Oxygen diffuses into an open-air surface of a vertically oriented thin layer of the Belousov-Zhabotinsky reaction and creates a millimeter-order inhibited layer where excitation fronts cease. When the excitability of the reaction is weakened via a decrement of [H2SO4] or [NaBrO3], the velocity of spiral waves located far from the open-air surface decreases and the width of the inhibited layer increases. The experimental findings agree well with simulations using the Oregonator model where the excitability is adjusted via two parameters epsilon(-1) and f which mimic the change in [H2SO4] or [NaBrO3] and the oxygen profile along the vertical direction, respectively. (C) 2014 Elsevier B.V. All rights reserved.