Translate the following English sentence to French:
"The main aim of the proposed legislation is to establish limit values for atmospheric concentrations of benzene and carbon monoxide in order to improve the quality of our air and to avoid, prevent and reduce the adverse effects of these substances on human health and the environment."
L' objectif principal est de fixer des valeurs limites pour les concentrations de benzène et de monoxyde de carbone, afin d' améliorer l' air ambiant et d' éviter, d' empêcher que des substances nuisibles puissent agir sur la santé de l' homme et l' environnement.