Since 1994, harmful air pollutants called BTEX (benzene, toluene, ethylbenzene and xylene) have declined by up to 89 % in the suburban area of Zurich thanks to the introduction of various air quality directives in Switzerland and in Europe. Although their contribution to ozone formation became less abundant, they still significantly contribute to the formation of airborne particles. While this study shows clear improvements in air quality, it also highlights the need for further efforts.