def remove_utc(time_string):
    """ Removes UTC from end of time string.

    The purpose is to clean up time strings so they can be converted to
    Numpy datetime64 objects, since datetime64 cannot be initialized if
    if the input string includes the UTC marker.

    Args:
        - time_string (string): timestamp string from Purple Air
        dataset.
    Returns:
        - (string): the cleaned-up timestamp string (without "UTC")
    """

    if time_string.endswith("UTC"):
        return time_string[:-3].strip()
    else:
        return time_string