Air quality in Spanish cities: pollution, ozone and how to check it

Key rules

• Worst pollutant: The index level on any given hour is set by whichever pollutant is worst at that moment.
• Sensitive people: From Regular upward, limit long outdoor exertion if you have asthma, heart or lung problems, or are a child or older adult.
• Summer ozone: Ozone is highest on summer afternoons and in areas downwind of cities, so exercise early in the morning.
• Local alerts: Large cities run their own NO2 alert systems, and the measures differ from city to city.

The short version

In Spanish cities, traffic fumes and particles are the everyday problem. Ozone is the summer problem, and it is often worse outside the city than in it. Spain publishes a six-level index, so you can check any day's air in a minute and decide how much to do outdoors.

The three pollutants

NO2 (nitrogen dioxide) is a gas from burning fuel. In Spanish cities it comes mainly from road traffic, especially diesel vehicles. It irritates the airways and can make asthma worse. It is highest next to busy roads, so a street with heavy traffic is worse than a park a few blocks away.

Particles (PM10 and PM2.5) are tiny specks of dust and soot, under 10 and under 2.5 micrometres. They come from exhaust, brake and tyre wear, heating, industry, construction and farming. Saharan dust also blows in and can push readings up for a few days. PM2.5 is the more worrying size because it goes deep into the lungs and bloodstream.

Ozone (O3) is not emitted directly. Sunlight turns traffic and industrial fumes into ozone. It irritates the airways and reduces lung function. Because the reaction takes time, ozone is highest downwind of cities and in rural areas, such as the Madrid sierra, the central plateau, inland Catalonia and parts of the Valencian coast. The Canary Islands have fewer episodes.

When ozone is worst

Ozone season runs from late spring to early autumn, with the highest values from June to August. On a hot day it builds through the afternoon, roughly 2pm to 8pm, and falls overnight. If you run or cycle in summer, go early in the morning. The timeline below shows the season.

How to read the official index

Spain uses a national air-quality index with six levels:

1. Buena (good)
2. Razonablemente buena
3. Regular
4. Desfavorable
5. Muy desfavorable
6. Extremadamente desfavorable

The level is set by whichever pollutant is worst at that moment. It covers PM10, PM2.5, NO2, O3 and SO2. For example, an hourly NO2 reading up to 40 µg/m3 is the best level, and one above 340 is the worst. For PM2.5 the best level is up to 10 and the worst is above 75.

What to do:

• Buena or Razonablemente buena: no restrictions.
• Regular or worse: if you are sensitive (asthma, heart or lung disease, young children, older people), limit long outdoor exertion.
• The two worst levels: everyone should avoid outdoor exertion.

The index lines up with the European one. Some cities also publish their own local index, so the colours and names may differ slightly on a city app. The decision below turns this into a quick choice.

Where to check

Start with the national ministry's real-time map, which covers all of Spain. Then use your city or regional portal, which usually has more stations and sometimes an app. Madrid and Catalonia both have their own. The resources below list the main places, including those for Saharan dust and pollen.

City pollution alerts

Large cities have graduated alerts for high NO2. Madrid has a pre-alert and three scenarios based on hourly NO2 readings. The first is 180 µg/m3 at two stations, the second is 200 for two hours, and the third is 400. Measures start with a 70 km/h limit on the M-30 ring road and its access roads. They then move to restricted parking in the centre, and finally to limits on vehicles by environmental label. Barcelona and its metropolitan area have an alert protocol for NO2 and PM10, with lower speeds on ring roads and a push for public transport. Valencia, Zaragoza, Sevilla and Bilbao have similar local plans. Details differ by city, so check your city's current rules.

How cities compare

Ozone limits are exceeded in many areas, including the Madrid region, Catalonia, the Valencian Community, Andalusia and Castilla-La Mancha. NO2 problems are concentrated in Madrid and in Barcelona and its surroundings, and have been easing. High particle readings are less common and often tied to Saharan dust and industry. Stricter EU limits are due from 2030.

Practical habits

• Check the index before outdoor exercise, especially in summer.
• If you are choosing where to live and you are sensitive to air quality, prefer streets away from main roads.
• In summer, do not assume the countryside is cleaner. Ozone can be higher there.

Choosing between options

How much outdoor activity is fine at today's air-quality reading?

• Carry on as normal: The index says Buena or Razonablemente buena. There are no restrictions.

• Limit long outdoor exertion if you are sensitive: The index says Regular or Desfavorable. Children, older people and people with asthma or heart or lung disease should cut back on prolonged effort outdoors.

• Avoid outdoor exertion altogether: The index says Muy desfavorable or Extremadamente desfavorable. Everyone should avoid prolonged effort outdoors.

The category is set by the worst pollutant at that moment among particles (PM10 and PM2.5), NO2, ozone and SO2, so read the overall category, not just one pollutant.

Timeline and deadlines

• Ozone season begins as the weather warms up: from late spring

• Highest ozone values of the year: June to August

• Ozone peaks during the day, so plan outdoor exercise outside these hours: roughly 2pm to 8pm

• Ozone falls overnight, so early morning is usually the better time to be outside: at night and early morning

• Ozone season ends as the weather cools: early autumn

Where to check air quality, calima and pollen

• Ministry for the Ecological Transition (MITECO), air-quality section: Check the national real-time air-quality map, which shows the official index (ICA) for stations across Spain.

• European Environment Agency air quality index map: Check the European air-quality index map, which also covers Spain, for a quick comparison between areas.

• Your city or regional government air-quality portal: Look up local readings and alerts on the portal for your area, such as Madrid's Calidad del Aire, Catalonia's Qualitat de l'aire, or the Andalusian, Basque, Valencian and Canarias networks. Madrid and Catalonia also have air-quality apps.

• AEMET, Spain's state weather agency: Read official weather warnings and forecasts, including Saharan dust (calima) warnings in the Canary Islands.

• Barcelona Dust Regional Center (WMO) and Copernicus atmosphere service: Follow Saharan dust forecasts for Spain, North Africa and Europe to see when calima is coming.

• Spanish Society of Allergology and Clinical Immunology (Polenes platform): Check pollen counts from stations across Spain. AEMET does not publish pollen counts.

• Regional aerobiology networks: Use the network for your region for local pollen counts and forecasts: Andalusia's Red Andaluza de Aerobiología, Catalonia's Xarxa Aerobiològica de Catalunya, or the Madrid regional health service. Other regions, such as Valencia and Galicia, have university or health-department stations.

Frequently asked questions

Where is ozone highest, in the city centre or outside it?

Ozone is usually highest outside the city centre, at suburban and rural spots downwind of large cities. Examples are the Madrid sierra, the central plateau, inland Catalonia, and Mediterranean areas such as Valencia and Castellón. A park on the edge of town can read worse than a busy central street.

What happens in Madrid when nitrogen dioxide levels get too high?

Madrid runs a three-scenario alert protocol, plus a pre-alert, based on hourly NO2 readings. Scenario 1 starts at 180 µg/m3 at two stations, scenario 2 at 200 for two hours, and scenario 3 at 400. Measures grow from a 70 km/h limit on the M-30 and access roads, to restricted parking in the centre, to restrictions by vehicle label.

Do other cities have pollution alerts like Madrid's?

Yes, Barcelona and its metropolitan area run an alert protocol for NO2 and PM10, with lower speeds on ring roads and promotion of public transport. Valencia, Zaragoza, Sevilla and Bilbao have local plans with similar graduated alerts. Details differ by city, so read your own city's plan.

Can Saharan dust make particle readings worse?

Yes, Saharan dust is one of the causes of high particle readings (PM10) in Spain, alongside industry. Traffic, heating, construction and farming also add particles. When the dust arrives, check your city's current PM10 reading before planning outdoor exercise.