def air_flux(air_flow: float, co2_source: float, co2_target: float) -> float:
    """
    Equation 8.46
    Args:
        co2_source, co2_target: CO2-concentration at location (mg m^-3)
        air_flow: the air flux from location 1 to location 2 (m^3 m^-2 s^-1)
    return: CO2 flux accompanying an air flux  from location 1 to location 2 [mg m^-2 s^-1]
    """
    return air_flow * (co2_source - co2_target)