Researchers at the University of Granada (Spain) are studying how the plants in urban green spaces in the city of Granada affect the air quality, and how that air quality affects human health — specifically seasonal allergies.

The researchers have found that many of the most common trees in Granada were among the trees causing unhealthy or hazardous air quality. The design of these green spaces thought about landscaping, climate, and fashion criteria, but didn’t think about pollen problems.

The Mediterranean has the highest occurrence of pollen allergies in the world, the researchers said. They hope their efforts will lead to fantastic urban green spaces that don’t cause allergic reactions for 30% of the city’s population.