This paper is concerned with the stationary problem of an aero-taxis system with physical boundary conditions proposed by Tuval et al (2005 Proc. Natl Acad. Sci. 102 2277 to describe the boundary layer formation in the air-uid interface in any dimensions. By considering a special case where uid is free, the stationary problem is essentially reduced to a singularly perturbed nonlocal semi-linear elliptic problem. Denoting the diffusion rate of oxygen by ε > 0, we show that the stationary problem admits a unique classical solution of boundarylayer pro le as ε → 0, where the boundary-layer thickness is of order ε. When the domain is a ball, we nd a re ned asymptotic boundary layer pro le up to the rst-order approximation of ε by which we nd that the slope of the layer pro le in the immediate vicinity of the boundary decreases with respect to (w.r.t.) the curvature while the boundary-layer thickness increases w.r.t. the curvature.