Air quality and land use across Swiss municipalities

Where fine particles are high and where they are low

Fine particles PM2.5 (annual mean) has a median of 6.1 µg/m³ across municipalities. The top of the table is concentrated in one corner of the country: Coldrerio reaches 15.1 µg/m³, followed by Morbio Inferiore at 14.9 µg/m³ and Vacallo at 14.8 µg/m³, and these three municipalities are all in the canton of Ticino.

At the other end, Zermatt has only 1.6 µg/m³. Täsch follows at 1.7 µg/m³ and Saas-Fee at 1.7 µg/m³, and the three municipalities lie in the canton of Valais. These are high-altitude places: Zermatt lies at an average altitude of 2,943 m, Saas-Fee at 2,907 m and Obergoms at 2,359 m. Across municipalities, higher altitude generally goes with lower fine-particle readings.

Nitrogen dioxide NO₂ (annual mean) tracks fine particles closely. Its median is 7.4 µg/m³, and municipalities with high fine-particle readings tend to have high nitrogen dioxide readings too. Geneva has 18.9 µg/m³, the highest of any municipality, and Morbio Inferiore follows with 18.4 µg/m³, together with 14.9 µg/m³ for fine particles.

Cities side by side

Among the larger cities, nitrogen dioxide readings are far from uniform. Geneva has 18.9 µg/m³, Basel has 15.3 µg/m³ and Zürich has 13.7 µg/m³, while Lausanne has 9.8 µg/m³ and Lugano has 9.4 µg/m³.

Mid-sized towns sit lower: St. Gallen has 10.6 µg/m³, Winterthur has 9.4 µg/m³ and Biel/Bienne has 9.3 µg/m³. Size is only part of the story. Coldrerio, with 2,838 residents, has 18.2 µg/m³, more than Zürich with 440,935 residents, and Morbio Inferiore also exceeds Basel.

Resorts at altitude have low readings: St. Moritz has 3.4 µg/m³ and Samnaun has 2.1 µg/m³, against a median of 7.4 µg/m³ across municipalities. Lugano, with 63,691 residents, has 9.4 µg/m³, below Coldrerio and Morbio Inferiore in the same canton of Ticino.

Ozone reverses the picture

Ozone O₃ (93.2nd percentile of daily maximum 8-hour means) has a median of 108 µg/m³, and its highest readings are not found in the cities. Breggia reaches 147 µg/m³, Castel San Pietro has 146 µg/m³ and Arogno has 142 µg/m³, and the three are all in the canton of Ticino.

Large cities lie near the median: Geneva has 106 µg/m³, Basel has 106 µg/m³ and Zürich has 112 µg/m³. High-altitude resorts read higher: Zermatt has 131 µg/m³, Saas-Fee has 130 µg/m³ and St. Moritz has 129 µg/m³, all above Zürich.

Some valley towns sit at the low end. Sion has 97 µg/m³, Sierre has 97 µg/m³ and Saint-Léonard has 97 µg/m³, and the three municipalities lie in the canton of Valais. Interlaken, in the canton of Bern, has 98 µg/m³.

A few municipalities are high on three counts at once. Mendrisio, with 15,076 residents, combines 12.1 µg/m³ for fine particles, 12.6 µg/m³ for nitrogen dioxide and 141 µg/m³ for ozone, against medians of 6.1 µg/m³, 7.4 µg/m³ and 108 µg/m³.

How much of the ground is built over

Share of settlement and urban areas has a median of 12.7%, so in the typical municipality most of the territory is open land. At the top, Massagno has 97.3%, Renens (VD) has 95.6% and Meyriez has 94.1%. Among the large cities, Geneva has 92.2%, Basel has 86.1%, Zürich has 62.3% and Lausanne has 46.6%.

Alpine municipalities form the other end: Vals has 0.6%, Zernez has 0.7% and Innertkirchen has 0.7%, so very little of their territory is built over.

Hard surfaces are covered by a separate measure. Sealed soil: average imperviousness density has a median of 5.0%, against 62.6% in Carouge (GE), 59.8% in Rorschach and 58.5% in Renens (VD). The two measures are related but not identical: Zürich has 62.3% of its territory as settlement area but 32.2% sealed soil. Sealed soil also goes with air readings: municipalities with a high share of sealed soil tend to have high nitrogen dioxide, as Carouge (GE) shows with 17.9 µg/m³.

Space used per resident

Settlement area per inhabitant is 526 m²/inh. in the median municipality. Dense places use far less: Geneva has 72 m²/inh., Carouge (GE) has 105 m²/inh., Vevey has 108 m²/inh. and Basel has 116 m²/inh., in line with the tendency of municipalities with more people per square kilometre to use less settlement area per resident.

At the other end, Obergoms has 3,077 m²/inh., Rheinwald has 2,874 m²/inh. and Bure has 2,710 m²/inh., in each case a small municipality where few residents share a large built area. The high values are not confined to the Alps: Bure, in the canton of Jura, has 2,710 m²/inh. with 660 residents.

Other cities and resorts fall in between: the figure is 136 m²/inh. in Zürich, 181 m²/inh. in Bern, 231 m²/inh. in Lugano and 549 m²/inh. in St. Moritz. Zermatt has 358 m²/inh., which divides a built area serving many visitors over 6,113 residents.

Roads, parks and forests

Share of transport surfaces (roads, rail, car parks) is 3.6% in the median municipality, but Le Grand-Saconnex stands at 46.3%, ahead of Balerna at 30.9% and Renens (VD) at 29.5%, while Meyrin reaches 28.4%. Le Grand-Saconnex has 12,775 residents, so roads, rail and car parks can take a large part of the territory even in a municipality of moderate size.

Parks and recreational land are rarer still. Share of recreational and green areas is 0.4% in the median municipality, yet Geneva has 15.8%, Tenero-Contra has 15.4% and Birsfelden has 14.7%. By comparison, Zürich has 9.1% and Lausanne has 7.4%.

Forest is far more common. Share of forest is 28.7% in the median municipality, and Morcote has 81.0%, Breggia has 79.9% and Arogno has 79.7%, and these three municipalities are all in the canton of Ticino. Cities vary widely: Lugano has 63.8%, Winterthur has 39.4% and Zürich has 25.4%, whereas Geneva has only 2.7%.