Cities remain at the center of the problem
AUrban areas have the greatest risks, namely Lisbon, Porto and Braga, with the highest concentrations of nitrogen dioxide and inhalable PM10 particles, mainly due to car traffic – “diesel vehicles represent major sources of NO₂ and particulate emissions.”
Lisbon is the most documented case “with persistent exceedances of nitrogen dioxide on Avenida da Liberdade”.
There are, however, signs of improvement, reveals the researcher.
“In 2025, concentrations in these areas met all limit values for the first time, that is, we are facing a situation of improved air quality. The reduction in concentrations was, in the case of NO2, sufficient to meet legal objectives, but with no room for deviations.”
Traffic, fireplaces and agriculture: the main sources of air pollution
Road transport continues to be the main source of air pollution in Portugal, with emphasis on diesel vehicles.
Despite technological improvements, namely with the introduction of particulate filters from 2009 and with more demanding standards for nitrogen oxide emissions in newer vehicles, diesel vehicles are the dominant source in an urban environment, highlights the researcher.
Furthermore, there is a factor that is holding back progress: the araise the use of an individual vehiclewith a consequent increase in urban congestion and atmospheric emissions.
“In 2025, traffic on highways exceeded pre-pandemic levels by 18%, worsening urban congestion and emissions. This context makes it more difficult to meet the new European targets, which require a significant reduction in nitrogen dioxide levels.”
Along with traffic, there is a less visible source, but with significant weight, especially in winter: domestic heating with wood.
“Domestic biomass burning (wood in fireplaces and wood stoves) represents an important national source of fine particles”, especially at night and in periods of less atmospheric dispersion.
Also the agriculture contributes to the problem, albeit indirectly. This sector dominates the ammonia emissionsa pollutant that does not directly affect air quality, but which participates in the formation of secondary particles, with an impact on health.
Me andindustry and the energy sector today have a smaller weight. The closure of the Sines and Pego coal plants in 2021 was one of the most relevant factors in reducing emissions of sulfur dioxide and nitrogen oxides.
The most worrying air pollutants in Portugal
There are three main culprits for degrading air quality: nitrogen dioxidesuspended particles and ozone.
O nitrogen dioxide (NO2) remains the most problematic, especially in cities, where its concentrations are highest.
“Over the last 20 years, exceedances of the limit values defined for this pollutant have been persistent in agglomerations, with the highest incidence in Lisbon, Porto and Braga.”
In relation to suspended particles – PM respirable particles10 and PM fine particles2,5, – improvements have been recorded. “Since 2018, there has been no non-compliance with the limit values” Still, they continue to be relevant from a health perspective.
As for the ozone tropospheric (O₃), “the concentration trend is decreasing, but is still at levels above the target value defined for health protection”.
The priority: changing urban mobility
For Joana Monjardino, “the priority must be to invest in the transformation of urban mobility” to attack the “chronic problem of cities”, pollution associated with road traffic, and ensure compliance with new European targets.
Among the solutions, it highlights the reinforcement of public transport, creation of conditioned access zones, especially in the most pressured urban centers.
“The reinforcement of the offer of public transport, the expansion of BUS lanes, the management of private vehicle use, the prioritization of active mobility, incentives for the electrification of fleets should be seen as priorities.”
Another relevant front of intervention is domestic heating. “The reduction of fine particle emissions from the burning of biomass […] This is an area with space to intervene”, through the replacement of equipment and restrictions in critical periods.
Overall, the message is clear: without structural changes, especially in the way we travel, it will be difficult to meet targets and sustainably improve air quality.
“The deadline is short: the new European limits come into force in 2030 and, to comply with them, the measures have to start now”, concludes Joana Monjardino.
An invisible risk, but with an impact on health
“Air pollution is the biggest environmental risk to health worldwide and the third risk factor for global mortality, after hypertension and smoking.”
In Portugal, the impact is significant and well documented. “According to data from the European Environment Agency for 2021, exposure to fine particles PM2.5 caused around 2,100 premature deaths”, to which are added “around 550 associated with nitrogen dioxide and 460 with ozone”.
When several pollutants are considered together, the number rises significantly. “More comprehensive methodologies estimate values greater than 5,000 premature deaths per year in Portugal”.
The effect of pollution is also felt in the pressure on the health system. This “consistently associated with 1% to 14% increases in emergency hospital admissions for every 10 μg/m³ increment in air pollutants”, a relationship confirmed by more than two decades of epidemiological investigation.
Impacts become more visible in extreme situations. During episodes of dust from North Africa, the risk of respiratory hospitalization increases by 12.6%. In the large fires of October 2017, the smoke would have caused up to 1,447 respiratory hospitalizations in a single day.
Air pollution is also associated with several causes of death in Portugal: 8.7% of deaths from ischemic heart disease, 6.6% from stroke, 6% from lung cancer and 15.3% from chronic obstructive pulmonary disease.
In the European context, the numbers reinforce the dimension of the problem: In 2023 alone, around 182,000 deaths were attributed to exposure to PM2.5 in the European Union.
The researcher emphasizes that “doesn’t exist a safe threshold of exposure: the effects persist, even at concentrations below the regulatory limits themselves”.
Extreme events and climate change exacerbate risks
As Dust from North Africa and forest fires are today two of the natural factors with the greatest impact on air qualitymainly because they significantly increase the concentrations of PM10 and PM2.5 particles.
However, the evolution of these phenomena is not linear. “Research based on hard data has not yet revealed clear trends,” despite particularly intense recent episodes of dust coming from the Sahara.
One of these cases occurred in March 2022: “It was the most extreme ever recorded in the Iberian Peninsula, with PM10 concentrations reaching 600-650 µg/m³ in the center of the country”, values much higher than usual and associated with a greater risk of hospitalizations for respiratory diseases.
In fires, the impact can be even more severe.
“In the 2017 fires, peak PM10 concentrations reached 704 µg/m³ in Leiria — 14 times the legal limit”, with direct health consequences: hundreds of cardiovascular admissions, thousands of asthma symptoms and premature deaths, explains the researcher.
Air quality improves, but more demanding targets are approaching
“Air quality in Portugal has improved consistently over the last two decades. The percentage of days with ‘Poor’ or ‘Bad’ quality has fallen from 17% in 2005 to just 1% in 2023 – a drastic improvement over almost two decades”, notes the researcher at the Department of Environmental Sciences and Engineering at NOVA FCT.
Despite this evolution, the scenario is far from resolved. “Currently, the limit values defined in national legislation are being met. Even so, there is a need for improvements”, underlines.
The researcher warns of the impact of the new European Air Quality Directive (2024/2881)which comes into force in four years and which establishes more ambitious limit values for greater protection of human health.
“Portugal will have difficulty complying with the new limits for some pollutants, such as nitrogen dioxide (NO2) and suspended particles (PM10), especially in densely populated urban areas.”
Portugal complies today, but starts from a history of default
“In 2025, Portugal complied for the first time with all current European Union limits for most pollutants”, says the researcher.
But this result contrasts with a recent past marked by default, especially in urban areas.
In recent years, the country has been condemned several times by European bodies due to systematic exceeding of limits, in particular with regard to nitrogen dioxide and suspended particles.
In recent decades, there has been significant progress in reducing emissions, mainly thanks to technological developments and structural changes in key sectors.
“The technological changes introduced in automobile manufacturing have been fundamental”, both in the reduction of particles, with the introduction of filters in diesel vehicles, and more recently in the reduction of nitrogen oxides.
Despite these advances, the main obstacle is the effective implementation of these measures and a “change of mentality”, emphasizes the researcher. Many of the solutions imply changes in people’s daily lives, especially in mobility. Measures such as reducing the use of individual cars or traffic restrictions face resistance, precisely because they “require behavioral changes”.
