def set_corr_keys(operator):
    """
    function to accept an operator string and return the dataframe keys in a dictionary
    :param operator: string specifying the operator, must be 'COSMOS-UK' or 'COSMOS-US'
    :return: dictionary containing the pressure and humidity correction keys

    """
    if "COSMOS-US" == operator:
        key_dict = {'p_corr': 'PRESS', 'h_corr': None}
    elif "COSMOS-UK" == operator:
        key_dict = {'p_corr': 'PA', 'h_corr': 'Q'}
    else:
        raise KeyError('%s is not a valid operator key' % operator)

    return key_dict