def calc_rho_air(temp_air):
    """
    Calculation of density of air according to 6.4.2.1 in [1]

    temp_air : air temperature in (°C)

    rho_air : air density in (kg/m3)

    """
    rho_air_ref = 1.23
    temp_air_ref_K = 283
    temp_air_K = temp_air + 273
    rho_air = temp_air_ref_K / temp_air_K * rho_air_ref
    return rho_air
