/m³. The national average PWE was 12 µg/m³ (range: 3–38 µg/m³).
Between 2016 and 2022, a downward trend in exposure levels was observed, with an average reduction of approximately 25%, primarily attributable to decreased emissions from road traffic.
The most widely accepted health estimates attribute a significant portion of premature deaths and reductions in life expectancy to exposure to atmospheric pollutants (WHO, 2016; EEA, 2022; WHO, 2021).
Assessing population exposure and its spatial and temporal variability in the outdoor environment is a crucial step for epidemiological studies that examine the relationship between air pollution exposure and health effects (Caplin et al., 2019).
This indicator provides an estimate of the population-weighted annual average exposure (Population Weighted Exposure, PWE) to nitrogen dioxide (NO₂) aggregated at the municipal level, enabling comparisons between different cities and offering a comprehensive overview of average exposure at the national level. It represents chronic population exposure and is useful for long-term health effect estimations.
Exposure values are compared with reference levels (guidelines and interim targets) updated by the World Health Organization (WHO, 2021).
To estimate the average population exposure to the main airborne pollutants, assess exposure levels in comparison with WHO reference values, and evaluate temporal trends in exposure.
Legislative Decree No. 155 of 13 August 2010 and subsequent amendments, implementing Directive 2008/50/EC and Directive 2004/107/EC.
WHO (2021), Global Air Quality Guidelines. Particulate matter (PM10, PM2.5), ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide. Geneva, World Health Organization, 2021.
“A Clean Air Programme for Europe.” Brussels, 18 December 2013 COM (2013) 918 final.
“Europe that Protects: Clean Air for All.” Brussels, 17 May 2018 COM (2018) 330 final.
“Pathway to a Healthy Planet for All — EU Action Plan: Towards Zero Pollution for Air, Water, and Soil.” Brussels, 12 May 2021 COM (2021) 400 final.
In its revision of the Guidelines, WHO produced quantitative risk estimates for a series of health effects associated with an increase of 10 µg/m³ in the annual average concentration of various pollutants. WHO does not define a threshold below which there is no risk but identifies an annual average exposure lower bound of 10 µg/m³ for nitrogen dioxide (NO₂), termed the “Air Quality Guideline level.” This level represents the lowest concentration at which increases in total mortality, cardiopulmonary mortality, and lung cancer mortality have been observed, with a 95% confidence interval. WHO has also defined “interim targets,” which are higher reference levels to be progressively achieved through air quality improvement policies. The WHO interim targets for NO₂ are 20 µg/m³ (IT 3), 30 µg/m³ (IT 2), and 40 µg/m³ (IT 1).
EU clean air programs set a medium- to long-term goal of aligning with WHO air quality guidelines, which are more stringent than the EU air quality directive standards and reflect what is necessary to protect human health.
The EU Clean Air Package and the Zero Pollution Action Plan aim to reduce premature deaths attributable to air pollution by more than half by 2030 compared to 2005 levels.
Panel 2
Caplin A., Ghandehari M., Lim C., Glimcher P., Thurston G. (2019) Advancing environmental exposure assessment science to benefit society. Nature communication (2019) 10:1236. https://doi.org/10.1038/s41467-019-09155-4.
EEA (2022), Health Risk Assessment of Air Pollution and the Impact of the New WHO Guidelines. Eionet Report – ETC/ATNI 2022/10.
EUROSTAT(2022), Sustainable development in the European Union — Monitoring report on progress towards the SDGs in an EU context — 2022 edition. (DOI): 10.2785/313289.
WHO (2016), Ambient air pollution: A global assessment of exposure and burden of disease. Geneva, World Health Organization, 2016.
WHO (2021), Global Air Quality Guidelines. Particulate matter (PM10, PM2.5), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Geneva, World Health Organization, 2021.
Stafoggia M, Bellander T, Bucci S et al. Estimation of daily PM10 and PM2.5 concentrations in Italy, 2013-2015, using a spatiotemporal land-use random-forest model. Environ Int 2019;124:170-79.
Stafoggia M, Cattani G, Ancona C, Ranzi A. (2021) La valutazione dell’esposizione della popolazione italiana all’inquinamento atmosferico nel periodo 2016-2019 per lo studio della relazione tra inquinamento atmosferico e COVID-19. Epidemiol Prev. 2021 Sep-Dec;44(5-6 Suppl 2):161-168. Italian. doi: 10.19191/EP20.5-6.S2.115. PMID: 33412807.
The population considered is that distributed within the 2011 permanent census sections, which is the most recent available territorial basis. The 2021 territorial bases are currently undergoing validation and will incorporate updates related to municipal demographics and territorial changes since the 2011 permanent census.
The indicator expresses an average exposure value for the population at the municipal level. It is known that within a single municipality there is variability in pollutant concentrations, with areas where levels may be higher than the average or background values. However, assessing exposure at a local or microscale level within individual municipalities is beyond the scope of this indicator. It is important to note, though, that areas with higher population density within the municipality are weighted more heavily in the calculation of the Population Weighted Exposure (PWE).
The exposure values obtained should not be compared directly with legal limit values; for compliance assessment with legal limits, the highest value measured at individual monitoring stations must be used.
Applicazione di modelli ad alta risoluzione spazio-temporale, con l’uso di predittori spazio-temporali, dati satellitari, dati di monitoraggio della qualità dell’aria.
Data quality assessment
DEP: Department of Epidemiology, Regional Health Service, Lazio Region – ASL RME
ISPRA: Higher Institute for Environmental Protection and Research
ISTAT: National Institute of Statistics
SNPA: National System for Environmental Protection
ISPRA - Database InfoARIA
ISTAT - www.demo.istat.it
National, Regional, Municipal (7,904/7,914)
2016-2022
Indicator assessment
The model uses as the response variable the daily average concentrations measured at monitoring stations distributed across the national territory, and as explanatory variables a selection of spatial and temporal predictors. Monitoring data are collected and archived by ISPRA in the InfoAria database, in accordance with Directive 2008/50/EC (and its national transposition, Legislative Decree No. 155/2010) and Commission Implementing Decision 2011/850/EU.
A machine learning model, the random forest, was developed to relate the daily concentrations measured at monitoring stations with spatial predictors (population density, road network, land cover, altitude, artificial surfaces, etc.) and spatiotemporal predictors (dispersion models, meteorology) in order to estimate daily average NO₂ levels for each square kilometer of the Italian territory.
Starting from the daily concentrations estimated by the random forest model, the average annual exposure of the Italian population was calculated by weighting the concentration of each pollutant at the cell level by the resident population within that cell.
The “national average concentration value” is computed as a population-weighted mean of the estimated concentrations for each municipality, weighted proportionally to the resident population.
Finally, the percentage distribution of the resident population exposed to different NO₂ concentration ranges is estimated.
In 2022, 82% of the population was exposed to levels exceeding the WHO guideline value of 10 µg/m³; 37% was exposed to levels above Interim Target (IT) 3 (20 µg/m³); and 7% of the population residing in 44 municipalities was exposed to levels exceeding IT2 (30 µg/m³). In this latter case, the exposed population is concentrated in the regions of Piedmont, Lombardy, and Campania, particularly in the municipalities of Turin and Naples, as well as in municipalities within the metropolitan area of Milan and the provinces of Monza and Brianza (Figure 1 - Table 1).
No municipality recorded Population Weighted Exposure (PWE) levels exceeding IT1 of 40 µg/m³ in 2022.
The national average PWE, considering all Italian municipalities, was 12 µg/m³ (range: 3–40 µg/m³) (Figure 2).
As shown in Figure 2, over the seven years considered, there is an overall decreasing trend in Population Weighted Exposure (PWE) values. The national average decreased from 16 µg/m³ in 2016 to 12 µg/m³ in 2022, representing a 25% reduction over the observation period.
Although 2020 may have been influenced by the lockdown measures implemented to contain the spread of the COVID-19 pandemic, the overall trend appears consistent over the years and is mainly attributed to reductions in emissions from road traffic.
However, the period analyzed is too short to quantitatively estimate a trend and its statistical significance, which therefore remains undefined. Such significance typically becomes evident when analyzing data over a time horizon of 10 years or more.
While the trend has not been statistically quantified and refers to a relatively short period, it aligns with observations made over the last decade at air quality monitoring stations.
The proportion of the population exposed to NO₂ concentrations below the WHO recommended threshold has increased from 6% in 2016 to 18% in 2022. At the same time, the PWE did not exceed 40 µg/m³ in 2022, as was the case in 2020 and 2021 (in 2016 and 2017, 5% of the population was still exposed to levels above this threshold) (Figure 3).
Data
Figure 1: Population-weighted average exposure to nitrogen dioxide (NO₂) at the municipal level (2022)
Analysis by ISPRA based on data from the Department of Epidemiology of the Regional Health Service of Lazio
Figure 2: Annual distribution of PWE values (population‑weighted average exposure to nitrogen dioxide (NO₂) at the municipal level)
Analysis by ISPRA based on data from the Department of Epidemiology of the Regional Health Service of Lazio
Figure 3: Percentage of population exposed to nitrogen dioxide (NO₂) by exposure range and year
Analysis by ISPRA based on data from the Department of Epidemiology of the Regional Health Service of Lazio
The five PWE categories shown correspond to the WHO guideline value and the three interim targets.
Table 1: NO₂ — Population-weighted exposure (PWE) by region: percentage distribution by exposure category (2022)
Analysis by ISPRA based on data from the Department of Epidemiology of the Regional Health Service of Lazio
PWE: population-weighted average exposure (Population Weighted Exposure).
The five PWE categories shown correspond to the WHO guideline value and the three interim targets.
The indicator aligns with those used at the European scale by the European Environment Agency (EEA) and globally by the World Health Organization (WHO) to monitor exposure. Furthermore, it forms the basis for exposure assessment to develop health risk assessments and burden of disease estimates consistent with the methodologies employed by these two supranational organizations.
With reference to the United Nations Sustainable Development Goals (SDGs), the methodological approach is consistent with that used for calculating the indicator supporting monitoring progress toward Goal 11 (making cities and human settlements inclusive, safe, resilient, and sustainable), specifically target 11.6 (by 2030, substantially reduce the adverse per capita environmental impact of cities, particularly regarding air quality and waste management).
From a methodological standpoint, the estimated exposure also underpins one of the indicators useful for monitoring progress toward Goal 3 (ensure healthy lives and promote well-being for all at all ages), specifically target 3.9 (by 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water, and soil pollution and contamination).