def pollutants_from_summary(summary):
    """
    Get the list of unique pollutants from the summary.

    :param list[dict] summary: The E1a summary.

    :return dict: The available pollutants, with name ("pl") as key
        and pollutant number ("shortpl") as value.
    """
    return {d["pl"]: d["shortpl"] for d in summary}